Unusual complexation of Cu(I) by pyrimidine/pyridine-pyrazole derived ligands exploiting the molecular function of 2-mercapto-4,6-dimethylpyrimidine - Syntheses, crystal structures and electrochemistry

Reaction of 2 equiv. amount of copper(II) chloride dihydrate with 2 equiv. of methyl-5-methyl-1-(4,6-dimethyl-2-pyrimidyl)pyrazole-3-carboxylate (DpymPzC) in presence of 1 equiv. of 2-mercapto-4,6-dimethylpyrimidine (DpymtH) at pH ∼ 6 afforded the tricoordinated copper(I) complex [Cu(DpymPzC)Cl] (1). The same reaction with copper(II) perchlorate hexahydrate, as the metal salt under the same equivalent ratio at pH ∼ 6 formed the tetracoordinated copper(I) complex [Cu(DpymPzC)₂]ClO₄ (2). In both the cases, the role of DpymtH is nothing but only to reduce the copper(II) salt in situ finally forming the copper(I) complex. On the other hand, the direct reaction between the copper(I) thiocyanate and DpymPzC in 2:2 equiv. ratio produced a tricoordinated copper(I) complex [Cu(DpymPzC)SCN] (3). In a similar reaction of 2 equiv. amount of copper(II) chloride dihydrate with 2 equiv. amount of ethyl-5-methyl-1-(2-pyridyl)pyrazole-3-carboxylate (PyPzC) in presence of 1 equiv. of DpymtH at pH ∼ 6, an intense red coloured microcrystalline compound (4) was obtained. In contrast, 1 equiv. of PyPzC and 2 equiv. of DpymtH on reaction with 1 equiv. of copper(II) chloride dihydrate at pH ∼ 6 produced a novel tetranuclear mixed coordinated [Cu₄(DpymtH)₄Cl₄] complex (5). Here DpymtH plays dual role - a reducing agent for the copper(II) salt followed by a chelating ligand towards copper(I) so formed in situ. Among the above species, 1, 2 and 5 are crystallographically characterized. In 1, the central copper atom is in distorted triangular planar geometry with N₂Cl chromophore whereas in 2, the same is in distorted tetrahedral geometry with N₄ chromophore. Notably, the extent of distortion from the ideal geometry is more in 2. In 5, which is in chair conformation, out of four copper atoms, two being in S₂Cl chromophore are tricoordinated and the remaining two are tetracoordinated with NS₂Cl chromophore. The metal centers are bridged through DpymtH in its ‘thione’ form. Interestingly, the chelation (in part) results in formation of the highly stable four-membered two chelate rings around the two tetracoordinated copper atoms in 5. The two copper centers along the long arm of the chair are separated through a distance of 5.190 Å while those in the short arm are at a length of 3.629 Å. The electronic, IR spectra and electrochemistry of the complexes 1, 2 and 5 have also been investigated.     

Syntheses, structure and properties of chiral copper(II) complexes with end-on azide bridge and chiral-bipyridine ligand

A novel one-dimensional chiral copper(II) complex with single end-on (EO) azide bridge and chiral 2,2-bipyridine ligand, [Cu(N₃)₂(L)]_n (1), and a mononuclear chiral copper(II) complex, [Cu(N₃)₂(L)] (2) (L = (1R)-6,6-dimethyl-5,7-methano-2-(2-pyridinyl)-4,5,6,7-tetrahydroquinoline), have been synthesized and characterized. The crystal structure determination shows that complex 1 is a one-dimensional chiral coordination polymer with non-equivalent Cu-N(azide) bonds, in which the central Cu(II) ion is penta-coordinated in the form of a slightly distorted square-based pyramid. Compound 2 is a four-coordinated mononuclear complex where the Cu(II) ion has a highly distorted tetrahedronal environment. Both complexes 1 and 2 crystallize in the chiral space group: P2₁2₁2₁ and P₁, respectively. The magnetic studies show that there exists antiferromagnetic interaction between the copper(II) ions in complex 1.     

Synthesis, characterization, and crystal structures of hydrotris(2-mercapto-1-imidazolyl)borate-based zinc(II) and copper(I) complexes

The reaction of the tripod ligand hydrotris(2-mercapto-1-imidazolyl)borate Tm^xylyl with zinc(II) perchlorate in methanol afforded the mononuclear complex of the type [Tm^xylyl-Zn(mim^xylyl)]ClO₄ (1). Whereas under the same conditions, the reaction with copper(II) perchlorate gives rise to the simultaneous formation of the dinuclear copper(I) complex [Tm^xylylCu]₂ (2). The chemical formulae of the complexes have been characterized by elemental chemical analysis, IR-NMR spectroscopies, and single crystal X-ray methods. In complex 1, the zinc(II) atom displays a distorted tetrahedral environment. While in complex 2, the Tm^xylyl ligand bridges the two copper(I) atoms in an asymmetric manner with trigonal geometry. The inverted conformation of the ligand Tm^xylyl at the boron center, allows the B-H units to be directed towards the copper centers. The greater reactivity of the borohydride groups towards metal centers enhances the reduction of Cu(II) to Cu(I). The obtained kinetic results for the methylation reactions of 1 and 2 indicate that these bound thione complexes are less suitable to electrophilic attack than the thiolate ligand.     

Chiral 2-pyridyl alcoholate copper complexes: crystal structures of [bis(2-pyridyl alcoholate)copper(II)] and the use of [(2-pyridyl alcoholate)copper(II)]and [(2-pyridyl alcoholate)copper(I)] in asymmetric cyclopropanation of styene and allylic oxidation of cyclohexene

Chiral N,O pyridine alcohols HL¹-HL⁶ were used to form complexes with copper(II) ions. Ligands HL¹ and HL² formed complexes with copper(II) ions when Cu(OAc)₂ and HL were refluxed in methanol/ethanol mixture. Ligand HL³ formed a complex with copper(II) when deprotonated with NaH and stirred in a Cu(II) acetate THF solution. Ligands HL⁴-HL⁶ did not form complexes with copper(II) under similar conditions. Two complexes, [Cu(L¹)₂] and [Cu(L²)₂], were isolated as single crystals and characterized by X-ray crystallography. These complexes showed low catalytic activities in asymmetric reactions. However, they became active when reacted with triflic acid. Copper complexes, [Cu(L)] or [Cu(L)]⁺, formed in situ by reacting ligands HL with copper(I) or (II) ions, respectively, were also found to be active copper catalysts for asymmetric cyclopropanation of styrene with ethyl diazoacetate and allylic oxidation of cyclohexene with t-butylperoxybenzoate. Enantioselectivities up to 56% and 38% were obtained in asymmetric cyclopropanation of styrene and asymmetric allylic oxidation of cyclohexene, respectively.     

Sterically-controlled nuclearity in new copper(II) complexes with di-compartmental ligands: Formation of antiferromagnetically coupled angular trimer and mononuclear inclusion complex

Two new copper(II) complexes, [Cu₃(L¹)₂(H₂O)₂](ClO₄)₂ (1) and [CuL²⊂ (H₂O)] (2) have been derived from two di-compartmental Schiff base ligands H₂L¹ and H₂L², respectively. Depending on slight modification of the substituent group of the potentially N₂O₄ donor ligands, tri- and mononuclear structures are obtained, which have been confirmed by single-crystal X-ray diffraction studies. Both complexes have been characterized by elemental analysis, IR, UV-vis and EPR spectroscopy. Complex 1 consists of an angular trinuclear array of copper ions, while complex 2 consists of a mononuclear copper center. Variable temperature magnetic susceptibility measurements have been performed to investigate the magnetic behaviour of complex 1 and the result indicates a strong antiferromagnetic exchange interaction (J = −120.1(2) cm⁻¹) between the adjacent copper(II) centers through two double μ₂-phenoxo bridges. Complex 2 is a mononuclear inclusion compound encapsulating one water molecule in the vacant external compartment of the ligand through hydrogen-bonding interactions.     

Copper(II) nitrato and chloro complexes with sterically hindered tridentate ligands: Influence of ligand framework and charge on their structure and physicochemical properties

Copper(II) coordination complexes of the neutral ligand, tris(3-tert-butyl-5-methyl-1-pyrazolyl)methane (L2′), i.e. the copper(II) nitrato complexes [Cu(L2′)(NO₃)][Cu(NO₃)₄]_1/2 (1) and [Cu(L2′)(NO₃)](ClO₄) (2) and the copper(II) chloro complex [Cu(L2′)(Cl)](ClO₄) (3), and its anionic borate analogue, hydrotris(3-tert-butyl-5-methyl-1-pyrazolyl)borate (L2⁻), i.e. the copper(II) nitrato complex [Cu(L2)(NO₃)] (4) and the copper(II) chloro complex [Cu(L2)(Cl)] (5), were synthesized in order to investigate the influence of ligand framework and charge on their structure and physicochemical properties. While X-ray crystallography did not show any definitive trends in terms of copper(II) atom geometry in four-coordinate copper(II) chloro complexes 3 and 5, different structural trends were observed in five-coordinate copper(II) nitrato complexes 1, 2, and 4. These complexes were also characterized by spectroscopic techniques, namely, UV-Vis, ESR, IR/far-IR, and X-ray absorption spectroscopy.     

Synthesis of Fe(II) and Cu(II) building blocks for metal-organic frameworks

In situ reaction of the aminobenzoic acids 2-aminobenzoic acid and 3,5-diaminobenzoic acid with salicylaldehyde provide easy access to the ligands 2-[{(2-hydroxyphenyl)methylene}amino]benzoic acid (L1) and 3,5-bis[{(2-hydroxyphenyl)methylene}amino]benzoic acid (L2). Addition of a Fe(II) or Cu(II) salt to the solution of the ligand yields the corresponding Fe and Cu complexes. The species synthesized have been structurally characterized by single-crystal X-ray diffraction. The Fe(II) complex [Fe(L1)(MeOH)₃] (1) crystallizes in the triclinic space group . The Cu(II) complex [Cu(L1)] (2) is a one-dimensional chain and crystallizes in the monoclinic space group P2₁. The Cu(II) complex [Et₃NH]₂[Cu₂(L2)₂] (3) crystallizes in the monoclinic space group P2₁/n. The magnetic properties of 1, 2 and 3 have been studied, showing that the Cu(II) ions of 2 and 3 are ferromagnetically coupled. Complexes 1 and 3 have strong potential as metal-bearing building blocks for the synthesis of metal-organic frameworks.     

Structural studies of copper catalyzed hydroxylation reactions

The reaction of 2,6-diacetylpyridine, CuCl₂, and semicarbazide hydrochloride was studied as a function of pH to yield three different products: aqua(2-acetylsemicarbazone-3-hydroxo-6-acetylpyridine) chlorocopper(II) hemihydrate, 1, bis(2,6-diacetylpyridinedisemicarbazone)copper(I) chloride dimer, 2, and bis(2,6-diacetylpyridinedisemicarbazone)copper(II) chloride dimer, 3. The reaction of 1 with a mol of semicarbazide hydrochloride gave chloro(3-hydroxo-2,6-diacetylpyridinedisemicarbazone)copper(II) chloride hydrate, 4, and with a mol of semicarbazide hydrochloride and cupric chloride gave aquachlorocopper(II)(μ-chloro)(μ′-[2-acetylsemicarbazone-O,N-3-hydroxy-6-acetylsemicarbazonepyridine-O,N,N])aquacopper(II) trihydrate, 5. The crystal structures of compounds 1-5 were determined by X-ray diffraction. Some observations on the course of the reactions are given.     

An oxamato bridged trinuclear copper(II) complex: Synthesis, crystal structure, reactivity, DNA binding study and magnetic properties

A linear tri-nuclear oxamato bridged copper(II) complex [Cu₃(pba)(dpa)₂(H₂O)(ClO₄)](ClO₄)·H₂O (1) (pbaH₄ = 1,3-propanediylbis(oxamic acid), dpa = 2,2′-dipyridylamine) was isolated from the reaction mixture of Na₂[Cu(pba)]·3H₂O, copper perchlorate hexahydrate and dipyridylamine in methanol. On reaction with dpa or DMF in basic medium (KOH) at ambient temperature complex 1 changed to dinuclear oxalate bridged copper(II) derivatives, [Cu₂(μ-C₂O₄)(dpa)₄](ClO₄)₂ (2) and [Cu₂(μ-C₂O₄)(dpa)₂(DMF)₂](ClO₄)₂ (3), respectively. The complexes 1, 2 and 3 have been characterized by physicochemical and spectroscopic tools, and also by the X-ray single crystal analysis. The hydrolysis of 1 in basic medium and thermo-gravimetric analysis has been studied. Absorption and emission spectral studies showed that complex 1 interacts with calf thymus-DNA (CT-DNA) with a binding constant (K_b) of 4.01 × 10⁴ M⁻¹ and linear Stern-Volmer quenching constant (K_sv) of 6.9 × 10⁴. A strong anti-ferromagnetic interaction with a coupling constant J_CuCu of 320.0 ± 0.3 cm⁻¹ was observed from the study of magnetic behavior of complex 1 in the temperature range of 2-300 K. Electrochemical equivalency of three copper(II) ions in 1 was identified by getting only one quasi reversible cyclic voltammogram.     

Synthesis, characterization and crystal structure of a monomeric and a macrocyclic copper (II) complex with a large cavity using benzylacetylacetone ligand

The bidentate ligand benzylacetylacetone was used to synthesize the Cu(II) complexes 1 and 2 without and with 4,4^′-bipyridine ligand, respectively. The complexes were characterized by analytical and spectroscopic studies. The mononuclear complex [Cu(C₁₀H₉O₂)₂] (1) has been synthesized by the reaction of copper acetate with the ligand whereas the tetranuclear complex [Cu₄(4,4^′-bpy)₄(C₁₀H₉O₂)₄(C₂H₃O₂)₄] (2) has been synthesized by the reaction of copper acetate with the ligand followed by the addition of 4,4^′-bipyridine. The X-ray analysis shows that the complex 1 has square planar geometry and the complex 2 has square pyramidal geometry around the metal centers. The thermogravimetric studies showed that the complexes undergo decomposition in multiple steps.     

Synthesis and transition metal complexes of 3,3-bis(1-vinylimidazol-2-yl)propionic acid, a new N,N,O ligand suitable for copolymerisation

The new N,N,O heteroscorpionate ligand 3,3-bis(1-vinylimidazol-2-yl)propionic acid (Hbvip) (5) was synthesised in five steps starting from 1-vinylimidazole. This ligand is closely related to 3,3-bis(1-methylimidazol-2-yl)propionic acid (Hbmip), but contains two vinyl linker groups which can be used for radical-induced polymerisation reactions. The κ³-N,N,O coordination behaviour of 5 was proven by the synthesis of the tricarbonyl complexes [Re(bvip)(CO)₃] (6), [Mn(bvip)(CO)₃] (7) and [Cu(bvip)₂] (8). To obtain good yields of 6, it was synthesised in water instead of THF. The ligand as well as all three complexes were characterised by X-ray crystallography. Copolymerisation of 5 with pure methyl methacrylate (MMA) or a combination of MMA and ethylene glycol dimethacrylate (EGDMA) led to the solid phases P1 and P2. Polymer-bound rhenium and manganese tricarbonyl complexes could be obtained by the reaction of deprotonated P1 with [MBr(CO)₅] (M = Re, Mn) and also by copolymerisation of 6 and 7 with MMA. In both cases, the facial tripodal binding behaviour was evidenced by IR spectra of the polymers. Furthermore, the content of metal incorporated in the polymers was determined by elemental analysis, AAS or ICP-OES measurements. Reaction of the deprotonated solid phase P1 with copper(II) chloride led to a blue solid-phase (P1-Cu). The UV-Vis absorption maximum of P1-Cu is found at 615 nm, which is almost identical to that found for 8. Thereby, it seems likely that P1 is flexible enough to form bisligand complexes with copper(II). This means that the copper centres act as a kind of crosslinking agents. In contrast, the heterogeneous reaction of P2 with copper(II) chloride yielded a lime green solid phase (P2-Cu). The bathochromic shift of the absorption maximum by 102 nm suggests one-sided bound copper centres.     

Synthesis of 2-(nitromethyl)ornithine from ornithine mediated by cobalt(III)

Rac.-p-(tris(2-aminoethyl)amine-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d) was obtained by a simple three-step procedure from ornithine using cobalt template chemistry. p-(Tris(2-aminoethyl)amine-ornithine)cobalt(III) trichloride (2a) was obtained from tris(2-aminoethyl)amine (tren) and (S)-ornithine in the presence of cobalt(II), which was oxidised to cobalt(III) during the reaction. Complex 2a was selectively oxidised with thionyl chloride-dimethyl formamide to p-(tris(2-aminoethyl)amine-dehydro-ornithine)cobalt(III) trichloride 2b. Complex 2c, in which reaction of thionyl chloride-dimethyl formamide has also occurred at the δ-amine of ornithine, was obtained at longer reaction times. Complex 2b reacted with nitromethane anion to give rac.-p-(tris(2-aminoethyl)amino-2-(nitromethyl)ornithine)cobalt(III) trichloride (2d). The amino acid rac.-2-(nitromethyl)ornithine (1b) was released by reducing complex 2d with aqueous ammonium sulfide. Complex 2d was expected to release 2-(nitromethyl)ornithine (1b) in hypoxic cells, where the amino acid could act as an inhibitor of ornithine decarboxylase. Preliminary data indicated that complex 2d was weakly cytotoxic in one cell type studied.     

Spectroscopic and structural studies of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one and of an unusual T4(2)7(2)6(2)7(2) water tape stabilized by the copper(II) coordination polymer

The solid-state structures of 6-(1-methylbenzimidazol-2-yl)-1H-pyridin-2-one (HL) and the copper(II) complex [Cu(L⁻)₂(OH₂)]·2H₂O (1) are established by X-ray crystallography and also by means of physicochemical and spectroscopic methods. The molecules of HL form a self-complementary head-to-tail hydrogen-bonded dimer through C-H?N and C-H?O contacts to give an infinite 1D chain. The copper(II) complex (1) is five-coordinate with distorted trigonal-bipyramidal (TBP) geometry of the N₄O donor atoms. The electronic and EPR data are in agreement with the X-ray structure of 1, showing that HL coordinates to copper(II) centre as a mono-anionic ligand through deprotonated pyridone N atom and the tertiary benzimidazole nitrogen atom to form a neutral complex in which the water molecule occupies the fifth position. The 1D water tape, T4(2)7(2)6(2)7(2) is anchored to the host through hydrogen bonds between coordinated water molecule [O(3w)] as acting double H-donor, pyridone carbonyl groups [O(2) and O(1)] as double H-acceptor and the lattice water molecules [O(4w) and O(5w)] as double H-donor and single H-acceptor).     

Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Solvent-controlled generation of two pairs of mononuclear single-strand helical copper(II) complexes of 2,6-pyridinediylbis(2-pyridinyl)methanone: metal-promoted hydrolysis and solvolysis with asymmetric induction

Two pairs of stable mononuclear single-strand helical complexes were obtained through controlled self-assembly using 2,6-pyridinediylbis(2-pyridinyl)methanone (L) and copper(II) salts. CuL(NO₃)₂ (1) and [CuL′(H₂O)](NO₃)₂ (2) represent a pair in which L takes the diketo form in 1 but hydrolyzed in 2, while CuLCl₂ (3) and [CuL″Cl]Cl (4) constitute another pair in which L remains intact in 3 but solvolyzed in 4. A mechanism of the metal-promoted hydrolysis and solvolysis of ligand L with asymmetric induction is proposed through studies on the crystal structures of these complexes.     

Structural analysis and magnetic properties of the copper(II) dicyanamide complexes [Cu2(dmphen)2(dca)4], [Cu(dmphen)(dca)(NO3)]n and [Cu(4,4-dmbpy)(H2O)(dca)2] (dca=dicyanamide; dmphen=2,9-dimethyl-1,10-phenanthroline; 4,4-dmbpy=4,4-dimethyl-2,2-bipyridine)

The preparation, crystal structures and magnetic properties of three copper(II) compounds of formulae [Cu₂(dmphen)₂(dca)₄] (1), [Cu(dmphen)(dca)(NO₃)]_n (2) and [Cu(4,4^′-dmbpy)(H₂O)(dca)₂] (3) (dmphen=2,9-dimethyl-1,10-phenanthroline, dca=dicyanamide and 4,4^′-dmbpy=4,4^′-dimethyl-2,2^′-bipyridine) are reported. The structure of 1 consists of discrete copper(II) dinuclear units with double end-to-end dca bridges whereas that of 2 is made up of neutral uniform copper(II) chains with a single symmetrical end-to-end dca bridge. Each copper atom in 1 and 2 is in a distorted square pyramidal environment: two (1) or one (2) nitrile-nitrogen atoms from bridging dca groups, one of the nitrogen atoms of the dmphen molecule (1 and 2) and either one nitrile-nitrogen from a terminal dca ligand (1) or a nitrate-oxygen atom (2) build the equatorial plane whereas the second nitrogen atom of the heterocyclic dmphen fills the axial position (1 and 2). The copper-copper separations through double (1) and single (2) end-to-end dca bridges are 7.1337(7) (1) and 7.6617(7) (2). Compound 3 is a mononuclear copper(II) complex whose structure contains two neutral and crystallographically independent [Cu(4,4^′-dmbpy)(H₂O)(dca)₂] molecules which are packed in two different layer arrangements running parallel to the bc-plane and alternating along the a-axis. The copper atoms in both molecules have slightly distorted square pyramidal surroundings with the two nitrogen atoms of the 4,4^′-dmbpy ligand and two dca nitrile-nitrogen atoms in the basal plane and a water oxygen in the apical position. A semi co-ordinated dca nitrile-nitrogen from a neighbour unit [2.952(6) Å for Cu(2)-N] is in trans position to the apical water molecule in one of the two molecules, this feature representing part of the difference in supramolecular connections in the alternating layers referred to above. Magnetic susceptibility measurements for 1-3 in the temperature range 1.9-290 K reveal the occurrence of weak antiferromagnetic interactions through double [J=−3.3 cm⁻¹ (1), ] and single [J=−0.57 cm⁻¹ (2), ] dca bridges and across intermolecular contacts [θ=−0.07 K (3)].     

Synthesis, X-ray structures, electrochemical properties and cytotoxic effects of Co(II) complexes

1-Benzothiazol-2-yl-3,5-dimethyl-1H-pyrazole (1a) and 1-benzothiazol-2-yl-5-(2-hydroxyphenyl)-3-methyl-1H-pyrazole-4-carboxylic acid methyl ester (1b) were reacted with the hexahydrates of cobalt(II) chloride, cobalt(II) nitrate and cobalt(II) perchlorate to give the corresponding complexes 2a-4a and 2b-5b, respectively. Obtained compounds differ in coordination spheres of central atoms. The complex 2a includes a fivefold coordinated cobalt(II) ion, whereas 3a shows a distorted octahedral configuration around the cobalt(II) ion. All complexes were characterised by FTIR spectroscopy, MS and elemental analysis. The X-ray structures of 2a, 3a and 5b complexes were also solved. The cytotoxic properties of the ligand 1a and both series of Co(II) complexes were examined on human leukemia NALM-6 and HL-60 cells and melanoma WM-115 cells. The ligands, were found to have very low cytotoxicity. Complex 3b exhibited the highest cytotoxic activity with IC₅₀ values in the range of 6.9-17.1 μM for three examined cell lines.     

Axial versus equatorial coordination of thioether sulfur: Mixed ligand copper(II) complexes of 2-pyridyl-N-(2′-methylthiophenyl)-methyleneimine with bidentate diimine ligands

The synthesis, structure and spectral and redox properties of the copper(II) complexes [Cu(pmtpm)Cl₂] (1) and [Cu(pmtpm)₂](ClO₄)₂ (6), where pmtpm is the linear tridentate ligand 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine containing a thioether and two pyridine donors, are described. Also, the mixed ligand complexes [Cu(pmtpm)(diimine)](ClO₄)₂ (2-5), where the diimine is 2,2′-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) (4) or dipyrido-[3,2-d:2′,3′-f]-quinoxaline (dpq) (5), have been isolated and studied. The X-ray crystal structures of the complexes 1, [Cu(pmtpm)(2,9-dmp)](ClO₄)₂4 and 6 have been successfully determined. The complex 1 possesses a trigonal bipyramidal distorted square based pyramidal (TBDSBP) coordination geometry in which three corners of the square plane are occupied by two nitrogens and thioether s of pmtpm ligand and the remaining equatorial and the axial positions by two chloride ions. The complex 4 contains a CuN₄S chromophore also with a TBDSBP coordination geometry in which two nitrogens and the thioether sulfur of pmtpm ligand occupy three corners of the square plane. One of the two nitrogens of 2,9-dmp ligand is equatorially coordinated and the other axially to copper. On the other hand, the complex 6 is found to possess a square based pyramidal distorted trigonal bipyramidal (SPDTBP) coordination geometry. The CuN₂S trigonal plane in it is comprised of the pyridine and imine nitrogens and the thioether sulfur of the pmtpm ligand. The pyridine nitrogens of the ligand occupy the axial positions and the second thioether sulfur remains uncoordinated. On long standing in acetonitrile solution the mixed ligand complexes 2 and 3 undergo ligand disproportionation to provide the corresponding bis-complexes of bpy and phen, respectively, and 6. The electronic and EPR spectral parameters and the positive redox potential of complex 4 are consistent with the equatorial location of the thioether sulfur in the square-based coordination geometry around copper(II). On the other hand, the higher g_∥ and lower A_∥ values and lower E_1/2 values for the complexes 2, 3 and 5 are consistent with the axial coordination of the thioether sulfur. Also, the Cu(II)/Cu(I) redox potentials increase with increase in number of aromatic rings of the diimine ligand. The steric and electronic effects of the bidentate diimine ligands in orienting the thioether coordination to axial or equatorial position are discussed.     

Examining the impact of steric and electronic variation in N2S scorpionate ligands on the properties of zinc(II) and cadmium(II) complexes

A series of LZn(II)Br (1-4) and LCd(II)Cl complexes (9-11) has been prepared by the reaction of metal halide precursors with the lithium salts of the N₂S⁻ ligands bis(3,5-diisopropylpyrazol-1-yl)dithioacetate (L¹), bis(3,5-di-tert-butylpyrazol-1-yl)dithioacetate (L²), N-phenyl-2,2-bis(3,5-diisopropylpyrazol-1-yl)thioacetamide (L³) and N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide (L⁴). Characterization by X-ray crystallography and DOSY NMR studies indicate that LZnBr complexes 1-4 are mononuclear both in the solid state and in solution. Steric differences between ligands L¹-L⁴ result in distortion from an ideal tetrahedral geometry for each complex, with the degree of distortion depending on the bulk of the ligand substituents. In contrast, the related complex L³CdCl was shown by X-ray crystallography to dimerize in the solid state to form the chloride-bridged five-coordinate complex [L³CdCl]₂ (10). Despite 10 having a dinuclear structure in the solid state, DOSY NMR studies indicate 9-11 exist as mononuclear LCdCl species in solution. In addition, Zn(II) cyanide complexes of the form LZnCN [L = L¹ (5), L³ (7), L⁴ (8)] have been characterized and the X-ray structure of 8 determined. Moreover, density functional theory calculations have been conducted which yield important insight into the bonding in 1-4 and 5-8 and the electronic impact of ligands L¹-L⁴ on the zinc(II) ion and its ability to function as a Lewis acid catalyst.     

Cyanato bridged binuclear nickel(II) and copper(II) complexes with pyridylpyrazole ligand: Synthesis, structure and magnetic properties

Binuclear cyanate bridged nickel(II) complex [Ni(L)(NCO)]₂(PF₆)₂ (1) and copper(II) complex [Cu(L)(NCO)]₂(PF₆)₂ (2), where L is N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine, a tetradentate N₄-coordinated ligand have been synthesized and characterized by physicochemical method. The structures of complexes 1 and 2 have been studied by single crystal X-ray diffraction analysis. The structure analysis reveals that both nickel(II) and copper(II) center are coordinated in distorted octahedral fashion and coordination mode of cyanate ligand is end-to-end (μ-1,3) for complex 1 but it is double end-on (μ-1,1) mode for complex 2. The variable temperature magnetic susceptibility data, measured from 2 to 300 K, show weak antiferromagnetic interaction with J value −6.2(1) cm⁻¹ for complex 1, whereas complex 2 has very weak ferromagnetic interaction with J value +0.5(1) cm⁻¹.