Diimine Complexes Research Articles

Platinum(II) diimine complexes containing phenylpyridine ligands decorated with anionic closo-monocarborane clusters [CB11H12

We report three Pt(II) diimine complexes containing ancillary ligands of phenylpyridine furnished with anionic closo-monocarborane clusters [CB11H12]-. Three neutral complexes exhibit intensive phosphorescence in the solid state and complex 1 was used to detect acetonitrile vapor in a quartz plate.

Reaching strong absorption up to 700 nm with new benzo[g]quinoxaline-based heteroleptic copper(I) complexes for light-harvesting applications.

Heteroleptic copper(I) complexes, with a diimine as a chromophoric unit and a bulky diphosphine as an ancillary ligand, have the advantage of a reduced pseudo Jahn-Teller effect in their excited state over the corresponding homoleptic bis(diimine) complexes. Nevertheless, their lowest absorption lies generally between 350 to 500 nm. Aiming at a strong absorption in the visible by stable heteroleptic Cu(I) complexes, we designed a novel diimine based on 4-(benzo[g]quinoxal-2'-yl)-1,2,3-triazole derivatives. The large π-conjugation of the benzoquinoxaline moiety shifted bathochromically the absorption with regard to other diimine-based Cu(I) complexes. Adding another Cu(I) core broadened the absorption and extended it to considerably longer wavelengths. Moreover, by fine-tuning the structure of the dichelating ligand, we achieved a panchromatic absorption up to 700 nm with a high molar extinction coefficient of 8000 M-1 cm-1 at maximum (λ = 570 nm), making this compound attractive for light-harvesting antennae.

Mixed ligand copper(II)-diimine complexes of 2-formylpyridine-N4-phenylthiosemicarbazone: diimine co-ligands tune the in vitro nanomolar cytotoxicity.

Recently, mixed-ligand copper(II) complexes have received much attention in searching for alternative metallodrugs to cisplatin. A series of mixed ligand Cu(II) complexes of the type [Cu(L)(diimine)](ClO4) 1-6, where the HL is 2-formylpyridine-N4-phenylthiosemicarbazone and the diimine is 2,2'-bipyridine (1), 4,4'-dimethyl-2,2'-bipyridine (2), 1,10-phenanthroline (3), 5,6-dimethyl-1,10-phenanathroline (4), 3,4,7,8-tetramethyl-1,10-phenanthroline (5) and dipyrido-[3,2-f:2',3'-h]quinoxaline (6), has been synthesized and their cytotoxicity in HeLa cervical cancer cells examined. In the molecular structures of 2 and 4, as determined by single-crystal X-ray studies, Cu(II) assumes a trigonal bipyramidal distorted square-based pyramidal (TBDSBP) coordination geometry. DFT studies reveal that the axial Cu-N4diimine bond length, interestingly, varies linearly with the experimental CuII/CuI reduction potential as well as the trigonality index τ of the five-coordinate complexes, and that methyl substitution on diimine co-ligands tunes the extent of the Jahn-Teller distortion at the Cu(II). While 4 is involved in strong DNA groove binding with a hydrophobic interaction of methyl substituents, 6 is involved in stronger binding through partial intercalation of dpq with DNA. Complexes 3, 4, 5, and 6 efficiently cleave supercoiled DNA into NC form in ascorbic acid by generating hydroxyl radicals. Interestingly, 4 exhibits higher DNA cleavage in hypoxic than at normoxic conditions. Notably, except for [CuL]+, all the complexes were stable in 0.5% DMSO-RPMI (without phenol red) cell culture medium up to 48 h at 37 °C. Remarkably, all the complexes show time-dependent cytotoxicity at nanomolar concentrations (IC50, 7.0-182 nM) in HeLa cervical cancer cells compared with uncoordinated ligand HL (IC50 > 10 000 nM). Except for 2 and 3, all the complexes exhibit higher cytotoxicity than [CuL]+ at 48 h. 4 shows (57.2 nM) higher cytotoxicity than 1 (181.5 nM) at 24 h incubation; however, notably, 1 demonstrates phenomenal cytotoxicity (7.0 nM) higher than 4 (13.6 nM) at 48 h incubation. The selectivity index (SI) reveals that complexes 1 and 4 are 53.5 and 37.3, respectively, times less toxic to HEK293 normal cells than to cancerous cells. Except for [CuL]+, all the complexes generate ROS to different extents at 24 h, with 1 producing the highest amount, which is consistent with their redox properties. Also, 1 and 4 exhibit, respectively, sub-G1 and G2-M phase cell arrest in the cell cycle. Therefore, complexes 1 and 4 have the potential to emerge as promising anticancer agents.

Synthesis and the photophysical and biological properties of tricarbonyl Re(I) diimine complexes bound to thiotetrazolato ligands.

Twelve Re(I) tricarbonyl diimine (2,2'-bipyridine and 1,10-phenanthroline) complexes with thiotetrazolato ligands have been synthesised and fully characterised. Structural characterisation revealed the capacity of the tetrazolato ligand to bind to the Re(I) centre through either the S atom or the N atom with crystallography revealing most complexes being bound to the N atom. However, an example where the Re(I) centre is linked via the S atom has been identified. In solution, the complexes exist as an equilibrating mixture of linkage isomers, as suggested by comparison of their NMR spectra at room temperature and 373 K, as well as 2D exchange spectroscopy. The complexes are photoluminescent in fluid solution at room temperature, with emission either at 625 or 640 nm from the metal-to-ligand charge transfer excited states of triplet multiplicity, which seems to be exclusively dependent on the nature of the diimine ligand. The oxygen-sensitive excited state lifetime decay ranges between 12.5 and 27.5 ns for the complexes bound to 2,2'-bipyrdine, or between 130.6 and 155.2 ns for those bound to 1.10-phenanthroline. Quantum yields were measured within 0.4 and 1.5%. The complexes were incubated with human lung (A549), brain (T98g), and breast (MDA-MB-231) cancer cells, as well as with normal human skin fibroblasts (HFF-1), revealing low to moderate cytotoxicity, which for some compounds exceeded that of a standard anti-cancer drug, cisplatin. Low cytotoxicity combined with significant cellular uptake and photoluminescence properties provides potential for their use as cellular imaging agents. Furthermore, the complexes were assessed in disc diffusion and broth microdilution assays against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, which revealed negligible antibacterial activity in the dark or after irradiation.

Manganese Tricarbonyl Diimine Bromide Complexes as Electrocatalysts for Proton Reduction.

Manganese tricarbonyl diimine complexes bearing pyridine and imidazole ligands have been prepared as electrocatalysts for proton reduction using acetic acid as the proton source. The electron-donor ability of the diimine ligand is found to play an important role in determining the efficiency of the electrocatalysts with [MnBr(pybz)(CO)3] (pybz = 2-(2-pyridyl)benzimidazole) exhibiting the lowest overpotential (0.28 V) toward proton reduction. The [Mn(pybz)(CO)3(MeCN)]+ cationic complex prepared via debromination of [MnBr(pybz)(CO)3] by a silver salt has also been shown to catalyze proton reduction upon its electrochemical reduction. A neutral complex [Mn(pyridine-benzimidazolate)(CO)3(MeCN)], which can be synthesized by reacting [MnBr(pybz)(CO)3] with a strong base, has been detected using IR-SEC (infrared spectroelectrochemistry) as an intermediate species in the catalytic process. Using [MnBr(pybz)(CO)3] as the model electrocatalyst, we have carried out density functional calculations to propose a proton reduction mechanism consistent with our experimental observations.

Proton-Coupled, Low-Energy Pathway for Electrocatalytic CO2 Reduction at Re(Diimine) Complexes with a Conjugated Pyrazinyl Moiety.

Large conjugated carbon framework has been incorporated as the diimine ligand for Re(α-diimine)(CO)3Cl complexes with a pyrazinyl linkage, either to increase energy efficiency or to turn them into heterogeneous catalysts for selective electrocatalytic CO2 reduction. However, there exists a nonmonotonic dependence of CO2 reduction overpotential on the conjugation size of the ligands. Understanding its origin could facilitate heterogenization of molecular catalysts with improved energy efficiency. Here, we show that the conjugated pyrazinyl moiety plays a crucial role in catalysis by enabling a proton-coupled, lower-energy pathway for CO2 reduction. With ligands of moderate size, the pathway leads to previously unknown intermediates and decreases CO2 reduction overpotential. Because the pathway hinges on the basicity of the pyrazinyl nitrogen, we propose that it imposes a limit on the conjugation size of the ligand for the pathway to be effective.

Fluoride Additive as a Simple Tool to Qualitatively Improve Performance of Nickel-Catalyzed Asymmetric Michael Addition of Malonates to Nitroolefins.

Nowadays, design of the new chiral ligands for organometallic catalysts is often based on the step-by-step increase in their complexity to improve efficiency. Herein we describe that simple in situ addition of the fluoride source to the asymmetric organometallic catalyst can improve not only activity but also enantioselectivity. Bromide-nickel diimine complexes were found to catalyze asymmetric Michael addition in low yields and ee, but activation with fluoride leads to a significant improvement in catalyst performance. The developed approach was applied to prepare several enantioenriched GABA analogues.

Synthesis and electronic structure of a series of first-row transition-metal pyrazine(diimine) complexes in two oxidation states

The synthesis, molecular and electronic structures, and redox properties of pyrazine(diimine) (PzDI) metal dihalide complexes (DiPPPZDI)MX2 (DiPP = 2,6-diisopropylphenyl; M = Mn, Fe, Co, Ni; X = Cl, Br) are presented and compared. The dihalide complexes are reduced to (DiPPPZDI)MX monohalide complexes, and the role of ligand redox non-innocence in the electronic structure of the reduced compounds is examined and compared to related pyridine(diimine) (PDI) compounds. The compounds were characterized by NMR spectroscopy, UV-VIS spectroscopy, cyclic voltammetry, X-ray crystallography, and Evans method magnetometry. Similar to previously reported PDI compounds, the reduced monohalide complexes are best described as divalent metal centers coupled to a reduced radical anion ligand. Structural and computational analyses show that the ligand in (DiPPPZDI)MX is reduced by one electron and bears significant spin density. Comparison across the series of first-row transition metals shows increasing metal-ligand covalency for the later metals. These results may be useful in the design of modified heteroarene(diimine) ligands for first-row transition-metal catalysis in the future.

Antimicrobial Activity of Rhenium Di- and Tricarbonyl Diimine Complexes: Insights on Membrane-Bound S. aureus Protein Binding.

Antimicrobial resistance is one of the major human health threats, with significant impacts on the global economy. Antibiotics are becoming increasingly ineffective as drug-resistance spreads, imposing an urgent need for new and innovative antimicrobial agents. Metal complexes are an untapped source of antimicrobial potential. Rhenium complexes, amongst others, are particularly attractive due to their low in vivo toxicity and high antimicrobial activity, but little is known about their targets and mechanism of action. In this study, a series of rhenium di- and tricarbonyl diimine complexes were prepared and evaluated for their antimicrobial potential against eight different microorganisms comprising Gram-negative and -positive bacteria. Our data showed that none of the Re dicarbonyl or neutral tricarbonyl species have either bactericidal or bacteriostatic potential. In order to identify possible targets of the molecules, and thus possibly understand the observed differences in the antimicrobial efficacy of the molecules, we computationally evaluated the binding affinity of active and inactive complexes against structurally characterized membrane-bound S. aureus proteins. The computational analysis indicates two possible major targets for this class of compounds, namely lipoteichoic acids flippase (LtaA) and lipoprotein signal peptidase II (LspA). Our results, consistent with the published in vitro studies, will be useful for the future design of rhenium tricarbonyl diimine-based antibiotics.

Photocatalytic Reduction of CO2 to CO in Aqueous Solution under Red-Light Irradiation by a Zn-Porphyrin-Sensitized Mn(I) Catalyst.

This work demonstrates photocatalytic CO2 reduction by a noble-metal-free photosensitizer-catalyst system in aqueous solution under red-light irradiation. A water-soluble Mn(I) tricarbonyl diimine complex, [MnBr(4,4′-{Et2O3PCH2}2-2,2′-bipyridyl)(CO)3] (1), has been fully characterized, including single-crystal X-ray crystallography, and shown to reduce CO2 to CO following photosensitization by tetra(N-methyl-4-pyridyl)porphyrin Zn(II) tetrachloride [Zn(TMPyP)]Cl4 (2) under 625 nm irradiation. This is the first example of 2 employed as a photosensitizer for CO2 reduction. The incorporation of −P(O)(OEt)2 groups, decoupled from the core of the catalyst by a −CH2– spacer, afforded water solubility without compromising the electronic properties of the catalyst. The photostability of the active Mn(I) catalyst over prolonged periods of irradiation with red light was confirmed by 1H and 13C{1H} NMR spectroscopy. This first report on Mn(I) species as a homogeneous photocatalyst, working in water and under red light, illustrates further future prospects of intrinsically photounstable Mn(I) complexes as solar-driven catalysts in an aqueous environment.

Mild and Efficient Heterogeneous Hydrogenation of Nitroarenes Facilitated by a Pyrolytically Activated Dinuclear Ni(II)-Ce(III) Diimine Complex.

We communicate the assembly of a solid, Ce-promoted Ni-based composite that was applied as catalyst for the hydrogenation of nitroarenes to afford the corresponding organic amines. The catalytically active material described herein was obtained through pyrolysis of a SiO2-pellet-supported bimetallic Ni-Ce complex that was readily synthesized prior to use from a MeO-functionalized salen congener, Ni(OAc)2·4 H2O, and Ce(NO3)3·6 H2O. Rewardingly, the requisite ligand for the pertinent solution phase precursor was accessible upon straightforward and time-saving imine condensation of ortho-vanillin with 1,3-diamino-2,2′-dimethylpropane. The introduced catalytic protocol is operationally simple in that the whole reaction set-up is quickly put together on the bench without the need of cumbersome handling in a glovebox or related containment systems. Moreover, the advantageous geometry and compact-sized nature of the used pellets renders the catalyst separation and recycling exceptionally easy.

Role of the Trifluoropropynyl Ligand in Blue-Shifting Charge-Transfer States in Emissive Pt Diimine Complexes and an Investigation into the PMMA-Imposed Rigidoluminescence and Rigidochromism.

Square-planar PtII complexes are of interest as dopants for the emissive layer of organic light-emitting diodes. Herein, the photophysics of three Pt bipyridyl complexes with the strongly e- withdrawing, high-field, 3,3,3-trifluoropropynyl ligand has been investigated. One complex, (phbpy)PtC2CF3 (phbpy = 6-phenyl-2,2'-dipyridyl), has also been characterized by single-crystal X-ray diffraction. All complexes reported are emissive in both RT CH2Cl2 solution (ΦPL = 0.007 to 0.027) and PMMA film (ΦPL = 0.25 to 0.42). The trifluoropropynyl ligand elevates the energy of the MLCT and LL'CT states above that of the IL π-π* state, resulting in IL emission in all cases. The emission energies of the trifluoropropynyl compounds are also blue-shifted relative to the analogous pentafluorophenylethynyl compounds, suggesting that the trifluoropropynyl ligand is one of the most electron-withdrawing alkynyl ligands. Rate constants for radiative and nonradiative deactivation were determined from experimentally determined values of ΦPL and excited-state lifetimes in both solution and PMMA films. The increase in ΦPL upon incorporation into PMMA film (rigidoluminescence) results from a decrease in the rate constant for non-radiative relaxation. Experimental activation energies for excited-state decay in combination with TDDFT are consistent with the rigidoluminescence resulting from an increase in the energy of the non-emissive triplet metal-centered state. Two of the complexes investigated, (Ph2bpy)Pt(C2CF3)2 and (t-Bu2bpy)Pt(C2CF3)2, where t-Bu2bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl and Ph2bpy = 4,4'-diphenyl-2,2'-dipyridyl, exhibit concentration-dependent excimer emission (orange) along with monomer emission (blue), enabling fine-tuning of the emission color. However, excimer emission was absent in cured PMMA films up to the solubility limit for solution processing of (Ph2bpy)Pt(C2CF3)2 in CH2Cl2, demonstrating the diffusional nature of excimer formation.

Copper(I) Bis(diimine) Complexes with High Photooxidation Power: Reductive Quenching of the Excited State with a Benzimidazoline Sacrificial Donor.

The reductive quenching of photoexcited photosensitizers is a very efficient way to achieve challenging reduction reactions. In this process, the excited photosensitizer is reduced by a sacrificial electron donor. This mechanism is rarely observed with copper(I) bis(diimine) complexes, which are nevertheless acknowledged as very promising photosensitizers. This is due to the fact that they are very poor photooxidants and prove unable to react with common donors once promoted in their excited state. In this article, we evidence the rare reductive quenching cycle with two specially designed copper(I) complexes. These complexes exhibit improved photooxidation power thanks to an optimized coordination sphere made of strongly π-accepting ligands. Reductive quenching of the excited state of the latter complexes with a classical benzimidazoline sacrificial donor is monitored, and reduced complexes are accumulated during prolonged photolysis. Trials to utilize the photogenerated reductive power are presented.

Red Absorbing Cyclometalated Ir(III) Diimine Photosensitizers Competent for Hydrogen Photocatalysis.

Two new cyclometalated Ir(III) diimine complexes were used as photosensitizers for homogeneous hydrogen evolution reaction (HER). These complexes were characterized by electrochemistry, ultraviolet-visible absorption, time-resolved and steady-state photoluminescence spectroscopy as well as by theoretical methods. The metal-ligand-to-ligand charge transfer character of their lowest excited state was shown to be competent for efficient H2 photoproduction in the presence of [Co(dmgH)2(py)Cl] as the hydrogen evolution catalyst, triethanolamine as the sacrificial electron donor, and HBF4 as the proton source. Under optimized experimental conditions, both complexes displayed HER over a period of more than 90 h, with turnover numbers reaching up to 11,650, 10,600, and 174 molH2 molPS-1 under blue-, green-, and red-light irradiation, respectively. Both complexes showed higher stability and efficiency vs HER than most of the previously described systems of the same kind.

Ruthenium(II) Complexes with (3-Polyamino)phenanthrolines: Synthesis and Application in Sensing of Cu(II) Ions

This work deals with the development of water-soluble optical sensors based on ruthenium(II) tris(diimine) complexes that exhibit high molar absorptivity and are emissive in aqueous media. Palladium-catalyzed arylation of polyamines with 3-bromo-1,10-phenanthroline (Brphen) and [Ru(bpy)2(Brphen)](PF6)2 (bpy = 2,2’-bipyridine) was explored to prepare Ru2+ complexes with 1,10-phenanthrolines (phen) substituted by linear polyamines (PAs) at position 3 of the heterocycle ([Ru(bpy)2(phen–PA)](PF6)2). The most convenient synthetic pathway leading to the target molecular probes includes the preparation of phen–PA ligands, followed by ruthenium complexation using cis-Ru(bpy)2Cl2. Complexes bearing a polyamine chain directly linked to phenanthroline core are emissive in aqueous media and their quantum yields are comparable to that of parent [Ru(bpy)3](PF6)2. Their structure can be easily adapted for detection of various analytes by modification of amine groups. As an example, we prepared the emissive complex Ru(N2P2phen) which is suitable for the dual channel (spectrophotometry and luminescence (ON–OFF probe)) selective detection of Cu2+ ions at the physiological pH levels with limits of detection (LOD) by spectrophotometry and fluorescence spectroscopy equal to 9 and 6 μM, respectively, that is lower than the action level in drinking water for copper as prescribed by the US Environmental Protection Agency.

Effect of the Ancillary Ligand on the Performance of Heteroleptic Cu(I) Diimine Complexes as Dyes in Dye-Sensitized Solar Cells.

A series of heteroleptic Cu(I) diimine complexes with different ancillary ligands and 6,6′-dimethyl-2,2′-bipyridine-4,4′-dibenzoic acid (dbda) as the anchoring ligand were self-assembled on TiO2 surfaces and used as dyes for dye-sensitized solar cells (DSSCs). The binding to the TiO2 surface was studied by hard X-ray photoelectron spectroscopy for a bromine-containing complex, confirming the complex formation. The performance of all complexes was assessed and rationalized on the basis of their respective ancillary ligand. The DSSC photocurrent–voltage characteristics, incident photon-to-current conversion efficiency (IPCE) spectra, and calculated lowest unoccupied molecular orbital (LUMO) distributions collectively show a push–pull structural dye design, in which the ancillary ligand exhibits an electron-donating effect that can lead to improved solar cell performance. By analyzing the optical properties of the dyes and their solar cell performance, we can conclude that the presence of ancillary ligands with bulky substituents protects the Cu(I) metal center from solvent coordination constituting a critical factor in the design of efficient Cu(I)-based dyes. Moreover, we have identified some components in the I–/I3–-based electrolyte that causes dissociation of the ancillary ligand, i.e., TiO2 photoelectrode bleaching. Finally, the detailed studies on one of the dyes revealed an electrolyte–dye interaction, leading to a dramatic change of the dye properties when adsorbed on the TiO2 surface.

Photoactive silicon surfaces functionalized with high-quality and redox-active platinum diimine complex monolayers

Platinum diimine complexes can covalently be grafted onto oxide-free, hydrogen-terminated silicon(111) surfaces into clean and high-quality monolayers. The so modified surfaces offer great prospects as photocathodes for solar-driven electrocatalysis.

Pt(II) diimine complexes bearing varied alkyl chains: Synthesis, tunable photophysical properties and aggregation-induced optical power limiting enhancement

A series of Pt(II) diimine complexes with varied alkyl chains on 2,2′- dipyridyl ligands (Pt-C1–Pt-C3) have been synthesized and characterized. The photophysical properties and nonlinear absorption properties were elucidated using UV–vis absorption, emission and transient absorption spectroscopy, density functional theory (DFT) calculations and electrochemical experiments. It was found that increasing the alkyl chain led to regular changes in the photophysical properties of Pt-C1–Pt-C3. The original conjugated skeleton of the Pt(II) complexes were affected when the alkyl chain was introduced and extended. All complexes exhibited an obvious aggregation-induced phosphorescence emission (AIPE) in a mixed solution comprised of tetrahydrofuran/water. The formation of nanoparticles in the aggregated state induced these complexes to exhibit different excited state properties. When the water content increased, the emission intensity increases 3 ∼ 13-flod and the excited state lifetime increased 98-flod due to the formation of Pt(II) complex nanoparticles. As a result, the optical power limiting (OPL) performance of these complexes was greatly improved. Based on the systematical investigation of nonlinear optical complexes in aggregated state, this work provided a theoretical basis for the development of new OPL materials. Furthermore, the Pt(II) complex nanoparticles will be more conducive to the potential application of OPL devices.

Luminescence quenching of Ru(II)-diimine complexes with Cr(VI) ions: Steady-state and time-resolved studies

Luminescence quenching of [Ru(bpy)(CN)4]2−, [Ru(phen)(CN)4]2−, [Ru(bpy)3]2+ and [Ru(phen)3]2+ by hexavalent chromium ion in aqueous media were investigated by steady-state and time-resolved measurements. Effect of pH on the luminescence quenching process is also investigated. It has been found that luminescence changes due to the interaction of all Ru(II) complexes with Cr(VI) ions were high at pH values less than or equal to 5.0 and negligible at pH ≥ 8.0. The experimental data of the quenching process were analyzed using Stern–Volmer (S–V) equations. The steady state luminescence emission data shows an upward curvature, indicating that the quenching is preceded by both dynamic and static quenching. For all studied complexes, the lifetime of the excited 3MLCT state decreases with increasing Cr(VI) concentration implying that the diffusion is mainly responsible for the quenching process. The Stern–Volmer dynamic quenching constants (KD) and the bimolecular quenching rate constant for the quenching process (kq) were calculated by applying the Stern–Volmer equation to the luminescence decay data. The bimolecular quenching rate constants (Kq) were found to increase in the order [Ru(bpy)(CN)4]2− < [Ru(phen)(CN)4]2− < [Ru(phen)3]2+ < [Ru(bpy)3]2+ which correlates will with the oxidation potentials of Ru(II) complexes. The association constants for Ru(II)-Cr(VI) system were calculated using the Benesi-Hildebrand equation and found to be 3.0 × 103, 2.5 × 103, 1.2 × 103, 7.1 × 103 M−1 for [Ru(bpy)(CN)4]2−, [Ru(phen)(CN)4]2−, [Ru(bpy)3]2+ and [Ru(phen)3]2+ respectively, which is interpreted in terms of the dynamic (diffusion) and the sphere of action (static) quenching models.

Evaluation of the Anticancer and DNA-Binding Characteristics of Dichloro(diimine)zinc(II) Complexes

Several metal diimine complexes have been reported to possess anticancer properties. To evaluate the anticancer properties of tetrahedral zinc(II) diimine complexes, six complexes were synthesized with the general formula M(N^N)Cl2 {where M = Zn, Pt and N^N = 2,2’-biquinoline (1), 2,2’-dipyridylketone (2) and 4-((pyridine-2-ylmethylene)amino)phenol (3)}. In general, the intrinsic DNA-binding constants for the different compounds exhibited values within close proximity; the changes in the viscosity of the CT-DNA upon binding to the compounds suggest intercalation-binding mode. Molecular docking study predicted that complexes containing the highly planar ligand 2,2’-biquinoline are capable to establish π–π interactions with nucleobases of the DNA; the other four complexes engaged in donor–acceptor interactions with DNA nucleobases. The six complexes and two reference drugs (cisplatin and sunitinib) were tested against two cancer cell lines (COLO 205 and RCC-PR) and one normal cell line (LLC-MK2), highlighting the better performance of the zinc(II) complexes compared to their platinum(II) analogues. Moreover, zinc(II) complexes have higher selectivity index values than the reference drugs, with promising anticancer properties.