Thermal Behavior of the Heteroligand (µ₃-Fluoro)hexakis(µ₂-trifluoroacetato)tris(pyridine)tricobaltate(II) Tetramethylammonium Complex (NMe₄)[Co₃F(TFA)₆(Py)₃]

Abstract—A new trinuclear triangular cobalt complex (NMe₄)[Co₃(μ₃F)(TFA)₆(Py)₃] (I) is synthesized by crystallization from a methanol solution. The crystal structure of complex I is solved by single-crystal X-ray diffraction analysis (CIF file CCDC no. 2151075). The Knudsen effusion method combined with mass spectral analysis of gaseous vaporization products shows that the heating of complex I under reduced pressure results in the removal of (CH₃)₄NF as (CH₃)₃N and CH₃F and of pyridine to form anhydrous cobalt trifluoroacetate Co(CF₃COO)₂, which sublimes on further heating to the monomer and dimer. The decomposition of Co(CF₃COO)₂ with the formation of CoF₂ and release of CO₂ and COF₂ occurs along with sublimation. Experiments on the iso- and polythermal vaporization makes it possible to calculate the partial pressures of the major gaseous products, to determine the standard enthalpies of sublimation of the monomer (137.9 ± 12.2 kJ/mol) and dimer (147.0 ± 21.6 kJ/mol) in a temperature range of 460–540 K, and to find the enthalpy of dissociation of the dimer (128.8 ± 25.8 kJ/mol). The study of the thermal stability of complex I in an argon flow (p = 1 atm) by gravimetry combined with mass spectral analysis of gaseous products confirms the three-stage decomposition of complex I. Unlike heating in vacuo, no sublimation of Co(TFA)₂ is observed under these conditions, and the decomposition of Co(TFA)₂ results in the formation of CoF₂ and is accompanied by the release of gaseous (CH₃)₃N, CH₃F, Py, CO, CO₂, CHF₃, СF₃COF, (CF₃CO)₂O, CF₃COCF₃, and C₂F₄. The presence of moisture and oxygen traces in argon leads to a decrease in the content of easily hydrolyzed products and formation of the oxidation and hydrolysis products: H₂O, HF, and CF₃COOH.