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 multidentate chelating side arms { 3,5-(R2NCH2)(2)C3N2H2; R2N = [Me2N(CH2)(3)](2)N (HL1) or (Et2NCH2CH2)(2)N (HL2)} have been prepared and characterised. 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)][BPh4](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- starting material in both cases. While the longer side arms in Ib allow for an exogenous bridging position of the fluoride, an additional water molecule is incorporated in 2b to form an FHO(H) moiety with an unusually short F-H-O bridge between the two cobalt centres, Evidence is reported for the reversible extrusion of the water molecule from 2b. Treatment of 2b with KBr or NaN3 yielded the respective bromide-and azide-bridged 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 studied in the temperature range 8-200 K. Complexes Ib, 2b, 3 and 4 were also characterised by means of X-ray crystallography.