A trinuclear crystallochromic Cd(II) complex with zwitterionic coordination terminals: Network of metalorganic motifs through C-H⋯N and charge promoted N^∂+-H⋯N associations in solid State

In aqueous medium at pH 6, cadmium acetate dihydrate combines with 4,6-dimethylpyrimidine-2-thiol to form a centrosymmetric Cl, S-bridged complex having zwitterionic terminals. The zwitterionic nature of this complex is evidenced by its pH and conductance values in methanol solution. It crystallizes in the space group P2₁/c (Z = 4 asymmetric units, two molecules), each molecule being uncommonly characterized by a centric Cd(II)S ₂Cl₂N₂ as well as two acentric and anionic Cd(II)S₃ClN₂ coordination chromophores with counter cationic ligands. Relevant literature reports indicate a template relation between the structural designs of this complex and hydrated cadmium acetate, the metalorganic precursor. Packing of molecular motifs through weak C-H···N and strong charge-enhanced N^δ+- H···N interactions generate the crystal structure with numerous screw-glide related small voids. Attempt has been made to rationalize the crystallochromic nature of the complex (pale green in solution, pale orange while crystalline) by time dependent DFT and ZINDO/S studies. Graphical Abstract: In aqueous medium, cadmium acetate combines with 4,6- dimethylpyrimidine-2-thiol to form a centrosymmetric, trinuclear complex with zwitterionic terminals. The crystallochromic behaviour of this complex is investigated by quantum chemical treatment.[Figure not available: see fulltext.]