Imidazole Complexes of Iron and Manganese Tetraphenylporphyrins

Article abstract of DOI:10.1021/ja00542a011

The possible importance of partially or completely deprotonated imidazole ligation in the hemoproteins has led us to investigate imidazolate, Im^-, complexes of iron(II,III) and manganese(II,III) meso-tetraphenylporphyrin (TPP).Tetrabutylammonium imidazolate is a convenient reagent for the synthesis of isolable complexes.By steric and stoichiometric control the stereochemistry can be manipulated to give complexes with most possible coordination numbers and spin states. ^- is the first example of a low-spin Mn(III) porphyrin complex and demonstrates the greater ligand field strength of imidazolate over imidazole.The X-ray crystal structure of the polymer _n is reported.It shiws layers of parallel chains with alternate layers having their quasi-linear chains approximately orthogonal to each other.There is a short-short/long-long alternation of Mn-N(Im) bond lengths (2.186 (5) and 2.280 (4) Angstroem) interpreted as reflecting alternating predominantly low- and high-spin Mn(III) atoms along the polymeric chain.The average Mn-N(porph) bond distance is 2.019 (4) Angstroem.Crystal data: a = 20.073 (3) Angstroem, b = 16.885 (3) Angstroem, c = 22.590 (5) Angstroem, β = 104.36 (2) deg, space group C2/c, Z = 8 (Mn(Im)(TPP) units).