Abstract
[Cu 4(succinato)(tpmc) 2](ClO 4) 6 · 2H 2O (tpmc = N, N′, N″, N‴-tetrakis-(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane, succinato = dianion of succinic acid) has been prepared and characterized by elemental analysis, UV/vis, IR, EPR (X-band) spectra, conductivity and magnetization measurements (SQUID). Based on a low-temperature measurements (100(2) K), X-ray analyses of the first tetranuclear Cu(II)-tpmc complex, single crystal of which corresponded to the [Cu 4(succinato)(tpmc) 2](ClO 4) 6·2C 2H 5OH·4H 2O ( 1) and of the previously described [Cu 2(C 6H 5COO)tpmc](ClO 4) 3·0.5CH 3OH·0.5H 2O ( 2) were also done. The complexes crystallize in triclinic P 1 ¯ ( 1) and monoclinic P2 1/ c ( 2) space groups. The geometry around the first Cu(II) coordination sphere in the tetranuclear complex ( 1) is almost regular square-based pyramidal, while significant distortion around the other metallic center was observed. The angular structural parameter ( τ), which is applicable to five coordinate structures as an index of degree of trigonality, was found to be 0.05 and 0.40, respectively. In the binuclear complex ( 2) the geometry around the first Cu(II) coordination sphere is regular square-based pyramidal ( τ = 0.09), while around the other is distorted trigonal bipyramidal ( τ = 0.79). In complexes ( 1) and ( 2) the bridging carboxylate groups are coordinated to metallic centres in a syn– anti mode. Weak ferromagnetic interactions are observed between copper(II) ions, connected through syn– anti monocarboxylate bridges (2 J = +1.26 and +1.84 cm −1 in complexes ( 1) and ( 2), respectively). Additional antiferromagnetic interaction through succinato anion ( zJ′ = −1.57 cm −1) gives finally rise to antiferromagnetic interactions, observed in magnetic measurements in tetrameric complex ( 1).
Published Version
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