Crystal structures, electronic properties and structural pathways of thirty [Cu(bipy)2X][Y] complexes, where X = Cl–, Br– or I–†

The crystal structures of ten distortion isomers of the [Cu(bipy)2X]+ cation have been determined, where X = Cl– (2), Br– (5) or I– (3), and compared by scatter plot analysis with twenty [Cu(bipy)2X]Y complexes of known crystal structure. In the ten new structures two involve a near regular trigonal bipyramidal stereochemistry (τ = 0.94–0.90) and eight show a square based pyramidal distorted trigonal bipyramidal stereochemistry (τ = 0.89–0.49), where τ = (α8 – α1)/60 [where α1 = N(2)–Cu–Cl, α8 = N(1)–Cu–N(3)]. Scatter plots of the eighteen cation distortion isomers of the [Cu(bipy)2Cl][Y] series of complexes suggest that all eighteen complexes lie on a common structural pathway, involving a mixture of the symmetric, C2, and the asymmetric, non-C2, in-plane modes of vibration of the CuN4Cl chromophore. The resulting structural pathways are consistent with the direct observation of the effect of the modes of vibration on the stereochemistries of the complexes. A comparison of the trends in the bipy/Cl, Br and I data suggests a size effect of the Br– and I– ligands.