A series of novel dinuclear, mixed-ligand complexes having the general formula [M2(tpt)(L)4]Cl4 · nH2O where M=Ni(II), Co(II) or Cu(II); tpt = 2,4,6-tris(2-pyridyl)-1,3,5-triazine; L = dithiooxamide (dto) or thiosemicarbazide (tsc); n = 2-4, have been synthesized and characterized. The tpt molecule is flexidentate, where it can behave as di- or tridentate dinucleating ligand. The coordination mode of tpt to M(II) apparently occurs through the pyridyl and a triazine nitrogen atoms. All the mixed-ligand complexes are dinuclear with a bridging tpt molecule and having an octahedral structure. The complexes were characterized by chemical analyses, spectral, molar conductance and thermal studies.

The metal ion complexes [Co(II), Ni(II), Cu(II) and Cd(II)] of some azopyrazolopyrimidine derivatives have been prepared and characterized using elemental analyses, molar conductivity, electronic and IR spectra. The azopyrazolopyrimidines are characterized by a high tendency towards complex formation with the neutral molecules coordinating to the metal ion as bidentate ligands. It is concluded that the ligands are bonded to the metal ion through the - or β-nitrogen atom of the arylazo group and the carbonyl oxygen of the pyrazolone ring where six- or five-membered chelate rings are formed. The apparent formation constants of the complexes in solution have been determined.

Square-planar copper(II) and nickel(II) derivatives of the cis-dithiolate N2S2 ligand bis(N,N‘-2-mercapto-2-methylpropyl)-1,5-diazocyclooctane, (bme*daco)M, nucleate four CuICl moieties, forming MII2CuI4S4 clusters with unusual triply bridging thiolates, μ3-SR, in the topological form of adamantane. As determined by X-ray crystallography, the (bme*daco)M (M = Cu or Ni) metallothiolate serves as a bidentate ligand that bridges four CuI ions, utilizing all lone pairs on sulfurs. Further characterization by electrochemical and electronic spectral measurements suggests greater electron delocalization in the all-copper complex as compared to the NiCu heterometallic complex. Mass spectral data imply that the mixed-metal NiII2CuI4S4 is more stable toward CuCl loss than CuII2CuI4S4, a result that is corroborated by extraction of CuI by 1,2-bis(diphenylphosphino)ethane in the latter but not the former.

[Ni(CH3PO3)(H2O)] (1) and [Ni{CH3-(CH2)17-PO3}(H2O)] (2) were synthesised by reaction of NiCl26 H2O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined ab initio from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn21, with a=5.587(1), b=8.698(1), c=4.731(1) Å. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of NiII ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van der Waals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a=5.478(7), b=42.31(4), c=4.725(3) Å. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d8 (S=1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss () constants were found to be 1.15 cm3 K mol-1 and -32 K, respectively. The negative value of indicates an antiferromagnetic exchange coupling between near-neighbouring NiII ions. No sign of 3D antiferromagnetic long-range order is observed down to T=5 K, the lowest measured temperature. Compound 2 is paramagnetic above T=50 K, and the values of C and were found to be 1.25 cm3 K mol-1 and -24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T=21 K. The irreversible magnetisation, Mfc-zfc, obtained as a difference from fc and zfc plots starts to increase at T=20 K, on lowering the temperature, and it becomes steady at T=5 K. The presence of spontaneous magnetisation below T=20 K indicates a transition to a weak-ferromagnetic state for compound 2.

[Ni(CH3PO3)(H2O)] (1) and [Ni{CH3-(CH2)17-PO3}(H2O)] (2) were synthesised by reaction of NiCl26 H2O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined ab initio from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn21, with a=5.587(1), b=8.698(1), c=4.731(1) Å. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of NiII ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van der Waals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a=5.478(7), b=42.31(4), c=4.725(3) Å. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d8 (S=1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss () constants were found to be 1.15 cm3 K mol-1 and -32 K, respectively. The negative value of indicates an antiferromagnetic exchange coupling between near-neighbouring NiII ions. No sign of 3D antiferromagnetic long-range order is observed down to T=5 K, the lowest measured temperature. Compound 2 is paramagnetic above T=50 K, and the values of C and were found to be 1.25 cm3 K mol-1 and -24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T=21 K. The irreversible magnetisation, Mfc-zfc, obtained as a difference from fc and zfc plots starts to increase at T=20 K, on lowering the temperature, and it becomes steady at T=5 K. The presence of spontaneous magnetisation below T=20 K indicates a transition to a weak-ferromagnetic state for compound 2.

The acid dissociation constants of 2,2‘,6‘,2‘ ‘-terpyridine were determined in aqueous + organic solvents mixtures. The organic solvents were methanol, ethanol, acetone, dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The ionization constants of terpyridine depend largely on both the proportion and nature of the organic cosolvent. Solvent properties play a major, but not exclusive, role in the ionization of the protonated terpyridine molecule. Basicity and stabilization of the different species existing in equilibrium through hydrogen bonding together with ion−solvent interaction play an important role in the acid dissociation in the presence of organic solvent. The overall dissociation constant (pKa1+ pKa2) of the protonated terpyridine increase in the various solvents according to the following order: methanol ethanol acetone dimethyl formamide dimethyl sulfoxide

The acid dissociation constants of 2,2‘,6‘,2‘ ‘-terpyridine were determined in aqueous + organic solvents mixtures. The organic solvents were methanol, ethanol, acetone, dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The ionization constants of terpyridine depend largely on both the proportion and nature of the organic cosolvent. Solvent properties play a major, but not exclusive, role in the ionization of the protonated terpyridine molecule. Basicity and stabilization of the different species existing in equilibrium through hydrogen bonding together with ion−solvent interaction play an important role in the acid dissociation in the presence of organic solvent. The overall dissociation constant (pKa1+ pKa2) of the protonated terpyridine increase in the various solvents according to the following order: methanol ethanol acetone dimethyl formamide dimethyl sulfoxide