## Piezochromism in copper(II) cation distortion isomers: Pressure-induced changes in the solid-state geometry of (diethylenetriamine)(2,2 prime -dipyridylamine)copper(II) complexes

The effects of high pressure on (Cu(dien)(bipyam))X{sub 2}{center dot}nH{sub 2}O (dien = diethylenetriamine, bipyam = 2,2{prime}-dipyridylamine; X = Cl{sup {minus}}, n = 2(1); X = ClO{sub 4}{sup {minus}}, n = 1 (2); and X = NO{sub 3}{sup {minus}}, n = 0 (3)) are described. Pressure-dependent electronic spectroscopy indicates a continuous transformation of 1 and 2 from distorted to more regular square pyramidal configurations with increasing pressure. A rearrangement in 3 from a distorted trigonal bipyramidal to a distorted square pyramidal configuration is observed over a pressure range of 30 kbar beginning at 45 kbar. Supporting infrared data are presented, andmore »