A three-dimensional triply interpenetrated mixed metal organic framework, Zn-2(BBA)(2)(CuPyen).G(x) (M'MOF-20; BBA = biphenyl-4,4'-dicarboxylate; G = guest solvent molecules), of primitive cubic net was obtained through the solvothermal reaction of Zn(NO3)(2), biphenyl-4,4'-dicarboxylic acid, and the salen precursor Cu(PyenH(2))-(NO3)(2) by a metallo-ligand approach. The triple framework interpenetration has stabilized the framework in which the activated M'MOF-20a displays type-I N-2 gas sorption behavior with a Langmuir surface area of 62 m(2) g(-1). The narrow pores of about 3.9 angstrom and the open metal sites on the pore surfaces within M'MOF-20a collaboratively induce its highly selective C2H2/CH4 and CO2/CH4 gas separation at ambient temperature.