Enthalpies of Formation of Chromium Fluorides. II. Higher Fluorides CrF4, CrF5, and CrF6

The paper presents critical analysis of experimental data, including the most recent published data on the gas-phase and heterogeneous equilibria of reactions involving higher chromium fluorides. The results of the analysis are presented as the enthalpies of formation (kJ/mol) of chromium fluorides in the condensed and gas phases: Δ f H °(CrF 4 , cr, 298.15 K) = –1202.5 ± 12.8; Δ f H °(CrF 4 , a, 298.15 K) = –1193.5 ± 13.1; Δ f H °(CrF 4 , g, 0) = –1098.9 ± 12.1; Δ f H °(CrF 5 , cr, 298.15 K) = –1243.8 ± 12.4; Δ f H °(CrF 5 , g, 0) = –1150.5 ± 12.1. The standard enthalpy of formation of chromium hexafluoride in the gas phase was determined to be Δ f H °(CrF 6 , g, 0) = –1077 kJ/mol. The possibility of existence of the mixed crystalline fluoride Cr IV Cr V F 9 was demonstrated and its enthalpy and entropy of formation from crystalline CrF 4 and CrF 5 were estimated to be ∆ r H °(298.15 K) = –12.6 kJ/mol, ∆ r S °(298.15 K) = –1.5 J/(mol K). The recommended values provide explanation for the thermal behavior of higher chromium fluorides and the possibility of conducting some procedures with them in the processes that are qualitatively described in available literature.