Synthesis and crystal structure of an octahedral nickel(II) complex derived from pentaerythrityl tetraamine

Abstract

The Ni(II) complex, Ni(Htam)24+ (tam = pentaerythrityl tetraamine), has been prepared under controlled conditions. In this ion, three of the four amino groups of each ligand are coordinated to yield an octahedral structure which shows tetragonal and trigonal distortion. The fourth amino group is protonated in each case and binds strongly to the counter ion SO42−. The crystal structure (triclinic, [Formula: see text], a = 8.913(3), b = 9.775(2), c = 7.505(3), α = 102.61(4)°, β = 106.28(4)°, γ = 96.40(3)°) has been refined, converging to final values of R = 0.0347 and Rw = 0.0386. The three dimensional nature of the hydrogen bonding in the crystal structure has been described. Differences in Ni—N bond lengths are observed. A transient nickel(III) species is generated chemically or electrochemically. The esr spectrum is consistent with a low spin d7 centre and is axial in nature. Keywords: nickel, pentaerythrityl tetraamine, hydrogen bonding, oxidation.