Infrared spectroscopy of geoporphyrins - I. Analysis of geochemically significant nickel(II) porphyrins

The infrared spectra of several nickel complexes of the Etioporphyrin (Etio ) class are presented. Included are the four isomers of classical etioporph yrin and three additional Etio compounds (13-desethyl etioporphyrin-III, 13 -desethyl-3-methyl etioporphyrin-III and deuteroetioporphyrin-IX) which hav e been previously identified from geological sources. Vibrational mode assi gnments are made based on comparison with recently published normal coordin ate analysis of the vibrational modes of nickel etioporphyrin-I and nickel etioporphyrin-III. Candidate 'marker' bands are identified for porphyrin st ructures with hydrogens at beta carbon positions. (C) 1998 Elsevier Science B.V. All rights reserved.