Aging results in copper accumulations in glial fibrillary acidic protein‐positive cells in the subventricular zone

Analysis of rodent brains with X‐ray fluorescence (XRF) microscopy combined with immunohistochemistry allowed us to demonstrate that local Cu concentrations are thousands of times higher in the glia of the subventricular zone (SVZ) than in other cells. Using XRF microscopy with subcellular resolution and intracellular X‐ray absorption spectroscopy we determined the copper (I) oxidation state and the sulfur ligand environment. Cu K‐edge X‐ray absorption near edge spectroscopy is consistent with Cu being bound as a multimetallic Cu‐S cluster similar to one present in Cu‐metallothionein. Analysis of age‐related changes show that Cu content in astrocytes of the SVZ increases fourfold from 3 weeks to 9 months, while Cu concentration in other brain areas remain essentially constant. This increase in Cu correlates with a decrease in adult neurogenesis assessed using the Ki67 marker (both, however, can be age‐related effects). We demonstrate that the Cu distribution and age‐related concentration changes in the brain are highly cell specific.     

Square-planar copper(II) halide complexes of tridentate ligands with π-π stacking interactions and alternating short and long Cu ? Cu distances

The preparation of a new tridentate N₂O-donor ligand N-(2-pyridylmethyl)-3-methoxysalicylaldiminato (HL) is described, together with the corresponding copper(II) complexes [Cu(L)X] (X = Cl⁻, Br⁻). The compounds were characterized by elemental analysis, spectral, magnetic and crystallographic studies. In both compounds, the local molecular structure of the Cu(II) ion involves a square-planar CuN₂OX chromophore, consisting of a deprotonated phenolate oxygen, an imine nitrogen, the pyridine nitrogen and X. In the solid state, π-π stacking interactions are dominantly present, involving the pyridine and phenolate rings of neighboring molecules, which lead to a one-dimensional arrangement with alternating short and long Cu ? Cu distances of [3.720, 4.599 Å] for the bromo complex and of [3.698, 4.696 Å] for the chloro complex. The temperature-dependent magnetic measurements and EPR data of polycrystalline samples, as well as of frozen solutions in CHCl₃ show that there is no observable exchange interaction between the Cu ions. The EPR parameters (g_∥, A_∥) agree with a perfect planar geometry, just as found in the X-ray analysis.     

The relationship of some copper (II) complexes of facultative tetrathioethers to the coordination environment in the "blue" copper proteins

The facultative potentially tetradentate thioether ligands 1,2-bis(methylthioethylthio)ethane (2,2,2), 1,3-bis(2-methylthioethylthio)propane (2,3,2) and 1,2-bis(3-methylthiopropylthio)ethane (3,2,3) react with copper(II) salts to form Cu2(2,2,2)Cl4, Cu3(ligand)X6 (ligand = 2,3,2 and 3,2,3 X = Cl; ligand = 2,2,2 2,3,2 and 3,2,3 X = Br), and Cu(ligand)(ClO4)2. The stoichiometry and structures of these complexes are discussed in terms of the steric demands of the ligand and the nature of the halide. The [Cu(2,3,2)(ClO4)] ClO4 and [Cu(3,2,3)(ClO4) [ClO4 complexes have electronic spectra which exhibit the intense 600 nm band characteristic of the "blue" copper proteins. In fact, the spectrum of [Cu(2,3,2)(ClO4)]ClO4 is very similar to that of pseudomonas aeroginosa azurin.     

Antibacterial,antifungal and in vitro antileukaemia activity of metal complexes with thiosemicarbazones

1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone 4‐ethyl‐thiosemicarbazone (HL) and its copper(II), vanadium(V) and nickel(II) complexes: [Cu(L)(Cl)]·C₂H₅OH·( 1 ), [Cu(L)₂]·H₂O ( 2 ), [Cu(L)(Br)]·H₂O·CH₃OH ( 3 ), [Cu(L)(NO₃)]·2C₂H₅OH ( 4 ), [VO₂(L)]·2H₂O ( 5 ), [Ni(L)₂]·H₂O ( 6 ), were synthesized and characterized. The ligand has been characterized by elemental analyses, IR, ¹H NMR and ¹³C NMR spectroscopy. The tridentate nature of the ligand is evident from the IR spectra. The copper(II), vanadium(V) and nickel(II) complexes have been characterized by different physico‐chemical techniques such as molar conductivity, magnetic susceptibility measurements and electronic, infrared and electron paramagnetic resonance spectral studies. The structures of the ligand and its copper(II) ( 2 , 4 ), and vanadium(V) ( 5 ) complexes have been determined by single‐crystal X‐ray diffraction. The composition of the coordination polyhedron of the central atom in 2 , 4 and 5 is different. The tetrahedral coordination geometry of Cu was found in complex 2 while in complex 4 , it is square planar, in complex 5 the coordination polyhedron of the central ion is distorted square pyramid. The in vitro antibacterial activity of the complexes against Escherichia coli, Salmonella abony, Staphylococcus aureus, Bacillus cereus and the antifungal activity against Candida albicans strains was higher for the metal complexes than for free ligand. The effect of the free ligand and its metal complexes on the proliferation of HL‐60 cells was tested.     

Synthesis, spectroscopic and structural characterization of Cu(II) derivatives of tris(pyrazol-1-yl)methanes

The reaction between CuX₂ (X=ClO₄, NO₃, Cl, Br and CH₃COO) and excess of tris(pyrazol-1-yl)methane ligands L (L=CH(pz)₃, CH(4-Mepz)₃, CH(3,5-Me₂pz)₃, CH(3,4,5-Me₃pz)₃ or CH(3-Mepz)₂(5-Mepz)) yields [CuX₂(L)], [{CuX₂}₃(L₂)₂] or [Cu(L₂)]X₂-type complexes. The ligand to metal ratio is dependent on the number and disposition of the Me substituents on the azole-type ligand and mainly on the nature of the counter-ion X. All complexes have been characterized in the solid state as well as in solution (IR and UV spectra, and conductivity determinations). The solid-state structures of [Cu{(3,5-Me₂pz)₃CH}₂](NO₃)₂, [Cu{(3,5-Me₂pz)₃CH}₂](ClO₄)₂·0.5H₂O, [Cu{(3,4,5-Me₃pz)₃CH}₂](NO₃)₂·H₂O, [Cu{(4-Mepz)₃CH}₂]Br₂·3H₂O have been determined by single crystal X-ray studies.     

1,4-Di(1,2,3,4-tetrazol-2-yl)butane as a precursor of new 2D and 3D coordination polymers of Cu(II)

A series of new coordination polymers of Cu(II) have been prepared in a reaction between copper(II) perchlorate or tetrafluoroborate salt and a novel ligand 1,4-di(1,2,3,4-tetrazol-2-yl)butane (bbtz). The compounds were characterised by an elemental analysis, TG measurements, IR, EPR and UV-Vis spectroscopy. Crystal structures of bbtz and five complexes of Cu(II) were determined by a single crystal X-ray diffraction measurement performed at 100 K. The composition and architecture of the obtained complexes strongly depend on the reaction conditions especially on the kind of solvent. Investigated complexes are composed of polymeric macrocations and non-coordinated anions. In all cases the bbtz molecules act as the bidentate ligand coordinated to metal(II) ions via N4, N4^′ nitrogen atoms from tetrazole rings. The complexes {[Cu(bbtz)₂(MeOH)₂]X₂}_∞ (X=ClO₄⁻, BF₄⁻) crystallise from methanol as 2D coordination polymers. In these compounds central metal ions are coplanar linked by molecules of bbtz and a coordination sphere is completed by axially coordinated solvent molecules. The complexes {[Cu(bbtz)₃]X₂}_∞ (X=ClO₄⁻, BF₄⁻) were synthesised in EtOH/H₂O solvent system and posses a common network topology. In this group of complexes each central atom is linked by ligand molecules to six other in plane arranged central atoms resulting in 2D networks. Reactions between Cu(II) salts and bbtz performed in absolute ethanol resulted in the formation of the next type of product. In {[Cu(bbtz)₃](ClO₄)₂·2EtOH}_∞ neighboured copper(II) ions are linked by ligand molecules in the three directions what leads to the formation of 3D net. A crystal of this complex is composed of two mutually interpenetrated 3D networks.     

Copper(I) halide complexes from cis-1,2-bis(diphenylphosphino) ethylene and some heterocyclic thiones

Reaction of copper(I) chloride or bromide with equimolar amounts of the diphos ligand cis-1,2-bis(diphenylphosphino)ethylene (dppet) and a heterocyclic thione (L) in acetonitrile/methanol solvent afforded mononuclear complexes of the type [CuX(dppet)(L)] with the diphosphine ligand acting as a chelating ligand. However, the same reaction carried out at higher temperatures proceeds, in some cases, with exclusion of the phosphine ligand from the coordination sphere leading to double-S-bridged dimers. In contrast, copper(I) iodide under the same conditions gave the thione-free dimeric compound [CuI(dppet)]₂ which contains double-bridging iodine atoms. A notable exception was for the reaction with 5-methyl-1,3,4-thiadiazole-2-thione (mtdztH) which, under the same conditions, gave rise to the unexpected, simultaneous formation of the monomer [CuI(dppet)(CH₃CN)] as well as the above mentioned dimeric [CuI(dppet)]₂. Furthermore treatment [CuX(dppet)(L)] with two equivalents of triphenylphosphine was found to cause replacement of the diphos ligand, while substitution of the chlorine atom under HCl elimination and formation of [Cu(dppet)(mftztH)₂] occured in the unique case of treating [CuCl(dppet)(mftztH)] with one additional equivalent of the same thione ligand. The structures of one representative for each of the above mentioned types of complexes, namely [CuBr(dppet)(mftztH)], [Cu(dppet)(mftztH)₂], [Cu(μ-I)(dppet)]₂ · [CuI(dppet)(CH₃CN)] and [CuBr{μ-S(pymtH)}(pymtH)]₂ have been established by single-crystal X-ray diffraction.     

The Cu/ligand stoichiometry effect on the coordination behavior of aroyl hydrazone with copper(II): Structure,anticancer activity and anticancer mechanism

In an effort to better understand the biological efficacy of the tridentate aroyl hydrazone Cu(II) complexes, three Cu(II) complexes of acetylpyridine benzoyl hydrazone (HL), [Cu(L)(NO₃) (H₂O)]·H₂O (C1), [Cu(L)₂] (C2) and [Cu(L)(HL)]·(NO₃)(Sas) (C3) (Sas = salicylic acid) were synthesized and characterized. X-ray crystal structures and infrared (IR) spectra of the complexes reveal that the L⁻ ligand of C1 and C2 are predominantly in the enolate resonance form, while one L⁻ ligand in C3 is represented enolate resonance form and the other HL ligand exhibits keto resonance form. All Cu(II) complexes showed significantly more anticancer activity than the ligand alone. Interestingly, the Cu complexes where the ligand/metal ratio was 1:1 (C1) rather than 2:1 (C2 and C3) had higher antitumor efficacy. Moreover, the 1:1 Cu/ligand complex, C1, promotes A549 cell apoptosis possibly through the intrinsic reactive oxygen species (ROS) mediated mitochondrial pathway, accompanied by the regulation of Bcl-2 family proteins.     

Coordination polymers derived from a bis-pyridyl-bis-amide ligand: Supramolecular structural diversities and anion binding properties

Six new coordination polymers namely [{Cu(μ-L1)(CH₃COO)₂}]_∝1a, [{Cu(μ-L1)₂(CH₃COO)₂]_∝1b, [{Cu(μ-L1)₂(H₂O)₂}(NO₃)₂]_∝2, [{Cu(μ-L1)₂(H₂O)₂}(ClO₄)₂]_∝3, [{Cu(μ-L1)(H₂O)₂(μ-SO₄)}·3H₂O]_∝4a and [{Cu(μ-L1)₂SO₄}·X]_∝4b (L1 = N,N′-bis-(3-pyridyl)terephthalamide) have been synthesized. Single crystal structures of five coordination polymers namely 1a, 2-4b and the free ligand L1 are discussed in the context of the effect of conformation dependent ligating topology of the ligands, hydrogen bonding backbone, counter anions on the resultant supramolecular structures observed in these coordination polymers. It was revealed from the single crystal X-ray structure analysis that conformation dependent ligating topology of the bis-amide ligand L1, counter anion’s ligating strength dependent metal: ligand ratio, hydrogen bonding ability of the ligand as well as counter anions are responsible for the formation of 1D zigzag, 1D looped chain, 2D corrugated sheet in 1a, 2-3, 4a−4b, respectively. By following in situ coordination polymer crystallization technique, anion binding and separation studies have also been performed; nitrate anion has been separated as neat coordination polymer crystals from a complex mixture of anions.     

Thiol-copper(I) and disulfide-dicopper(I) complex O2-reactivity leading to sulfonate-copper(II) complex or the formation of a cross-linked thioether-phenol product with phenol addition

In order to better understand copper mediated oxidative chemistry via ligand-Cu(I)/O(2) reactivity employing S-donor ligands for copper, O(2)-reactivity studies of the copper(I) complexes (1 and 2, Chart 2) have been carried out with a tridentate N(2)S thiol ligand (1-(N-methyl-N-(2-(pyridin-2-yl)ethyl)amino)propane-2-thiol; L(SH)) or its oxidized disulfide form (L(SS)). Reactions of [L(SH)Cu(I)](+) (1) and [L(SS)(Cu(I))(2)(X)(2)](2+) (2) with O(2) give approximately 90% and approximately 70% yields of [L(SO3)Cu(II)(MeOH)(2)](+) (3), respectively, where L(SO3) is S-oxygenated sulfonate; 3 was characterized by electrospray ionization (ESI) mass spectrometry and X-ray crystallography. Mimicking TyrCys galactose oxidase cofactor biogenesis, a new C-S bond is formed (within new thioether moiety L(SPhOH)) from cuprous complex (both 1 and 2) dioxygen reactivity in the presence of 2,4-tBu(2)-phenolate. In addition, the disulfide ligand (L(SS)) reacts with 2equiv. cupric ion salts and the phenolate to efficiently give the cross-linked product L(SPhOH) in high yield (>90%) under anaerobic conditions. Separately, complex [L(SPhO)Cu(II)(ClO(4))] (4), possessing the cross-linked L(SPhOH), was characterized by ESI mass spectrometry and X-ray crystallography.     

Anticancer activity, structure, and theoretical calculation of N-(1-phenyl-3-methyl-4-propyl-pyrazolone-5)-salicylidene hydrazone and its copper(II) complex

The pyrazolone derivative N-(1-phenyl-3-methyl-4-propyl-pyrazolone-5)-salicylidene hydrazone (H₂L) and its copper(II) complex [Cu₂L₂CH₃OH]·2CH₃OH have been both synthesized and characterized by elemental analyses, IR spectroscopy, X-ray crystallography, theoretical calculation and pharmacological testing. It’s found that the Cu(II) complex possesses more powerful anticancer effectivity than that of the ligand. In order to make its anticancer principium clearly, we investigate their structures. In ligand there are several coordination spots, such as N, O atoms, which are close to biological environment. The crystallographic structural analysis of the complex reveals that the two Cu centers display two different coordination patterns. O1, O2, N3, and N4 from the ligand take part in the coordination with Cu atoms, resulting in the formation of the double-nuclear complex. The pharmacological testing results show that the coordination effect improves the antitumor activity of the ligand. The calculated Fukui function for H₂L and its deprotonated form L²⁻ predicts that the most probable reactive sites for electrophilic attack are oxygen atoms. The result is agreement well with the experimental data of the crystal structure analyses.     

2-methyl- and 2-ethylamino-3-pieoline N-oxide complexes formed from various copper(II) salts

Copper(II) complexes with 2-methylamino-3-picoline N-oxide (3MMH) and 2-ethylamino-3-picoline N- oxide (3MEH) have been prepared from the following salts: tetrafluoroborate, nitrate, chloride, bromide and acetate. Solids of the general formula [Cu(LH)₄]- (X₂) (where LH = either ligand when X = BF₄^tau; and LH = 3MMH when X = NO₃^tau; ); [Cu(3MEH)₂- (ONO₂)₂]; [Cu(LH)X₂] (where LH = either ligand and X = Cl^tau; , Br^tau; ) and CuL₂ (where L = either ligand's conjugate base) were characterized using spectral methods (i.e., IR, UV-Vis and ESR). Both coordinate as monodentate ligands via their N-oxide oxygen in their complexes with salts having polyatomic anions. They bond as neutral bidentate ligands in their halide complexes, but as anionic bidentate ligands in the complexes formed from copper(II) acetate. The bonding to Cu(II) ccnters via the N-oxide oxygen is the strongest tor these two ligands based on spectral data than any of the 2-aminopyridine N-oxides or 2- aminopicoline N-oxides studied to date.     

The kinetics of primary events in the reactions of L2Cu2X2 complexes (L is an N,N,N′N′-tetraalkyldiamine; X is Cl or Br) with M(NS)2 reagents

The rate laws for the earliest events in the transmetalation of dimeric copper(I) complexes L₂Cu₂X₂ (L = N,N,N′N′-tetraalkyldiamine; X = Cl or Br) by M(NS)₂ reagents (M = Co, Ni, Cu, Zn; NS is a monoanionic S-methylhydrazinecarbodithioate Schiff base ligand) depend on L, X, M and NS and the aprotic solvent. The kinetic data are compared with those for monotransmetalation of copper(II) complexes (μ₄-O)N₄Cu₄X₆ by M(NS)₂. Different kinetic behavior is particularly marked for cobalt(II) reactants. Unexpectedly high rates of reactions with Cu(NS)₂ are attributed to electron transfer. The results provide a basis for discussion of transmetalation specificity.     

Nitrogen, sulfur and oxygen donor adducts with copper(II) complexes of antitumor 2-formylpyridinethiosemicarbazone analogs: Physicochemical and cytotoxic studies

The preparation of N-, S- and O-donor ligand adducts with CuX⁺(HX=6-methyl-2-formylpyridinethiosemicarbazone (6HL); 2-formylpyridine-2^′-methylthiosemicarbazone (2′L); 2-formylpyridine-4′-methylthiosemicarbazone (4′HL)) is described. The N-donors, 2,2′-bipyridyl (bipy), 4-dimethylaminopyridine (dmap) give the complexes [Cu(6L)(bipy)]PF₆, [Cu(6L)(bipy)]Cl·5H₂O, [Cu(4′L)(bipy)]PF₆, [Cu(6L)(dmap)₂]PF₆·2.5 H₂O and [Cu(4′L)(dmap)₂]PF₆·H₂O which have been characterized by physical and spectroscopic techniques. Pentafluorothiophenolate (pftp) gives S-donor complexes [CuX(pftp)] (X=6L and 4′L) and thiolato co-ordination is proposed on the basis of spectroscopic evidence. Paratritylphenolate (ptp) and HPO²⁻₄ give O-donor complexes [Cu(6L)(ptp)], [Cu(4′L)(ptp)], [{Cu(6L)}₂HPO₄]·4H₂O, and [{Cu(4^′L)}₂HPO₄]·5H₂O which have been characterized by physical and spectroscopic techniques, as have the precursor complexes [Cu(6L)(CH₃COO)]·H₂O, [Cu(4′L)(CH₃COO)], Cu(6HL)(CF₃COO)](CF₃COO)·0.5H₂O, [Cu(4′HL)(CF₃COO)](CF₃COO), [Cu(2′L)Cl₂] and [Cu(2′L)(NO₃)₂]. Protonation constants for the ligands and some of their complexes have been determined. 2-Formylpyridinethiosemicarbazone (HL) complexes of silver, gold, zinc, mercury, cadmium and lead are also discussed. Cytotoxicity against the human tumor cell line HCT-8 and antiviral data for selected compounds are presented.     

Conformational Flip of Nonactivated HCN2 Channel Subunits Evoked by Cyclic Nucleotides

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetrameric proteins that evoke electrical rhythmicity in specialized neurons and cardiomyocytes. The channels are activated by hyperpolarizing voltage but are also receptors for the intracellular ligand adenosine-3′,5′-cyclic monophosphate (cAMP) that enhances activation but is unable to activate the channels alone. Using fcAMP, a fluorescent derivative of cAMP, we analyzed the effect of ligand binding on HCN2 channels not preactivated by voltage. We identified a conformational flip of the channel as an intermediate state following the ligand binding and quantified it kinetically. Globally fitting the time courses of ligand binding and unbinding revealed modest cooperativity among the subunits in the conformational flip. The intensity of this cooperativity, however, was only moderate compared to channels preactivated by hyperpolarizing voltage. These data provide kinetic information about conformational changes proceeding in nonactivated HCN2 channels when cAMP binds. Moreover, our approach bears potential for analyzing the function of any other membrane receptor if a potent fluorescent ligand is available.     

New macrocyclic Cu(II)-bischelates with paddle wheel Cu2-acetate cage

Two novel bolaamphiphile based dicarboxylic ligands L1H₂ and L2H₂ are synthesized by desymmetrizing aromatic anhydrides. The corresponding Cu(II) complexes [Cu(L1) · EtOH]₂ (1), [Cu(L2) · (CH₃CN)]₂ (2) are synthesized and characterized. The crystal structure obtained for (1) and (2) indicates that they are new class of tetralactone type macrocyclic Cu(II) chelate complexes with paddle wheel Cu₂-acetate cage structure. The 1:1, Cu(II) and ligand ratio leads into formation of a novel binuclear Cu(II) tetracarboxylate complexes. The macrocyclic chelate ring size in compounds 1 and 2 was altered from [15] membered to [19] membered by introducing phthalyl and diphenyl head groups as discussed in detail. The single crystal X-ray structure shows the Cu(II)?Cu(II) distance 2.613(13) Å for 1 and 2.626(13) Å for 2, the corresponding room temperature EPR spectra recorded for powdered polycrystalline samples indicate the existence of Cu(II)?Cu(II) dimeric system.     

Synthesis, spectroscopic and magnetostructural evidence for the formation of Cu(II) complexes of pyridyl-2-carboxylate (2-pca) and quinolyl-2-carboxylate (2-qca) as a result of a novel oxidative P-dealkylation reaction of diethyl 2-pyridylmethylphosphonate (2-pmpe) and diethyl 2-quinolylmethylphosphonate (2-qmpe) ligands

The interaction of diethyl 2-pyridylmethylphosphonate (2-pmpe) ligand with CuX₂ salts unexpectedly leads to the formation of compounds of the formula Cu(2-pca)₂ [X=Cl⁻ (1), CH₃COO⁻ (3)], and Cu(2-pca)Cl [X=Cl⁻ (2)] (2-pca=pyridine-2-carboxylate ion). The diethyl 2-quinolylmethylphosphonate ligand (2-qmpe) reacts with CuX₂ salts to similarly yield compounds of stoichiometry Cu(2-qca)₂ · H₂O (X=ClO₄ ⁻ (4)], and for X=Cl Cu(2-qca)₂ · H₂O (5) and Cu(2-qca)Cl (6), (2-qca=quinoline-2-carboxylate ion). These compounds are products of a novel oxidative P-dealkylation reaction, which takes place on 2-pmpe and 2-qmpe ligands under the used conditions. The compounds were characterized by infrared, ligand field, EPR spectroscopy and magnetic studies. Cu(2-pca)₂ exists in two crystalline forms, a blue form (1) and a violet form (3). For 3 the single-crystal structure was determined. The copper atom is four-coordinated in a square-planar geometry. The stack between related (and hence parallel) pca moieties involves interatomic distances of 3.27 Å. Cu(2-qca)₂ · H₂O also exists in two forms, a green (4) and a blue-green (5). Both these complexes are five coordinated, involve the same CuN₂O₃ chromophore and are examples of the distortion isomers. Variable-temperature magnetic susceptibility measurements (1.9-300 K) have shown that the antiferromagnetic coupling observed is much stronger in 6 than in 1, 3, 4 and 5. For 2 a ferromagnetic exchange occurs.     

Copper(II) assisted hydrolysis of 2,4,6-tris(pyrazol-1-yl)-1,3,5-triazine. Crystal and molecular structure of catena-[CuL(H2O)Cl]n (L = 2,4-dione-1,3,5-(1H)-triazin-1-amido)

This article describes the partial hydrolysis of the multidentate ligand 2,4,6-tris(pyrazol-1-yl)-1,3,5-triazine in the presence of copper(II), to give the anionic ligand 2,4-dione-1,3,5-(1H)-triazin-1-amido, which was isolated as the cupric complex catena-[CuL(H₂O)Cl]_n, where L is the amido ligand. No other hydrolysis products were isolated or identified.The complex defines a zigzag 1D covalent chain, along the b cell axis, through apical copper-oxygen bonds (Cu-N-C-O···Cu bridges).     

Magnetic, spectroscopic and X-ray crystallographic structural studies on copper(II) complexes of tridentate NNS Schiff base ligands formed from 2-acetylpyrazine and S-methyl- and S-benzyldithiocarbazates

New copper(II) complexes of general empirical formula, [Cu(NNS)X] (NNS = anionic forms of the 2-acetylpyrazine Schiff bases of S-methyl- and S-benzyldithiocarbazate, Hapsme and Hapsbz) and X = Cl⁻, Br⁻, NCS⁻ and NO₃⁻ have been synthesized and characterized. X-ray crystal structures of the free ligand, Hapsbz and the complexes, [Cu(apsbz)(NO₃)]_∞, [Cu(apsme)(NCS)]₂ and [Cu(apsme)Cl]₂ have been determined. In the solid state, the Schiff base, Hapsbz remains in its thione tautomeric form with the thione sulfur atom trans to the azomethine nitrogen atom. X-ray diffraction shows that the [Cu(apsbz)(NO₃)]_∞ complex is a novel coordination polymer in which one of the nitrogen atoms of the pyrazine ring bridges two adjacent copper(II) ions. The Schiff base is coordinated to the copper(II) ion in its iminothiolate form via the thiolate sulfur atom, the azomethine nitrogen atom and one of the pyrazine nitrogen atoms, the overall geometry of each copper atom in the polymer being close to a square-pyramid. The complexes, [Cu(apsme)X]₂ (X = NCS⁻, Cl⁻) are dimers in which each copper atom adopts a five-coordinate near square-pyramidal geometry with an N₃S₂ coordination environment. The Schiff base coordinates as a uninegatively charged tridentate ligand chelating via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atoms. A nitrogen atom of a unidentate thiocayanate or chloride ligand and a bridging sulfur atom from a second ligand completes the coordination sphere. Room temperature μ_eff values for the complexes in the solid state are in the range 1.70-2.0 μ_B typical of uncoupled or weakly coupled Cu(II) centres. Variable temperature susceptibility studies show that the chain complex displays weak ferromagnetic coupling across the pyrazine bridges, while the S-bridged dinuclear compounds display either weak ferromagnetic or weak antiferromagnetic coupling that relates to subtle bridging geometry differences. EPR studies of frozen DMF solutions give rather similar g and A_Cu values for all compounds indicative of Cu(d_x²-y²) ground state orbitals on the Cu centers.     

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.