Abstract :
The crystal structures of three new [Cu(bipy)2(ONO)][Y] complexes, [Y]2 ¼ [PF6]2, 1, [ClO4]2, 2, and [I]2, 3, have been determined at
room temperature by single crystal X-ray analysis. All three complexes involve a CuN4O2 chromophore, with an asymmetric cis-distorted
octahedral (CDO) stereochemistry. The stereochemistries of 1, 2 and 3, are compared with three other cation distortion isomers,
[Y]2 ¼ [NO3]2, 4, [BF4]2, 5, and [HSO4]2, 6, by scatter plot analysis to characterise a possible structural pathway involving the
[Cu(bipy)2(ONO)]þ cation only, accounting for the occurrence of discrete a3 angles and right-pointing arrowhead structures, features which
are not readily accounted for by the original tris-chelate Jahn–Teller/Pseudo Jahn–Teller (JT/PJT) model. Further insights into the
stereochemistry of the CuN4O2 chromophore as an independent PJT system involving vibronic coupling between the degenerate 2A type
ground state in low point group symmetry (C2 or C1 symmetry) and a corresponding excited state are presented. This paper raises some
question marks about the original PJT model of CDO chromophores which do not take into account the experimental observation of the
ranges of the a3 discrete angles or the arrowhead fine structure of the data, within the range of the cluster of a3 angles.
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