The crystal structures of three [Cu(dien) (bipyam)]X,*nH,O (dien = diethylenetriamine, bipyam = di-2-pyridylamine) complexes have been determined by X-ray crystallographic methods, where X = CI-, n = 2 (1 ) ; X = C104-, n = 1 (2) ; and X = NO3-, n = 0 (3). All three crystallise in the monoclinic space group P2Jc with 2 = 4; in (1) a = 7.78(2), b = 9.75(3), c = 28.01(5) A, and p = 115.0(5)"; in (2) a = 15.683( 5), b = 7.621(5), c = 21.044(9) P\, and p = 121.42(2)"; and in (3) a = 12,201 ( 5), b = 16.052(6), c = 9.851 (4) A, and p = 90.76(2)".All three structures were solved by heavy-atom techniques and successive Fourier syntheses; all three complexes involve a distorted five-co-ordinate CUN, chromophore, whose stereochemistry ranges from distorted square pyramidal in (l), through an intermediate geometry in (2), to a distorted trigonal-bipyramidal stereochemistry in (3). The three stereochemistries represent individual structures in the pathway of the Berry twist and represent cation distortion isomers of the [Cu(dien) (bipyam)]2+ cation. The angular changes in the CuN, stereochemistry are Darallelled in the electronic reflectance spectra of the three complexes and in the calculated crystal-field energy level of the copper(l1) ion.

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