A novel right-angled ligand that forms polymeric metal-organic frameworks with nanometer-sized square cavities

A new right angle-shaped ligand, 2,2'-bis(4-pyridyl)-9,9'-spirobifluorene (L), is designed and synthesized. Treatment of L with silver(l) ions leads to linear polymeric metal-organic frameworks, [Ag(L)(2)](+) (1), that feature square subunits. Single-crystal X-ray analysis reveals that [Ag(L)(2)](+) has a one-dimensional double-stranded polymeric chain comprising square grids with cavity dimensions of ca. 8 angstrom x 8 angstrom. By pi-pi stacking of adjacent double-stranded chains, the structure is extended into a two-dimensional (2D) layer framework with a unique quasi-aperture (dimensions of ca. 14 angstrom x 8 angstrom). Each 2D layer is inclined and mutually interpenetrated, which gives rise to the three-dimensional interlocked network structure. Compound 1 center dot(BF4)(CH3OH) crystallizes in the monoclinic system, space group C2/c, with chemical formula C71H49N4OBF4Ag, a = 25.709(1) angstrom, b = 14.4164(6) angstrom, c = 15.6865(7) angstrom, beta = 109.220(2)degrees, and Z = 4.