(6), respectively (Hhap = o-hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO 4 ) 2 ·6H 2 O or Ni(NO 3 ) 2 ·6H 2 O to yield [Ni(hap) 2 ] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, Ni II possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group.