Comparative crystallography .4. Crystal structures, electronic properties and structural pathways of two [Cu(phen)(2)(OH2)][Y], complexes (phen equals 1,10-phenanthroline, Y=CF3SO3- or ClO4-)

The crystal structures of [Cu(phen)(2)(OH2)][CF3SO3](2) 1 and [Cu(phen)(2)(OH2)][ClO4](2) 2 (phen = 1,10-phenanthroline) have been determined by diffractometer data collection. The CuN4O chromophores in both complexes 1 and 2 lie on a crystallographic two-fold axis, with a square pyramidal distorted trigonal bipyramidal stereochemistry, an elongation along the Cu-O direction, Cu-O 2.066(3) and 2.245(4) Angstrom, and an increase in the N(4)-Cu-N(2) alpha(3) angle to 123.4(1) and 136.0(1)degrees, respectively. This suggests that the stereochemistry of 1 is best described as near regular trigonal bipyramidal, RTB, and that of 2 as square based pyramidal distorted trigonal bipyramidal, SBPDTB. The structures of 1 and 2 were compared by scatter-plot analysis, with other [Cu(chelate ligand)(2)(OH2)][Y](2) complexes involving two-fold axes of symmetry. This shows that the spread of the data points is not random, is relatively large and suggests the presence of vibronic coupling to account for the distortion from the RTB CuN4O chromophore, along the C-2 dominated +A and -A route distortions. A continuous linear structural pathway is suggested, determined by the coupled nu(sym)(str) and nu(sym)(bend) modes of vibration, involving a progression of 40-50 modes, spanning an angular distortion range of 91-140 degrees, which correlate with electronic and ESR spectral data.