Supramolecular complexation of alkali cations through mechanochemical reactions between crystalline solids.

The organometallic zwitterion [CoIII(h5-C5H4COOH)(h5-C5H4COO)] reacts quant. as a solid polycryst. phase with a no. of cryst. alkali salts MX (M = K+, Rb+, Cs+, NH4+; X = Cl-, Br-, I-, PF6-, although not in all cation/anion permutations) to afford supramol. complexes of the formula [CoIII(h5-C5H4COOH)(h5-C5H4COO)]2.M+X-. In some cases, the mechanochem. complexation requires kneading of the two solids with a catalytic amt. of water. The solid-state products were characterized by a combination of x-ray single-crystal and powder-diffraction data. The existence of hydrogen-bonding interactions was confirmed by solid-state NMR spectroscopy. The mechanochem. reactions imply a profound solid-state rearrangement accompanied by breaking and forming of O-H...O hydrogen-bonding interactions between the organometallic mols. All compds. could also be obtained by soln. crystn. of the inorg. salts in the presence of the organometallic unit. The solid-state complexation of alkali cations by the organometallic zwitterion was rationalized as a special kind of solvation process taking place in the solid state.