A new isoreticular metal-organic framework Zn4O(FMA)(3)center dot xG (1; FMA = fumarate; G = guest molecules) of a primitive cubic net was synthesized and structurally characterized. With intersecting pores of about 6.8 x 6.8 angstrom, the activated 1 a exhibits high gas adsorption with respect to H-2, CH4, and CO2.