TUNING THE METAL-METAL SEPARATION IN PYRAZOLATE-BASED DINUCLEAR COMPLEXES BY THE LENGTH OF CHELATING SIDE ARMS

Six dinuclear cobalt(II) complexes of pyrazolate ligands with multiden tate chelating side arms { 3,5-(R2NCH2)(2)C3N2H2; R2N = [Me2N(CH2)(3)] (2)N (HL1) or (Et2NCH2CH2)(2)N (HL2)} have been prepared and character ised. The reaction of L-1 and L-2 with 2 equivalents of [Co(MeCN)(6)][ BF4](2) and NaBPh4 proceeds via the isolable compounds [Co2L1(BF4)][BP h4](2) 1a and [Co2L2(BF4)][BPh4](2) 2a finally to afford the dinuclear complexes [(Co2LF)-F-1][BPh4](2) 1b and [Co2L2(F)(H2O)I[BPh4](2) 2b, respectively, where a fluoride has been abstracted from the BF4- start ing material in both cases. While the longer side arms in Ib allow for an exogenous bridging position of the fluoride, an additional water m olecule is incorporated in 2b to form an FHO(H) moiety with an unusual ly short F-H-O bridge between the two cobalt centres, Evidence is repo rted for the reversible extrusion of the water molecule from 2b. Treat ment of 2b with KBr or NaN3 yielded the respective bromide-and azide-b ridged complexes 3 and 4, where in the latter case the azide adopts a mu-1,3-bridging mode. The magnetic properties of 3 and 4 have been stu died in the temperature range 8-200 K. Complexes Ib, 2b, 3 and 4 were also characterised by means of X-ray crystallography.