The crystal structure and electronic properties of catena-bis(2,2′-bipyridyl)-µ-tetrafluoroborato-copper(II) tetrafluoroborate and catena-bis(2,2′-bipyridyl)-µ-perchlorato-copper(II) perchlorate

Abstract

The crystal structure of [Cu(bipy)₂(F₂BF₂)][BF₄](3)(bipy = 2,2′-bipyridyl) has been determined by X-ray analysis [triclinic, space group P, with a= 11.275(4), b= 14.760(5), c= 7.366(3)Å, α= 96.44(3), β= 101.63(4), γ= 110.25(4)°, and Z= 2], and that of [Cu(bipy)₂(O₂ClO₂)][ClO₄](1) has been redetermined [triclinic, space group P, a= 11.238(4), b= 14.863(5), c= 7.403(3)Å, α= 96.28(3), β= 99.49(4), γ= 110.21(4)°, and Z= 2]. The two structures are isomorphous with near isostructural, six-co-ordinate, elongated rhombic trans octahedral CuN₄X₂ chromophores. The co-ordination of the bipy ligands is approximately planar, with a tetrahedral twist of the CuN₄ chromophore [dihedral angle 44.6 and 46.7° for (3) and (1), respectively]. The six-co-ordination is completed by one bridging (and one ionic) tetrafluoroborato and perchlorate anions, in (3) and (1), respectively, at non-equivalent copper–ligand distances consistent with semi-co-ordination. The structure of complex (3) represents the first crystallographic example of a bridging tetrafluoroborato anion and the i.r. spectrum at liquid-nitrogen temperature is consistent with this, showing clear splitting of the ν₃ band. The electronic and e.s.r. spectra of the complexes are consistent with their elongated rhombic octahedral stereochemistries and are discussed as a ‘criterion of stereochemistry’ for this geometry in the structural pathway of [Cu(bipy)₂X]Y complexes.