Spectral studies of transition metal complexes of dihydrobis(1-pyrazoyl)borate with some Lewis bases

Co(II), Ni(II) and Cu(II) complexes of dihydrobis(1-pyrazolyl)borate and their adducts with some Lewis bases have been prepared and characterized by elemental analyses, IR and UV–vis spectroscopic techniques. The adducts were either 1:1 or 1:2 complexes depending on whether the Lewis base was bidentate or monodentate. The results indicate that adducts with 1,10-phenanthroline were the most stable due to the chelating effect of the Lewis base. The order of reactivity of the complexes was determined to be Ni(H2BPz2)2 > Cu(H2BPz2)2 > CoH2(BPz2)2 > Co(H2BPz2)2. The effects of various solvents (i.e., benzene, chloroform and DMF) on the structure were studied. The solvents appear to minimally affect the visible spectra of Co(H2BPz2)2. The Ni(H2BPz2)2 and Cu(H2BPz2)2 adducts exhibit a four-coordinate structure in non-coordinating solvents. However, in coordinating solvents, such as DMF, the adducts exhibit six-coordinate structures.