Synthesis and investigation of nickel (II) 4-substituted 2,6- dichlorophenolates.

Abstract

Monodentate or bidentate ligands (L) of nitrogen and phosphorus were used in the synthesis of nickel(II) complexes of the type M({dollar}\rm OC\sb6H\sb2Cl\sb2X)\sb2(L)\sb{lcub}n{rcub}{dollar} (X = Cl, Br, H). Nuclear quadrupole resonance (NQR) spectroscopy was utilized to examine the secondary bonding of ortho-chlorines of 2,4,6-trichlorophenolate, 2,6-dichlorophenolate, and 4-bromo-2,6-dichlorophenolate ions to the nickel in the presence of various ligands. Trends in the strength of the M-Cl interaction as a function of M were explained by crystal field theory: they are largely determined by the octahedral site stabilization energy (OSSE) of the metal ion. Steric effects and strong ligand fields also play a role. Difficulties in forming complexes using both monodentate and bidentate phosphorus ligands may indicate only a small role for back bonding, while the presence of extra ligands capable of forming normal strength bonds to nickel(II) can prevent secondary bonding altogether. Secondary bonding in octahedral (N,N,N{dollar}\sp\prime{dollar}N{dollar}\sp\prime{dollar}-tetramethyl-1,2- ethanediamine)bis-(2,4,6-trichlorophenolato-O,Cl)nickel(II) and pentacoordinate tris(pyridine)bis(2,4,6-trichlorophenolato-O)nickel(II) is discussed.