Synthesis of bimetallic trifluoroacetates through a crystallochemical investigation of their monometallic counterparts: the case of (A, A′)(CF3COO)2·nH2O (A, A′ = Mg, Ca, Sr, Ba, Mn)

Abstract

Owing to their potential as single-source precursors for compositionally complex materials, there is growing interest in the rational design of multimetallic compounds containing fluorinated ligands. In this work, we show that chemical and structural principles for a materials-by-design approach to bimetallic trifluoroacetates can be established through a systematic investigation of the crystal-chemistry of their monometallic counterparts. A(CF₃COO)₂·nH₂O (A = Mg, Ca, Sr, Ba, Mn) monometallic trifluoroacetates were employed to demonstrate the feasibility of this approach. The crystal-chemistry of monometallic trifluoroacetates was mapped using variable-temperature single-crystal X-ray diffraction, powder X-ray diffraction, and thermal analysis. The evolution with temperature of the previously unknown crystal structure of Mg(CF₃COO)₂·4H₂O was found to be identical to that of Mn(CF₃COO)₂·4H₂O. More important, the flexibility of Mn_x(CF₃COO)_2x·4H₂O (x = 1, 3) to adopt two structures, one isostructural to Mg(CF₃COO)₂·4H₂O, the other isostructural to Ca₃(CF₃COO)₆·4H₂O, enabled the synthesis of Mg–Mn and Ca–Mn bimetallic trifluoroacetates. Mg_0.45Mn_0.55(CF₃COO)₂·4H₂O was found to be isostructural to Mg(CF₃COO)₂·4H₂O and exhibited isolated metal–oxygen octahedra with Mg²⁺ and Mn²⁺ nearly equally distributed over the metal sites (Mg/Mn: 45/55). Ca_1.72Mn_1.28(CF₃COO)₆·4H₂O was isostructural to Ca₃(CF₃COO)₆·4H₂O and displayed trimers of metal–oxygen corner-sharing octahedra; Ca²⁺ and Mn²⁺ were unequally distributed over the central (Ca/Mn: 96/4) and terminal (Ca/Mn: 38/62) octahedral sites.