Squarato-metal(II) complexes. 1: Structural and magnetic characterization of squarato-bridged dinuclear nickel(II) and copper(II) complexes

Abstract

A new series of dinuclear squarato-bridged nickel(II) and copper(II) complexes [Ni 2(2,3,2-tet) 2(μ 1,3-C 4O 4)(H 2O) 2](ClO 4) 2 ( 1), [Ni 2(aepn) 2(μ 1,3-C 4O 4)(H 2O) 2](ClO 4) 2 ( 2), [Cu 2(pmedien) 2(μ 1,3-C 4O 4)(H 2O) 2](ClO 4) 2.4H 2O ( 3) and [Cu 2(DPA) 2(μ 1,2-C 4O 4)(H 2O) 2](ClO 4) 2 ( 4) where C 4 O 4 2 - is the dianion of 3,4-dihydroxycyclobut-3-en-1,2-dione (squaric acid), 2,3,2-tet = 1,4,8,11-tetraazaundecane, aepn = N-(2-aminoethyl)-1,3-propanediamine, pmedien = N, N, N′, N″, N″-pentamethyldiethylenetriamine and DPA = di(2-pyridylmethyl)amine were synthesized and structurally characterized by X-ray crystallography. The spectral and structural characterization as well as the magnetic behaviour of these complexes is reported. In this series, structures consist of the ClO 4 - groups as counter ions and the C 4 O 4 2 - bridging the two M(II) centers in a μ-1,3- ( 1– 3) and in a μ-1,2-bis(monodentate) ( 4) bonding fashions. The coordination geometry around the Ni(II) ions in 1 and 2 is six-coordinate with distorted octahedral environment achieved by N atoms of the amines and by one or two oxygen atoms from coordinated water molecules, respectively. In the Cu(II) complexes 3 and 4, a distorted square pyramidal geometry is achieved by the three N-atoms of the aepn or DPA and by an oxygen atom from a coordinated water molecule. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the M(II) centers. The complexes show weak antiferromagnetic coupling with ∣ J∣ = 1.8–4.2 cm −1 in the μ-1,3- bridged squarato compounds 1– 3, and J = −16.1 cm −1 in the corresponding μ-1,2- bridged squarato complex 4. The magnetic properties are discussed in relation to the structural data.