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Fig. 4. View of the structure of the double torus in 1 a; colors as in Fig. 3 Cu2+); in addition, C u 2 + is a redox-active transition metal, and water is bound in precisely this region.There is evidence that these units also exist in solution. Preliminary investigations of solvent equilibria indicate that simple polyols and monosaccharide derivatives form complexes with large stability constants in alkaline solution. At p H values above 11 even ethylenediamine is displaced from copper by diolate(2-) ligands; in amine-free solutions diolatocopper compounds form at pH z57.['] We d o not yet know, however, to what extent alkali metal cations associate with large, highly charged anions as in 1. E.xperimenta1 ProcedureA solution ofCu(OH), (0 97 g, 10 mmol). a-cyclodextrin (cyclomaltoheptaose; 5.68 g, 5 mmol), 8 mL H,O. and 8 mL 5~ LiOH (40 mmol LiOH) was sealed under N, and in the dark. and ethanol vapors were allowed to diffuse into the solution. Blue crystals formed within a few weeks; m.p. 205°C (decomp after gradual dehydration). The crystal of 1 a examined by X-ray crystallography originated from this sort of sample; the elemental analysis indicates 3.6 instead of4Cuatomsandl3.2insteadofll Liatoms;inotherwords, laisinamixture with other complexes.