The cyclic structure of 2-phenyl-2-(2-pyridyl)imidazolidine (1) derived from the condensation of 1,2-diaminoethane and 2-benzoylpyridine has been confirmed by X-ray crystallography. Reaction of (1) with salts of nickel(II) and copper(II) leads to metal induced ring opening and the formation of complexes containing the tridentate ligand (L). The formulae of the complexes derived from NiX2 and CuX2 are [NiL2]X-2 and [CuLY]X-2 (X=ClO4-, Y = H2O, CH3CN and N-3(-)). Crystal structures were obtained for (1), [NiL2][ClO4](2), [CuL(CH3CN)][ClO4](2), [CuL(H2O)][NO3](2) and [CuLN3][ClO4]. (C) 2008 Elsevier Ltd. All rights reserved.