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Synthesis and Magnetic Properties of Dinuclear Oxovanadium(IV) Complexes Bridged by Tetracarboxylato Groups

Li Y., Yan C., Guan H.

Polish Journal of Chemistry

2004

Vol. 78 / nr 1

1-7

Three novel _-tetracarboxylato-bridged oxovanadium(IV) dinuclear complexes described by the overall formula [(VO)2(PMTA)L2], where PMTAstands for the tetraanion of pyromellitic acid, and L denotes 2,2_-bipyridine (bpy), 4,4_-dimethyl-2,2_-bipyridine (Me2bpy) or 1,10-phenanthroline (phen), respectively, have been synthesized and characterized by elemental analyses, molar conductivity and room-temperature magnetic moment measurements, IR, ESR and electronic spectral studies. It is proposed that these complexes have PMTA-bridged structures and consist of two oxovanadium(IV) ions, each in a square-pyramidal environment. The [(VO)2(PMTA)(bpy)2] (1) and [(VO)2(PMTA)(phen)2] (2) complexes were further characterized by variable temperature (4.2~300 K) magnetic susceptibility measurements and the observed data were fitted to the modified Bleaney-Bowers equation by the least-squares method, giving the exchange integral J = -2.75 cm-1 for (1) and J = -3.91 cm-1 for (2). This result indicates that there is a weak antiferromagnetic spin-exchange interaction between the two VO2+ ions within each molecule.

Synthesis and Magnetic Studies of Binuclear Iron(II) Complexes Bridged by Tetracarboxylato Groups

Li Y., Yan C. -W.

Polish Journal of Chemistry

2002

Vol. 76 / nr 12

1681-1687

Four novel binuclear iron(II) complexes, namely [Fe2(PMTA)L4], where L denotes 4,4_-dimethyl-2,2_-bipyridine (Me2-bpy); 1,10-phenanthroline (phen); 5-chloro-1,10- phenanthroline (Cl-phen) or 5-bromo-1,10-phenanthroline (Br-phen), respectively, and PMTA stands for the tetraanion of pyromellitic acid, have been synthesized and characterized. Based on elemental analyses, magnetic moments at room-temperature and molar conductivity measurements, and spectroscopic (electronic and IR spectra) studies, extended PMTA-bridged structures consisting of two iron(II) ions, each in a distorted octahedral environment, are proposed for these complexes. The variable temperature magnetic susceptibilities (4_300 K) of the complexes [Fe2(PMTA)(Me2-bpy)4] (1) and [Fe2(PMTA)(phen)4] (2) were measured and the magnetic analysis was carried out by least-square method to the observed data with the susceptibility equation derived from the spin Hamiltonian operator, _ _ _ H 2JS S 1 2 _ _ _ , giving the exchange integrals J = _1.09 cm_1 for (1) and J = ___18 cm_1 for (2). The results indicate that there is a very weak antiferromagnetic spin-exchange interaction between the Fe(II) ions within each molecule.