Effect of temperature and ligand protonation on the electronic ground state in Cu(ii) polymers having unusual secondary interactions: a magnetic and catechol oxidase study.

Two new copper(ii) polymeric complexes, {[Cu(HPymat)(H2O)](NO3)}n (1) and [Cu2(Pymat)2(H2O)3]n (2), have been synthesized using the Schiff base ligand H2Pymat [H2Pymat = (E)-2-(1-(pyridin-2-yl)-methyleneamino)terephthalic acid]. Complex 1 is a cationic 1D polymer, whereas complex 2 is a two dimensional polymer. Both complexes were crystallographically, spectroscopically and magnetically characterized. Theoretical studies were performed and the catecholase activity of the complexes was also examined. Complex 1 is a ferromagnetically coupled complex with J = 2.8 cm-1 and 2 shows antiferromagnetic coupling with J = -1.6 cm-1. Both complexes show notable features in the EPR study. They show rhombic spectra at 77 K in the solid state, but by varying the temperature or solvents the nature of the spectra can be changed or inverted. This behaviour indicates a change of the ground state from dx2-y2 to dz2 orbitals. Theoretical calculations of 1 focus on the evaluation and characterization of interesting anion-π-anion assemblies that are formed in the solid state. In 2 we have analysed the unconventional chelate ringchelate ring π-stacking interactions that govern its solid state architecture. Both complexes act as functional models and show catechol oxidase activity with a kcat value of the order of 103 h-1.

Synthesis, Crystal structure, and Hirshfeld Surface Analysis of a New Mixed Ligand Copper(II) Complex.

A new mixed ligand copper(II) complex, [Cu(2,4-pydc)(pic)(H(2)O)]∙H(2)O (1) (where 2,4-pydc = pyridine-2,4-dicarboxylate, pic = 2-picolylamine) has been synthesized and characterized by elemental analysis, FT-IR and UV-Vis spectroscopic and thermogravimetric methods. Single crystal X-ray diffraction analysis reveals that copper(II) atom in the title complex adopts distorted square pyramidal geometry. Structural characterization also reveals that interplay of O-H···O, N-H···O, C-H···O, and C-H···π interactions between lattice and coordinated water and ligands significantly contribute to the crystal packing leading to the formation and strengthening of three dimensional supramolecular assembly. Hirshfeld surface analysis employing 3D molecular surface contours and 2D fingerprint plots have been used to analyze intermolecular interactions present in the solid state of the crystal.

Switching and redox isomerism in first-row transition metal complexes containing redox active Schiff base ligands.

The reversible redox isomerisms in first row transition metal complexes of the type ML2 were studied. The six ML2 complexes (M = Mn(III) (), Fe(II) (), Co(III) (), Ni(II) (), Cu(II) () and Zn(II) ()) were synthesized with a redox active Schiff base ligand [2-(3,5-di-tert-butyl-2-hydroxyphenylamino)-4-chlorophenol] (H3L) presenting different oxidation states from -2 to 0 (L(2-), L(-) and L(0)). EPR spectra and magnetic susceptibility measurements indicate the presence of complexes of the type [Mn(III)(L(2-))(L(-))] () with S = 1/2, [Fe(II)(L(-))2] () with S = 2, [Co(III)(L(2-))(L(-))] () with S = 1/2, [Ni(II)(L(-))2] () with S = 1, [Cu(II)(L(-))2] () with S = 1/2 and [Zn(II)(L(-))2] () with S = 0 at high temperatures. Temperature and solvents influence the electronic structures of the species and give several valence tautomers. At low temperatures these complexes present thermally induced metal-to-ligand (, , ) or ligand-to-ligand (in , ) electron transfer (partial or total), resulting in compounds of the type [Mn(IV)(L(2-))2] () with S = 1/2, [Fe(III)(L(-))(L(2-))] () with S = 1, [Ni(III)(L(2-))(L(-))] () with S = 0, [Cu(II)(L(2-))(L(0))] () with S = 1/2 and [Zn(II)(L(2-))(L(0))] () with S = 1. This electron transfer is in agreement with the general trend in the redox potentials of the first row transition metal ions from Mn(ii) to Zn(ii), and it allows us to prepare and stabilize reversibly switchable tautomeric forms in transition metal complexes with redox-active ligands.

Reversible switching of electronic ground state in a pentacoordinated Cu(II) 1D cationic polymer and structural diversity.

Two copper(II) polymeric complexes {[Cu(HPymat)(MeOH)](NO3)}n (1) and {[Cu4(Pymab)4(H2O)4](NO3)4} (2) were synthesized with the carboxylate-containing Schiff-base ligands HPymat(-) and Pymab(-) [H2Pymat = (E)-2-(1-(pyridin-2-yl)methyleneamino)terephthalic acid, HPymab = (E)-2-((pyridine-2-yl)methyleneamino)benzoic acid]. Complex 1 is a one-dimensional Cu(II) cationic polymeric complex containing free protonated carboxylic groups and nitrate anions as counterions. Complex 2 is a zero-dimensional tetranuclear cationic Cu(II) complex containing nitrate anions as counterions. Complex 1 shows rhombic electron paramagnetic resonance (EPR) spectra in the solid state at room temperature (RT) and 77 K and tetragonal EPR spectra in dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) and "inverse" EPR spectrum in CH3CN. Complex 2 shows rhombic EPR spectra in the solid state at RT and 77 K. But complex 2 shows tetragonal spectra in DMSO, DMF, and CH3CN. Thermogravimetric analysis was also performed for both complexes 1 and 2. Mean-square displacement amplitude analysis was carried out to detect librational disorder along the metal-ligand bonds in crystal structures.

Relevant and unprecedented C-H/σ supramolecular interactions involving σ-aromatic M2X2 cores.

A novel type of C-H/σ supramolecular interaction involving σ-aromatic M2X2 (M = Cu, Hg; X = Cl, Br, I, S) cores is reported for the first time. Three new polymeric coordination copper complexes, {[Cu(µ-Cl)(Cl)(µ-L)]2}n (1), {[Cu(µ-I)(µ-L)]2}n (2) and [Cu(Br)2(µ-L)(CH3CN)2]2 (3), have been synthesized with the organic ligand α,ω-bis(benzotriazoloxy)propane system (L) and halides as counterions. A very interesting C-H/σ supramolecular interaction has been observed in the solid state structure of compound 2, similar to a C-Hπ interaction, which has been confirmed by Bader's "atoms-in-molecules" AIM analysis. The Nucleus Independent Chemical Shift (NICs) method was used to evaluate the aromatic character of the different cores in this study. The influence of the nature of the metal ions, bridging atoms, oxidation states, and coordination environments around the metal centers on the strength of the aromaticity of the M2X2 cores was theoretically analyzed and explained. The binding ability of the 1-alkoxy-1,2,3-benzotriazole ring to establish π-π and C-H/π interactions and how its coordination to Cu(I) and Cu(II) ions affects the strength of the aforementioned interactions have been discussed. The electron deficient triazole ring and its π-acidity increases upon coordination of the Cu ion, leading to the formation of a lone pair (lp)-π interaction involving the five-membered ring of the ligand, which has also been analyzed. We have also analyzed the C-H/σ interactions of previously reported X-ray crystal structures of different coordination polymers based on a binuclear copper(I) complex and 2,3-dimethylpyrazine, dithioethers, and benzotriazol-1-yl-based pyridyl units as ligands using I- as a counter-ion. Complex 1 shows antiferromagnetic behavior with a magnetic coupling constant of J = -7.9 cm(-1). Moreover, photoluminescence and TGA studies of the complexes were also carried out.

Novel mixed-valence Cu compounds formed by Cu(II) dimers with double oximato bridges: in situ formation of anionic layer [Cu2(SCN)3]n(n-).

Two new N3O donor ketoxime Schiff bases (HL(1) and HL(2)) have been synthesized by condensing N,N-dimethylethylenediamine with diacetylmonoxime and benzilmonoxime, respectively in a 1:1 ratio. Reaction of Cu(ClO4)2·6H2O with HL(1) resulted in a discrete oximato-bridged dinuclear Cu(II) complex [Cu2(L(1))2(H2O)2](ClO4)2 (1). The same reaction in presence of NaSCN affords the complex {[Cu(II)2(L(1))2][Cu(I)4(µ(1,3)-SCN)4(µ(1,1,3)-SCN)2]}n (2), where partial Cu(II)→Cu(I) reduction is observed. In 2, arrays of [Cu(II)2(L(1))2](2+) cationic units are inserted in between 2D {[Cu(I)4(SCN)6](2-)}n layers and connected via µ(1,1,3)-SCN(-) links, thus forming a 3D network. On the other hand, reaction of Cu(CH3COO)2 and HL(2) in the presence of NaSCN gave rise to a mixed-valence pentanuclear cluster {[Cu(II)2(L(2))2(NCS)]2[Cu(I)(SCN)(µ(1,1)-SCN)(µ(1,3)-SCN)]} (3) where Cu(II) is also partly reduced to Cu(I). In compound 3, two cationic [Cu(II)2(L(2))2(NCS)](+) units are bridged by the anionic [Cu(I)(SCN)3](2-) unit through long Cu-SCN linkages. The ligands and the complexes have been characterized by elemental analysis, UV/Vis and IR spectroscopy. The complexes are further characterized by single crystal X-ray diffraction and variable temperature magnetic (VTM) studies. Finally a complete magneto-structural correlation has been established between compounds 1-3 and all the characterized Cu dimers with a double NO bridge.

Reversible switching of the electronic ground state in a pentacoordinated Cu(II) complex.

An easy reversible switching of the electronic ground state in a pentacoordinated copper(II) complex is reported for the first time. The simple protonation of a carboxylic group in a Cu(II) complex with a {dx(2)-y(2)}(1) electronic configuration leads to a flip of the ground electronic configuration from {dx(2)-y(2)}(1) to {dz(2)}(1) in the metal ion.

Series of dicyanamide-interlaced assembly of zinc-Schiff-base complexes: crystal structure and photophysical and thermal studies.

Four new dicyanamide (dca) bridged multinuclear Zn(II)-Schiff-base complexes, {[Zn2L(1)(µ1,5-dca)dca]·CH3OH}2 (1), [Zn2L(2)(µ1,5-dca)dca]n (2), [Zn3L(3)2(µ1,5-dca)2]n (3), and [(ZnL(4))2Zn(µ1,5-dca)dca]n (4), have been synthesized using four different Schiff bases L(1)H2 = N,N(/)-bis(3-methoxysalicylidenimino)-1,3-diaminopentane, L(2)H2 = N,N'-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane, L(3)H2 = N,N'-bis(5-bromosalicylidenimino)-1,3-diaminopropane, and L(4)H2 = N,N'-bis(5-chlorosalicylidenimino)-1,3-diaminopropane and NaN(CN)2 in order to extend the metal-ligand assembly. The directional properties of linear end-to-end bridging dca ligands have resulted in different metal ion connectivities leading to unique variety of templates in each of the complexes. All the ligands and complexes have been characterized by microanalytical and spectroscopic techniques. The structures of the complexes have been conclusively determined by single crystal X-ray diffraction studies. Thermogravimetric analyses have been performed to investigate the thermal stability of the metal-organic frameworks. Finally, the photoluminescence properties of the complexes as well as their respective ligands have been investigated with a comparative approach.

Framework solids based on copper(II) halides (Cl/Br) and methylene-bridged bis(1-hydroxybenzotriazole): synthesis, crystal structures, magneto-structural correlation, and density functional theory (DFT) studies.

A methylene-bridged 1-hydroxybenzotriazole derived ligand L [L = 1, 3-bis(benzotriazol-1-yl)-1,3-dioxapropane] has been synthesized and characterized by spectroscopic and structural methods. Reaction of L with two different copper(II) halides [CuX(2); X = Br, Cl] in an identical condition yields two different compounds of similar compositions, {[Cu(µ-Br)(Br)(µ-L)](2)}(n)·2nH(2)O (1) and {[Cu(µ-Cl)(Cl)(µ-L)](2)}(n)·2nH(2)O (2), both being characterized by various physicochemical techniques. Single crystal X-ray studies reveal that they appear as 2D coordination polymers with similar bridging fashion of L. Low temperature magnetic susceptibility measurements reveal antiferromagnetic and ferromagnetic behaviors for 1 and 2 with magnetic coupling constants J = -15.2 and +1.7 cm(-1), which are in a reasonable agreement with their calculated values (J = -9.79 and +0.68 cm(-1) respectively, for 1 and 2). The role of bridging halides in the structure and magnetic properties of the complexes are investigated, and a possible magneto-structural correlation has been established. Influence of spin density of bridging halides on the magnitude of coupling constants has been discussed with the help of density functional theory (DFT) calculations.

A novel mixed valent Cu(II)-Cu(I) 2D framework made of a hydrazone and µ-SCN bridged metallacyclic loops cross-linked by µ3-SCN chains.

A mixed valent copper complex [Cu(II)Cu(I)(L)(µ-SCN)(µ(3)-SCN)](n) (LH = N'-((pyridin-2-yl)methylene)acetohydrazide) has been synthesized and characterized. It is a unique example of a 2D mixed valent Cu(II)-Cu(I) interlinked molecular assembly with a very unusual bridging property of the hydrazone ligand. An extraordinary in situ partial Cu(II)→ Cu(I) reduction is observed in this system at room temperature.

Weak interactions modulating the dimensionality in supramolecular architectures in three new nickel(II)-hydrazone complexes, magnetostructural correlation, and catalytic potential for epoxidation of alkenes under phase transfer conditions.

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL(1)), 2-hydroxyacetophenone (HL(2)), and 2, 3-dihydroxybenzaldehyde (HL(3)). These tridentate ligands are reacted with Ni(OOCCF(3))(2)·xH(2)O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L(1))(OOCCF(3))(CH(3)OH)](2) (1), [Ni(L(2))(OOCCF(3))(H(2)O)](2) (2), and [Ni(L(3))(L(3)H)](OOCCF(3))(H(2)O)(1.65)(CH(3)OH)(0.35) (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni(III)-OCl or Ni(III)-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396).

Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies.

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new Co(II)/Co(III) and Ni(II) complexes with a pentadentate Schiff base ligand H(3)L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1:2 molar ratio. The room temperature syntheses involving Co(II) and Ni(II) nitrates and the ligand H(3)L lead to the isolation of the dinuclear species [Co(2)L(2)(H(2)O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [Co(II)(2)Co(III)(2)L(2)(µ(3)-OMe)(2)(NO(3))(H(2)O)(2)]NO(3)·2(H(2)O) (2), and [Ni(4)L(2)(µ(3)-OMe)(2)(H(2)O)(2)]·2H(2)O (4). 1 is found to be a simple mono alkoxo-bridged Co(III) dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and µ(3)-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered Co(II) and Co(III) ions and 4 has both six- and five-coordinate Ni(II) centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, (1)H-NMR and ESI mass study results and is supposed to have one Ni(II) center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.

Syntheses, characterisation, magnetism and photoluminescence of a homodinuclear Ln(III)-Schiff base family.

A novel family of homodinuclear complexes of the general formula [Ln(2)L(2)(X)(2)] (where Ln = Nd(3+), Pr(3+), Sm(3+) and Tb(3+) for 1, 2, 3 and 4, respectively and X, the coordinated NO(3)(-) or Cl(-) anion) has been synthesised from the corresponding lanthanide(III) salts with the pentadentate dianionic Schiff base ligand, H(2)L [N(1),N(3)-bis(salicylideneimino)diethylenetriamine], that exhibits a N(3)O(2) donor set. Single crystal X-ray diffraction studies evidenced the isostructurality of this family of centrosymmetric neutral dinuclear entities where the Ln(III) metal centres are coupled together by two phenolato oxygen atoms belonging to two units of ligand (H(2)L). Interestingly, the two other phenolato groups of H(2)L are mono-coordinated to the metal ions. Temperature dependence (2-300K) magnetic susceptibility studies suggest the presence of an antiferromagnetic interaction operating via double phenolato bridges. Photoluminescence activities of the complexes have been studied and compared with their precursor ligand. All the complexes have been characterised with microanalytical and several spectroscopic techniques.

Na(I)/Cu(I-II) heterometallic cages interconnected by unusual linear 2-coordinate OCN-Cu(I)-NCO links: synthesis, structural, magnetostructural correlation and computational studies.

A new Na(I)/Cu(I-II) heterometallic coordination complex [Cu(2)L(2)Na(NCO)(2)Cu](n) (1) with an unusual architecture has been synthesised. In 1 cyclic Na-O-Cu-O-Cu cages constructed by the tetradentate N(2)O(2) donor Schiff base ligand (H(2)L = N,N'-bis(2-hydroxyacetophenone)propylenediimine) are interconnected to each other by a rare singly end-to-end bridged OCN-Cu(I)-NCO link generating 1D chain. The complex has been characterised by elemental, spectral and structural analysis. The cyclic voltammogram of 1 has been compared with the analogous complexes. Cryomagnetic susceptibility studies indicate the copper(II) centers in the cyclic Na-O-Cu-O-Cu cages are antiferromagnetically coupled with J = -13.8 cm(-1). Complex 1 is a new addition to a class of rare singly end-to-end cyanato bridged copper(I) species and interestingly the copper ions involved in OCN-Cu(I)-NCO links possess a linear 2-coordinate geometry. Density functional theory calculations have been carried out to gain additional insights into the metal and ligand orbitals participating in this unusual structure.

Four new dinuclear Cu(ii) hydrazone complexes using various organic spacers: syntheses, crystal structures, DNA binding and cleavage studies and selective cell inhibitory effect towards leukemic and normal lymphocytes.

Syntheses and crystal structures of four new hydrazone-based Cu(ii) complexes, [{Cu(L(1))(H(2)O)}(2)(mu-pyraz)](ClO(4))(2) (), [{Cu(L(1))(OClO(3))}(2)(mu-4,4'-bipy)] (), [{Cu(L(2)H)}(mu-pyraz){Cu(L(2)H)(OClO(3))}].(ClO(4)) () and [{Cu(L(2))}(2)(mu-bpe)] () [L(1)H = condensation product of benzhydrazide and pyridine-2-carbaldehyde and L(2)H(2) = condensation product of benzoyl acetone and benzhydrazide], bridged by various organic spacers [pyrazine (pyraz), 4,4'-bipyridine (4,4'-bipy) and 1,2-di(4-pyridyl)ethane (bpe)] are reported in this paper. The single-crystal X-ray crystallographic studies reveal that all are dinuclear units where and form strong intermolecular H-bonding to form sheets of interconnected ions, whereas forms sheets of dinuclear chains through pi-pi interactions; in , molecules are linked only through van der Waals interactions. The variable-temperature magnetic moment studies reveal that and show antiferromagnetic coupling between the Cu(ii) centers at lower temperatures. The binding ability of with calf thymus DNA [CT-DNA] is reported using various spectroscopic studies (UV-Vis titration, circular dichroism and fluorescence). The binding constants of with CT-DNA, as calculated by different methodologies, are of the order of 10(5) M(-1). The mode of interaction between and CT-DNA has been predicted using circular dichroic (CD) spectroscopy, where it has been shown that most probably interacts with DNA via intercalation between the base pairs leading to a change in B-DNA conformation. is also able to cleave supercoiled (SC) plasmid DNA pUC19 in a time and dose dependent manner as demonstrated by agarose gel electrophoresis, and also demonstrates its potential to cleave the SC plasmid DNA via both oxidative and hydrolytic mechanisms. Approximately 50% of leukemic cells are found to be dead when two representative leukemic cell lines are exposed to ( approximately 80 muM) even for 24 h as determined by different cell cytotoxicity assays. Preliminary results also showed that, at 20 muM, could selectively induce apoptosis in leukemic cells without affecting normal lymphocytes.

Synthesis of two new linear trinuclear Cu(II) complexes: mechanism of magnetic coupling through hybrid B3LYP functional and CShM studies.

Two new Cu(II) linear trinuclear Schiff base complexes, [Cu3(L)2(CH3COO)2] (1) and [Cu3(L)2(CF3COO)2] (2), have been prepared using a symmetrical Schiff base ligand H2L [where H2L = N,N'-bis(2-hydroxyacetophenone)propylenediimine]. Both of the complexes have been characterized by elemental analyses, Fourier transform IR, UV/vis, and electron paramagnetic resonance spectroscopy. Single-crystal X-ray structures show that the adjacent Cu(II) ions are linked by double phenoxo bridges and a mu(2)-eta(1):eta(1) carboxylato bridge. In each complex, the central copper atom is located in an inversion center with distorted octahedral coordination geometry, while the terminal copper atoms have square-pyramidal geometry. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit a distinct antiferromagnetic interaction of J = -36.5 and -72.3 cm(-1) for 1 and 2, respectively. Density functional theory calculations (B3LYP functional) and continuous-shape measurement (CShM) studies have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the antiferromagnetic behavior shown by the complexes.

Synthesis and structural characterization of a novel dinuclear complex compound formed by the aerial oxidation of cobalt(II) having an interligand C-C sigma-bond.

The aerial oxidation of cobalt(II) salt, in a methanolic solution, containing a hydrazone ligand, (E)-N'-(4-oxo-4-phenylbutan-2-ylidene)benzohydrazide (condensation product of benzoyl acetone and benzhydrazide, LH2) leads to the coupling of two such ligand units through the formation of a rather long C-C bond [1.601(6) A] giving rise to a dinuclear Co (III) hydrazone complex, [Co2(L)2(L')(].0.25H2O (L' = C-C coupled hydrazone ligand). The structure of the complex has been determined by X-ray crystallography and IR, UV-Vis spectroscopy and elemental analysis have characterized the complex.

Weak metamagnetic-like 1D manganese(II) complex with a double mu(1,1)-azido bridge: a structure and magnetic study.

The azido-bridged manganese complex of formula [Mn(tptz)(mu(1,1)-N3)2]n [1; tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine] has been synthesized and characterized by single-crystal X-ray diffraction analysis and a low-temperature magnetic study. The complex 1 crystallizes in the orthorhombic space group Pbcn, with a = 17.911(5) A, b = 15.804(5) A, c = 6.6538(18) A, and Z = 4. The Mn atoms are coordinated by three N atoms of the tptz ligands and connected to each other by double end-on (EO) azide ligands, forming a neutral 1D chain. The adjacent 1D chains are connected by face-to-face pi-pi-stacking interactions and C-H...pi interactions of pyridine rings of the tptz ligands, which leads to the formation of a supramolecular 2D sheet structure. Temperature- and field-dependent magnetic analyses reveal dominant intrachain ferromagnetic interactions with EO azide-bridge and weak interchain antiferromagnetic interactions with overall metamagnetic behavior having 3D magnetic ordering at 2.7 K. The critical field is approximately 80 G, at which the interlayer antiferromagnetic ground-state switches to a ferromagnetic state.

Ligating properties of a potentially tetradentate Schiff base [(CH3)2NCH2CH2N=CHC6H3(OH)(OMe)] with zinc(II), cadmium(II), cobalt(II), cobalt(III) and manganese(III) ions: synthesis and structural studies.

A series of Zn(II), Cd(II), Co(II), Co(III) and Mn(III) complexes with the Schiff base [(CH3)2NCH2CH2N=CHC6H3(OH)(OMe)], LH, derived from 2-dimethylaminoethylamine and o-vanillin, has been synthesised and structures of all the products have been established by X-ray crystallography. In the cases of zinc and cadmium, dimeric complexes [Zn(LH)2(NCS)] [Zn2(L)(mu(1,1)-CH3COO)(NCS)3] (1), [Cd2(L)2(Cl)2] (2) and [Cd2(L)2(NCS)2] (3), and for cobalt and manganese, monomeric complexes [Co(LH)2(NCS)]2 [Co(NCS)4] (4), [Co(LH)2(NCS)]ClO4 (5), [Co(L)(N3)(o-vanillinate)] x 0.5 MeOH (6) and [Mn(LH)2(MeOH)2](ClO4)3 (7), are formed with various terminal ligands. All the complexes have been characterised by elemental analysis and IR spectra. UV-Vis and NMR spectroscopy, magnetic, and electrochemical studies, were also carried out where feasible. The Schiff base functions as a bi-, tri- or tetra-dentate chelating agent and coordinates via the protonated or deprotonated phenolic oxygen, amine and imine nitrogens, and only in case of 1 with the methoxy oxygen atoms, to the metal ion leading to the formation of mono- or bi-metallic complexes.

Isolation of a new two-dimensional honeycomb carbonato-bridged copper(II) complex exhibiting long-range ferromagnetic ordering.

Atmospheric CO2 fixation by an aqueous solution containing Cu(ClO4)2.6H2O and 4-aminopyridine (4-apy) yields a novel example of a two-dimensional mu3-CO3 bridged copper(II) complex {[Cu(4-apy)2]3(mu3-CO3)2(ClO4)2.(1/2)CH3OH}n that has been characterized by IR, UV and X-ray crystallography; preliminary magnetic measurements show that complex exhibits long-range ordered ferromagnetic coupling.