Toward the Design and Synthesis of Lithium-Ion Intercalation into a Coordination π-π Framework Host

A pi-stacked coordination solid, [[[(VO)2(OH)2(C4O4)(phen)2] x H2O]n] (1: phen = phenanthroline), was synthesized by hydrothermal methods and structurally characterized by X-ray single-crystal diffraction. The structure of 1 adopts a neutral open framework in which channeling apertures and windows are surrounded by four oxovanadyl dimers, two squarates, and two pairs of pi-pi interactions of phenanthroline groups; the dimensions of the windows are about 5.38 x 7.55 A along the c axis. Surprisingly, the porous framework with hydrophilic and hydrophobic characteristics was thermally stable up to 250 degrees C, as indicated from powder X-ray diffraction patterns and thermogravimetric analysis. Further investigation of lithium-ion intercalation into the channel matrix of 1 was conformed by 7Li NMR spectroscopy and cyclic votammetry measurements. The present case represents the first example of a porous coordination solid that possesses polar channels capable of mediating lithium-ion insertion.