Cyano-bridged molecular squares: Synthesis and structures of [Ni(cyclen)]2[Pt(CN)4]2·6H2O, [Ni(cyclen)]2[Ni(CN)4]2·6H2O and [Mn(cyclen)]2[Ni(CN)4]2·6H2O

Three cyano-bridged molecular squares, [Ni(cyclen)]2[Pt(CN)4]2·6H2O (1), [Ni(cyclen)]2[Ni(CN)4]2·6H2O (2) and [Mn(cyclen)]2[Ni(CN)4]2·6H2O (3) (cyclen=1,4,7,10-tetraazacyclododecane) have been synthesized and characterized by X-ray crystallography. The magnetic data suggest that there is very weak ferromagnetic intradimer interaction and an even weaker interdimer antiferromagnetic coupling in (1) and (2).