The crystal structure and electronic properties of bis(2,2′-bipyridyl)-copper(II) bis(hexafluorophosphate)

The crystal structure of the title compound, [Cu(bipy)2][PF6]2(1), has been determined by X-ray crystallographic methods, using diffractometer data collection; the structure was solved by the heavy-atom method and by successive Fourier syntheses. Compound (1) crystallises in the tetragonal space group I41/acd, a= 16.228(3), c= 18.954(3)A, Z= 8.319 unique reflections gave a final R= 0.0487. The structure of (1) involves a unique compressed tetrahedral CuN4 chromophore (dihedral angle 44.6°) with four additional non-bonding PF6– anions at 3.3 A. The e.s.r. spectrum is axial (g∥g⊥ > 2.0) and the dark green crystals have an electronic reflectance spectrum with a band maximum at 15 040 cm–1 with a high-frequency shoulder at 16 950 cm–1. This represents the highest electronic transition yet observed in the [Cu(bipy)2X]Y type complexes and establishes an ‘electronic criterion of stereochemistry’ for the compressed tetrahedral CuN4 chromophore.