The Magnetic Properties and Chemical Structures of Solid Haemins

Abstract

The magnetic properties of protoporphyrin and a representative group of its iron derivatives have been studied in order to gain more detail of their structural characteristics. The greater diamagnetism of protoporphyrin than that expected on the basis of Pascal's additivity law indicates an increased stability of pyrrole units when linked in resonating porphin form. The majority of iron-porphyrin complexes possess ionically bound metal when crystallized from non-aqueous liquids. In the presence of water, the lower values of magnetic moment reveal that iron tends to form covalent bonds. The iron bonds of various haematin compounds are compared with those of simple iron hydroxides and ferritin. There is strong evidence to support the assumption that haematin in dilute al6ali possesses covalent iron bonds involving only one d eigen-function. In concentrated alkali the magnetic moment of haematin (2.4) indicates that six covalent iron bonds should be directed to the corners of either an octahedron or a trigonal prism, but the steric restrictions imposed by the planar porphyrin nucleus and the covalent bond angle of oxygen make it difficult to assign such specific bond directions to the metal.