Exchange interaction in tetrameric oxygen-bridged copper(II) clusters of the cubane type

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Abstract
The magnetic properties of the tetrameric oxygen-bridged copper (II) complexes [{CuX(OCH2CH2NR2)}4](1)(R = Me, X = NCO; R =Prn, X = NCO; and R = Bun, X = NCO or NCS) have been determined in the temperature range 3.4–300 K. The cubane-type complexes exhibit magnetic interactions between the single copper (II) ions, which can be explained on the basis of the isotropic Heisenberg–Dirac–van Vleck model. The magnetism of (1; R = Me, X = NCO) can be explained on the basis of four non-interacting ‘dimeric’ units with the exchange integrals J1=–65 ± 3, J2=–0.6 ± 2, J3=–0.3 ± 2, and J4=–0.9 ± 2 cm–1. A linear relationship between the exchange integral and the Cu–O–Cu bridge angle has been established for symmetric bridged complexes. The magnetic properties of (1; R = Prn, X = NCO; R = Bun, X = NCO or NCS) could be fitted with a theoretical equation assuming C2v symmetry. The resulting exchange integrals J12=–30 ± 1, J34=–53 ± 3, J13= 8 ± 4 (1; R = Prn, X = NCO), J12=–28 ± 2, J34=–84 ± 10, J13= 21 ± 10 (1; R = Bun, X = NCO), and J12=–27 ± 2, J34=–72 ± 5, and J13=+15 ± 10 cm–1(1; R = Bun, X = NCS) reveal the existence of antiferromagnetic interaction within the ‘dimeric’ units and ferromagnetic interaction between them.

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