Abstract
A novel series of dinuclear squarato‐bridged copper(II) and nickel(II) complexes Cu~2~(TPA)~2~(μ~1,3~‐C~4~O~4~)~2~·4H~2~O (1), Cu~2~(MeDPA)~2~(μ~1,3~‐C~4~O~4~)(H~2~O)~4~~2~ (2) and Ni~2~(TPA)~2~(μ~1,2~‐C~4~O~4~)(H~2~O)~2~~2~ (3) [C~4~O~4~^2–^ = dianion of 3,4‐dihydroxycyclobut‐3‐en‐1,2‐dione (squaric acid), MeDPA = N‐methylbis(2‐pyridylmethyl)amine, TPA = tris(2‐pyridylmethyl)amine] were synthesized and structurally characterized by X‐ray crystallography. The spectral and structural characterizations as well as their magnetic properties are reported. In this series, the structures consist of the ClO~4~^–^ groups as counterions and the C~4~O~4~^2–^ anions bridging the two M^II^ centers in a μ‐1,3‐ (1 and 2) or in a μ‐1,2‐bis(monodentate) (3) bonding fashion. The coordination geometry around the five‐coordinate Cu^II^ centers in 1 is a distorted trigonal bipyramid, where the coordination environment is achieved by the four N‐donor atoms of the TPA ligand and one oxygen atom of the bridging squarato ligand. The complexes 2 and 3 adopt a distorted octahedral geometry. The six‐coordinate 4+2 environment in 2 is achieved by the three N‐atoms of the MeDPA ligand, by an oxygen atom of a bridging squarato ligand and, at longest distances, by two oxygen atoms from coordinated water molecules. In the nickel complex 3, the geometry is attained by the four N‐atoms of TPA and by two oxygen atoms supplied by a coordinated water molecule and by a bridging squarato ligand. The results manifested the effects of the blocking amine variations on the structure and on the bonding mode of the bridging squarato ligand. The complexes show antiferromagnetic coupling with |J| = 9.1 and 1.2 cm^–1^ in the μ‐1,3‐bridged squarato compounds 1 and 2, and with J = –1.4 cm^–1^ in the corresponding μ‐1,2‐bridged squarato complex 3. The magnetic properties are discussed in relation to other related compounds and the structural data.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)