A novel сalcium trifluoroacetate structure

Objectives. The study was devoted to considering the features of the synthesis and crystal structure of calcium trifluoroacetate Ca₂(CF₃COO)₄·8CF₃COOH and investigating the products of its thermal behavior.Methods. The compositions of the proposed structural form were characterized by various physicochemical methods (X-ray diffraction, IR spectroscopy), and the products of thermal decomposition were determined under dynamic vacuum conditions.Results. The reaction between calcium carbonate and 99% trifluoroacetic acid yielded a new structural type of calcium trifluoroacetate Ca₂(CF₃COO)₄·8CF₃COOH (I) in the form of colorless prismatic crystals unstable air. X-ray diffraction results confirmed the composition I: space group P2₁, with unit cell parameters: a = 10.0193(5) Å, b = 15.2612(7) Å, c = 16.3342(8) Å, β = 106.106(2)°, V = 2399.6(2) ų, Z = 2. The structure is molecular, constructed from Ca₂(CF₃COO)4·8CF₃COOH dimers. The end molecules of the trifluoroacetic acid were involved in the formation of intramolecular hydrogen bonds with oxygen atoms of the bidentate bridging anions CF₃COO⁻. There were strongly pronouncedsymmetric and asymmetric absorption bands of COO and CF₃-groups in the IR spectrum of the resulting compound in the range of 1200–1800 cm⁻¹. The definite peak of the oscillation of the OH-group at 3683 cm⁻¹ corresponds to the trifluoroacetic acid molecules present in the structure. The broadpeak of the valence oscillations in the range of 3300–3500 cm⁻¹ is caused by the presence of intramolecular hydrogen bonds. Decomposition began at 250°C and 10⁻² mm Hg with calcium fluoride CaF₂ as the final decomposition product.Conclusions. We obtained a previously undescribed calcium–trifluoroacetic acid complex whose composition can be represented by Ca₂(CF₃COO)₄·8CF₃COOH. The crystal island structure is a dimeric molecule where the calcium atoms are bound into dimers by four trifluoroacetate groups. The complex was deposited in the Cambridge Structural Data Bank with a deposit number CCDC 2081186. Although the compound has a molecular structure, thermal decomposition leads to the formation of calcium fluoride characterized by a small particle size, which may further determine its applications.