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1 2006

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Hydrazinium Complexes of Lanthanide and Transition Metal Squarates

Vairam S., Govindarajan S.

Polish Journal of Chemistry

2006

Vol. 80, nr 10

1601-1614

Reaction of the ligands, squaric acid and hydrazine with Ln(NO3)3 where Ln(III) = La, Pr, Nd, Sm, Gd and Ce results in the formation of the complexes of the formula, N2H5[Ln(C4O4)2]xH2O where x = 3, 5 and 6 and their reaction with transition metal nitrates, M(NO3)2xH2O, where M(II) = Co, Ni, Cu, Zn and Cd in aqueous solution yields the squarates of the types, [(N2H5)3M(C4O4)2.5]2H2O where M(II) = Co, Ni and Cd; [(N2H5)2Zn(C4O4)2]2H2O and [(N2H5)Cu(C4O4)1.5 ]. Neutralization of the acid with hydrazine hydrate gives dihydrazinium squarate hydrate, (N2H5)2(C4O4)H2O. All the above complexes, except Cd, are sparingly soluble in water and are characterized by IR, UV-visible, ESR and thermoanalytical methods. The squarates appear to behave as bis-monodentate and tetrakis-monodentate bridged ligands in transition metal and lanthanide complexes respectively. Hydrazinium cation acts as a coordinating ligand in transition metal complexes whereas it is a charge compensating species in lanthanide squarates. This fact is revealed from their IR spectra by displayingN-N frequency at 1000 cm–1 in the former case and at 950 cm–1 in the latter. Squarate compounds exhibit very high exothermic decomposition. Hydrazinium lanthanide squarates show weight losses due to dehydration and dehydrazination from 68 graduate C to 258 graduate C and a strong exothermic decomposition between 176 graduate C and 700 graduate C leading to the formation of metal oxides/oxy carbonates as the end products possibly via H[Ln(C4O4)2] intermediate. Transitionmetal compounds loose water and hydrazine in the range of 50–275 graduate C, and then undergo strong exothermic decomposition above 200 graduate C with no stable intermediate formation. Simple hydrazinium salt decomposes completely exothermally at 179 graduate C. The electronic spectra indicate the coordination number (CN) and geometry; CN 8 with square anti-prism for lanthanides and CN 6 with octahedral arrangement for transition metals. The geometry of the complexes is substantiated by their electronic spectra, magnetic