Molecular structure of dimeric iron trichloride in the vapour phase as determined by electron diffraction

Abstract

The molecular structure of the title compound has been determined by gas-phase electron diffraction, the vapour composition being obtained by quadrupole mass spectrometry. The experimental data can best be approximated by a model with a puckered four-membered ring (C_2v symmetry). This deviation from D_2h symmetry may be a consequence of large-amplitude vibrations around an imaginary axis connecting the two bridging chlorine atoms. The bond lengths and angles for the puckered-ring model are r_a(Fe–Cl)(terminal) 2.127(4), r_a(Fe–Cl)(bridge) 2.326(5)Å, Cl_t–Fe–Cl_t 124.3(7), and Cl_b–Fe–Cl_b 90.7(4)°. The bond lengths and force constants indicate that the terminal Fe–Cl bonds are considerably stronger than the bridging ones.