Design of metamagnetic layered cobalt(II) coordination polymers with controlled magnetic phase transitions.

Three coordination compounds of formula [CoCl2(N,N')]n [N,N' = 4,4'-bipyridine (4,4'-bpy), (Cobpy); trans-4,4'-azopyridine (t-apy), (Coapy); and trans-1,2-bis(4-pyridyl)ethylene (t-bpee), (Cobpee)] have been prepared using solvothermal procedures. They have been characterized by different techniques, including the ab initio crystal structure determination of Cobpee. The structures of Cobpy and Cobpee are formed by octahedral trans-CoCl4N2 nodes, which construct rectangular grid layers that are stacked in an ABAB pattern. The three complexes show a similar metamagnetic behavior, which suggests that Coapy displays a layered structure equally built. The magnetic phase transitions of the compounds from an antiferromagnetic state to a paramagnetic-like or ferromagnetic-like state have been analyzed, and magnetic phase diagrams are provided. The use of N,N'-donor ligands with different lengths allows controlling the strength of the interchain interactions and the critical temperature (T c) and critical magnetic field (H c) of the metamagnetic phase transitions.