Three‐Dimensional Framework with Channeling Cavities for Small Molecules: {[M2(4, 4′‐bpy)3(NO3)4]·xH2O}n (M  Co, Ni, Zn)

Reversible adsorption of gases distinguishes the coordination polymers {[M2(4,4′-bpy)3(NO3)4](H2O)x}n (M = Co., x = 4; M = Ni, x = 4; M = Zn, x = 2), which are formed from M(NO3)2 and 4,4′-bipyridine in acetone/ethanol. The channeling cavities in the crystal frameworks (shown schematically on the right) have dimensions of about 3 × 6 Å along the a axis and about 3 × 3 Å along the b axis, and reversibly adsorb CH4, N2, and O2 in the pressure range of 1–36 atm without deformation of the crystal framework.