Pseudo-symmetry, rotation- and inversion-twinning of a structure with dinuclear and trinuclear Cd complexes. CP-MAS-NMR and IR spectroscopies characterisation

Abstract

The structure of the complex [C18H30Cd3Cl6N18S12·2(C18H30Cd2Cl3N18S12)·CdCl4], or [L6Cd3Cl6·2(L6Cd2Cl3)·CdCl4], with L being 2-amino-5-(methylthio)-1,3,4-thiadiazole, C3H5N3S2, crystallizes in the trigonal polar space group R3. The crystal packing features three chemically distinct cadmium complex species with eight crystallographically independent Cd(II) ions distributed over two types of L ligand complexes with two and three Cd(II) centers, respectively, and a tetrachlorocadmate(II) ion. The coordination environment of the cadmium ions in the dinuclear and trinuclear complexes is a distorted octahedron. The tetrachlorocadmate(II) is disordered around a crystallographic threefold rotation axis, which is, in turn, inducing disorder onto the two methyl-thio groups in closest proximity to a CdCl4anion. The crystal under investigation was found to be twinned by rotational and inversion merohedry. In the higher symmetry setting, the trinuclear complex would feature exact inversion symmetry, and the two binuclear cationic complexes would be inversion counterparts of each other. The R3¯ symmetry is broken by a mismatch of less than 1Å between one pair of ligands L between the dinuclear cations, which feature slightly different rotational angles around the Cd ion in the otherwise symmetry equivalent complexes. This compound is also investigated by FT-IR and solid-state 13CCP-MAS NMR spectroscopies.