Syntheses, crystal structures and magnetic properties of [Ni2(C2O4)(tren)2][ClO 4]2 and [Ni2(C4O4)(tren)2(H2 O)2][ClO4]2 [tren = tris(2-aminoethyl)amine]

Abstract

Two dinuclear nickel(II) complexes [Ni ₂ (C ₂ O ₄ )(tren) ₂ ][ClO ₄ ] ₂ 1 and [Ni ₂ (C ₄ O ₄ )(tren) ₂ (H ₂ O) ₂ ][ClO ₄ ] ₂ 2 [tren = tris(2-aminoethyl)amine, C ₂ O ₄ ^2- = oxalate dianion and C ₄ O ₄ ^2- = dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of dinuclear nickel(II) cations and unco-ordinated perchlorate anions. The nickel environment is distorted octahedral NiN ₄ O ₂ in both complexes: four nitrogen atoms of the tren group acting as a tetradentate ligand and two oxygen atoms of oxalate (1) or a water molecule and a squarate oxygen (2) comprise the co-ordination. The oxalate acts as a bis(chelating) ligand whereas the squarate adopts a µ-1,2-bis(monodentate) co-ordination mode. The intradimer metal–metal separation is 5.413(1) and 6.224(1) Å in 1 and 2, respectively. The co-ordinated water molecule in 2 forms an intramolecular hydrogen bond to an unco-ordinated squarate-oxygen atom. Variable-temperature susceptibility measurements revealed the occurrence of relatively strong (1) and weak (2) intramolecular antiferromagnetic coupling, the relevant parameters being J = -28.8 cm ^-1 and g = 2.16 for 1 and J = -0.4 cm ^-1 and g = 2.15 for 2 (J being the exchange parameter in the isotropic spin Hamiltonian = -J _A · _B ). A comparative study of the ability of oxalate and squarate groups to mediate electronic interactions in the structurally characterized oxalato- and squarato-bridged nickel(II) complexes was carried out.