Abstract
The crystal and molecular structure of the title complex has been determined from single-crystal X-ray diffraction data and refined to R 0.068 for 1 423 independent reflections. Four oxygen-bridged cubane-type molecules with a Cu4O4 core, having crystallographically imposed S4 point symmetry, occupy a tetragonal unit cell, space group /2d, of dimensions a= 17.85(1) and c= 11.92(1)A. The four copper atoms in the tetranuclear cluster are situated in an almost tetrahedral arrangement, the two independent copper–copper separations being 3.194(2)(× 2) and 3.193(2)A(× 4). Copper–oxygen distances within the Cu4O4 framework [1.936(6)(× 4), 2.243(6)(× 4), and 2.113(6)A(× 4)] are different and show unsymmetric bridging of the copper atoms. The co-ordination around copper (amine nitrogen, isocyanate nitrogen, and three alkoxide triply bridging oxygens) may be described as between distorted square pyramidal and distorted trigonal bipyramidal. The magnetic susceptibility measured over the range 2.6—300 K shows a maximum at ca. 35 K and thus indicates overall antiferromagnetic spin coupling. The magnetism of the complex can be explained on the basis of the isotropic Heisenberg–Dirac–van Vleck model. The resulting values for the magnetic exchange integrals: [J12-21.4 ± 0.5 (× 2), J13 12.3 ± 1.0 cm–1(× 4)] indicate the simultaneous presence of antiferromagnetic and ferromagnetic interactions between copper atoms within the same molecule.
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