X-ray Absorption Spectroscopic Study of the Structure and Bonding in M[B(3-isopropylpyrazol-l-yl)₄]₂, Where M is Fe, Co, Ni, Cu, and Zn

An X-ray absorption spectroscopic study of M[B(3-isopropylpyrazol-1-yl)₄]₂, where M is Fe, Co, Ni, Cu, and Zn, has been undertaken to compare the local structure about the iron(II) ion with that of the other divalent transition metal ions. Earlier Mossbauer spectral studies have indicated the presence of an unusual displacement of the iron ion within its coordination sphere, especially at temperatures above 160 K; a displacement which might or might not occur in the cobalt complex whose X-ray structure is normal or in the remaining complexes. An extended X-ray absorption fine structure analysis of the absorption spectra reveals very similar coordination environments and metal to nitrogen bond lengths for the various complexes. The preedge X-ray absorption does reveal differences in the complexes, differences which result from electronic transitions of the metal Is electron into the differing crystal field split states of the divalent metal ions.