A rational synthesis of a new discrete anion [trans-CdBr4Cl2]4− and its comparison with newly synthesized anion [CdBr6]4−

Two new cobalt(III) complex salts, [Co(en)3]2[CdBr6]·Br2·2H2O (1) and [Co(en)3]2[trans-CdBr4Cl2]·Br2·2H2O (2) have been synthesized while attempting to synthesize [CdBr5]3− complex ion. The newly synthesized complex salts have been characterized by elemental analyses, spectroscopic techniques (e.g. UV/Visible, IR and NMR), solubility product, conductance measurements and luminescent studies. Both the complex salts 1 and 2 crystallize in monoclinic crystal system with space group P21/c. Single crystal X-ray structure determination revealed the presence of ionic structures and discrete anions [CdBr6]4− and [trans-CdBr4Cl2]4− in 1 and 2, respectively. This is the first report of synthesis and single crystal X-ray structure determination of discrete and mixed halogenocadmate(II) anion, [trans-CdBr4Cl2]4−. The crystal lattices of both complex salts are stabilized by N–H⋯Br/Cl, C–H⋯Br/Cl and O–H⋯Br hydrogen bonds besides electrostatic forces of attraction.

► Syntheses of two new Co(III) complex salts have been described.
► The new anion [trans-CdBr4Cl2]4− has been isolated for first time.
► Complex salts have been characterized by single crystal X-ray crystallography.
► Non-covalent interactions are playing crucial role in lattice stabilization.