Crystal and molecular structure and magnetic properties of tetrakis-[bromo(2-diethylaminoethanolato)copper(II)]–tetrachloromethane (1/4), a complex with a ferromagnetic ground state

Abstract

The crystal and molecular structure of [{CuBr(OCH2CH2NEt2)}4]·4CCl4(A) has been determined from three-dimensional X-ray diffractometer data and refined to R 0.061 using 1 581 independent reflections. The tetragonal unit cell of space group I41/a with dimensions a= 19.47(2) and c= 15.78(1)A contains four oxygen-bridged cubane-type clusters of symmetry S4 with a Cu4O4 core. Copper–copper distances are 3.523(2)(× 2), 3.176(2)A(× 4) and copper–oxygen distances 1.924(5)(× 2), 2.524(5)(× 2), and 1.982(5)A(× 4), respectively. The co-ordination around copper (amine nitrogen, bromine, three bridging alkoxide oxygens) is distorted square pyramidal. Sixteen molecules of tetrachloromethane act as solvent of crystallization in the unit cell. The isomorphic [{CuCl(OCH2CH2NEt2)}4]·4CCl4(B) has cell dimensions a= 19.21(2) and c= 15.96(1)A. The decomposition of (A) and (B) has been followed by Debye–Scherrer investigation. The magnetic susceptibility of (A) and (B) in the temperature range 3.4–300 K and of the α and β modifications of [{CuBr(OCH2CH2NEt2)}n](n= 2 or ∞) in the range 70–300 K have also been determined and interpreted in terms of the isotropic Heisenberg–Dirac–van Vleck model. Whereas the α and β modifications show strong antiferromagnetic exchange interaction [2J=–817 and –744 (±20) cm–1], there is simultaneous antiferromagnetic and ferromagnetic exchange interaction in compounds (A) and (B) with the latter interaction dominating. The evaluated exchange parameters are: J12=–4.5 ± 3, J13= 40.0 ± 3 cm–1(A); J12=–5.2 ± 3, J13= 46.9 ± 3 cm–1(B). These can be understood in terms of the Cu–O–Cu bridging angle and the Cu–O bond distances.