Reversible switching of coordination modes of nickel(ΙΙ) complexes using a hemilabile 4,7-diazadecanediamide ligand

The reaction of NiCl2·6H2O with a hemilabile diaminodiamide ligand 4,7-diazadecanediamide gave a pale blue compound [Ni(C8H18N4O2)(H2O)2]·2Cl (1). In basic solution, 1 was transformed to a yellow species [Ni(C8H16N4O2)]·3H2O (2) by the Ni–O to Ni–N bond rearrangement at two amide sites of the complex. Structures of 1 and 2 were characterized by single-crystal X-ray diffraction analysis. Structural data for 1 indicated that the nickel atom adopts a six-coordinated N2O4 environment and gives an octahedral geometry. The structure of 2 showed that the nickel atom adopts a four-coordinated N4 environment, giving a square-planar geometry. Compounds 1 and 2 are structurally switchable in response to pH in an aqueous solution. The results presented could be useful in the design of new Ni(II)-based switching materials.