Gas-phase, liquid and solid complexes in the POCl3–FeCl3 system

Abstract

Raman and UV/VIS spectra were obtained at temperatures up to 625 K for the gas-phase complex formed over POCl₃–FeCl₃ molten mixtures under static equilibrium conditions. Raman spectra were also measured for molten POCl₃–FeCl₃ salt mixtures. A comparison of the spectral features of the POCl₃–FeCl₃ vapours with those of the POCl₃–FeCl₃ molten mixtures at 525 K indicates that the gas-phase complex has a 1 : 1 stoichiometry (POCl₃·FeCl₃) with characteristic vibrational bands at 95, 362, 530, 1218 and 1268 cm^–1. The data indicate a C_3v symmetry for the POCl₃·FeCl₃ complex. The energies of the Mâ†�L charge-transfer transitions in the electronic absorption spectra of the POCl₃·FeCl₃ gas-phase complex suggest, in agreement with the Raman data, that complexing occurs through oxygen bridging. The 1 : 1 POCl₃·FeCl₃ molecular liquid complex is the predominant species in equilibrium with POCl₃ and iron chloride at temperatures around 500 K. At temperatures below 450 K and in POCl₃-rich mixtures the ‘3 : 2’ ionic liquid compound [Fe(POCl₃)₆][FeCl₄]₃ was formed at the expense of POCl₃·FeCl₃(1). Two solids were identified at room temperature, yellow POCl₃·FeCl₃ and red [Fe(POCl₃)₆][FeCl₄]₃, and their Raman spectra have been recorded.