Ni(salen): a System That Forms Many Solvates with Interacting Ni Atoms

Recrystallization of [N,N’-Ethylene-bis(salicylideneiminato)]-nickel(II) [Ni(salen)] has been carried out from a large selection of solvents. Crystals can be either solvent free or solvates. This study is based on X-ray crystal structure determinations, which include the redetermination of Ni(salen) at low-temperature, the finding of three new solvates of Ni(salen), that is, Ni(salen)·CH2Cl2, Ni(salen)·AcOH, and Ni(salen)·1.5MeOH, and the reexamination of the known solvate Ni(salen)·chloroform at low- and room-temperature. The crystal structures of Ni(salen) and its solvates are stabilized by salen···salen and/or solvent···salen and/or solvent···solvent intermolecular interactions. A special case is the crystal structure of Ni(salen)·1.5MeOH where the salen/solvent ratio is 2:3 rather than 1:1. For all solvated structures, the solvent and Ni(salen) molecules always interact via Dsolvent−H···Osalen (Dsolvent = C, O) hydrogen bond interactions, the strengths of which depend on the solvent of recrystallization. All structures are characterized by weak Ni−Ni interactions, which are found either in centrosymmetric dimeric units or along one-dimensional chains. Such interactions are favored because of the d8 electronic configuration of Ni(II) and the pseudoplanar geometry of Ni(salen).