Abstract. M r = 182.22, monoclinic, P21/c, a = 15.219(4), b=5.7855(8), c=12.177 (4) A, fl= 112.42(2) ° , V=991.1 (4)A a, Z=4, Dx= 1.189(1) Mg m -a, 2(Mo Ka) = 0.7107 A,, /t = 0.41 mm -1, F(000) = 384, room temperature. A model in which disorder at one of the two crystallographically independent molecule sites was taken into account refined, using constraints and restraints, with 2121 diffractometer data to an R of 0.061 (Rw=0.075). The degree of misorientation is 17%. The molecules at the disordered site are approximately related to one another by 180 ° rotation around their longest axes.

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Abstract. (C 14 HI2) 71069A; no structure determination. The mixed crystals not only exhibit substitutional disorder but both molecules, trans-azobenzene and trans-stilbene, also show configurational disorder at one of the two independent sites with symmetry 1. The structure refinements, in which both kinds of disorder were taken into account, were performed with constraints and restraints. The trans-stilbene molecules show a slight preference for substitution at the disordered sites. This preference can be understood by geometrical considerations.

Abstract.(8-Dimethylamino-1-naphthyl)dimethylammonium 2-hydroxy-3,4-dioxocyclobut-1-en-1-olate, CI4HI9Nf.CnHO4, Mr = 328"37, ortho-