OLIGOMETALLIC COBALT 3,5-DIMETHYLPYRAZOLATE COMPLEXES - SYNTHESIS, STRUCTURAL AND MAGNETIC STUDIES

Three oligometallic 5-dimethylpyrazolate (dmpz) bridged Co(II) compounds have been synthesized and characterized spectroscopically: dimeric [Co(dmpz)2(Hdmpz)]2. the related oligometallic compound, Co(dmpz)2 . 0.344(Hdmpz), and the trimetallic [Co(dmpz)2Cl(Hdmpz)]2Co. The first and last of these compounds have been studied magnetically and by single crystal X-ray diffraction. Crystals of [Co(dmpz)2(Hdmpz)]2 are orthorhombic, = 17.022(1), b = 29.224(2), c = 13.576(3) angstrom, Z = 8, space group Fddd: and those of [Co(dmpz)2Cl(Hdmpz)]2Co are triclinic, a = 11.742(3), b 18.604(4), c = 8.950(2) angstrom, alpha = 99.76(2)-degrees, beta = 102.32(2)-degrees, gamma = 93.36(2)-degrees, Z = 2, space group P1BAR. The structures were solved by the Patterson method and were refined by full-matrix least-squares procedures to R = 0.035 and 0.042 (R(w) = 0.034, 0.047) for 938 and 3853 reflections with I greater-than-or-equal-to 3sigma(F2), respectively. Magnetic susceptibility studies on the dimeric and trimetallic complex show them to exhibit antiferromagnetic behaviour. Analysis of the magnetic data (2-300 K) for the trimetallic complexes reveals antiferromagnetic coupling between the terminal and central Co(II) ions with J (Heisenberg) almost-equal-to -3 cm-1. Either intramolecular next-nearest neighbour or intermolecular antiferromagnetic exchange is also present in this compound. The dimeric complex shows significant antiferromagnetic exchange between cobalt centres. Susceptibility data over the range 12-300 K are adequately modelled with the Ising S = 1/2 dimer model (J almost-equal-to -23 cm-1).