The effect of substituents at C2/N1 atoms of salicyladehyde and 2-hydroxyacetophenone based thiosemicarbazones on the nature of nickel(II) complexes with 1,10-phenathroline and terpyridine as co-ligands

Abstract

Coordination chemistry of nickel(II) with salicyladehyde and 2-hydroxyacetophenone based thiosemicarbazones {(2-OH-5-X-C6H3)-C2(R2)=N3-N2H-C1(=S)-N1HR3, LH2} and 1,10-phenanthroline (phen)/terpyridine (terpy) as a co-ligand has been investigated by varying the substituents at C2 (X = H, Me, MeO; R2 = H, Me) and N1 (R3 = H, Me, Et, Ph) atoms of thiosemicarbazones. Reactions of nickel(II) acetate with various thio-ligands, LH2 {X = H, R2 = H: L1H2 (R3 = H), L2H2 (R3 = Me), L3H2 (R3 = Et), L4H2 (R3 = Ph); X = Me, R2 = H, L5H2 (R3 = Me), L6H2 (R3 = Et); X = H, R2 = Me, L7H2 (R3 = Me), L8H2 (R3 = Et); X = MeO, R2 = H, L9H2 (R3 = Me)} have yielded dinuclear, [Ni2L2(phen)(D)] (D = H2O, L2− = L1–L4, 1–4; MeOH, L5, L6, 5, 6) and tetranuclear [Ni4L4(phen)2] (L2− = L7, 7, L8, 8) complexes in the presence of phen as a co-ligand, while in the presence of terpy as a co-ligand, only mononuclear [NiL(terpy)] (L2− = L2 , 9; L4, 10; L9, 11) complexes were formed. All these complexes have been characterized with the help of analytical data, spectroscopic techniques (IR and UV-visible), magnetic moments and single crystal X-ray crystallography (2, 3, 5, 6, 8–11). Thio-ligands undergo deprotonation of OH and N2H groups during complexation and coordinate to the metal centers as dianions in these complexes. In dinuclear complexes 1–6, one metal center is octahedral and second metal center is square planar (6, 4-coordination pair) and one site is occupied by H2O or MeOH ligands, thus completing six coordination. Tetranuclear complexes, 7 and 8, have 4, 6, 6, 4-coordination pattern and finally mononuclear complexes, 9–11, are octahedral with the thio-ligands forming O, N3, S- chelation and terpyridine coordinating as a terdentate ligand. All complexes are paramagnetic with magnetic moment (μeff) values in the range, 2.92–3.12 BM. Complexes 1–8 represent a less common type of dinuclear coordination pairs/tetranuclear oligomers in the metal-thiosemicarbazone chemistry.