Homoleptic cuprates(II) with multiply deprotonated alpha-cyclodextrin ligands

In the presence of cupric ions, alpha-cyclodextrin (alpha-CD) is multiply deprotonated in alkaline aqueous solution. With lithium or sodium as the counterions, trinuclear sandwich-type cuprate ions of the formula [Cu-3(alpha-CDH-6)(2)](6-) are formed (1 and 2), whereas dinuclear [Cu-2(alpha-CDH-4)(2)](4-) ions are isolated in the form of the potassium (3a) and the rubidium salts (3b). The structures of the cyclodextrinatocuprate ions resemble cylinders, since the usual conical shape of a cyclodextrin is altered due to the formation of shorter hydrogen bonds on the O2/O3 rim of the alpha-cyclodextrin torus. Despite anion formation, the cavity of the cyclodextrin is still hydrophobic, giving rise to the intercalation of acetone guests in 2 and 3.