X-RAY-ABSORPTION SPECTROSCOPIC STUDY OF THE STRUCTURE AND BONDING IN M[B(3-ISOPROPYLPYRAZOL-1-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 co mpare the local structure about the iron(II) ion With that of the othe r divalent transition metal ions. Earlier Mossbauer spectral studies h ave 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 exte nded X-ray absorption fine structure analysis of the absorption spectr a 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-fro m electronic transitions of the metal Is electron into the differing c rystal field split states of the divalent metal ions.