XAFS AND CRYSTALLOGRAPHIC STUDIES OF NI(II) PORPHYRINS IN SINGLE-CRYSTALS AND SOLUTION

Nickel porphyrins serve as models for the active sites of several biol ogical processes. Crystallographic and EXAFS results for a Ni meso-tet rapropyl porphyrin (NiTPrP) yield different Ni-N distances in solution and in the solid state. The Ni-N distances determined by single cryst al polarized XAS and X-ray diffraction agree well. Polarized XANES exp eriments further establish that the pre-edge feature observed in squar e planar Ni(II) complexes is a 1s-4pz transition. The single crystal a nd solution EXAFS results demonstrate that conformational variations o f the porphyrin macrocycle can readily be imposed by environmental and /or packing forces and can thereby modulate the chemical and physical properties of porphyrinic chromophores and prosthetic groups.