Temperature effects on structure: Five-coordinate (nitrosyl)(tetratolylporphinato)iron(II)

Abstract

We have prepared crystals of [Fe(TTP)(NO)] (TTP = tetratolylporphyrin), a five-coordinate nitrosyl complex and determined its crystal and molecular structure at two temperatures. The crystal structure at 100 K reveals two independent molecules in the asymmetric unit of the structure. One molecule is completely ordered and the second molecule has a moderately disordered nitrosyl ligand. Both molecules show similar structural features: a substantial off-axis tilt of the Fe–N(NO) bond and an asymmetry of the equatorial Fe–N[Formula: see text] bonds that is correlated with the tilt. The axial Fe–N(NO) bond distances are 1.7230 (9) and 1.7210 (10) Å; the Fe–N–O bond angles are 141.62 (8) and 140.04 (10)[Formula: see text]. Determination of the structure at ambient temperature (293 K) showed an unexpected phase change, a crystal structure with one molecule per asymmetric unit containing the superposition of the two molecules at lower temperature. However, there was an increase in the NO disorder.