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

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 C_2v 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.