Crystal Structures and Thermal Behavior of Bis(dibenzyldimethylammonium) Tetrabromometallates(II) [M = Mn(II), Co(II) and Zn(II)] and Their Solvates

Abstract

Six new A₂MBr₄ structures [A = dibenzyldimethylammonium cation,M = Mn(II), Co(II) or Zn(II)] were crystallized with or without solvent molecules from acetonitrile, methanol and/or aqueous solutions. The isomorphous compounds [(Bz₂Me₂N)₂][MnBr₄]·CH₃CN·H₂O (1) and [(Bz₂Me₂N)₂]-[ZnBr₄]·CH₃CN·H₂O (4) crystallize in the triclinic space group P1̄ from acetonitrile solutions. The solvent molecules participate in the hydrogen bonding network inside the crystal structure. [(Bz₂Me₂N)₂][CoBr₄]·0.5CH₃CN (2) crystallizes from an acetonitrile solution in the monoclinic space group P2₁/c. The solvent molecules fill the voids of the crystal structure. Compound 2 is isostructural with the previously reported compounds [(Bz₂Me₂N)₂][MCl₄]·0.5CH₃CN with M = Mn(II), Co(II), Ni(II), Cu(II) or Zn(II). [(Bz₂Me₂N)₂][CoBr₄] (3) and [(Bz₂Me₂N)₂][ZnBr₄] (5a) crystallize from a methanol solution in the monoclinic space group P2₁/c without solvents. A polymorph of compound 5a, [(Bz₂Me₂N)₂][ZnBr₄] (5b), was crystallized from aqueous solution in the monoclinic space group P2₁/c. The packing of the components of the two polymorphs differs clearly. One cation of 5a appears in the W-conformation whereas the other cation of 5a and both cations of 5b appear in twisted conformations. In addition to the ionic interactions between the ion pairs, the packing of the compounds is stabilized by hydrogen bonds and weak intermolecular π-π interactions in all cases. The compounds melt around 200 °C and decompose mainly in two steps just above the melting point. Slow evaporation of solvents is observed both in the TG and DSC diagrams of the solvates (1, 2 and 4) below 100 °C.