Ferromagnetic vs. antiferromagnetic coupling in bis(µ2-1,1-azido)dinickel(ii) complexes with syn- and anti-conformations of the end-on azide bridges

Abstract

Reaction of a 1 : 1 : 1 molar ratio of NiCl₂, NaN₃ and H₂L, a tetradentate ligand N-(2-pyridyl)methyl)-N,N-bis(2′-hydroxy-3′,5′-dimethylbenzyl)amine in methanol in presence of Et₃N results in a turquoise precipitate, which affords deep green crystals of [Ni₂(HL)₂(N₃)₂]·1.5CH₂Cl₂ (1) and [Ni₂(HL)₂(N₃)₂]·H₂O (2) upon crystallization from CH₂Cl₂–MeOH or THF–MeOH, respectively. Both complexes reveal distorted octahedral NiN₄O₂ coordination environments around the Ni(II) centers with bis(µ-1,1-azido) bridging ligands. Complex 1 displays an unprecedented small Ni–N–Ni bridge angle of 90.4°, whereas 2 contains the said angle of av. 98.7° lying in the usual range observed for other comparable structures. The variable-temperature magnetic susceptibility together with the variable-field, variable-temperature (VTVH) magnetization measurements discern different ground states of S_t = 0 for 1 and S_t = 2 for 2. The magnetic behaviours of these compounds are discussed in the context of the known bis(end-on azido) bridging dinickel(II) complexes.