CRYSTAL-STRUCTURE AND MAGNETISM OF 4,4'-BIPYRIDYLIUM DI-MU-BROMOTETRABROMODICUPRATE(II)

A new bromocuprate complex of formula C10H10N2Cu2Br6 has been synthesized and its crystal structure investigated by single-crystal X-ray methods. Stable, black, needle-like crystals are isostructural with the analogous chloride compound.1 The crystals are triclinic, a = 4.1018(5), b = 10.2755(10), c = 11.0355(9) Å, a = 113.894(7), β = 94.975(8), γ = 95.935(9)°. The structure was refined by least-squares methods to R = 0.031 and Rw = 0.038 for 1930 reflections. It consists of cationic columns formed by stacking of planar (4,4'-bipy H2)2+ cations and anionic columns formed by stacking of nearly planar [formula ommited] anions. Cationic and anionic columns are parallel to the needle axis. The geometry and interionic interactions for the chloride and bromide crystals were compared. The EPR spectrum of a polycrystalline sample of the complex displayed only one broad line centred at 2.08 (T = 293 K). Variable temperature (ca 4.2-290 K) magnetic susceptibility data indicated an antiferromagnetic superexchange interaction between copper(II) centres much stronger than observed for the chloride analogue. © 1990 Gordon and Breach Science Publishers S.A.