Crystal Structure of Bis(4-methylimidazole)tetraphenylporphyrinatoiron(III) Chloride and Related Compounds. Correlation of Ground State with Fe−N Bond Lengths

The crystal structure of the title compound is presented and shown to be one of a class of low-spin iron porphyrin complexes having a ground-state electronic configuration of (d xy )2(d xz )2(d yz )1. If their Fe−N bond lengths (average N-porphyrin plotted against average N-axial) are considered, this class of low-spin iron(III) porphyrins of general formula [FeIIIPor(L)2]+X- and of 2B ground state is shown to be distinctly different crystallographically from a similar class of compounds with the same general formula but with a 2E or a (d xy )2(d xz ,d yz )3 ground state. A third group of compounds with the same general formula have a (d xz ,d yz )4(d xy )1 ground state and again are in a different region of the plot. Compounds showing intermediate properties can be forecast from the simple relationship presented in this work. The electron paramagenetic resonance data are shown to be dependent on the ground state, and those of configuration (d xy ) 2 (d xz ,d yz )3 and the 2B ground state obey a correlation previously suggested in the literature.