Synthesis, characterization, and thermal properties of N,N,N′,N′-tetramethyl guanidinium tribromidocadmate(II) exhibiting an unusual coordination geometry

International audience ; The reaction of N,N,N′,N′-tetramethyl guanidine, NHC(N(CH3)2)2 (TMGD) and CdBr2·4H2O in ethanol led to the formation of [TMGDH][CdBr3] (1), which crystallizes in the monoclinic space group Cc with Z=4, a=8.9079(7) Å, b=18.5810(14) Å, c=8.1637(6) Å, β=107.953(3)°, and V=1285.44(17) Å3. In the crystal lattice, 1 is organized in one-dimensional anionic chains of CdBr4 tetrahedra sharing two corners. To our knowledge, this is the first evidence of such a coordination geometry described for a bromocadmate derivative. The negative charges are compensated by monoprotonated N,N,N′,N′-tetramethyl guanidinium cations (TMGDHs), which are in N-H hydrogen bonding interaction with the terminal bromide atoms of the anionic chain. The title compound was also characterized by middle and far-infrared spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The elemental analysis corroborates as well the X-ray elucidation. Multinuclear solution nuclear magnetic resonance (NMR) spectroscopic measurements (1H, 13C{1H}) were conducted in D2O.