Search

A study deals with the selection and pattern of trianionic symmetrical heptadentate ligands and the binding of these to vanadium. The research work presented offers an invaluable understanding of the synthetic approach in the field of mixed-valence chemistry of vanadium.

A non-porphyrinic [N.sub.4][O.sub.3]-coordinating heptadentate ligand was used to synthesis and characterize various properties of two new binuclear copper(II) complexes, [[Cu.sub.2]([H.sub.2]L)([mu]-OH)][(Cl[O.sub.4]).sub.2] and [[Cu.sub.2](L)[([H.sub.2]O).sub.2]P[F.sub.6]. The complexes were found to exhibit antiferromagnetic interaction in solid state and catecholase activity at pH 8.5.

The existence of ferromagnetic interactions between Ni(II) centers via N3-ligands and antiferromagnetic interactions through the H-bonded moiety are revealed by the synthesis, structural characteristics, magnetic studies and DFT calculations in Ni(II) dinuclear complexes containing two bridging N3- and an O-H...O linkage. The magnetic behavior of the system depends on the delicate balance between these two competing interactions.

The N4O3 coordinating heptadentate ligand afforded binuclear complex [Cu2(H2L)(μ-OH)](ClO4)2 (1) and [Cu2(L)(H2O)2]PF6 (2). In complex 1, two copper ions are held together by μ-phenoxo and μ-hydroxo bridges, whereas in complex 2, the copper centers are connected only by a μ-phenoxo bridge. In 1, both the Cu(II) centers have square pyramidal geometry (r = 0.01-0.205), whereas in the case of 2, one Cu(II) center has square pyramidal (r = 0.2517) and other one has square based pyramidal distorted trigonal bipyramidal (r = 0.54) geometry. Complexes 1 and 2 show an strong intramolecular and very weak antiferromagnetic interaction, respectively. Density-functional theory calculations were performed to establish the magneto structural correlation between the two paramagnetic copper(II) centers. Both of the complexes display a couple of one-electron reductive responses near -0.80 and -1.10 V. The complexes show significant catalytic activity at pH 8.5 on the oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ), and the activity measured in terms of kcat = 29-37 h-1. [ABSTRACT FROM AUTHOR]

Abstract: The pale blue colored complex of the formula [Ni2(L)(HL)(μ1,1-N3)2]ClO4 (1) has been synthesised in good yield by the reaction of Ni(ClO4)2 ·6H2O with N,N-bis(2-methylpyridyl)-3,5-dimethyl-2-hydroxybenzylamine (HL) in methanol in the presence of sodium azide. The crystal structure of the complex has been determined. The X-ray structure reveals that the metal centres are linked by both an end-on bridged azide ligand as well as through an [O–H⋯O] interacting unit. Magnetic susceptibility measurements confirm the ferromagnetic character of the complex. [Copyright &y& Elsevier]

Abstract: The light green coloured complexes of general formula [ReVO(L)Cl(OH2)]Cl have been synthesised in good yields by reacting [ReVOCl3(AsPh3)2] with HL in dichloromethane in dinitrogen atmosphere. Here, L− is the deprotonated form of N,N-bis(2-pyridylmethyl)amine (HL1); N-(2-pyridylmethyl)-N′,N′-dimethylethylenediamine (HL2) and N-(2-pyridylmethyl)-N′,N′-diethylethylenediamine (HL3). Single crystal X-ray structure determination of [ReVO(L1)Cl(OH2)]Cl confirms the amido binding of ReO3+ species. In the solid state of [ReVO(L1)Cl(OH2)]Cl, the coordinated and counter chloride ions are engaged in Re–Cl…H–C(ring), Cl…H–C(ring) and Re–(OH2)…Cl hydrogen bonding and forming of a supramolecular network in the solid state. The subunit of the supramolecular network consists of one eight-membered and two nine-membered hydrogen bonded rings. The average diameters of eight-membered and nine-membered rings are ∼3.70 and ∼5.26Å, respectively. [Copyright &y& Elsevier]

Dinuclear (VIVVV) oxophenoxovanadates of general formula [V2O3L] have been synthesized in excellent yields by reacting bis(acetylacetonato)oxovanadium(IV) with H3L in a 2:1 ratio in acetone under an N2 atmosphere. Here L3- is the deprotonated form of 2,6-bis[{{(2-hydroxybenzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L¹), 2,6-bis[{.{(5-methyl-2-hydroxy-benzyl)(N',N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L²), 2,6, bis[{{(5-tert-butyl-2-hydroxybenzyl)(N'-N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L³), 2,6-bis[{{(5chloro-2-hydroxybenzyl)(N'-N'-(dimethylamino)ethyl)}amino}methyl]-4-methylpheno(H3L4), 2,6-bis[{{(5-bromo-2hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}amino}methyl]-4-methylphenol (H3L5), or 2,6-bis[{{(5-methoxy-2hydroxybenzyl)(N'N'-(dimethylamino)ethyl)}methyl]-4-methylphenol (H3L6). In [V2O3L¹], both the metal atoms have distorted octahedral geometry. The relative disposition of two terminal V=O groups in the complex is essentially cis. The O=V…V=O torsion angle is 24.6(2)°. The V-Ooxo-V and V-Ophenoxo-V angles are 117.5(4) and 93.4(3)°, respectively. The V…V bond distance is 3.173(5) Å. X-ray crystallography, IR, UV-vis, and ¹H and 51V NMR measurements show that the mixed-valence complexes contain two indistinguishable vanadium atoms (type III). The thermal ellipsoids of 02, 04, C10, C14, and C15 also suggests a type III complex in the solid state. EPR spectra of solid complexes at 77 K display a single line indicating the localization of the odd electron (3dxy&supl;). Valence localization at 77 K is also consistent with the 51V hyperfine structure of the axial EPR spectra (3dxy¹ ground state) of the complexes in frozen (77 K) dichloromethane solution: S= ½, gII ∼ 1.94, g⊥ ∼ 1.98, AII ∼ 166 x 10-4 cm-1, and A⊥ ∼ 68 x 10-4 cm-1. In contrast isotropic room-temperature solution spectra of the family have 15 hyperfine lines (giso ∼ 1.974 and Aiso ∼ 50 x 10-4 cm-1) revealing that the unpaired electron is delocalized between the metal centers. Crystal data for the [V2O3L¹]·CH2Cl2 complex are as follows: chemical formula, C32H43O6N4Cl2V2; crystal system, monoclinic; space group, C2/c; a: 18.461(4), b = 17.230(3), c = 13.700(3) Å; β = 117.88(3)°; Z = 8. [ABSTRACT FROM AUTHOR]