Crystal and molecular structure of piperidinium μ-acetato-di-μ-1,2-benzenediolato- bis-1,2-benzenediolatoferrate(III), (C 5H 12N) 3 [(CH 3COO){Fe(C 6H 4O 2) 2} 2]: a compound of relevance to the 2Fe-active site of the respiratory protein hemerythrin

Abstract

The title compound is readily prepared as chunky purple-black crystals with the space group P 4 . The crystal structure was determined to a conventional R value of 0.088. The two FeO 6 octahedra in the anion share a common edge using oxygens of two equatorially disposed catechol dianions and one pair of adjacent coordination sites is bridged by the acetate moiety. Bidentate catecholates complete the coordination array. The Fe-O distances range from 1.95(3) to 2.03(3)Å with chelate bite angles of 82.3(9)° and 84.0(4)°. The basal Fe 2O 2 ring is folded about the O-O vector with dihedral angles of 150.0° and 149.4°. For the two dimers pres per asymmetric unit, Fe-Fe separations are 3.137(4) and 3.172(4)Å. Extensive hydrogen bonding creates rosettes of four anions and eight cations alternating about inversion centers. These structural data together with magnetic and spectroscopic properties of the dimer strongly suggest that such a (near) confacial bioctahedral structure is not an appropriate model for the active site of the respiratory protein hemerythrin.