Comparative crystallography.: 5.: Crystal structures, electronic properties, and structural pathways of five [Cu(phen)2Br][Y] complexes, Y = [Br]-•H2O, [ClO4]-, [NO3]-•H2O, [PF6]-, and [BPh4]-

The crystal structures of [Cu(phen)(2)Br][Br]. H2O (1, phen = 1,10-phenanthroline), [Cu(phen)(2)Br][ClO4] (2), [Cu(phen)(2)Br][NO3]. H2O (3), [Cu(phen)(2)Br][PF6] (4), and [Cu(phen)(2)Br][BPh4] (5) have been determined by X-ray diffraction. Four of the complexes, 1-4, have a CuN4Br chromophore with a square based pyramidal distorted trigonal bipyramidal (SBPDTB) stereochemistry, while 5 involves an extreme trigonal bipyramidal distorted square based pyramidal (TBDSBP) stereochemistry. The geometries of the CuN4Br chromophores in 1-5 are compared by scatter plot analysis with a single [Cu(phen)(2)Br][ClO4] complex, 6, of known crystal structure involving a crystallographic 2-fold axis of symmetry. The distortion isomers of 2 and 6 are significantly different. The scatter plots of the six cation distortion isomers of the [Cu(phen)(2)Br][Y] series of complexes suggest that all six complexes lie on a common structural pathway, involving a mixture of the symmetric, v(sym), C-2 mode and the asymmetric, v(asym), non-C-2 mode of vibration of the CuN4Br chromophore. The resulting linear and parallel structural pathways are consistent with the direct observation of the effect of vibronic coupling on the stereochemistries of the complexes, which can range from near regular trigonal bipyramidal (RTB) to TBDSBP for the cation distortion isomers of the [Cu(phen)(2)Br][Y] complexes.