Construction of octanuclear polyoxomolybdenum(v)-based porous materials with lithium additives

Abstract

Crown-ether-like octanuclear polyoxymolybdenum(V) cluster (NH₄)₄[Mo₈O₈(μ₂-OH)₄(μ₂-O)₈(dmtrz)₈]·62.5H₂O (dmtrz = 3,5-dimethyltriazole, 1) was successfully synthesized by a hydrothermal method. Its lithium additives Li₄[Mo₈O₈(μ₂-OH)₄(μ₂-O)₈(dmtrz)₈]·2(Hdmtrz)·27H₂O (2), Li₄[Mo₈O₈(μ₂-OH)₄(μ₂-O)₈(dmtrz)₈]·20.5H₂O (3) and Li₄[Mo₈O₈(μ₂-OH)₄(μ₂-O)₈(dmtrz)₈]·25H₂O (4) have also been obtained and fully characterized respectively. The lithium cations are in the forms of mononuclear, dinuclear and tetranuclear units. X-ray structural analyses show that polyoxometalate-based materials 1–4 constitute round pores formed by eight molybdenum-oxygen groups connected sequentially with sizes of 4.6 Å. With 1 as the basic framework, 2–4 combine lithium cations in the forms of different hydrates, respectively. In addition, 1 stacked up intermolecularly with pores of sizes 10.0 × 18.0 Ų, while 4 stacked up inter-molecularly with 6.0 × 4.0 Ų in the a axis and 8.0 × 5.8 Ų in the c axis, respectively. The results show that 1 can selectively adsorb CO₂ and O₂, respectively.