The structures, solvent-free synthesis and interconversions of the complexes [MCl2(CEAP)2] and their hydrogen-bonded salts [CEAPH]2[MCl4] {M = Zn, Co and Hg, CEAP = 4-[N,N-bis(2-cyanoethyl)amino]pyridine}

Discrete metal complexes, [MCl2(CEAP)2] {M = Zn (1), Co (2) and Hg (3), CEAP = 4-[N,N-bis(2-cyanoethyl)amino]pyridine} and their hydrogen-bonded salts [CEAPH]2[MCl4] {M = Zn (4), Co (5) and Hg (6), CEAPH = 4-[N,N-bis(2-cyanoethyl)amino]pyridium} were prepared using CEAP or CEAP·HCl ligands and metal chlorides (molar ratio = 2:1) by both solvent-thermal synthesis method and solvent-free method. The crystal structure and powder X-ray diffraction (PXDR) studies revealed that the discrete metal complexes 1–3 could be converted into their hydrogen-bonded salts 4–6 respectively by absorbing HCl vapor in solid-gas station and these salts except for 6 could be converted back to their corresponding discrete metal complexes by grinding with KOH in solid station.