Square-planar and octahedral nickel complexes of an acylhydrazone ligand and the serendipitous isolation of a potential octahedral nickel acylhydrazone precursor

An investigation of the coordination chemistry of the (( E )- N ′-(4-hydroxybenzylidene)-4-hydroxybenzohydrazide) Schiff-based ligand ( HL ) towards Ni( ii ) acetate was performed using single crystal X-ray diffraction. The compounds [Ni(L) 2 ]·H 2 O ( 2 ) and [Ni( HL ) 2 (H 2 O) 2 ](CH 3 CO 2 ) 2 ·2CH 3 CH 2 OH ( 1a ) were isolated. Also, two solvated complexes of general formula [Ni(L) 2 ]·solvent ( 2a , 2b ) could be obtained as single crystals. Theoretical calculations were performed to evaluate the formation of the square-planar complex 2 from the octahedral 1a and to study the thermodynamic stability of the different compounds. The study of the reactivity of 2 with 1,2-di(4-pyridyl)ethylene (bpe) yielded single crystals of [Ni(L) 2 (bpe) 2 ]·solvent ( 3 ). An investigation of the coordination chemistry of the (( E )- N ′-(4-hydroxybenzylidene)-4-hydroxybenzohydrazide) Schiff-based ligand ( HL ) towards Ni( ii ) acetate was performed using single crystal X-ray diffraction.