Structural diversity and spectral and thermal properties of the first alkaline earth metal tetracyanidoborates: [Mg(H2O)6][B(CN)4]2, [Mg(H2O)2][B(CN)4]2, [Mg(DMF)6][B(CN)4]2, [Ca(H2O)3][B(CN)4]2, and [Ca(H2O)2(CH3CN)][B(CN)4]2

Abstract

The first members of tetracyanidoborate salts with alkaline earth cations, [Mg(H₂O)₆][B(CN)₄]₂ (1), [Mg(H₂O)₂][B(CN)₄]₂ (2), [Mg(DMF)₆][B(CN)₄]₂ (3), [Ca(H₂O)₃][B(CN)₄]₂ (4), and [Ca(H₂O)₂(CH₃CN)][B(CN)₄]₂ (5), were synthesized. Their structures, obtained by single crystal X-ray diffraction, IR- and Raman spectra, as well as their thermal properties were determined. Whereas 1 and 3 consist of isolated ions, the other three compounds comprise coordination polymers. IR and Raman spectra give information about the coordination modes of the respective tetracyanidoborate anions. Calorimetric measurements show that the coordinated solvent molecules can be removed at elevated temperatures and anhydrous/solvent free compounds form. The anhydrous compounds are thermally very stable. They do not start to decompose below 500 °C. No melting is observed below decomposition.