Co-ordination chemistry of 1,4-bis(o-aminobenzyl)-1,4-diazacyclohexane (L) with nickel(II), copper(II) and palladium(II)

Abstract

1,4-bis(o-aminobenzyl)-1,4-diazacyclohexane (L) has been synthesized and its co-ordination chemistry with nickel(II), copper(II) and palladium(II) investigated. The reaction of L with Ni(ClO₄)₂·6H₂O in a chloroform–ethanol mixture affords orange, diamagnetic [NiL][ClO₄]₂1 which consists of the square-planar dication [NiL]²⁺ in the solid state and in weakly or non-co-ordinating solvents (nitromethane, acetone). In co-ordinating solvents (acetonitrile, pyridine, dimethylformamide) or in the presence of co-ordinating anions (NCS^–) blue solutions of 1 are obtained from which blue, paramagnetic species were isolated as crystalline materials: [NiL(NCS)₂]2 and [NiL(MeCN)₂][ClO₄]₂·1.5 MeCN 3. Complex 2 was shown by X-ray crystallography to consist of neutral, octahedral [NiL(NCS)₂]. Using Ni(NO₃)₂·4H₂O as starting material both square-planar, orange [NiL][NO₃]₂4a and blue, octahedral [NiL(NO₃)₂]4b containing two monodentate NO₃^– ligands were isolated. Reaction of L with Cu(ClO₄)₂·6H₂O and Cu(NO₃)₂·4H₂O in CHCl₃–EtOH produced blue crystals of square-planar [CuL][ClO₄]₂5 and five-co-ordinate [CuL(H₂O)][NO₃]₂·H₂O 7, respectively. Recrystallization of 5 from MeCN produced blue crystals of [CuL][ClO₄]₂·2MeCN 6. Palladium(II) acetate reacts with L in CHCl₃–EtOH affording orange-brown crystals of [PdL][ClO₄]₂8. The crystal structures of 1, 2, 5, 7 and 8 have been determined by X-ray crystallography. In the solid state the ligand is always equatorially co-ordinated in a transoid fashion where one of the two [graphic omitted]_aniline chelate rings adopts a boat and the other a twist-boat conformation. This has been corroborated by solid-state ¹³C cross-polarization magic angle spinning NMR spectroscopy of 1 and 8.