Synthesis, crystal structures and density functional theory study of dimeric copper(II) complexes of a tridentate Schiff-base ligand

Oxalate- or 4,4′-bipyridine-bridged dimeric copper(II) complexes, [Cu₂L₂(μ-ox)] (1) and [Cu₂L₂(μ-bipy)](BF₄)₂ (2) [where ox = oxalate, bipy = 4,4′-bipyridine, HL = N-(1H-pyrrol-2-ylmethylene)-2-pyridineethanamine, L⁻ = HL−H⁺], have been synthesised and characterised by elemental analysis, IR, UV-Vis and single crystal X-ray diffraction. Crystal structure determinations carried out on 1 and 2 reveal that 1 is an oxalate-bridged centrosymmetrical square pyramidal dimeric copper(II) complex while 2 is a 4,4′-bipyridine-bridged non-centrosymmetric square planar dinuclear copper(II) complex. Comparison of the optimised geometries with the corresponding crystal structures suggests that the B3LYP/LANL2DZ level can reproduce the structures of 1 and 2 on the whole. The electronic spectra of 1 and 2 predicted by B3LYP/LANL2DZ method show some blue shifts compared with their experimental data. Thermal analysis carried out on 1 shows that there is only one exothermal peak at about 260 °C and the residue is presumably Cu₂O₄N₆.     

Synthesis and characterization of a dinuclear Ni complex containing a bridging CNC pincer ligand

The reaction of the bis(carbene) pincer ligand ^MeCNC with nickel acetate and Bu₄NBr produced [(^MeCNC)₃Ni₂]⁴⁺[Br]₄ (2), a complex that contains the ^MeCNC ligand in both traditional tridentate chelating modes as well as in a unique, bridging mode between two Ni²⁺ ions. While 2 could not be crystallized or isolated in a pure form, the anion exchange of bromide with triflate yielded [(^MeCNC)₃Ni₂]⁴⁺[OTf]₄ (4), which could be recrystallized from methanol and isolated pure. Single-crystal X-ray analysis of 4 confirmed the unusual dual-coordination modes of the ^MeCNC ligand towards Ni²⁺ in these species, and represents the initial example of a Group 10 complex of a bridging CNC ligand.     

Time-dependent density functional calculations of ligand K-edge X-ray absorption spectra

The Cl K-edge spectra of a series of metal tetrachloride complexes have been simulated using a simple TD-DFT based protocol. The influence of the chosen density functional, relativistics, basis set, and solvation has been systematically investigated. The results show that good agreement between the calculated spectra and the relative experimental energies and intensities can be achieved by using the BP86 functional with standard polarized triple-ζ basis sets (such as the TZVP basis of Ahlrichs’s and co-workers). Calculated energies and intensities are improved by using the more flexible CP(PPP) basis set on the metal atom. The inclusion of scalar-relativistic effects or solvation does not yield any significant improvement in the results. The subtleties arising from the incorporation of electric quadrupole and magnetic dipole intensity contributions into the calculations are discussed in some detail, and the contributions are shown to be negligible (∼1%) at the Cl K-edge.     

Synthesis, crystal structures and magnetic properties of mononuclear tris(croconate)ferrate(III) complexes

A straightforward synthetic method to prepare mononuclear croconato-containing iron (III) complexes, (A)₃[Fe(C₅O₅)₃] [A = tetrabutylammonium = n-Bu₄N⁺ (1) and along with their crystal structures and magnetic properties, are reported. The Fe(III) atom adopts a pseudo-octahedral geometry while magnetic susceptibility measurements, in the 2-300 K temperature range, show the occurrence of a high spin state (S = 5/2) in both complexes.     

Determination of the absolute configurations of chiral organometallic complexes via density functional theory calculations of their vibrational circular dichroism spectra: The chiral chromium tricarbonyl complex of N-pivaloyl-tetrahydroquinoline

The racemate of the chiral tricarbonyl-η⁶-arene-chromium(0) complex, tricarbonyl-η⁶-N-pivaloyl-tetrahydroquinoline-chromium(0), 1, has been synthesized and resolved using chromatography on a (R,R)-Whelk-O1 column. The Absolute Configuration (AC) of 1 has been determined using vibrational circular dichroism (VCD) spectroscopy. The VCD spectrum of 1 has been predicted using the Stephens equation for vibrational rotational strengths, implemented using density functional theory (DFT) in the gaussian program. Using the B3PW91 functional and the 6-311++G (2d,2p) basis set, the predicted VCD spectrum of S-1 is in excellent agreement with the experimental VCD spectrum of (+)-1, leading unambiguously to the AC S-(+). It is concluded that VCD is a useful technique for determining the ACs of chiral organometallic complexes, given the use of optimum functionals and basis sets.     

Ternary uranyl hydroxo acetate complexes: A computational study of structure, energetics, and stability constants

We studied computationally uranyl monohydroxo monoacetate complexes in aqueous solution using a scalar relativistic all-electron density functional method. Such ternary uranyl complexes may serve as models of ternary uranyl humate complexes which are important for the speciation of uranyl in the environment. As for simple uranyl monocarboxylate complexes, we calculated bidentate coordination to be slightly preferred due to entropy and solvation effects. Compared to uranyl acetate, uranyl hydroxo acetate exhibits an elongated uranyl bond and a short U-OH bond of ∼214 pm. The latter may provide a signature for direct identification of such ternary complexes by EXAFS. As expected from the lower charge of uranyl monohydroxide, complexation by acetate is less exoenergetic than acetate complexation of uranyl. In contrast, experimental complexation constants of uranyl humate and uranyl hydroxo humate are quite similar. Thus, one may question the interpretation of experimental results that assign simple ternary complexes as result of uranyl humate complexation at neutral pH.     

Syntheses, characterization, and reactivity of copper complexes with tridentate N-donor ligands

The reaction of dioxygen with the copper(I) complex of the tridentate ligand 1,1,4,7,7-pentamethyldiethylenetriamine (Me₅dien) has been investigated using low-temperature stopped-flow techniques. The formation of a bis(μ-oxo)copper(III) complex as a reactive intermediate could be detected spectroscopically at low temperatures and a quantitative kinetic analysis was performed for this system. Crystal structures of the copper(II) complexes [(Me-bpa)Cu(Cl)₂] (1), [{(Me-bpa)Cu(Cl)(ClO₄)}₂] (2), [{(MeL)Cu(Cl)(ClO₄)}₂] (3), and [(MeL)Cu(NCS)₂] (4) (Me-bpa = N-methyl-[bis(2-pyridyl)methyl]amine; MeL = N-methyl-[(2-pyridyl)ethyl(2-pyridyl)methyl]amine) are reported.     

Synthesis, and characterization of cobalt(III) complexes with Schiff bases derived from 2-hydroxynaphthaldehyde, (naph)2dien and (naph)2dpt, and monodentate amine ligands: Crystal structure, spectral and redox properties

Two series of complexes of the type [Co^III{(naph)₂dien}(amine)]BPh₄ {(naph)₂dien = bis-(2-hydroxy-1-naphthaldimine)-N-diethylenetriamine dianion, and amine = piperidine (pprdn) (1), pyrrolidine (prldn) (2), pyridine (py) (3), N-methylimidazole (N-MeIm) (4)}, and [Co^III{(naph)₂dpt}(amine)]BPh₄ {(naph)₂dpt = bis-(2-hydroxy-1-naphthaldimine)-N-dipropylenetriamine dianion, and amine = piperidine (pprdn) (5), 3-methylpyridine (3-Mepy) (6)} have been synthesized and characterized by elemental analyses, IR, UV-Vis, and ¹H NMR spectroscopy. The crystal structures of (2) and (6) have been determined by X-ray diffraction. The redox potentials of the central cobalt ion show a relatively good correlation with the σ-donor ability of the axial ligands. The spectroscopic and electrochemical properties of these complexes are also influenced by the mutual steric hindrance between the pentadentate Schiff base and the ancillary ligands.     

Synthesis and properties of new trinuclear Mo(II) complexes containing imidazole and benzimidazole ferrocene units

The reaction of FcCOCl (Fc = (C₅H₅)Fe(C₅H₄)) with benzimidazole or imidazole in 1:1 ratio gives the ferrocenyl derivatives FcCO(benzim) (L1) or FcCO(im) (L2), respectively. Two molecules of L1 or L2 can replace two nitrile ligands in [Mo(η³-C₃H₅)(CO)₂(CH₃CN)₂Br] or [Mo(η³- C₅H₅O)(CO)₂(CH₃CN)₂Br] leading to the new trinuclear complexes [Mo(η³-C₃H₅)(CO)₂(L)₂Br] (C1 for L = L1; C3 for L = L2) and [Mo(η³-C₅H₅O)(CO)₂(L)₂Br] (C2 for L = L1; C4 for L = L2) with L1 and L2 acting as N-monodentade ligands. L1, L2 and C2 were characterized by X-ray diffraction studies. [Mo(η³-C₅H₅O)(CO)₂(L1)₂Br] was shown to be a trinuclear species, with the two L1 molecules occupying one equatorial and one axial position in the coordination sphere of Mo(II). Cyclic voltammetric studies were performed for the two ligands L1 and L2, as well as for their molybdenum complexes, and kinetic and thermodynamic data for the corresponding redox processes obtained. In agreement with the nature of the frontier orbitals obtained from DFT calculations, L1 and L2 exhibit one oxidation process at the Fe(II) center, while C1, C3, and C4 display another oxidation wave at lower potentials, associated with the oxidation of Mo(II).     

Interaction energies in non-covalently bound intermolecular complexes derived using the subsystem formulation of density functional theory

Interaction energies for a representative sample of 39 intermolecular complexes are calculated using two computational approaches based on the subsystem formulation of density functional theory introduced by Cortona (Phys. Rev. B 44:8454, 1991), adopted for studies of intermolecular complexes (Wesolowski and Weber in Chem. Phys. Lett. 248:71, 1996). The energy components (exchange-correlation and non-additive kinetic) expressed as explicit density functionals are approximated by means of gradient-free- (local density approximation) of gradient-dependent- (generalized gradient approximation) approximations. The sample of the considered intermolecular complexes was used previously by Zhao and Truhlar to compare the interaction energies derived using various methods based on the Kohn-Sham equations with high-level quantum chemistry results considered as the reference. It stretches from rare gas dimers up to strong hydrogen bonds. Our results indicate that the subsystem-based methods provide an interesting alternative to that based on the Kohn-Sham equations. Local density approximation, which is the simplest approximation for the relevant density functionals and which does not rely on any empirical data, leads to a computational approach comparing favorably with more than twenty methods based on the Kohn-Sham equations including the ones, which use extensively empirical parameterizations. For various types of non-bonding interactions, the strengths and weaknesses of gradient-free and gradient-dependent approximations to exchange-correlation and non-additive kinetic energy density functionals are discussed in detail.     

Nickel and copper complexes based on tridentate nitrogen donor ligand 2,6-bis-(1-phenyliminoethyl) pyridine: Synthesis, spectral and structural characterization

The reaction of CuCl₂ · 2H₂O with 2,6-bis(1-phenyliminoethyl)pyridine (referred hereafter as L) in 1:1 molar ratio in methanol or acetronitrile at room temperature afforded distorted trigonal-bipyramidal complex [Cu(κ³-L)Cl₂]. On the other hand, the reaction of NiCl₂ · 6H₂O with 2 equivalents of L gave an octahedral complex [Ni(κ³-L)₂]²⁺, which was isolated as [Ni(κ³-L)₂][BF₄]₂ using NH₄BF₄. The complexes have been characterized by elemental analyses, FAB-MS, IR, EPR and electronic spectral studies. Molecular structures of both the [Cu(κ³-L)Cl₂] (1) and [Ni(κ³-L)₂](BF₄)₂ (2) have been determined by single crystal X-ray analyses. Weak interaction studies on 1 and 2 revealed stabilisation of the crystal packing by inter and intra-molecular C-H?X (X = F, Cl, π) interactions. In complex 2 ortho C-H bond from phenyl rings leads to unexpected C-H?π interaction with nickel α,α′-diimine chelate ring. This provides structural support for metalloaromaticity in the chelate ring of complex 2.     

Synthesis, structural characterization and electrochemical activity of oxidovanadium(IV/V) complexes of a diprotic ONS chelating ligand

The present work reports the chemistry of a few oxidovanadium(IV) and (V) complexes of the ONS chelating ligand S-benzyl-β-N-(2-hydroxyphenylethylidine) dithiocarbazate (H₂L). Major objective of this work is to arrive at some general conclusions about the influence of binding environment generated by the replacement of an O-donor center by a S-donor point in a ligand (of a similar arrangement of the other O- and N-donor points) on the redox behavior and on the structural features of comparable [VO(OEt)(ONS)] and [VO(OEt)(ONO)] complexes. Synthesis, characterization by various physicochemical techniques (UV-Vis, IR, EPR and elemental analysis), exploration of electrochemical activity of the oxidovanadium(V) complex [V^VO(OEt)L] (1), the mixed ligand complex [V^VO(N-O)L] (3) (where N-O is the mono anion of 8-hydroxyquinoline) and a binuclear complex [V^VO(OEt)L]₂(μ-4,4′-bipy) (2) are reported. Similar studies on of mixed ligand oxidovanadium(IV) complexes of the formula [V^VO(N-N)L] (4,5) (where N-N = 2,2′-bipy and o-phen) are also presented here. The [V^VO(OEt)L] complex is pentacoordinated and distorted square pyramidal, while the [V^IV(N-N)L] complexes are hexacoordinated and octahedral. Structural features of the complex 1 were compared with the corresponding aspects of the previously reported analogous complex [V^VO(OEt)(ONO)] (1′).     

Insight into the copper coordination environment in the prion protein through density functional theory calculations of EPR parameters

Density functional theory (DFT) calculations of Cu(II) electron paramagnetic resonance (EPR) parameters for the octarepeat unit of the prion protein were conducted. Model complexes were constructed and optimized using the crystal structure of the octarepeat unit of the prion protein. Copper g and A tensors and nitrogen hyperfine and quadrupole coupling constants were calculated using DFT. Solvent effects were incorporated using the conductor-like screening model as well as through the inclusion of explicit water molecules. Calculations using the model with an additional axial water molecule added to the coordination sphere of the Cu(II) metal center give the best qualitative agreement for the copper g and A tensors. The S-band experimental EPR spectra were interpreted in light of the DFT calculations of the directly coordinated nitrogen hyperfine coupling constants which indicate that the three directly coordinated nitrogen atoms in the octarepeat unit are not equivalent. These results demonstrate that DFT calculations of EPR parameters can provide important insight with respect to the structural interpretation of experimental EPR data. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis, characterization and cytotoxic activity of gallium(III) complexes anchored by tridentate pyrazole-based ligands

Reactions of GaCl₃ with pyrazole-containing ligands of the pyrazole-imine-phenol (HL¹-HL³) or pyrazole-amine-phenol (HL⁴-HL⁶) types led to the synthesis of well-defined [GaL₂]⁺ homoleptic complexes (1-6). Complexes 1-6 were characterized by elemental analysis, ESI-MS (electrospray ionization-mass spectrometry), IR and NMR spectroscopies, and in the case of Complex 1 also by X-ray diffraction analysis. In complexes 1-3, the pyrazole-imine-phenolate ligands act as monoanionic chelators that coordinate to the metal in a meridional fashion, while 4-6 contain monoanionic and facially coordinated pyrazole-amine-phenolate ligands. Complexes 1-3 have a greater stability in solution compared to 4-6, which have shown a more pronounced tendency to release the respective ancillary ligands. The cytotoxicity of 1-6 and of the respective ligands (HL¹-HL⁶) was evaluated against human prostate cancer cells PC-3 and human breast cancer cells MCF-7. The substituents of the phenolate rings strongly influenced the cytotoxicity of the compounds. Complexes 3 and 6 that contain chloride substituents at the phenolate rings have shown the highest cytotoxicity, including in the cisplatin-resistant PC-3 cell line. The cytotoxic profile of 3 and 6 is very similar to the one displayed by the respective anchor ligands, respectively HL¹ and HL⁶. The cytotoxic activity of 3 and 6 is slightly increased by the presence of transferrin, and both complexes provoke cell death mainly by induction of apoptotic pathways.     

Malonato complexes of oxidovanadium(IV): Synthesis, structural characterization and exploration of their insulin mimetic properties

Several bis-malonatooxidovanadium(IV) complexes of the general type [M₂(H₂O)_n][VO(mal)₂(H₂O)] (where M = Li(1), Na(2), K(3), Cs(4) and NH₄(5); n = 3.5, 1, 3, 1 and 1, respectively) were isolated in good yield and high purity. These complexes were fully characterized by various physicochemical techniques (elemental analysis, UV-Vis, IR, EPR, CV, etc.) complexes 1, 2 and 3 were structurally characterized by single crystal X-ray diffraction technique. In vivo antidiabetic properties of bis-malonato complexes 1, 2, 3 and 5 have been studied using Streptozotocin induced diabetic rats. Significant lowering of blood sugar level has been noticed. At the same time these complexes were found to regulate secondary pathophysiological complications like liver damage and lowering of the total antioxidant status (TAS) in diabetic rats. Results of these study are expected to a expand the possibility of designing new oxidovanadium(IV) complexes of O,O chelating ligands with significant antidiabetic properties.     

Novel p-tolylimido rhenium(V) complexes incorporating quinoline-2-carboxylate ion - Synthesis, X-ray studies, spectroscopic characterization and DFT calculations

Novel p-tolylimido rhenium(V) complexes trans-[Re(p-NC₆H₄CH₃)X₂(quin-2-COO)(PPh₃)] and cis-[Re(p-NC₆H₄CH₃)X₂(quin-2-COO)(PPh₃)]·MeCN have been obtained in the reactions of [Re(p-NC₆H₄CH₃)X₃(PPh₃)₂] (X = Cl, Br) with quinoline-2-carboxylic acid. The compounds were identified by elemental analysis IR, UV-Vis spectroscopy and X-ray crystallography. The electronic structures of trans- and cis-halide isomers of [Re(p-NC₆H₄CH₃)Cl₂(quin-2-COO)(PPh₃)] have been calculated with the density functional theory (DFT) method. Additional information about binding in the compounds [Re(p-NC₆H₄CH₃)Cl₂(quin-2-COO)(PPh₃)] with cis- and trans-halide arrangement has been obtained by NBO analysis. The electronic spectra of trans and cis isomers of [Re(p-NC₆H₄CH₃)Cl₂(quin-2-COO)(PPh₃)] were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Electronic and steric effects in cobalt Schiff bases complexes: Synthesis, characterization and catalytic activity of some cobalt(II) tetra-halogens-dimethyl salen complexes

The synthesis, characterization and catalytic activity of a series of tetra-halogeno-dimethyl salen cobalt (II) complexes are reported in this paper. The investigated complexes of cobalt (II) with Schiff bases are: αα′-di-methyl Salen cobalt (II) [Co(dMeSalen)], 3,3′,5,5′-tetra chloro α,α′-di-methyl Salen cobalt (II), [Co(tCldMeSalen)], 3,3′-di-bromo 5,5′-di-chloro α,α′-di-methyl Salen cobalt (II), [Co(tBrdMeSalen)], 3,3′,5,5′-tetra bromo α,α′-di-methyl Salen cobalt (II), [Co(tBrdMeSalen)] and 3,3′,5,5′-tetra iodo α,α′-di-methyl Salen cobalt (II), [Co(tIdMeSalen)] (where Salen is bis(salicylaldehyde)ethylenediamine). The characterization of the complexes was performed by elemental analysis, cyclic voltammetry, UV-Vis, IR and EPR spectroscopies. The study was made in DMF, and pyridine was used for coordination as axial base. The redox potential is influenced by the substituent grafted on aromatic ring and in the azomethynic position and also by the molecules coordinating in axial position (solvent, DMF, or pyridine). The catalytic oxygenation of 2,6-di-tert-butylphenol by these complexes leads to the obtention of benzoquinone and diphenoquinone products. The cobalt (II) complexes form reversible adducts with molecular oxygen.     

Conformational preferences of 1,4,7-trithiacyclononane: a molecular mechanics and density functional theory study

Conformational preferences of 1,4,7-trithiacyclononane were studied using a highly efficient sampling technique based on local nonstochastic deformations and the MM2(91) force field. The results show that conformers that the molecule adopts in the crystal state were found to be low-energy conformers (LECs) within 5 kcal mol(-1) of the global minimum. A conformation with C1 symmetry was the global minimum and the C3 and C2 conformations were calculated to be 0.03 and 1.78 kcal mol(-1) higher in energy, respectively. The structures were further minimized using Density Functional Theory (DFT) calculations with two different functionals. The C2 and the C1 conformations were found to be LECs with the C3 conformation more than 4.0 kcal mol(-1) above the global minimum. The relative energies and structural ordering obtained using the BP86 functional are in agreement with the previously reported relative energies calculated using second-order Moller-Plesset (MP2) ab initio calculations. With the energy ordering being dependent on the molecular mechanics force field used, the approach of MM-->DFT (searching exhaustively the available conformational space at the MM level followed by generating the energy ordering through DFT calculations) appears to be appropriate for thiacrown ethers.     

Spectroscopic description of an unusual protonated ferryl species in the catalase from <Emphasis Type="Italic">Proteus mirabilis</Emphasis> and density functional theory calculations on related models. Consequences for the ferryl protonation state in catalase,peroxidase and chloroperoxidase

The catalase from Proteus mirabilis peroxide-resistant bacteria is one of the most efficient heme-containing catalases. It forms a relatively stable compound II. We were able to prepare samples of compound II from P. mirabilis catalase enriched in ⁵⁷Fe and to study them by spectroscopic methods. Two different forms of compound II, namely, low-pH compound II (LpH II) and high-pH compound II (HpH II), have been characterized by Mössbauer, extended X-ray absorption fine structure (EXAFS) and UV-vis absorption spectroscopies. The proportions of the two forms are pH-dependent and the pH conversion between HpH II and LpH II is irreversible. Considering (1) the Mössbauer parameters evaluated for four related models by density functional theory methods, (2) the existence of two different Fe–O_ferryl bond lengths (1.80 and 1.66 Å) compatible with our EXAFS data and (3) the pH dependence of the α band to β band intensity ratio in the absorption spectra, we attribute the LpH II compound to a protonated ferryl Fe^IV–OH complex (Fe–O approximately 1.80 Å), whereas the HpH II compound corresponds to the classic ferryl Fe^IV=O complex (Fe=O approximately 1.66 Å). The large quadrupole splitting value of LpH II (measured 2.29 mm s^?1 vs. computed 2.15 mm s^?1) compared with that of HpH II (measured 1.47 mm s^?1 vs. computed 1.46 mm s^?1) reflects the protonation of the ferryl group. The relevancy and involvement of such (Fe^IV=O/Fe^IV–OH) species in the reactivity of catalase, peroxidase and chloroperoxidase are discussed.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.