COBALT(II) TRIAZENE 1-OXIDE BIS(CHELATES) - A CASE OF PLANAR (LOW-SPIN) TETRAHEDRAL (HIGH-SPIN) ISOMERISM

High- and low-spin cobalt(II) triazene 1-oxide bis(chelates) have been isolated. The low-spin complexes possess square-planar structure whil st the high-spin complexes are tetrahedral. The molecular structure of high-spin [Co(OMeN3C6H4Me-4)2] has been determined: triclinic, space group P1BAR, Z = 2, a = 7.970(5), b = 10.174(5), c = 11.676(5) angstro m, alpha = 87.18(4), beta = 74.31 (4) and gamma = 74.06(4)degrees. For some complexes the isolation of both planar (low-spin) and tetrahedra l (high-spin) isomers or of their conglomerates is possible depending on the synthesis conditions. The crystal structure of square-planar [N i(OMeN3C6H4Me-4)2], which is isomorphous with the low-spin isomer of [ Co(OMeN3C6H4Me-4)2], has been determined: triclinic, space group P1BAR , Z = 1, with a = 7.495(2), b = 7.694(5), c = 8.612(3) angstrom, alpha = 64.64(5), beta = 87.84(2) and gamma = 78.64(3)degrees. The complexe s exhibit a planar-tetrahedral equilibrium in non-co-ordinating solven ts, the DELTAAH(formal) and DELTAS(formal) values of which, determined from solution magnetic susceptibility measurements, are in the range 1-1 5 kJ mol 1 and 5-30 J K-1 mol-1, respectively. The electrochemical properties of the complexes are given.