Synthesis and structural elucidation of cytotoxic mono and dinuclear rhenium carbonyl complexes bearing bis-{1,3-(imino pyrrolyl)-m-chloro phenyl)} ligand

{"full_text": " Journal of Molecular Structure 1319 (2025) 139506\n\n\n Contents lists available at ScienceDirect\n\n\n Journal of Molecular Structure\n journal homepage: www.elsevier.com/locate/molstr\n\n\n\n\nSynthesis and structural elucidation of cytotoxic mono and dinuclear\nrhenium carbonyl complexes bearing bis-{1,3-(imino pyrrolyl)-m-chloro\nphenyl)} ligand\nDiksha a , Maharaja Somasundaram c , Mathan Ganeshan c , Satish Kumar Samal d ,\nDhanasekaran Dharumadurai e , Sherzod Madrahimov f , Akshi Deshwal a , Harminder Kaur a, * ,\nAlessandro Sinopoli b, * , Veeranna Yempally f, *\na\n Chemistry Department, Punjab Engineering College, Chandigarh 160012, India\nb\n Qatar Environment and Energy Research Institute (QEERI), Hamad Bin Khalifa University, Doha, Qatar\nc\n Department of Biomedical Science, Bharathidasan University, Tiruchirappalli, Tamil Nadu 620024, India\nd\n Institute of Nano Science and Technology, Sector-81, Knowledge City, Mohali, Punjab 140306, India\ne\n Department of Microbiology, Bharathidasan University Tiruchirappalli, Tamil Nadu 620 024, India\nf\n Division of Arts&Sciences, Texas A&M University at Qatar, Doha, Qatar\n\n\n\n\nA R T I C L E I N F O A B S T R A C T\n\nKeywords: A mononuclear and dinuclear rhenium tricarbonyl compounds were synthesized by the one-pot condensation\nImino pyrrolyl ligands reaction of [Re(CO)5Br], pyrrole-2-carboxaldehyde and 4\u2011chloro-m-phenylene diamine. The mononuclear\nRhenium (I) complexes rhenium tricarbonyl complex containing {3-(imino pyrrolyl)-6\u2011chloro phenylamine)} ligand (IPP) with formula\nDFT\n {[Re(CO)3Br(IPP)], (1), was obtained by refluxing stoichiometric quantities of amine, aldehyde and rhenium\nAnticancer\n metal precursor in methanol solution. Similarly, dinuclear rhenium tricarbonyl compound {[Re(CO)3Br]2(BIPP)],\nIC50 values\n BIPP = bis-{1,3-(imino pyrrolyl)-m-chlorophenyl)}, (2) has been synthesized by refluxing appropriate amounts\n of aldehyde, and rhenium metal precursor in the presence of one equivalent of amine ligand. Compounds 1 and 2\n were characterized by FT-IR, 1H NMR, and UV\u2013Vis spectroscopy, elemental analysis, and mass spectrometry. The\n luminescence properties of the formed complexes were studied in solution at room temperature, revealing an\n extended lifetime for the dinuclear complex 2 in comparison to 1. DFT calculations for the optimized structures\n helped to understand the geometry of the complexes, whereas TD-DFT revealed the vertical transitions\n responsible for the photophysical properties of the complexes. The cytotoxicity of such complexes against MCF-7\n breast cancer has been also reported, revealing a dose-dependent growth inhibition attributed to a DNA-\n intercalating mode of binding for both complexes. The pronounced effect of the two metals on the cytotoxic\n studies and lifetime of the excited species were investigated. The greater intercalation ability of the complex 2 in\n comparison to complex1 obtained from circular dichroism studies also indicates the greater efficacy of Re\n complex 2.\n\n\n\n\n1. Introduction limited their use and necessitated the discovery of new anticancer\n scaffolds with greater specificity and selectivity [3,4]. In this regard,\n The rampant growth of cancer is one of the leading causes of death organometallic Rhenium complexes are arising as potential alternatives\nworldwide which has led to the development of several therapeutic to platinum-based anticancer agents [5,6]. Rhenium and technetium\napproaches including radiation therapy, chemotherapy, immuno- carbonyl complexes with various chelating bidentate ligands have been\ntherapy, etc. [1]. The success of cisplatin and other platinum-based explored recently as potential candidates in the development of radio-\ndrugs has paved the way for the employment of metal complexes as pharmaceuticals and imaging applications [7]. The past decade has seen\npotent agents for chemotherapy [2]. However, the lack of selectivity and a rapid rise in the design and development of novel (Re(CO)3) complexes\nthe severe side effects associated with platinum-based anticancer agents for exploration of their anti-proliferative activity [8]. Researchers have\n\n\n * Corresponding authors.\n E-mail addresses: hkaur@pec.edu.in (H. Kaur), asinopoli@hbku.edu.qa (A. Sinopoli), vyempally@gmail.com (V. Yempally).\n\nhttps://doi.org/10.1016/j.molstruc.2024.139506\nReceived 15 April 2024; Received in revised form 16 July 2024; Accepted 29 July 2024\nAvailable online 30 July 2024\n0022-2860/\u00a9 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\nexploited the facile coordination capacity of ancillary ligands to the established, and recently similar research findings have pointed to the\nbiological molecule of interest (tumor cells, estrogen receptors) and the remarkable increase in the cytotoxicity and cell penetration selectively\nkinetic inertness of these complexes due to the presence of strong-field to tumor cells[26]. The success of several monometallic complexes has\nligands for developing new anti-proliferative drugs containing inspired researchers to develop novel strategies to combine various\nrhenium carbonyl complexes [9,10]. The stable fac-[Re(CO)3]+ core is metal centers in one compound, to create a heterobimetallic complex\nwell suited for the synthesis of hexacoordinate fac-rhenium carbonyl that could integrate the diverse modes of action that are typical of the\ncomplexes with a variety of chelating ligands possessing unique features constituent metal centers [27\u201329]. The corresponding treatment strat-\nsuch as high photostability, long emission lifetimes, and large stokes egy should require less concentration of the drug due to the combining\nshifts which makes them attractive candidates for biological imaging of multiple activities into a single molecule while reducing the side ef-\n[11]. Rhenium tricarbonyl complexes with diimine ligands such as fects associated with high dosages of less effective drugs. This will be\nphenanthroline, bipyridine can also be employed for fluorescent cellular translated in a lower IC50 value or in overcoming issues associated with\nimaging owing to the presence of accessible long-lived triplet resistance to the available treatments. The conjunction of (Re(CO)3) core\nmetal-to-ligand charge transfer (3MLCT) states [12,13]. These salient with other metal centers, to obtain bimetallic complexes, has led to the\nfeatures afford additional advantage over the traditional platinum based synergistic effect between the two metals [30]. This synergistic effect\ncomplexes as they can be explored for the theranostic applications [11, often leads to enhanced cytotoxicity and improved biological activity, as\n14]. reported by several studies [31]. Furthermore, Re(I) complexes with\n The plethora of research in this field is now aiming at incorporating diimine ligands have found applications in fluorescent bioimaging [32,\nselective functional groups on the backbone of chelating ligands to 33].\nenhance permeability into the tumor cells, selective binding to the In the current work, our main target is to synthesize novel rhenium\nspecific target, and improving their solubility in the aqueous medium carbonyl complexes with pyrrolylimine ligands, decorated with het-\n[15]. Heteroaromatic compounds, such as pyrrole and indole, are pre- eroatom substituents, for investigating their photoluminescence and\ndominantly present in several natural products and also in several bio- biological activity. We report the synthesis of mono and dinuclear\nlogically active molecules possessing excellent pharmacological rhenium (I) tricarbonyl (Re(CO)3) complexes bearing iminopyrrolyl\nactivities and antiproliferative properties [16]. There are only a few ligand by one-pot condensation method involving aromatic diamines\ncoordination complexes of rhenium (MRP-20) with pyrrole derivatives and pyrrole-2-carboxaldehyde (pyca). The synthesized (Re(CO)3) com-\nreported in the literature regarding application in radiopharmaceuticals plexes were fully characterized with the help of FT-IR, 1H NMR,\nand anti-cancer drugs [17,18]. Moreover, there are only a handful of UV\u2013visible spectroscopy, and DFT calculations. The in vitro cytotoxic\npyrrolyl imine ligands coordinated rhenium carbonyl complexes re- activities of the synthesized Re complexes against human breast cancer\nported in the literature [18\u201321], as shown in Scheme 1. cell line MCF-7 were evaluated. The experimental investigation pointed\n The biological activity of such Re (I) complexes can be tuned by out that the addition of a second metal center, in the dinuclear complex,\nvarying the structural properties of the diimine ligand while retaining induced a pronounced effect on the cytotoxicity and increased the life-\ntheir photophysical properties [22\u201324]. The binding of Re(I) carbonyl time of excited species. DNA binding studies, including absorption ti-\ncomplexes containing pyrrolyl imine ligands to biological molecules of trations and circular dichroism, indicated that both complexes bind to\ninterest (MOI) can be controlled by decorating the ligand with selective DNA through an intercalative mode.\nfunctional groups such as hydroxyl, amine, or aldehyde [25]. Another\nstrategy adopted to enhance cellular uptake and cytotoxicity is by\nincorporating halogen substituents either in the primary coordination\nsphere or the secondary coordination sphere. The beneficial effect of Cl\nand F atoms in enhancing the biological potency of several drugs is well\n\n\n\n\n Scheme 1. Main rhenium pyrrolyl imine carbonyl complexes reported so in literature [18\u201321].\n\n 2\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n2. Experimental section pyrrole-2-carboxaldehyde and 1 equivalent of 4-chloro-m-phenylene\n diamine were mixed in absolute ethanol in the presence of catalytic\n2.1. Materials and methods amount of p-toluenesulfonic acid (ptsa). The mixture was refluxed\n overnight and all the volatiles were removed and washed with\n All chemicals and solvents used were purchased from Sigma-Aldrich dichloromethane to obtain the corresponding BIPP ligand.\n 1\nand used as received without further purification. Infrared Spectra of H-NMR data (CDCl3, ppm): \u03b4 9.5 (s, 1H), 8.19 (s, 1H), 7.87 (s, 1H),\nformed metal complexes were recorded with a Perkin Elmer Spectrum 7.26\u20136.1 (aromatic H), IR (KBr, cm\u2212 1): (NH stretch) 3238 cm\u2212 1, (CN\nTwo spectrometer. NMR Spectra was recorded on Bruker Avanche II stretch) 1627 cm\u2212 1. HRMS-ESI (m/z): 297.1110.\n400NMR Spectrometer. Absorption spectra were recorded on Systronics\nDouble Beam Spectrophotometer 2203 using DMF and DMSO as sol- 2.6. Synthesis of [Re(CO)3(IPP)Br] (1)\nvents. Circular dichroism (CD) measurements were carried out using a\nBiologic spectrophotometer (Science Instruments) with a 1 mm path- 4-chloro-m-phenylene diamine (1 mmol) was mixed with pyrrole-2-\nlength quartz cell. The concentration of CT-DNA used for the CD mea- carboxaldehyde (1 mmol) in methanol for 20 min. [Re(CO)5Br] (1\nsurement was 50 \u03bcg/mL and 1 mM for metal ions in a 5 mM Tris-HCl mmol) was added and the mixture was refluxed for 4 h. Compound 1\n(pH=7) buffer. was obtained by slow evaporation of the solvent, washed with hexane\n and diethyl ether, and dried. (Scheme 3)\n2.2. Computational calculations Yield (80 %), IR (KBr, cm\u2212 1): (CO stretch) 2020, 1886 cm\u2212 1, UV/Vis\n (DMSO): \u03bbmax (\u03b5, M\u20131cm\u20131) = 267 nm, 322 nm. 1H-NMR data (DMSO-d6,\n The ground state geometries and electronic structures of (Re ppm): \u03b4 8.3 (s, 1H), 7.30\u20137.25 (m, 1H), 7.24\u20137.21 (m, 1H), 6.74\u20136.71\n(CO)3(IPP)Br)) (1) and (Re(CO)3Br(BIPP)Re(CO)3Br) (2) were calcu- (m, 1H),6.3\u20136.2 (m,1H), 5.8\u20135.2 (bs,2H).\nlated according to density functional theory (DFT) calculations using the Elemental analysis C14H12BrClN3O3Re (569.81); calc. C 29.41; H\nGAUSSIAN-09 software package (Gaussian, Inc.)[34]. The computa- 2.12; N 7.35; Meas. C 29.81, H 2.10, N 7.41. HRMS-ESI (m/z): 569.8772\ntional investigation has been done using the LANL2DZ basis set for the\nRe atom and 6\u2013311+G(d,p) basis set for other atoms like C, H, N, O, Cl, 2.7. Synthesis of [Re(CO)3Br(BIPP)Re(CO)3Br] (2)\nand Br[35], to obtain the molecular geometry optimization, vibrational\nfrequencies, and vertical transitions at the DFT/B3LYP level for the Re The bimetallic compound was prepared by the one-pot condensation\ncomplexes in the ground state. method [4,Re(CO)5Br]. (2 mmol), 4-chloro-m-phenylene diamine (1\n mmol), and pyrrole-2-carboxaldehyde (2 mmol) were refluxed in\n2.3. Cytotoxic studies methanol for 4 h resulting in a violet color solution. The solvent was\n evaporated slowly on a rotary evaporator to obtain compound 2, fol-\n Human breast cancer cell line MCF-7 was obtained from the National lowed by washing with hexane and diethyl ether. (Scheme 3) Yield (85\nCentre for Cell Science, Pune, India. Cells were grown in Dulbecco\u2019s %)\nModified Eagle Medium (DMEM) high glucose media containing 10 % IR (KBr, cm\u2212 1): (CO stretch) 2016, 1893, UV/Vis (DMSO): \u03bbmax (\u03b5,\nFetal Bovine Serum (FBS), Antibiotic, and Antimitotic solution (Hi M\u20131cm\u20131) = 281 nm, 577.5 nm. 1H-NMR data (DMSO-d6, ppm): \u03b4 7.95\nMedia, India). Cells were incubated at 37 \u25e6 C humidified chamber at 5 % (s, 2H), 7.30\u20137.26 (m, 1H), 7.26\u20137.23 (m, 2H), 7.18\u20137.16 (m, 2H),\nCO2 condition. Cell viability was determined using MTT (3-(4, 5- 7.15\u20137.13(m, 1H), 6.74\u20136.73(s, 1H). Elemental analysis\nDimethylthiazol-2-yl)\u2212 2, 5-Diphenyltetrazolium Bromide). MCF-7 C22H13Br2ClN4O6Re2 (997.04); calc C 26.50; H 1.31; N 5.62; Meas. C\nbreast cancer cells are planted at 5\u22c5103 cells/well in 96 well plates for 27.0, H 1.59, N 5.59. HRMS-ESI (m/z): 996.7579\n24 h. Following that, cells were treated with varying concentrations of\nthe two metallic complexes. Each metallic complex was removed after 3. Results and discussion\n24 h of incubation and replaced with 30 \u00b5l of MTT reagent (0.5 mg/mL).\nAfter 4 h of incubation at 37 \u25e6 C, the MTT solution was removed, and the The general interest in developing new rhenium carbonyl complexes\nFormazan crystals were dissolved in DMSO (200 mL/well). After that, for theranostic applications has motivated us to design two new pyrro-\nthe plate was read at 570 nm. The obtained data was visually repre- lylimine ligands IPP and BIPP, with desired functionalities appropriate\nsented as percent viability vs. concentrations, and the IC50 was calcu- for enhancing the cytotoxicity of the corresponding complexes. As\nlated. For the apoptosis analysis, the cells were plated in a 6-well plate shown in Scheme 2, the ligand IPP is characterized by a bidentate\nand treated with the two different metallic complexes. The treated and moiety, with nitrogen from the pyrrole and one from the imine frag-\nuntreated cells were incubated with acridine orange and ethidium bro- ments, together with a halogen Cl and an amine substituent to facilitate\nmide solution and examined under a fluorescent microscope. The per- coordination to biological MOI. Similarly, the ligand BIPP also possesses\ncentage of apoptosis cell death is then calculated. a Cl substituent, an extended conjugation to enhance absorption in\n visible light, and two bidentate moieties to accommodate two metal\n2.4. Synthesis of IPP centers. We explored the effect of two metal centers and heteroatoms on\n the biological activity of the metal complexes [Re(CO)3(IPP)Br] (1), and\n The ligand IPP was synthesized by stirring pyrrole-2-carboxaldehyde [Re(CO)3Br(BIPP)Re(CO)3Br] (2), specifically in their anti-cancer ac-\n(1 mmol) and 4-chloro-m-phenylene diamine (1 mmol) in dry CH2C l2 tivity. The synthesis of phenylene bridged dinuclear Re(I) complex (2)\nfor 24 h. The reaction mixture was concentrated on a rotary evaporator, and mononuclear Re(I) complex (1) by one-pot condensation method is\nwashed with hexane, and dried to obtain IPP. (70 % yield) here reported. These two Re complexes (1 and 2) were easily synthesized\n 1\n H-NMR data (CDCl3, ppm): \u03b4 8.19 (s, 1H), 7.21\u20137.20 (m, 1H), 6.92 by the reaction of Re(CO)5Br, phenylene diamines, and pyrrole-2-\n(s, 1H), 6.67\u20136.66 (m, 1H), 6.58 (s,1H), 6.54\u20136.52 (m,1H), 6.29\u20136.28 carboxaldehyde in appropriate stoichiometries as shown in Scheme 3.\n(m, 1H). IR (KBr, cm\u2212 1): (NH stretch) 3438, 3290, 3217 cm\u2212 1 (CN The one-pot reaction of [Re(CO)5Br], pyrrole-2-carboxaldehyde, and\nstretch) 1597 cm\u2212 1, HRMS-ESI (m/z): 220.0650. phenylene diamine produced metal-bound Schiff base complexes in\n good yields(80\u201385 %). The reaction proceeded through the initial for-\n2.5. Synthesis of BIPP mation of a yellow solution of Schiff base and subsequently the change\n of color to red indicates the formation of metal complexes.\n The BIPP ligand was synthesized according to the procedures already Both compounds 1 and 2 are air-stable in a solid state for several\nreported in the literature but with slight modification. 2 equivalents of months. Compound 1 is completely soluble in polar solvents like\n\n 3\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Scheme 2. Ligands and rhenium carbonyl complexes are reported in this work.\n\n\n\n\n Scheme 3. One pot synthesis of Rhenium carbonyl complexes 1 (top), and 2 (bottom).\n\n\nacetonitrile and methanol, and sparingly soluble in dichloromethane. of carbonyl ligands occurs successively and peaks were obtained at m/z\nCompound 2 has limited solubility in methanol and acetonitrile, but is 462, 434, and 406. Whereas the dinuclear Re (I) complex [Re(CO)3Br\nhighly soluble in DMSO and DMF. Both compounds are stable in air even (BIPP)Re(CO)3Br] (2) shows the molecular ion peak at m/z 998.9.\nin a solution state for several weeks without decomposition. Unfortu- The synthesis of compounds 1 and 2 by two-step synthesis with the\nnately, several attempts to isolate suitable crystals of 1 and 2 for single- use of monomer ligands IPP and dimer ligand BIPP was also attempted\ncrystal XRD studies were unsuccessful even after several attempts. to compare and identify any new intermediate species in the two-step\nHowever, structural elucidation of compounds 1 and 2 was completed reaction [36]. The ligands IPP and BIPP were synthesized separately\nwith the help of FT-IR, DFT, and 1H NMR spectroscopic techniques. The in pure form and they were used in stoichiometric proportion in the\nsynthesized Re complexes were fully characterized by UV-visible spec- reaction with rhenium pentacarbonyl bromide in the toluene solution to\ntroscopy, photoluminescence, and TGA to prove the thermal stability of yield compounds 1 and 2 respectively. No other intermediate species or\n1 and 2. The ESI-mass spectra of both compounds also match with the new products were observed. However, the isolated yields from one pot\nassigned structures of the rhenium carbonyl complexes. synthesis were higher compared to the two-step process as described\n HRMS of the synthesized ligands IPP, BIPP, and their corresponding earlier. The Schematic representation of the synthesis of complexes 1,\nrhenium complexes 1 and 2 are shown in supplementary data. The and 2 using two-step procedures is summarised in Scheme 4.\nmolecular ion peak for the ligands IPP, and BIPP was observed at m/z The rhenium carbonyl complexes 1 and 2 have facial geometry as\n220.06, and 297.09 corresponding to the M+1 peak respectively, con- confirmed by both carbonyl stretching frequencies in the region\nfirming the formation of the ligands IPP and BIPP. The high-resolution observed for similar fac-rhenium carbonyl complexes [37,38]. Unlike\nmass spectrum of mononuclear Re (I) complex [Re(CO)3(IPP)Br] (1), other reported rhenium carbonyl complexes with pyrrolyl imine ligands,\ncontains the molecular ion peak and other fragmentation peaks were compounds 1 and 2 both retain the proton on the pyrrolic nitrogen atom\nalso obtained by successive loss of CO ligands, -Br ligand, etc. The mo- and halide bromine atom coordinated to rhenium metal in the axial\nlecular ion peak for 1 was obtained at m/z 570, and the loss of the position. The 1H-NMR spectra of both 1 and 2 in DMSO-d6 have distinct\nbromine ligand gave a peak in the mass spectra at 490. Further, the loss peaks at around 9.0 to 9.5 ppm corresponding to the imine hydrogen\n\n 4\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Scheme 4. Synthesis protocol for rhenium carbonyl complexes 1 and 2.\n\n\natom which appears in the deshielded region [39]). The 1H NMR of 1 Table 1 [41\u201343]. The FT-IR spectra of the synthesized Re complexes 1\nand 2 are shown in Figs S14 and S15. The 1H NMR of both the ligands and 2, match well with the already reported facial-rhenium tricarbonyl\nIPP and BIPP is recorded in CDCl3. For the ligand IPP, the peak at \u03b4 10 complexes showing three CO stretching frequencies [44,45] with the\nppm corresponds to \u2013NH proton of the pyrrole ring [39]. The free \u2013NH2 two lower energy CO bands sometimes merged into a single broad band\ngroups show peak at around 4 ppm. The imine proton shows peak at [41]. The synthesized Re carbonyl complexes contain only two carbonyl\naround 8.1 ppm. The aromatic protons of the phenyl ring were observed stretching vibrational bands showing the merging of the two closely\nat around 7 ppm with the protons of the pyrrole ring were slightly spaced CO bands.\nshielded and obtained at around 6 ppm. Similarly, for the ligand BIPP, To better understand the vibrational frequencies of the reported\nthe imine proton shows sharp peak at \u03b4 8.25 ppm. The characteristic molecules, we performed DFT frequency calculations on the synthesized\npeak in the synthesized complexes 1 and 2 are the imine proton peaks Re complexes 1 and 2 using the B3LYP model and LANL2DZ basis set\nobtained at around 9.5 ppm and are shifted downfield compared to [46,47]. A scale factor of 0.9679 is introduced to account for the basis\nimine protons in the ligands. The aromatic protons are obtained as set deficiencies and electron correlation effects in the calculations. The\nmultiplet in the range 6.9\u20138 ppm. experimentally and theoretically observed FT-IR spectra for complexes 1\n The complex 2 showed limited solubility in most solvents. In addi- and 2 are shown in supplementary data. The theoretically obtained\ntion to this, the presence of the bromine on the same and opposite sides FT-IR contains three CO stretching peaks (2095, 1976, and 1920) for\nof the phenylenediimine plane leads to isomerization and is also complex 1, whereas the experimental spectra show the merging of two\nresponsible for the complex nmr spectra. The elemental analysis shows lower energy CO bands. Similarly, the C=N stretching frequencies were\nthe experimentally observed elemental analysis data matches with the obtained experimentally at 1597 cm\u2212 1 and theoretically at 1634 cm\u2212 1.\ncalculated data. Upon taking into consideration scaling factor, the theoretical CO\n stretching frequencies were reduced to 2027, 1912, 1858 cm\u2212 1). Simi-\n larly, the C=N stretching frequency became 1581 cm\u2212 1 upon intro-\n3.1. Vibrational properties duction of scaling factor to account for the basis set deficiencies. The\n theoretical vibrational frequencies matches well with the experimen-\n The FT-IR spectra of ligands IPP and BIPP contain azomethine link- tally obtained values. The scenario is more articulated for the dinuclear\nage i.e. \u03bd (C=N) groups in the range 1580\u20131630 cm\u2212 1 as shown in rhenium complex 2 due to the presence of a large number of possible\nFigs. S3 and S4. The significant elongation of the Re-Br bond in 1 and 2, distinct vibrational modes for the dinuclear complexes [41].\ncompared to the similarly reported compound [Re(CO)3(bpy)Br] (Re-Br\n2.58 \u00c5), with bond length of 2.638 and 2.640 \u00c5 in 1 and 2 respectively,\nsuggests increased donation of electron density from the diimine ligands 3.2. Photophysical properties\nIPP and BIPP to rhenium metal, and reducing the donation of \u03c3 electron\ndensity from the bromide ligand making its release more facile [40]. The UV-visible absorption spectra of complexes were recorded in DMSO.\nmononuclear complex 1 and dinuclear complex 2 have markedly Typically, UV-visible absorption spectra of Re(CO)3 diimine complexes\ndifferent IR spectra. The observed carbonyl stretching frequency values show two types of electronic transitions [5]. The first absorption band\nare slightly higher for mononuclear complex 1 (2029, 1892 cm\u2212 1) than below 300 nm can arise result from \u03c0\u2192\u03c0* transitions. Instead, the\nthe corresponding dinuclear rhenium complex 2 (2012, 1883 cm\u2212 1) weaker bands at lower energy are assigned to singlet metal to ligand\nwhich is associated with the enhanced \u03c0 back bonding in dinuclear charge transfer MLCT bands [48], characterized by low absorptivity due\ncomplexes. The stretching vibrational frequencies of 1 and 2 are listed in to their spin-forbidden nature. The lower energy charge transfer band\n\n 5\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\narising due to the t2g\u2192\u03c0* transition is sensitive to the nature of the (2) (Fig. 4). The electronic properties of the synthesized Re complexes\nsolvent. More polar solvents shift the band to higher energy. The are summarized in Table 2.\nmononuclear complex Re(CO)3(pyca-pH)Br shows two strong absorp-\ntion peaks at 262, 319 nm assigned as Ligand Centered (LC) \u03c0\u2192\u03c0*\ntransition. Whereas the main transition in dinuclear complex 2 lies at 3.3. Theoretical calculations on Re(I) complexes\n261 nm and peaks arising due to metal to ligand charge transfer at 526\nnm as shown in Fig. 1. In comparison to the mononuclear complex, the The GAUSSIAN 09 software package[51] with B3LYP functional is\ndinuclear complex exhibits more intense MLCT absorption band. employed for optimizing the geometries of mononuclear and dinuclear\n The mononuclear and dinuclear complexes 1 and 2, upon photoex- Re complexes 1 and 2 respectively with LANL2DZ basis set [46] for the\ncitation at different wavelengths, i.e., 271, 332, 402, 455 and 464 nm, Re atom and 6\u2013311+G(d,p) basis set [46] for other atoms like C, H, N, Cl,\ndisplayed broad and featureless emission in the visible region of light, Br and O. As per the DFT calculations, the optimized ground state ge-\ncharacterized by two bands at 498 and other at ~650 nm, as shown in ometry exhibited by (Re(CO)3(IPP)Br)) (1) and (Re(CO)3Br(BIPP)Re\nFig. 2. The emission features are independent of the excitation energy (CO)3Br) (2) is distorted octahedral around the rhenium metal center. In\nand similar spectra are observed for tricarbonyl-Re based complexes both Re complexes, rhenium metal is coordinated to nitrogen of the\n[35]. The emission intensity resulted higher for Complex 2 than for imine group of the Schiff base and nitrogen of the pyrrole ring. The three\nComplex 1 when excited with higher energy (271, 332, 402 nm), carbonyl ligands are coordinated to Re (I) facially and the sixth coor-\nwhereas the trend is just opposite when excited with low energy light dination site is occupied by the bromine ligand. The equatorial position\n(455, 464 nm). The excitation spectra of both the complexes corre- is occupied by the other two carbonyl groups and two nitrogen atoms of\nsponding to the 498, 650 nm emissions are shown in Fig. 3 and they the ligand IPP and BIPP in 1 and 2 respectively. The Re \u2013CO bond\nconsist of four bands at 271, 332, 402, and 455 nm. These band positions lengths are found in the range 1.90\u20131.92 \u00c5, these bond lengths obtained\nare in accordance with the absorbance spectra of these complexes. are consistent with the reported rhenium carbonyl complexes [52].\nHowever, the intensity is different because the non-radiative decay of The DFT-optimized structures of Re complex 1 and 2 are shown in\nthe excited state plays a crucial role in the intensity of the excitation (Fig. 5).\nbands. The emission profile for rhenium tricarbonyl species generally Among the electronic properties, the energies of the HOMO and\nconsists of a single broad band due to the transition from the lowest LUMO orbitals are very important in quantum chemistry. The highest\n3\n MLCT excited state to the ground state, generally associated with a occupied molecular orbital (HOMO is mainly localized on the metal\nrelatively short lifetime in the ns range [49]. centre. The HOMO of both 1 and 2 exhibits mixed contribution from d\u03c0\n The lifetime analysis of excited species for 1 and 2 after excitation at (Re), p\u03c0(Br), and \u03c0 orbitals of carbonyl groups, whereas the LUMO has\n455 nm was investigated in DMSO solvent at 498 and 650 nm emissions. more \u03c0* character corresponding to \u03c0* orbital of Schiff base ligand as\nThe decay plots for both compounds 1 and 2 for 498 emissions follow shown in Fig. 6. The HOMO-LUMO analysis further reveals the transfer\nthe single exponential decay pathway with the excited state lifetime of electron density from ligand to metal which further suggests that the\nvalues of 3.7 and 4.2 ns, respectively as shown in Fig. 4. However, the possible transitions are LMCT charge transfer transitions. The stability of\n650 nm emission decays biexponentially for both the complexes. The the synthesized Re complexes 1 and 2 was evaluated by finding various\nshorter lived component (\u03c42) due to decay of LLCT excited state (\u03c0-\u03c0*), chemical reactivity parameters such as electronegativity (\u03c7), ionization\nand (\u03c41) component is assigned to decay of MLCT state. The assignments potential (IP), electron affinity (EA), hardness (\u03b7), chemical potential\nof transitions arising from excited state were investigated in detail using (\u00b5), and electrophilicity index (\u03c9) etc. as listed in Table 3. The chemical\nthe TD-DFT calculations and will be discussed in detail in the compu- reactivity parameters were obtained from the energy of HOMO and\ntational calculations section. A similar biexponential decay pathway was LUMO orbitals. The energy difference between the highest occupied\nalso observed for the compound [Re(CO)3((n-N)(btpz)], where bptz = molecular orbital (HOMO) and the lowest unoccupied molecular orbital\n3,5-bis(trifluoromethyl) pyrazolate[50]. The emission lifetime of the (LUMO) also known as energy gap (Eg) determines the stability and\nmononuclear complex Re(CO)3(IPP)Br (1) is found to be shorter than the reactivity of the compounds. The lower energy gap of complex 2 (2.99\nemission lifetime of the dinuclear complex Re(CO)3Br(BIPP)Re(CO)3Br eV) in comparison to 1 (2.99 eV) suggests the greater reactivity of\n complex 2. The synthesized Re complexes show higher ionization\n\n\n\n\n Fig. 1. UV-visible absorption spectra of formed complexes in DMSO at room temperature.\n\n 6\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Fig. 2. Emission spectra of Re complex 1 and 2 at different excitation wavelengths.\n\n\npotential values than the electron affinity values indicating the greater 3.4. Cytotoxic studies of the synthesized re complexes (1 and 2) against\nelectron donation ability of the complexes than the electron accepting MCF-7 breast cancer cell line\npower. The compound 2 has higher electronegativity and electrophi-\nlicity index than 1 as shown in Table 3 which further suggests the greater The cytotoxic activity of the synthesized rhenium carbonyl com-\nability of compound 2 to interact with a biological target by means of plexes has been explored against the MCF-7, the breast cancer cell line\ncovalent bond or H-bonding. The findings of global reactivity parame- (Fig. 7). The results obtained indicate that 1 and 2 inhibit MCF-7 cells in\nters provide evidence regarding the acceptance and donor ability, a dose-dependent manner. MCF-7 cells were inhibited by exposure to\nhardness, chemical reactivity of the synthesized complexes which is complex 2, with an IC50 of 40 \u00b5M. 1 inhibited breast cancer cell growth\nrelated to the biological activities. at 75 \u00b5M. The higher efficacy of 2 in comparison to 1 against the MCF-7\n breast cancer line was attributed to the possible synergistic effect of 2\n rhenium centers in 2. Also, the cellular uptake and cytotoxicity are\n largely affected by lipophilicity and molecular size of the compound\n [53]. The presence of a halogen atom on the aromatic ring enhances the\n\n\n 7\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Fig. 3. Excitation spectra of Re complex 1 and 2 at different emission wavelengths.\n\n\n\nTable 1\n Table 2\nSelected vibrational frequencies in (cm\u2212 1) for the Re complexes 1 and 2.\n Electronic spectral data of Re complexes (1, 2) at room temperature.\n Complex \u03bdCO [cm\u2212 1] \u2013N [cm\u2212 1]\n \u03bdC\u2013\n Complex UV visible absorption/nm\n A1 E\n LC MLCT \u03bbem \u03c4/ns\n Re(CO)3(IPP)Br (1) 2029 1892 1597\n Re(CO)3(pyca-pH)Br 262, 319 530 498, 650 3.7,6.7\n Re(CO)3Br(BIPP)Re(CO)3Br (2) 2012 1883 1627\n Re(CO)3Br(m-PPC)Re(CO)3Br 261 526 498, 650 4.2, 9.5\n\n\n\n\nFig. 4. Photoluminescence lifetime decay measurements of Re complex 2 (top right), Re complex 1(top left) recorded at 498 nm corresponding to the 1st emission\npeak, and lifetime decay measurements of Re complex 2 (bottom right), Re complex 1(bottom left) recorded at 650 nm corresponding to the 2nd emission peak.\n\n 8\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Fig. 5. Optimised geometry of 2(left), and 1 (right). Color code: red for O, blue for N, gray for C, white for H, green for Cl, dark red for Br, steel blue for Re.\n\n\n\n\n Fig. 6. Molecular orbital surfaces for 1 and 2, HOMO (top) and LUMO (bottom).\n\n\n lipophilicity which increases the ability of the molecule to interact with\nTable 3\n various cancer lines [54]. Further, the greater cytotoxicity of dinuclear\nCalculated Global reactivity descriptor parameters of 1 and 2.\n rhenium complex 2 might be due to the possible synergistic effect and\n Global reactivity descriptors 1 2 greater lipophilicity of the rhenium complex 2 in comparison to\n EHOMO (eV) \u2212 6.07 \u2212 6.07 mononuclear rhenium complex 1. Ye et al. have also observed increased\n ELUMO (eV) \u2212 2.91 \u2212 3.08 lipophilicity of bidentate ligands in dinuclear rhenium complexes and\n \u0394E (LUMO-HOMO) (eV) 3.16 2.99\n found that the dinuclear complexes possess improved anticancer effi-\n Chemical hardness (\u03b7) 1.58 1.49\n Ionization potential (IP) 6.07 6.07\n cacy than the mononuclear counterparts [53].\n Electron affinity (EA) 2.91 3.08\n Electronegativity (\u03c7) 4.49 4.57 3.5. Apoptotic nuclear morphology assessment\n Chemical potential (\u00b5) \u2212 4.49 \u2212 4.57\n Electrophilicity index (\u03c9) 6.37 6.94\n Cells that have been treated with the two organometallic complexes\n\n 9\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Fig. 7. Breast cancer growth inhibition by complex 1 and 2. Data shown are mean \u00b1 SD. *p < 0.05, compared with respective control (untreated cells).\n\n\nare subject to different biological changes, that accompany apoptotic varying the concentration of CT-DNA.\ncell death, including cell shrinkage, nuclear condensation, DNA UV-visible absorption spectroscopy is one of the simplest methods to\nbreakage, blebbing, and the creation of apoptotic bodies. The chromatin study the binding affinity between the CT-DNA and the synthesized\ncondensation in the stained nucleus was confirmed by the results of the complexes. The change in the electronic absorption spectra upon the\nAO/EB staining, which also helped to distinguish between viable, gradual addition of CT-DNA is shown in Fig. 9. It was observed that the\napoptotic, and necrotic cells (Fig. 8). The apoptotic cells had uniform addition of CT-DNA leads to a decrease in the absorbance value of the\nbright orange nuclei. The nuclei of the viable cells were uniformly green. complexes leading to a hypochromic effect. The significant hypochromic\nCancer cells treated with compounds 1 and 2 showed signs of apoptosis, shift suggests intercalative mode of binding,\nsuch as altered cell size and nuclear fragmentation, when stained with\nAO/EB. Compounds 1 and 2\u2032s anticancer activity may result from the\ninduction of apoptosis against MCF-7. The fluorescence pattern of the 3.7. Circular dichroism\nstain is determined by the vitality and membrane integrity of the cells in\nthis staining approach. Live cells are exclusively permeable to acridine CD spectroscopic technique has been successfully employed to\norange and so glow green, but dead cells are permeable to ethidium determine the conformational changes induced by the interaction of\nbromide and fluoresce orange-red. After the complex was treated, all of DNA with the metal complex. The CD spectra of CT-DNA were recorded\nthese morphological alterations were found. over a scan range of 220\u2013360 nm and it has been found to contain one\n positive band at 275 nm arising due to base stacking and one negative\n band at 247 nm due to helicity [55]. The minor groove binding mode of\n3.6. DNA binding studies interaction showed only a little perturbation on the base stacking and\n helicity bands while the intercalative binding mode caused enhance-\n The calf-thymus (CT-DNA) was prepared in 5 mM Tris\u2013HCl buffer ment in the intensities of both the bands. Incubation of DNA with\nsolution (pH= 7.4) and stored at 4 \u25e6 C. The CT-DNA was adequately free complexes 1 and 2 leads to enhancement of the intensity of both the\nof protein contamination as indicated by the UV absorption ratio of 1.86 positive and negative bands with no considerable shift in \u03bbmax observed\nat 260 and 280 nm. The interaction between the synthesized metal (Fig. 10). These changes observed support the intercalative mode of\ncomplexes 1 and 2 with the DNA was carried out by performing the binding [56]. Furthermore, large spectral band changes were observed\nabsorption titrations at fixed concentrations of metal complexes while in dinuclear rhenium complex 2 in comparison to mononuclear rhenium\n\n\n\n\n Fig. 8. Apoptotic nuclear morphology assessment, control (left), complex 1 (middle), complex 2 (right).\n\n 10\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\n\n\n Fig. 9. Absorption spectra of complex 2 (1 mM) in 5 mM Tris\u2013HCl/50 mM NaCl buffer upon addition of increasing amounts of DNA.\n\n\n\n\nFig. 10. CD spectra of CT-DNA, and the interaction with complexes (1 and 2). All the spectra were recorded in 5 mM Tris\u2013HCl/50 mM NaCl buffer, pH 7.2 and 25 \u25e6 C.\n\n\ncomplex 1 suggesting the greater intercalation ability of complex 2 [55]. growth at 40 \u00b5M while the IC50 value of mononuclear rhenium complex\n 1 is 75 \u00b5M. The greater efficacy of rhenium carbonyl complex 2 in\n4. Conclusion comparison to 1 could be due to the possible synergistic effect of 2\n rhenium centers in complex 2. This is further supported by the CD\n Two new rhenium carbonyl complexes with iminopyrrolyl ligands studies which suggest the greater intercalation ability of complex 2. The\nwere synthesized, characterized and their photophysical properties were findings contribute valuable insights into the design and application of\nstudied. The cytotoxic activity of the synthesized rhenium complexes rhenium carbonyl complexes in cancer therapy.\nwas evaluated against breast cancer cell line MCF-7. The rhenium\ncomplexes 1 and 2 induce cell death by apoptosis causing damage to Funding\nmitochondria, nucleus, and intracellular generation of reactive oxygen\nspecies (ROS). Complexes 1 and 2 interact with cellular DNA via inter- The authors declare that no funds or grants were received during the\ncalative binding mode as evidenced by DNA binding studies and circular preparation of this manuscript.\ndichroism. The dinuclear rhenium complex 2 inhibits breast cancer cell\n\n 11\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n\nEthics approval [6] L.D. Ramos, H.M. Da Cruz, K.P. Morelli Frin, Photophysical properties of rhenium\n (i) complexes and photosensitized generation of singlet oxygen, Photochem.\n Photobiol. Sci. 16 (2017) 459\u2013466, https://doi.org/10.1039/c6pp00364h.\n Not Applicable. [7] G.V. Sidorenko, A.E. Miroslavov, Higher technetium (i) carbonyls and possibility of\n using them in nuclear medicine : problems and prospects, Radiochemistry 63\n (2021) 253\u2013262, https://doi.org/10.1134/S1066362221030012.\nConsent to participate [8] A. Sharma S, V. Nee, B. Kar, U. Das, P. Paira, Target-specific mononuclear and\n binuclear rhenium(I) tricarbonyl complexes as upcoming anticancer drugs, RSC\n Informed consent was obtained from all the authors involved. Adv. 12 (2022) 20264\u201320295, https://doi.org/10.1039/d2ra03434d.\n [9] A. Leonidova, G. Gasser, Underestimated potential of organometallic rhenium\n complexes as anticancer agents, ACS Chem. Biol. (2014) 2180\u20132193.\nConsent to publish [10] Influence of the substituent on the phosphine ligand in novel rhenium(I)\n aldehydes. Synthesis, computational studies and first insights into the\n antiproliferative activity, Dalton Trans. (2018) 13861\u201313869, https://doi.org/\n The authors have consented to the submission of research work to 10.1039/c8dt03160f.\nthe Journal of Molecular Structure. [11] K. Ranasinghe, S. Handunnetti, I.C. Perera, T. Perera, Synthesis and\n characterization of novel rhenium (I) complexes towards potential biological\n imaging applications, Chem. Cent. J. (2016) 1\u201310, https://doi.org/10.1186/\nCRediT authorship contribution statement s13065-016-0218-4.\n [12] L.K. Mckenzie, H.E. Bryant, J.A. Weinstein, Transition metal complexes as\n photosensitisers in one- and two-photon photodynamic therapy, Coord. Chem. Rev.\n Diksha: Writing \u2013 review & editing, Writing \u2013 original draft, Inves- 379 (2019) 2\u201329, https://doi.org/10.1016/j.ccr.2018.03.020.\ntigation, Formal analysis, Data curation. Maharaja Somasundaram: [13] T.M. Mclean, J.L. Moody, M.R. Waterland, S.G. Telfer, Luminescent rhenium(I)-\nFormal analysis. Mathan Ganeshan: Data curation. Satish Kumar dipyrrinato complexes, Inorg. Chem. 51 (2012) 446\u2013455, https://doi.org/\n 10.1021/ic201877t.\nSamal: Data curation. Dhanasekaran Dharumadurai: Formal analysis. [14] C.C. Konkankit, S.C. Marker, K.M. Knopf, J.J. Wilson, Anticancer activity of\nSherzod Madrahimov: Data curation. Akshi Deshwal: Data curation. complexes of the third row transition metals, rhenium, osmium, and iridium,\nHarminder Kaur: Supervision, Resources. Alessandro Sinopoli: Dalton Trans. (2018) 9934\u20139974, https://doi.org/10.1039/c8dt01858h.\n [15] M.N. Pinto, P.K. Mascharak, Light-assisted and remote delivery of carbon\nInvestigation, Formal analysis, Data curation. Veeranna Yempally: monoxide to malignant cells and tissues: photochemotherapy in the spotlight,\nWriting \u2013 review & editing, Supervision, Methodology, J. Photochem. Photobiol. C Photochem. Rev. 42 (2020) 100341.\nConceptualization. [16] Computational design of rhenium(I) carbonyl complexes for anticancer\n photodynamic therapy, Inorg. Chem. 61 (2022) 439\u2013455, https://doi.org/\n 10.1021/acs.inorgchem.1c03130.\n [17] F. Morgan, R. Thornback, Rhenium(V) and technetium(V) complexes with N-[2\nDeclaration of competing interest (1H-pyrolylmethyl)]-N\u2032-(4-pentene-3-one-2) ethane-1,2-diaminate (C12H16N3O,\n MRP 20). X-ray crystal structures of H3MRP 20 and TcO(MRP 20), Inorg. Chim.\n Acta (1991) 257\u2013264.\n The authors declare that they have no known competing financial [18] P. Yadav, N. Fridman, A. Mizrahi, Z. Gross, Rhenium(i) sapphyrins: remarkable\ninterests or personal relationships that could have appeared to influence difference between the C6F5 and CF3-substituted derivatives, Chem. Commun. 56\nthe work reported in this paper. (2020) 980\u2013983, https://doi.org/10.1039/c9cc08877f.\n [19] J. Mirebeau, F.Le Bideau, Synthesis of Rhenium Carbonyl Complexes Bearing\n Substituted Pyrrolyl Ligands, Organometallics 27 (2008) 2911\u20132914.\nData availability [20] C.Y. Chan, P.A. Pellegrini, I. Greguric, P.J. Barnard, Rhenium and technetium\n tricarbonyl complexes of N-heterocyclic carbene ligands, Inorg. Chem. 53 (2014)\n 10862\u201310873, https://doi.org/10.1021/ic500917s.\n Data will be made available on request.\n [21] A. Shegani, C. Triantis, C. Kiritsis, C. Raptopoulou, V. Psycharis, M. Pelecanou,\n I. Pirmettis, M. Papadopoulos, Neutral fac-[Re(NNN)(CO)3] complexes with NNN\n tridentate ligands containing pyrrole or indole, Inorg. Chem. Commun. 63 (2016)\n 1\u20134, https://doi.org/10.1016/j.inoche.2015.11.002.\nAcknowledgements [22] C.C. Konkankit, B.A. Vaughn, S.N. Macmillan, E. Boros, J.J. Wilson, Combinatorial\n synthesis to identify a potent, necrosis-inducing rhenium anticancer agent, Inorg.\n Diksha would like to acknowledge Punjab Engineering College (PEC) Chem. (2019), https://doi.org/10.1021/acs.inorgchem.8b03552.\n [23] S. I\u0307ris\u0327li, S. G\u00fcnnaz, O\u0308. O\u0308zcan, A. Ar\u0131, M. Maral, A. Erdem, D. O\u0308zel, F. Yurt, Platinum\nand MHRD for providing GATE fellowship.We would like to thank Sci- (II) schiff base complexes and their effects on the inhibition of amyloid \u03b21\u201342\nence & Engineering Research Board (SERB) (File.No: EEQ/2018/ aggregation, Appl. Organomet. Chem. (2024) 1\u201316, https://doi.org/10.1002/\n001446 Dated 22 March 2019) for providing their project funding and aoc.7540.\n [24] A.E.M. Abdallah, S.A. Abdel-Latif, G.H. Elgemeie, Novel fluorescent\nstudent fellowship.\n benzothiazolyl-coumarin hybrids as anti-SARS-COVID-2 agents supported by\n molecular docking studies: design, synthesis, X-ray crystal structures, DFT, and TD-\nSupplementary materials DFT/PCM calculations, ACS Omega 8 (2023) 19587\u201319602, https://doi.org/\n 10.1021/acsomega.3c01085.\n [25] S. Muhammad, V. Yempally, M. Anas, S. Moncho, S.J. Kyran, E.N. Brothers, D.\n Supplementary material associated with this article can be found, in J. Darensbourg, A.A. Bengali, Mechanism of CO displacement from an unusually\nthe online version, at doi:10.1016/j.molstruc.2024.139506. labile rhenium complex: an experimental and theoretical investigation, Inorg.\n Chem. (2012) 13041\u201313049.\n [26] D. Chiodi, Y. Ishihara, Magic Chloro \u201d: profound effects of the chlorine atom in\nReferences drug discovery, J. Med.Chem. 66 (2023) 5305\u20135331.\n [27] Z. Pan, L. He, Dinuclear phosphorescent rhenium(i) complexes as potential\n anticancer and photodynamic therapy agents, Dalton Trans. 49 (2020)\n[1] B.K. Singh, Spectroscopic, electrochemical and biological studies of the metal\n 11583\u201311590, https://doi.org/10.1039/d0dt02424d.\n complexes of the Schiff base derived from pyrrole-2-carbaldehyde and\n [28] E.B. Bauer, A.A. Haase, R.M. Reich, D.C. Crans, F.E. K\u00fchn, Organometallic and\n ethylenediamine, Arab. J. Chem. (2012), https://doi.org/10.1016/j.\n coordination rhenium compounds and their potential in cancer therapy, Coord.\n arabjc.2012.10.007.\n Chem. Rev. 393 (2019) 79\u2013117, https://doi.org/10.1016/j.ccr.2019.04.014.\n[2] C. Ko, G. Li, C. Leung, D. Ma, Dual function luminescent transition metal complexes\n [29] E. Giorgi, F. Binacchi, C. Marotta, A. Pratesi, D. Cirri, C. Gabbiani, Highlights of\n for cancer theranostics : the combination of diagnosis and therapy, Coord. Chem.\n new strategies to increase the efficacy of transition metal complexes for cancer\n Rev. 381 (2019) 79\u2013103, https://doi.org/10.1016/j.ccr.2018.11.013.\n treatments, Molecules 28 (2023) 273.\n[3] Z. Huang, J.J. Wilson, Therapeutic and diagnostic applications of multimetallic\n [30] V. Fern, M. Concepci, Heterobimetallic complexes for theranostic applications,\n rhenium (I)tricarbonyl complexes, Eur. J. Inorg. Chem. (2021) 1312\u20131324,\n Chem. Eur. J. 24 (2018) 3345\u20133353, https://doi.org/10.1002/chem.201705335.\n https://doi.org/10.1002/ejic.202100031.\n [31] C.B. Smith, L.C. Days, D.R. Alajroush, K. Faye, Y. Khodour, S.J. Beebe, A.A. Holder,\n[4] A. Hasheminasab, H.M. Rhoda, L.A. Crandall, J.T. Ayers, V.N. Nemykin, R.\n Special issue invited review photodynamic therapy of inorganic complexes for the\n S. Herrick, C.J. Ziegler, Hydrazine-mediated strongly coupled Re(CO)3 dimers,\n treatment of cancer, Photochem. Photobiol. (2022) 17\u201341, https://doi.org/\n Dalton Trans. 44 (2015) 17268\u201317277, https://doi.org/10.1039/c5dt02821c.\n 10.1111/php.13467.\n[5] I. Maisuls, E. Wolcan, O.E. Piro, E.E. Castellano, G. Petroselli, R. Erra-Balsells, F.\n [32] C.C. Konkankit, E. Boros, Combinatorial synthesis to identify a potent, necrosis-\n M. Cabrerizo, G.T. Ruiz, Synthesis, structural characterization and biological\n inducing rhenium anticancer agent, Inorg. Chem. 58 (2019) 3895\u20133909, https://\n evaluation of rhenium(I) tricarbonyl complexes with \u03b2-carboline ligands,\n doi.org/10.1021/acs.inorgchem.8b03552.\n ChemistrySelect 2 (2017) 8666\u20138672, https://doi.org/10.1002/slct.201701961.\n\n\n 12\n\fDiksha et al. Journal of Molecular Structure 1319 (2025) 139506\n\n[33] K. Schindler, F. Zobi, Photochemistry of rhenium (I) diimine tricarbonyl complexes [45] H. Hartmann, T. Scheiring, J. Fiedler, W. Kaim, Structures and\n in biological applications, Chimia 75 (2021) 837\u2013844, https://doi.org/10.2533/ spectroelectrochemistry (UV-vis, IR, EPR) of complexes [(OC)3ClRe]n(abpy), n =\n chimia.2021.837 (Aarau). 1, 2; abpy = 2,2\u2032-azobispyridine, J. Organomet. Chem. 604 (2000) 267\u2013272,\n[34] M. Caricato, M.J. Frisch, A. Frisch, J. Hiscocks, M.J. Frisch, Gaussian 09 IOps https://doi.org/10.1016/S0022-328X(00)00282-5.\n reference manual, 2013. http://www.gaussian.com/g_tech/g_iops/iops2.pdf. [46] D. A\u0301lvarez, M.I. Mene\u0301ndez, R. Lo\u0301pez, Computational design of rhenium(I) carbonyl\n[35] A. Comia, L. Charalambou, S.A.E. Omar, P.A. Scattergood, P.I.P. Elliott, complexes for anticancer photodynamic therapy, Inorg. Chem. 61 (2022) 439\u2013455,\n A. Sinopoli, Photophysical and electrocatalytic properties of rhenium(I) triazole- https://doi.org/10.1021/acs.inorgchem.1c03130.\n based complexes, Inorganics 8 (2020) 1\u201313, https://doi.org/10.3390/ [47] K. Choroba, A. Maron\u0301, A. S\u0301witlicka, A. Sz\u0142apa-Kula, M. Siwy, J. Grzelak,\n inorganics8030022. S. Mac\u0301kowski, T. Pedzinski, E. Schab-Balcerzak, B. Machura, Carbazole effect on\n[36] A.I. Adebomi, A.O. Abimbola, O.E. Gabriel, Synthesis, physicochemical and ground- and excited-state properties of rhenium(i) carbonyl complexes with\n antimicrobial properties of rhenium (I) tricarbonyl complexes of isatin Schiff bases, extendedterpy-like ligands, Dalton Trans. 50 (2021) 3943\u20133958, https://doi.org/\n African J. Biotechnol. 20 (2021) 175\u2013185, https://doi.org/10.5897/ 10.1039/d0dt04340k.\n ajb2020.17291. [48] K.K. Lo, J.S. Lau, V.W. Fong, Properties of a luminescent rhenium (I) polypyridine\n[37] D. Vitale, Facial rhenium tricarbonyl complexes with modified DII ligands facial anthraquinone complex with a thiourea receptor, Mercury (2004) 1098\u20131106.\n rhenium tricarbonyl complexes with modified DII ligands, Inorg. Chem. Commons [49] H. Xia, X. Liu, Synthesis, structure, and luminescence of rhenium (I) complexes\n (2019). with substituted bipyridines, J. Coord. Chem. (2012) 37\u201341, https://doi.org/\n[38] R. Kia, S. Mahmoudi, P.R. Raithby, New rhenium-tricarbonyl complexes bearing 10.1080/00958972.2012.671479.\n halogen-substituted bidentate ligands structural, computational and Hirshfeld [50] A. Coleman, C. Brennan, J.G. Vos, M.T. Pryce, Photophysical properties and\n surfaces studies, CrystEngComm 21 (2019) 77\u201393, https://doi.org/10.1039/ applications of Re(I) and Re(I)-Ru(II) carbonyl polypyridyl complexes, Coord.\n c8ce01860j. Chem. Rev. 252 (2008) 2585\u20132595, https://doi.org/10.1016/j.ccr.2008.07.001.\n[39] A. Charles, R. Krishnaveni, K. Sivaraj, Synthesis, characterization of metal [51] L.O. Ahmed, R.A. Omer, Journal of physical chemistry and functional materials\n complexes of schiff base derived from pyrrole-2-carbaldehyde and 4-methoxy population analysis and UV\u2013Vis spectra of dopamine molecule using gaussian 09,\n aniline and their biological studies, Asian J. Chem. 32 (2020) 3012\u20133018. J. Phys. Chem. Funct. Mater. 3 (2020) 48\u201358. https://dergipark.org.tr/jphcfum.\n[40] T. Auvray, A.K. Pal, G.S. Hanan, Electronic properties of rhenium(I) carbonyl [52] J.F. Martinez, N.T. La Porte, S. Chaudhuri, A. Sinopoli, Y.J. Bae, M. Sohail, V.\n complexes bearing strongly donating hexahydro-pyrimidopyrimidine based S. Batista, M.R. Wasielewski, Effect of electronic coupling on electron transfer rates\n ligands, Eur. J. Inorg. Chem. 2021 (2021) 2570\u20132577, https://doi.org/10.1002/ from photoexcited naphthalenediimide radical anion to Re(bpy)(CO)3X, J. Phys.\n ejic.202100028. Chem. C 123 (2019) 10178\u201310190, https://doi.org/10.1021/acs.jpcc.8b12264.\n[41] R. Jordan, M. Niazi, S. Scha\u0308fer, W. Kaim, A. Klein, Rhenium tricarbonyl complexes [53] R.R. Ye, C.P. Tan, M.H. Chen, L. Hao, L.N. Ji, Z.W. Mao, Mono- and dinuclear\n of azodicarboxylate ligands, Molecules 27 (2022), https://doi.org/10.3390/ phosphorescent rhenium(I) complexes: impact of subcellular localization on\n molecules27238159. anticancer mechanisms, Chem. A Eur. J. 22 (2016) 7800\u20137809, https://doi.org/\n[42] S. Frantz, M. Sieger, I. Hartenbach, F. Lissner, T. Schleid, J. Fiedler, C. Duboc, 10.1002/chem.201505160.\n W. Kaim, Structure, electrochemistry, spectroscopy, and magnetic resonance, [54] A.M. El-Agrody, A.M. Fouda, E.S.A.E.H. Khattab, Halogenated 2-amino-4H-benzo\n including high-field EPR, of {(\u03bc-abpy)[Re(CO)3X]2}o/\u2022-, where abpy = 2,2\u2032- [h]chromene derivatives as antitumor agents and the relationship between\n azobispyridine and X = F, Cl, Br, I, J. Organomet. Chem. 694 (2009) 1122\u20131133, lipophilicity and antitumor activity, Med. Chem. Res. 26 (2017) 691\u2013700, https://\n https://doi.org/10.1016/j.jorganchem.2008.09.034. doi.org/10.1007/s00044-016-1773-x.\n[43] W. Kaim, S. Kohlmann, The nature of reduced and excited states of \u03c0-electron- [55] J. Zhao, S. Zhi, H. Yu, R. Mao, J. Hu, W. Song, J. Zhang, Mitochondrial and nuclear\n deficient complexes between Re(CO)3Hal and diimine ligands, Inorg. Chem. 29 DNA dual damage induced by 2-(2\u2032-quinolyl)benzimidazole copper complexes with\n (1990) 2909\u20132914, https://doi.org/10.1021/ic00341a010. potential anticancer activity, RSC Ad. 7 (2017) 51162\u201351174, https://doi.org/\n[44] S. Frantz, J. Fiedler, I. Hartenbach, T. Schleid, W. Kaim, A complete series of 10.1039/c7ra09102h.\n tricarbonylhalidorhenium(I) complexes (abpy)Re(CO)3(Hal), Hal = F, Cl, Br, I; [56] V. Thamilarasan, N. Sengottuvelan, N. Stalin, P. Srinivasan, G. Chakkaravarthi,\n abpy = 2,2\u2032-azobispyridine: structures, spectroelectrochemistry and EPR of Synthesis, interactions, molecular structure, biological properties and molecular\n reduced forms, J. Organomet. Chem. 689 (2004) 3031\u20133039, https://doi.org/ docking studies on Mn, Co, Zn complexes containing acetylacetone and pyridine\n 10.1016/j.jorganchem.2004.06.047. ligands with DNA duplex, J. Photochem. Photobiol. B Biol. 160 (2016) 110\u2013120,\n https://doi.org/10.1016/j.jphotobiol.2016.03.018.\n\n\n\n\n 13\n\f", "pages_extracted": 13, "text_length": 74591}