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Communications
Ring-Induced Rhombicity in Chlorin and Isobacteriochlorin Complexes of Square-Planar Iron(I1)
Sir:Our interest in the ~t r u c t u r a l ,~~~ and properties of iron chlorins and isobacteriochlorins derives from their occurrence in a wide variety of heme proteins and enzymes.6 Magnetic properties are of fundamental importance to biochemists who isolate and work with heme proteins, because data such as EPR and Mossbauer spectra, paramagnetic 'H N M R spectra, and effective magnetic moments have been used to eludicate the molecular and electronic structure of the heme active site, usually by comparison with well-defined iron porphyrinEarly EPR studies on model compounds found no significant macrocycle effect on the spin state or g values for high-spin Fe(II1) derivatives or for Co(I1) or Cu(1I) derivatives, supporting the view that metalloporphyrins are competent magnetic models for metallochlorin-and metalloisobacteriochlorinantaining protein^.'^^'^ (1) Stolzenberg, A. M.; Straws, S. H.; Holm, R. H. J. Am. Chem. SOC. (2) Straws, S. H.; Holm, R. H. Inorg. Chem. 1982, 21, 863-868. (3) Straw, S. H.; Silver, M. E.; Ibers, J. A. J. Am. Chem. Soc. 1983,105, (4) Straws, S. H.; Silver, M. E.; Long, K. M.; Thompson, R. G.; Hudgens, R. A.; Spartalian, K.; Ibers, J. A. J. Am. Chem. SOC. 1985, 107, 1981, 103, 4763-4778. 4 108-4 109. 4207-4215. 25n P -/ r Pe(TPC) o r t h o . rg 16 :TPC) m e t a , metal Y (5) (a) Andersson, L. A.; Loehr, T. M.; Lim, A. R.; Mauk, A. G. J. Bioi. Chem. 1984, 259, 15 340-15 349. (b) Koland, J. G.; Miller, M. J.; Gennis, R. B. Biochemisfry 1984, 23, 445-453. (c) Timkovich, R.; Cork, M. S.; Gennis, R. B.; Johnson, P. Y.
