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By slightly changing the synthetic conditions, we have prepared two closely related linear tetranuclear CuII complexes with the symmetrical ONNO donor tetradentate Schiff-base ligand [H2L = (OH)C6H4(CH3)C＝N(CH2)3N＝C(CH3)C6H4(OH)] and with azide ions. These two distinctly coloured crystalline products were characterized by elemental analysis, IR and UV–Vis spectroscopy, CV, EPR spectra and variable temperature magnetic measurements. Single crystal X-ray diffraction studies of the green [Cu4(μ-L)2(μ1,1-N3)2(N3)2] (1) and the red [Cu4(μ-L)2(μ1,1-N3)2(N3)2(H2O)2] (2) crystals show that the coordination environment of the two μ-phenoxo and μ1,1-azido bridged isomorphous tetranuclear CuII complexes are slightly different. Thus, both complexes are formed by very similar building units, although with a significant variation in the bridging Cu–O(phenoxo)–Cu and Cu–N(azido)–Cu bond angles. The consequences of these structural variations on the magnetic properties have been investigated from both the experimental and theoretical points of view by variable temperature magnetic measurements and DFT calculations. [ABSTRACT FROM AUTHOR]

Abstract: A novel hydroxo-bridged cyclic tetranuclear copper(II) complex with the guanazole ligand (3,5-diamino-1,2,4-triazole=Hdatrz), [Cu4(datrz)4(μ2-OH)2(NO3) (H2O)6]·(NO3) ·5(H2O) (1) has been synthesised and characterised by X-ray crystallography. In 1, the four copper(II) centres are linked by hydroxo bridges and the N1,N2-coordination of the deprotonated guanazole ligands. The core has considerably short Cu⋯Cu distances in the range of 3.3550(4)–3.3611(4)Å. Thermal analysis of 1 reveals that the cyclic framework constructed with hydroxo and guanazole ligands is stable up to 285°C. [Copyright &y& Elsevier]

Two new dicyanamide bridged 1D polynuclear copper(II) complexes [Cu(L1){μ1,5-N(CN)2}]n (1) [L1H=C6H5C(O)NHNC(CH3)C5H4N] and [Cu(L2){μ1,5-N(CN)2}]n (2) [L2H=C6H5C(O)CHC(CH3)NCH2CH2N(CH3)2] have been synthesised and structures of both the complexes and their crystal packing arrangements have been established by X-ray crystallography. For complex 1, a tridentate hydrazone ligand (L1H) obtained by the condensation of benzhydrazide and 2-acetylpyridine is used, whereas a tridentate Schiff base (L2H) derived from benzoylacetone and 2-dimethylaminoethylamine is employed for the preparation of complex 2. Variable temperature magnetic susceptibility measurement studies indicate there are weak antiferromagnetic interactions with J values −0.10 and −1.41cm−1 for 1 and 2, respectively. [Copyright &y& Elsevier]

Two new pseudohalide bridged di- and poly-nuclear copper(II) complexes [Cu2(L)2(μ1,1-N3)2] (1), [Cu(L)(μ1,3-NCS)]n (2), [LH = C6H5C(O)NHN=C(CH3)C5H4N] have been synthesised and characterised by elemental analysis, IR and UV–Vis spectral studies. Structures of both the complexes have been established by X-ray crystallography. A tridentate hydrazone ligand (LH) obtained by the condensation of benzhydrazide and 2-acetylpyridine is used for the preparation of complexes 1 and 2. Variable temperature magnetic susceptibility measurement studies indicate there is a weak ferromagnetic interaction between the two copper(II) ions in 1 (J = +0.75 cm−1), while weak antiferromagnetic interaction is observed with J values −0.23 cm−1 for 2. [Copyright &y& Elsevier]

Abstract: A μ2-dicarboxylato bridged dinuclear manganese(II) Schiff base complex [Mn2(L1)2(NCS)2] (1), and a mononuclear manganese(III) Schiff base complex [Mn(L2)(N3)(H2O)] (2), have been synthesised and characterised by elemental analysis, IR and UV–Vis spectra (only complex 2). Structures of both the complexes are established by single crystal X-ray analysis. A variable temperature magnetic susceptibility measurement study has been performed for complex 1 and the result indicates there is a very weak antiferromagnetic interaction (J =−0.41±0.02cm−1) between the two manganese(II) centres. Complex 2 forms a dimer through strong hydrogen bonding and the room temperature magnetic moment value shows there is no significant interaction between the low spin manganese(III) centres connected through hydrogen bonds. [Copyright &y& Elsevier]

A new singly bridging complex [Cu(dach)(μ-NCS)(NCS)]n (dach=1,4-diazacycloheptane) has been synthesised and its crystal structure determined. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones. IR, ESR and temperature variable magnetic studies are described but no magnetic interaction was found between the copper centres. [Cu(dach)2(N3)]ClO4 has also been characterised by IR, ESR spectra and magnetic studies. The crystal structure determination shows that it is a penta-coordinated monomeric species with an axially coordinated azide linked to the perchlorate counterion by hydrogen bonding. [Copyright &y& Elsevier]

A new mixed ligand copper(II) complex, [Cu(2,4-pydc)(pic)(H2O)] · H2O (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. [ABSTRACT FROM AUTHOR]

Abstract: A new tetra-nuclear coordination complex [Cu4(HL)4] (1) containing Cu4O4 cubane core has been synthesized by using Schiff base ligand [(OH)C6H4CHh name="sbnd" />C(CH3)(CH2OH)2] (H3L), obtained by the 1:1 condensation of 2-amino-2-methyl-1,3-propanediol with salicylaldehyde and thoroughly characterized by micro-analytical, FT-IR, UV–Vis, thermal and room temperature magnetic susceptibility measurements. Structural characterization of the complex has been done by single crystal X-ray diffraction analysis. Structural elucidation reveals versatile coordination modes for two identical alkoxo oxygen atoms of the Schiff base ligand; one in its deprotonated form exhibits μ3-bridging to bind three similar copper(II) centers whilst the protonated one remains as monodentate or non-coordinating. Structural analysis also shows that the Cu4O4 cubane core in 1 consists of four μ3-alkoxo oxygen bridged copper(II) atoms giving an approximately cubic array of alternating oxygen atoms and copper(II) atoms where the metal centers display both distorted square pyramidal and distorted octahedral geometries. [Copyright &y& Elsevier]

Abstract: The trinuclear complex [L2Cu3(CF3CO2)4] (1) has been synthesized and its crystal structure determined. It consists of a linear arrangement of Cu(II) centers. The central copper atom is bonded to six oxygen atoms and has a tetragonally distorted octahedral geometry, while the terminal copper atoms are bonded to three oxygen and two nitrogen atoms and show a distorted square pyramidal geometry. The complex shows di-μ(O,O′) syn–syn carboxylate bridging as well as monoatomic (μ-O) bridging, along with phenolate (μ-O) oxygen bridging. Cryomagnetic investigations in the range 2–300K revealed an antiferromagnetic spin exchange interaction with J =−95.7cm−1, based on the isotropic exchange model H ex =−2J[S 1 · S 2 + S 2 · S 3]. [Copyright &y& Elsevier]

Abstract: Two new dicyanamide bridged complexes [Mn(μ1,5-dca)2(salicyh)2] n (1) and {[Ni(μ1,5-dca)(TTA)](ClO4)} n (2) (dca=dicyanamide, ; salicyh=salicylic hydrazide; TTA=triethylenetetramine) have been synthesised and structurally characterised. Both the compounds 1 and 2 consist in 1-D coordination polymers. In 1 the manganese atoms are doubly bridged by μ1,5-dca ligands, whereas in 2 the nickel atoms are bridged by a single μ1,5-dca ligand. The magnetic measurements indicate that whereas intrachain interactions take place between the metal ions for compound 1 (J =−0.26cm−1), no evidence for any exchange coupling is found for compound 2. [Copyright &y& Elsevier]

Two diorganotin(IV) complexes of the general formula R2Sn[Ph(O)CCH–C(Me)N–NC(O)Ph] (R=Ph, 1; R=Me, 2) have been synthesised from the corresponding diorganotin(IV) dichloride and the ligand 4-phenyl-2,4-butanedionebenzoylhydrazone(2−) (H2L), derived from benzoyl acetone and benzoyl hydrazide in methanol at room temperature in presence of triethylamine. The syntheses were performed under very mild conditions, at room temperature and without exclusion of air or moisture from the reaction vessel. Previously, rigorous conditions have been considered necessary for these species. The two compounds have been characterised by elemental analysis, IR and 1H, 13C, 15N, 119Sn NMR spectra, and their structures have been confirmed single crystal X-ray structure analysis. The central tin atom of both complexes adopts a distorted trigonal bipyramidal coordination with two ligand oxygen atoms in axial positions, the nitrogen atom of the ligand and two organic groups on tin occupying equatorial sites. 2 has crystallised with two crystallographically independent molecules in the asymmetric unit. The δ(119Sn) values for the complexes 1 and 2 are −151.5 and −146.8 ppm, respectively, thus indicating penta-coordinated tin centres.Two diorganotin(IV) complexes, R2Sn[Ph(O)CCH–C(Me)N–NC(O)Ph] (R=Ph, 1; R=Me, 2) have been synthesized in methanol under mild conditions, in contrast to the more severe conditions employed in previous studies. Compounds have been characterized by IR, NMR (1H, 13C, 15N, 119Sn) spectra, and structures confirmed X-ray crystallography. The δ(119Sn) values for the complexes 1 and 2 are −151.5 and −146.8 ppm, respectively, indicating penta-coordinated tin centres. [Copyright &y& Elsevier]

A new trimeric cyano-bridged complex [(Phen)2(H2O)2CaNC(NC)4FeCNCa(OH2)(Phen)2NO3]·H2O (1) (where phen=1,10-phenanthroline) has been synthesised and its crystal structure is determined by single crystal X-ray diffraction. The behaviour of the nitrate anion in this structure is noticeable. It seems that 50% of the time, this anion is coordinating in the monodentate mode and 50% in the bidentate mode. The structure features a central [Fe(CN)6]3− unit that links a [Ca(Phen)2(OH2)2]2+ dication and a [Ca(Phen)2(OH2)(NO3]+ cation via two trans-cyanide bridges. Each Ca atom is seven coordinated and achieves a capped octahedral geometry. Both intramolecular and intermolecular hydrogen-bonding interactions are present in the structure leading to the formation of a cohesive three-dimensional network. [Copyright &y& Elsevier]

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 ring…chelate 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. [ABSTRACT FROM AUTHOR]

An asymmetrical Schiff base ligand, 4-bromo-2-(2-pyridylmethy liminomethyl)phenol (HL), and its copper(II) complex, [Cu(L)SCN] (1), have been synthesized. Complex 1 is experimentally characterized by elemental analysis, FT-IR and UV-vis spectroscopic techniques, and cyclic voltammetry. The structure of the complex has been established by single-crystal X-ray diffraction studies, which reveal a square planar geometry of the central copper(II) ion in 1. The neighboring molecules of the complex connect each other by Π-Π stacking interactions with centroid-to-centroid ring distance 3.653 A. The ligand can display two possible tautomeric forms; therefore, 1 can have an alternate molecular structure. DFT calculations have been employed to investigate the structure and relative stabilities of the suggested tautomeric forms of the ligand and its corresponding copper(II) complex. [ABSTRACT FROM AUTHOR]

An asymmetrical Schiff base ligand, 4-bromo-2-(2-pyridylmethyliminomethyl)phenol (HL), and its copper(II) complex, [Cu(L)SCN] (1), have been synthesized. Complex1is experimentally characterized by elemental analysis, FT-IR and UV–vis spectroscopic techniques, and cyclic voltammetry. The structure of the complex has been established by single-crystal X-ray diffraction studies, which reveal a square planar geometry of the central copper(II) ion in1. The neighboring molecules of the complex connect each other by π–π stacking interactions with centroid-to-centroid ring distance 3.653 Å. The ligand can display two possible tautomeric forms; therefore,1can have an alternate molecular structure. DFT calculations have been employed to investigate the structure and relative stabilities of the suggested tautomeric forms of the ligand and its corresponding copper(II) complex. [ABSTRACT FROM PUBLISHER]

A new iron(iii) complex, [Et3NH][FeIII(L2−Ṗ)2] (1) with a substituted o-aminophenol based ligand is reported. Complex 1 is an anionic complex with a triethylammonium cation in the lattice. It contains two O,O,N-coordinated o-iminobenzosemiquinonate(2−) radical anions with an Fe(iii) centre in a high-spin configuration. The crystal structure of 1 was determined by X-ray diffraction, which revealed a trigonal prismatic coordination environment whose electronic structure was established by various physical methods including EPR, Mössbauer spectroscopy and variable-temperature (2–300 K) magnetic susceptibility measurements. Electrochemical analysis indicated primarily ligand-centred redox processes. Complex 1 retained the high-spin character of Fe(iii) throughout the temperature range studied (2–300 K) and exhibited, as expected, strong antiferromagnetic coupling operating between two radicals (SR = 1/2) and the high-spin Fe(iii) centre (SFe = 5/2), yielding a St = 3/2 as the ground state. This was confirmed by means of DFT calculations (M06-2X/6-31+G*) and a spin density analysis of the high spin and low spin configurations. [ABSTRACT FROM AUTHOR]

The Mn(II) complex {[Mn(atpa)(H 2 O) 2 ]·H 2 O} n ( 1 ),with the dicarboxylate ligand 2-aminoterephthalic acid (H 2 atpa), has been synthesized and crystallographically, spectroscopically and magnetically characterized. Complex 1 shows a very unusual 1 κ 2 N,O coordination mode of the aminoterephthalate dianion with the Mn(II) ion. One of the carboxylate groups shows a syn-anti-μ 2 - η 1 : η 1 binding mode to form a 2D square grid. The magnetic properties of this compound can be very well reproduced with a regular S = 5/2 chain model with a very weak antiferromagnetic coupling constant of J = −0.2 cm −1 through the single syn-anti carboxylate bridges. EPR measurement also supports the experimental data obtained from the magnetic study. The influence of the torsion angle between the carboxylate groups on the various interaction energies of 1 is calculated by means of DFT study. [ABSTRACT FROM AUTHOR]

One ONNO-donor tetradentate Schiff base ligand LH2was derived from the condensation of salicylaldehyde and 1,3-diaminopropane and reacted with Cu(NO3)2·6H2O and NaNCO to yield one trinuclear complex with molecular formula [Cu3L2(µ1,1-NCO)2]. The synthesized complex was characterized by IR, UV–vis spectroscopy, and electrochemical analysis. Single-crystal X-ray diffraction study explores that the two terminal copper atoms adopt square pyramidal geometry, whereas the central copper atom situated at the inversion center is surrounded by four phenoxo oxygens and twoend-oncyanato anions to adopt an octahedral geometry. The ONNO-tetradentate Schiff base ligand coordinates with the copper(II) ion via two oxygen atoms of the phenoxo-group and two nitrogen atoms from the imine moiety. A theoretical density functional theory (DFT) calculation was also carried out to supplement the experimental results. All the DFT calculations were done in gas phase. [ABSTRACT FROM AUTHOR]

The transition metal complexes of ethylvanillin [Mn(L) 2 (H 2 O) 2 ] ( 1 ), [Co(L) 2 (H 2 O) 2 ] ( 2 ), [Ni(L) 2 (H 2 O) 2 ] ( 3 ), and [Zn(L) 2 (H 2 O) 2 ] ( 4 ) have been synthesized. The geometric and electronic structure of 1 , 2 , 3 and 4 has been solved by X-ray diffraction analysis and EPR spectroscopy. They are octahedral complexes with a cis arrangement of the two water molecules. All the structures were calculated by DFT methods at the level of theory B3P86/6-311g. The EPR spectra of 1 are isotropic both at 298 and 77 K with g values at 2.034 ± 0.010 and 2.040 ± 0.010, respectively indicating Mn(II) ion (3d 5 ) with a S = 5/2 spin. 1 shows a hyperfine structure with six strong absorptions, corresponding to the |−1/2, m > → |1/2, m > ‘allowed’ transitions (Δ M = ±1, Δ m = 0), and five pairs of ‘forbidden’ absorptions (Δ M = ±1, Δ m = ±1), between the Δ m = 0 hyperfine transitions in an organic solvent such as DMF, DMSO and CH 3 CN. EPR spectroscopy and DFT calculations suggest that in the temperature range 77–298 K 2 presents a high-spin S = 3/2 state, whereas the low-spin state S = 1/2 begins to be populated at temperatures higher than 77 K (liquid nitrogen temperature). In 3 , the weak signal due to a small amount of an octahedral Ni(III) complex (NiL 3 ), is characterized by a rhombic spectrum. DFT simulations on 4 indicate that the octahedral structure with a cis arrangement of the two water ligands is more stable than the octahedral one with a trans arrangement and the tetrahedral geometry. [ABSTRACT FROM AUTHOR]

A new 1D polymeric copper(II) complex [{Cu(L)(CFCOO)}] has been synthesized using a potentially tetradentate Schiff base ligand, HL, ((E)-2-((pyridin-2-yl)methyleneamino)-5-chlorobenzoic acid) and characterized by different spectroscopic methods. Single crystal X-ray structural characterization reveals that the side arm carboxylate group of the coordinated Schiff base exhibits a μ-bridging mode and connects the neighbouring copper(II) ions leading to a zigzag 1D chain structure where the copper(II) ions display distorted square pyramidal geometries. Variable temperature magnetic susceptibility measurement reveals a weak antiferromagnetic exchange ( J = −0.47 ± 0.01 cm) prevails between copper(II) ions in the chain mediated by the bridging carboxylate group, is also supported by the room temperature EPR spectral study. Electrochemical property of the complex is also reported. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A potentially tetradentate Schiff base ligand containing carboxylic acid group, HL, (E)-2-((pyridin-2-yl)methyleneamino)-5-chlorobenzoic acid is synthesized and characterized. Reaction of HL with hydrated zinc(II) trichloroacetate and zinc(II) trifluoroacetate under similar reaction condition yields two discrete dinuclear complexes, [Zn(L)(Cl)] 2 ( 1 ) and [Zn(L)(CF 3 COO)] 2 ( 2 ) and characterized by different physicochemical methods. Single crystal X-ray structural characterization reveals different ligating properties of the coordinated anionic ligand (L − ) in its zinc(II) complexes. The side arm carboxylate of L − shows μ 1,3 -carboxylato-bridging mode in 1 and connects zinc(II) atoms in s yn - anti fashion while it exhibits a μ 1,1 -carboxylato-bridging mode in 2 . The metal ions display distorted square pyramidal geometries in both the structures and associated with different degrees of distortions. The fluorescence spectra of HL and its zinc(II) complexes recorded in methanol at room temperature which reveal the enhancement of emission intensity for the complexes compared to that of the free ligand. Thermogravimetric analyses (TGA) reveal high thermal stabilities of the complexes. [ABSTRACT FROM AUTHOR]

A neutral tridentate nitrogen donor Schiff base ligand L (L = (E)-N-(phenyl(pyridin-2-yl)methylene)-2-(pyridin-2-yl)ethanamine) has been synthesized and characterized by spectroscopic techniques, and employed to synthesize two new μ 1,1 -azido/cyanato bridged dinuclear copper(II) complexes, [Cu(L)( μ 1,1 -N 3 )(ClO 4 )] 2 ( 1 ) and [Cu(L)( μ 1,1 -NCO)(ClO 4 )] 2 ( 2 ). Both compounds have been spectroscopically and structurally characterized. Structural investigation reveals centro-symmetric nature of the complexes in which the center of inversion lies at the midpoint of the two copper(II) ions. The metal ions display distorted octahedral geometry. The tridentate neutral ligand L coordinates the metal ion in mer -orientation. Crystal packing reveals that hydrogen bonding and π ⋯ π stacking interactions play a dominant role on the solid state structure of the complexes. Low temperature susceptibility measurements support EPR studies and reveal antiferromagnetic ( J = −7.2 cm –1 ) and ferromagnetic ( J = +0.41 cm –1 ) behavior for 1 and 2 , respectively. [ABSTRACT FROM AUTHOR]

A mixed-valence 2-D Cu(I/II) complex, [{Cu(II)(dmen)(μ-Cl)(μ1,5-dca)}{Cu(I)(μ1,5-dca)}]n(1) (dmen = N,N-dimethylethylenediamine, dca = dicyanamide = [N(CN)2]−), has been synthesized byin situpartial reduction of Cu(II) to Cu(I) using benzoin (2-hydroxy-1,2-di(phenyl)ethanone) as reductant. Complex1was characterized by spectroscopic techniques, single crystal X-ray diffraction, and low temperature magnetic measurements. Structural investigation reveals that1represents a mixed-valence 2-D coordination polymer formed by parallel 1-D [Cu(II)(dmen)(Cl)Cu(I)(μ1,5-dca)2]nchains running along thebaxis, where chloride bridges Cu(II) ions of adjacent polymers through long connections (2.8401(1) Å) to form a 2-D network. The metal centers have two different geometrical environments (distorted square pyramidal and distorted trigonal planar geometries for Cu(II) and Cu(I), respectively). The Cu(II) ions in [Cu(II)(dmen)(μ-Cl)(dca)]nare interconnected through single chloride bridges while within the [Cu(I)(μ1,5-dca)]nunits, the dca connects adjacent Cu(I) ions throughμ1,5-dca bridges. Magnetic susceptibility measurements reveal weak ferromagnetic interactions (J = +0.3 cm−1) within the chlorido-bridged Cu(II) regular chain present in1. Simultaneous presence ofμ1,5-dca and single chlorido bridges with ferromagnetic coupling is believed to be unique in mixed-valence Cu(I)/Cu(II) complexes. [ABSTRACT FROM AUTHOR]

Three new cis -dioxomolybdenum(VI) complexes, [MoO 2 (L 1 )(CH 3 OH)] ( 1 ), [MoO 2 (L 2 )(CH 3 OH)] ( 2 ), and [MoO 2 (L 3 )(CH 3 OH)] ( 3 ) have been synthesized using three different tridentate hydrazone Schiff bases, (E)- N ′-(4-oxopentan-2-ylidene)isonicotinohydrazide (H 2 L 1 ), (E)- N ′-(4-oxo-4-phenylbutan-2-ylidene)isonicotinohydrazide) (H 2 L 2 ), and (E)- N ′-(2,3-dihydroxybenzylidene)benzohydrazide (H 2 L 3 ), respectively. The ligands and their metal complexes were characterized by different physicochemical techniques. The molecular structures of the complexes were conclusively established by single crystal X-ray diffraction which reveals that six coordinated molybdenum(VI) atom adopts distorted octahedral geometry. The tridentate hydrazone coordinates to the metal centers in their di-anionic form. The crystal packing of the complexes also reveals that classical hydrogen bonding between adjacent units result in stair-like 1D structure for 1 while an interlocked dimer for 2 and 3 , respectively. Crystal packing also reveals that further non-classical interactions lead to 2D (for 1 and 3 ) and 3D (for 2 ) supramolecular structures in their solid state. Hirshfeld surface analyses were carried out to get insight to the intermolecular interactions. Thermal stabilities and electrochemical behavior of the complexes have also been investigated. [ABSTRACT FROM AUTHOR]

Nickel(II), cobalt(II) and zinc(II) mononuclear Schiff base complexes of general formula [M II L(H 2 O) 3 ]·2H 2 O (where M = Ni, Co and Zn) have been synthesized using a new Schiff base ligand (LH 2 = 2-((Pyridin-2-yl)methyleneamino)benzene-1,4-dioic acid). All the complexes and the ligand have been characterized by various physical measurements such as elemental analyses, FT-IR and UV–Vis spectroscopic techniques. The crystal structure analyses of the complexes revealed that extensive supramolecular interactions such as hydrogen bond and π – π stacking results 3D array of packing. The hydrogen bonding interaction distances are very similar in all complexes and are around 2.0 Å and for the π – π interactions the values are close to 3.8 Å. The interaction energies are comparable for Ni and Co complexes and is somewhat stronger for Zn complex. The strength of the aforementioned interactions have been evaluated by means of DFT calculations. For in vitro antimicrobial activity study, the complexes were screened against some bacteria and fungi. This study shows that the zone of inhibition against growth of microorganisms is much larger for Zn complex due to strong binding energy. The Hirshfeld surfaces of Ni, Co and Zn complexes were also analyzed to clarify the nature of the intermolecular interactions. Thermogravimetric analyses were performed to investigate the thermal stability of the complexes. [ABSTRACT FROM AUTHOR]

The reversible redox isomerisms in first row transition metal complexes of the type ML2 were studied. The six ML2 complexes (M = MnIII (1), FeII (2), CoIII (3), NiII (4), CuII (5) and ZnII (6)) 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 (L2-, L- and L0). EPR spectra and magnetic susceptibility measurements indicate the presence of complexes of the type [MnIII(L2-)(L-)] (1) with S = 1/2, [FeII(L-)2] (2) with S = 2, [CoIII(L2-)(L-)] (3) with S = 1/2, [NiII(L-)2] (4) with S = 1, [CuII(L-)2] (5) with S = 1/2 and [ZnII(L-)2] (6) 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 (1, 2, 4) or ligand-to-ligand (in 5, 6) electron transfer (partial or total), resulting in compounds of the type [MnIV(L2-)2] (1') with S = 1/2, [FeIII(L-)(L2-)] (2') with S = 1, [NiIII(L2-)(L-)] (4') with S = 0, [CuII(L2-)(L0)] (5') with S = 1/2 and [ZnII(L2-)(L0)] (6') 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. [ABSTRACT FROM AUTHOR]

Two new Cu(II)–hydrazone complexes, [Cu(L)(Hbpe)ClO4]·ClO4·[Cu(L)Cl] (1) and [Cu(HL)2]·1.5ClO4·0.5OH (2) (where HL = (E)-N′-(1-(pyridine-2-yl)ethylidene)benzohydrazide and bpe = trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene), have been synthesized and characterized by physicochemical methods. The structures of the complexes have been established by single-crystal X-ray diffraction direct methods, which reveal that the metal ions have distorted square-pyramidal and square-planar geometries in1, and a distorted octahedral geometry in2. DNA binding of HL,1, and2, performed by UV–vis titration in tris-buffer medium, yielded binding constants, which are 9.5 × 103, 1.88 × 104, and 4.66 × 104 M−1, respectively. Viscosity measurements suggest a surface or groove-binding mode of interaction between CT-DNA with HL,1, and2. [ABSTRACT FROM PUBLISHER]

The 1D polymer complex [Cu2(L)2(SCN)2]n (1) has been syn-thesised in a one-step in situ reaction of picolinaldehyde with sodium thiocyanate. The complex 1 was characterised by FTIR spectroscopy, UV/Vis spectrophotometry and elemental analysis. The crystal structure of complex 1 shows that chains of dimer complexes are formed with tetra- and pentacoordi-nate copper centres alternately linked by one thiocyanato and two alkoxido bridges. Variable-temperature magnetic measurements showed a strong antiferromagnetic interaction between the copper centres within the dimer mediated by the two alkoxido bridges with a J value of -374 cm-1, which is in agreement with the DFT-calculated value of -284 cm-1. EPR and cyclic voltammetric analyses were also carried out, as well as DFT calculations to evaluate the packing forces and their energies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: Potentially hexadentate N2O4 donor Schiff base ligands N,N′-bis(3-ethoxysalicylidenimino)-1,2-diaminoethane (L1H2) and N,N′-bis(3-methoxysalicylidenimino)-1,3-diaminopropane (L2H2) have been used to synthesize two manganese(III) compounds [MnL1(SCN)(H2O)].[MnL1(H2O)2](ClO4)·CH3CN (1) and [MnL2(SCN)(H2O)] (2). All the ligands and the complexes have been characterized by microanalytical and spectroscopic techniques. The X-ray structural characterization of all the complexes shows a tetragonally elongated octahedral geometry for the manganese coordination sphere. The octahedron entities are further connected in pairs through intermolecular hydrogen bonding to form μ-aquo dimers, which are further stabilized by π–π interactions occurring between the aryl rings of the Schiff base ligands. These noncovalent interactions have been investigated in terms of energies and geometries using theoretical calculations. The catalytic activity of compounds 1 and 2 on the oxidation of 3,5-di-tert-butylcatechol was determined spectrophotometrically by monitoring the increase of the 3,5-di-tert-butyl-o-benzoquinone characteristic absorption band at about 400nm over time in methanol saturated with O2. The complexes were able to oxidize 3,5-di-tert-butylcatechol to the corresponding o-quinone with distinct catalytic activity. [Copyright &y& Elsevier]

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–H⋯π 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. [ABSTRACT FROM AUTHOR]

Abstract: The tetradentate (ONNO) donor Schiff base ligand LH2, derived from the condensation of salicylaldehyde and 1,3-diaminopropane, has been synthesized and reacted with CuBr2 to yield a trinuclear complex with the molecular formula [Cu3L2Br2]. Single crystal X-ray diffraction study reveals that the two terminal copper atoms adopt a square pyramidal geometry, whereas the central copper atom, situated at the inversion centre, is surrounded by four phenoxide oxygen atoms in a square planar fashion. Variable temperature magnetic susceptibility measurement study shows strong antiferromagnetic intra-trimer interactions between the copper centers with a J value of −302cm−1. EPR study of the complex depicts that, due to the exchange coupling between the copper ions, the EPR spectra were unresolved, having very broad resonances with g =2.133. A theoretical DFT calculation was also carried out to supplement the experimental results. [Copyright &y& Elsevier]

Abstract: We have synthesized a μ-oxido divanadium compound [(VOL)2(μ-O)] with an aliphatic hydrazone ligand LH2 =(E)-N′-(1-(2-hydroxyphenyl)ethylidene)acetohydrazide. The complex was characterized by elemental analysis, IR and UV–Vis spectroscopy and the molecular structure was established by single crystal X-ray diffraction technique. The complex has been infused over alumina to prepare a heterogeneous catalyst which was characterized by IR spectroscopy, thermogravimetric and powder XRD analyses. The catalyst has been studied for the oxidation of styrene in presence of H2O2 and appears to be easily recyclable. A conversion of 99.7% and selectivity of 88.1% for benzaldehyde formation and a turnover number of 1354 was detected under the most favorable reaction conditions. [Copyright &y& Elsevier]

A novel type of NO...NO supramolecular interaction is reported for the first time. Three new polymeric coordination complexes, two nickel(II) complexes, {[Ni(μ-L1)2(NCS)2]}n, (1) {[Ni(μ-L2)2(NCS)2]}n, (2) and a cobalt(II) complex {[Co(μ-L3)2(NCS)2]}n (3) have been synthesized with the organic ligand α,ω- bis(benzotriazoloxy)alkane (L1 = 1,3-bis(benzotriazol-1-yl)-1,3-dioxapropane; L2 = 1,5-bis (benzotriazol-1- yl)-1,5-dioxapentane; L3 = 1,6-bis(benzotriazol-1-yl)-1,6-dioxahexane) and thiocyanate as counterions. The complexes were characterized by various physical measurements such as elemental analysis, FT-IR, UV-Vis, NMR and mass spectroscopy. The single crystal X-ray analysis revealed that complexes 1 and 2 have a 1D coordination polymer helical structure whereas complex 3 has a 2D polymer anti corrugate structure. Complexes 2 and 3 were found to be involved in packing in the crystal structures by a very unusual anti-parallel strong NO...NO interaction. In addition, the π-acidity of the triazole ring moiety increased upon the coordination of the Ni ion which led to the establishment of lone pair-π (lp-π) interactions. Moreover, all of the complexes show different intermolecular interactions (H-bonds, π-π, lone pair-π and anti-parallel NO...NO) whose energetics and role in the crystal packing have been evaluated with theoretical DFT calculations. [ABSTRACT FROM AUTHOR]

Abstract: Three new complexes, [{Cu(L)I}2] n (1), [Ag(L)] n ·nClO4 (2) and [{Ag(L)(CF3COO)}2] n (3), have been synthesised and characterized by different physico-chemical methods with the aim of exploring the ligating properties of pyridine-4-amidoxime (L). Single crystal X-ray structure analysis reveals that 1 is a 2D coordination polymer, while 2 and 3 are wavy 1D chains in spite of the same coordination mode adopted by the ligand. The crystal structures also show that the coordination geometry of the metals is different in each complex, being tetrahedral in 1, but distorted trigonal planar and distorted linear in 2 and 3, respectively. The asymmetric units of 1 and 3 consist of two independent metal centres and each is associated with a counter anion of the metal salt used, while the asymmetric unit of 2 is cationic in nature, the perchlorate anion being non-coordinated. Structural diversities are also evident as the 2D structure of 1 is stabilized by O–H⋯I interactions, while several classical and non-classical hydrogen bonds lead to 3D supra-molecular structures for complexes 2 and 3. The solid state fluorescence of L and of its complexes were studied revealing that both 1 and 2 show a broad emission band with a maxima at 525 and 522nm, respectively, strongly red shifted when compared to the free ligand band (463nm), while 3 is found surprisingly to be non-emissive. [Copyright &y& Elsevier]

Abstract: A single thiocyanato bridged 1D polymeric zinc complex with dinuclear asymmetric unit [Zn2L1(μ 1,3-SCN)(SCN)] n (1) and a dimeric zinc complex [Zn2L2(NCS)(OOCCH3)(CH3OH)2] (2) have been synthesized using two different Schiff bases N,N/ -bis(3-methoxysalicylidenimino)-1,3-diaminopropane (L1H2) and N,N/ -bis(3-ethoxysalicylidenimino)-1,3-diaminopropane (L2H2), respectively. All the ligands and the 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. Thermo-gravimetric analysis has been performed to investigate their thermal stability. Finally, the photoluminescence properties of the complexes as well as their respective ligands have been investigated with a comparative approach. [Copyright &y& Elsevier]

Two new N3O donor ketoxime Schiff bases (HL1 and HL2) 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 HL1 resulted in a discrete oximato-bridged dinuclear Cuii complex [Cu2(L1)2(H2O)2](ClO4)2 (1). The same reaction in presence of NaSCN affords the complex {[Cuii2(L1)2][Cui4(μ1,3-SCN)4(μ1,1,3-SCN)2]}n (2), where partial Cuii→Cui reduction is observed. In 2, arrays of [Cuii2(L1)2]2+ cationic units are inserted in between 2D {[Cui4(SCN)6]2−}n layers and connected viaμ1,1,3-SCN− links, thus forming a 3D network. On the other hand, reaction of Cu(CH3COO)2 and HL2 in the presence of NaSCN gave rise to a mixed-valence pentanuclear cluster {[Cuii2(L2)2(NCS)]2[Cui(SCN)(μ1,1-SCN)(μ1,3-SCN)]} (3) where Cuii is also partly reduced to Cui. In compound 3, two cationic [Cuii2(L2)2(NCS)]+ units are bridged by the anionic [Cui(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. [ABSTRACT FROM AUTHOR]

Abstract: The new tetranuclear nickel(II) complex [Ni4(OH)(L)(HL)2(CH3OH)1.5(H2O)1.5]·9H2O (1) has been synthesised by the reaction of NiCl2·6H2O and the Schiff base ligand H3L (H3L=(CH3O)(OH)C6H3CH N–C(CH3)(CH2OH)2), prepared by the 1:1 condensation of 2-amino-2-methyl-1,3-propanediol and o-vanillin, and characterized by different physicochemical methods. Single crystal X-ray structural determination identifies a Ni4O4 cubane moiety as the central part of the complex unit. The presence of a single μ 3-hydroxido bridged oxygen occupying only one vertex of the Ni4O4 cubane core is rare in Ni4O4 cubanes (ca. 5% of occurrence). Structural analysis also reveals two similar alkoxido oxygen atoms of the Schiff base coordinating the metals in two different modes; one in the μ 3-bridging mode whilst the other binds in a monodentate fashion. The metal centers display distorted octahedral geometries with two different coordination environments. The magnetic properties reveal the presence of ferromagnetic nickel(II)–nickel(II) interactions in the cluster with two different exchange pathways. The magnetic data can be fitted to a Ni4O4 cubane model with g =2.058, J 1 =+17.2cm−1 and J 2 =+6.6cm−1. Isothermal magnetization measurements confirm the S =4 spin ground state. Both J values agree with previous magneto-structural correlations in doubly oxido-bridged nickel(II) complexes. [Copyright &y& Elsevier]

Sodium-assisted self-assembly of two nickel(II) Schiff base complexes under similar reaction conditions yield hetero-metallic compounds [{Ni(salpn)}2Na(ClO4)] (1) and [{Ni(salpr)}3Na][Ni(salpr)]2ClO4·2H2O (2) (where salpn = N,N′-bis-(salicylidene)-1,3-diaminopropane and salpr = N,N′-bis-(salicylidene)-1,2-diaminopropane). Both have been characterized by physico-chemical techniques and single-crystal X-ray diffraction. Crystal structure reveals that in the tri-metallic system of1sodium is sandwiched between two [Ni(salpn)] units while the hexametallic system of2consists of tetrametallic cluster ion [{Ni(salpr)}3Na]+with encapsulated sodium by three [Ni(salpr)] units. In both complexes, sodium adopts distorted trigonal prismatic geometry leaving nickel(II) in a distorted square-planar environment. Structural characterization also reveals that 2 : 1 (for1) and 3 : 1 (for2) self-assemblies of metallo-ligand and sodium were achieved with slight variation in ligand backbone. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of Cu2(CH3COO)4·2H2O with the Schiff base ligand, H4L [(OH)2C6H3CHC(CH3)(CH2OH)2], yields a novel hexanuclear copper (II) cluster {[Cu6(HL)4]·CH3OH·0.5CH3CN·6.5H2O} (1) with a rare “bicapped cubane” core. Title complex has been characterized by different physico-chemical techniques. Single-crystal X-ray structure reveals that the “bicapped cubane” core was formed by a cubane-like Cu4O4 subcore capped by two copper(II) atoms over opposite faces. The cubane copper(II) atoms are in distorted square pyramidal geometry and connected each other via μ 3-alkoxo oxygens while two apical copper(II) atoms are in distorted square planar environments and connected to the main cubane subcore by doubly phenoxo bridged oxygen atoms. EPR spectra of the complex reveals overall strong antiferromagnetic behavior, well supported by cryomagnetic susceptibility measurements in the range 2–300K under the magnetic field of 0.1T leading different coupling constants: J 1 =+60cm−1, J 2 =−45.5±1cm−1; J 3 =−140±1cm−1, using the general Hamiltonian H=−J(Si·Sj). A plausible magneto-structural correlation has also been established. [Copyright &y& Elsevier]

Three new hetero-bimetallic coordination complexes [Na(CuII L1)2](ClO4) ·0.5H2O ( 1), [Na(CuII L2)2][CuI2(μ1,3-NCS)3] n ( 2), and {[Na(CuII L3)2](μ1,5-dca)} n ( 3; dca = dicyanamide) have been synthesized by using different Schiff base ligands [e.g., L1H2 = N, N′-bis(3-methoxysalicylidenimino)-1,3-diaminopentane, L2H2 = N, N′-bis(3-ethoxysalicylidenimino)-1,3-diaminopropane, and L3H2 = N, N′-bis(5-bromo-3-methoxysalicylidenimino)-1,3-diaminopropane] in the presence of pseudohalide coligands N3-, SCN-, and N(CN)2- (dca), respectively. The ligands and the complexes have been characterized by microanalytical and spectroscopic techniques. The structures of the complexes, determined by single-crystal X-ray diffraction studies, show that in all cases a trinuclear Na(CuII L)2 unit is formed, but of different configurations. 1 does not include N3- anions. In contrast, in 2, SCN- extrudes partial in situ reduction of CuII to lead to the formation of an infinite [CuI2(μ1,3-NCS)3] n anionic chain; and in 3, N(CN)2- bridges the metal-ligand assemblies to form a 1D polymeric chain. ESI-MS, UV/Vis spectroscopy, and cyclic voltammetry were performed to investigate the solution-state behavior of the complexes. Theoretical calculations of the optimized geometries of the complexes were carried out at the BLYP/DNP level to determine their relative stabilities from the HOMO-LUMO gap and chemical softness values. [ABSTRACT FROM AUTHOR]

Four new dicyanamide(dca) bridged multinuclear ZnⅡ-Schiff-base complexes, {[Zn2L¹(μ1,5-dca)dca]-CH3OH}2 (1), [Zn2L²(μ1,5-dca)dca]n (2), [Zn3L³2(μ1,5-dca)2]n (3), and [(ZnL4)2Zn(μ1-5-dca)dca]n (4), have been synthesized using four different Schiff bases L¹H2 = N,N'-bis(3-methoxysalicylidenimino)-l,3-diaminopentane, L²H2 = N,N'-bis(5-bromo-3-methoxysalicylidenimino)-l,3-diaminopropane, L³H2 = N,N'-bis(5-bromosalicyIidenimino)-l,3-diaminopropane, and L4H2 = 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. [ABSTRACT FROM AUTHOR]

A methylene-bridged 1-hydroxybenzotriazole derived ligand L [L = 1, 3-bis(benzotriazol-dioxapropane] has been synthesized and characterized by spectroscopic and structural methods. Reaction of L with two different copper(II) halides [CuX2; X = Br, CI] in an identical condition yields two different compounds of similar compositions, {[Cu(/μ-Br)(Br)(μ-L)]2}n·2nH2O (1) and {[Cu(μ-Cl)(Cl)(μ-L)]2}n-2nH2O (2), both being character-ized 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. [ABSTRACT FROM AUTHOR]

Abstract: A dicyanamide bridged 2D polynuclear complex of copper(II) having molecular formula [Cu2(L)(μ1,5-dca)2] n (1) has been synthesized using the Schiff base ligand N,N′-bis(salicylidene)-1,3-diaminopentane, (H2L) and sodium dicyanamide (dca). The complex presents a 2D hexagonal structure formed by 1,5-dca singly bridged helical chains connected through double 1,5-dca bridges. The chelating characteristics of the H2L Schiff base ligand results in the formation of copper(II) dimer with a double phenoxo bridge presenting a very strong antiferromagnetic coupling in the copper(II) derivative (1) (J =−510cm−1). The dimeric asymmetric unit of 1 is very similar to the active site of the catechol oxidase and, as expected, also presents catalytic activity for the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone in presence of O2, as demonstrated by kinetic studies of this oxidation reaction monitored by absorption spectroscopy resulting in high turnover number (K cat =259h−1). [Copyright &y& Elsevier]

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL¹), 2-hydroxyacetophenone (HL²), and 2, 3-dihydroxybenzaldehyde (HL³). These tridentate ligands are reacted with Ni(OOCCF3)2·xH2O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L¹)(OOCCF3)(CH3OH)]2 (1), [Ni(L²)(OOCCF3)(H2O)]2 (2), and [Ni(L³)(L³H)](OOCCF³)(H2O)1.65(CH3OH)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 NiIII-OCl or NiIII-O·intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396). [ABSTRACT FROM AUTHOR]

Abstract: A tridentate NNO donor Schiff base ligand [(1Z,3E)-3-((pyridin-2-yl)methylimino)-1-phenylbut-1-en-1-ol= LH] in presence of azide ions coordinates with cobalt(II) and copper(II) ions giving rise to three new coordination complexes [Co2(L)2(μ1,1-N3)2(N3)2] (1), [Cu2(L)2(μ1,3-N3)]·ClO4 (2) and [(μ1,1-N3)2Cu5(μ-OL)2(μ1,1-N3)4(μ1,1,1-N3)2] n (3). The complexes have been characterized by elemental analysis, FT-IR, UV–Vis spectral studies, and single crystal X-ray diffraction studies. These complexes demonstrate that under different synthetic conditions the azide ions and the Schiff base ligand (LH) show different coordination modes with cobalt(II) and copper(II) ions, giving rise to unusual dinuclear and polynuclear species (1, 2 and 3) whose structural variations are discussed. Magneto-structural correlation for the very rare singly μ1,3-N3 bridged CuII–Schiff base dinuclear species (2) has been studied. In addition, the catalytic properties of 1 for alkene oxidation and the general catalase-like activity behavior of 2 have been discussed. [Copyright &y& Elsevier]

A novel hexanuclear complex [{(CuL)2Cu}2(μ-dca)2](ClO4)2·2L′(1) (where H2L=(OH)C6H4C(CH3)=N(CH2)3N=C(CH3)C6H4(OH) or N,N′-bis(2-hydroxyacetophenone) propylenediimine and dca=N(CN)2− and L′=2-hydroxyacetophenone) has been synthesized and characterized by elemental analysis, UV–Vis, FT-IR spectroscopic and electrochemical methods. Single crystal X-ray structural characterization reveals a centrosymmetric nature of the complex unit, where the metal centers adopt distorted square-planar and distorted octahedral geometries. Structural analysis also reveals μ2-phenoxo bridges between terminal and the central copper(II) centers of the asymmetric [(CuL)2Cu(dca)] unit, the latter being interconnected to its symmetry related counterpart by double μ1,5-dca bridges, leading to the hexanuclear complex ion [{(CuL)2Cu}2(μ-dca)2]2+. Low temperature susceptibility measurements of 1 revealed the presence of strong antiferromagnetic coupling (2J = −407cm−1) between the copper(II) centers. [Copyright &y& Elsevier]

Abstract: Three new Cu(II) complexes of formula [Cu(L1)(pyz)(CH3OH)]ClO4 (1), [Cu(L1)(4,4′-bpy)(ClO4)]·0.5H2O (2) and [{Cu(L2)(ClO4)}2(μ-4,4′-bpy)] (3) have been synthesised by using pyrazine (pyz) and 4,4′-bipyridine (4,4′-bpy) and tridentate O,N,O-donor hydrazone ligands, L1H and L2H, obtained by the condensation of 1,1,1-trifluoro-2,4-pentanedione with salicyloylhydrazide and benzhydrazide, respectively. The ligands and their complexes have been characterized by elemental analyses, FT-IR, and UV–Vis spectroscopies. Single crystal X-ray structure analysis evidences the metal ion in a slightly deformed square pyramidal geometry in all the complexes. However complexes 1 and 2 are mononuclear with pyz and 4,4′-bpy, respectively, showing an unusual monodentate behavior, while complex 3 is dinuclear with 4,4′-bpy adopting the typical bridging coordination mode. Self assembly of the complex units by hydrogen bonding interactions produces one-dimensional arrangement in each crystal packing. The magnetic characterization of complex 3 indicates a weak antiferromagnetic exchange interaction between the Cu(II) ions (J =−0.96cm−1) mediated through the long 4,4′-bpy bridge. Electrochemical behavior of the complexes is also discussed. [Copyright &y& Elsevier]

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new CoII/CoIIIand NiIIcomplexes with a pentadentate Schiff base ligand H3L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1 : 2 molar ratio. The room temperature syntheses involving CoIIand NiIInitrates and the ligand H3L lead to the isolation of the dinuclear species [Co2L2(H2O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [CoII2CoIII2L2(μ3-OMe)2(NO3)(H2O)2]NO3·2(H2O) (2), and [Ni4L2(μ3-OMe)2(H2O)2]·2H2O (4). 1is found to be a simple mono alkoxo-bridged CoIIIdinuclear species, whereas 2and 4are both rhomb-like tetrameric complexes with double oxo bridges and μ3-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2shows six coordinate ordered CoIIand CoIIIions and 4has both six- and five-coordinate NiIIcenters. Compound 3is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, 1H-NMR and ESI mass study results and is supposed to have one NiIIcenter coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2and 4is performed which indicate for both 2and 4the presence of intracluster dominant ferromagnetic interactions. [ABSTRACT FROM AUTHOR]

Abstract: A new two-dimensional (2D) thiocyanato-bridged cobalt(II) network formulated as [LCo2(NCS)2] n (1), has been synthesized with the Schiff base ligand N,N′-bis(3-methoxysalicylidenimino)-1,3-diaminopropane (H2L) and thiocyanate anions. This novel layered compound has been completely characterized by elemental analysis, FT-IR, UV–Vis spectroscopy and the structure has been established by single crystal X-ray diffraction studies. The structure of 1 consists of a doubly phenoxo-bridged dimer comprising two different cobalt(II) centers with different coordination geometries (octahedral and tetrahedral). The 2D network is accomplished by bridging thiocyanate ligands, connecting the dimeric motifs in an end-to-end fashion. Variable-temperature magnetic susceptibility and EPR measurements reveal predominant antiferromagnetic exchange interaction in the complex. [ABSTRACT FROM AUTHOR]