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

Abstract

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)Å, 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 Å. 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.