Crown ether-like discrete clusters for sodium binding and gas adsorption.

Hexanuclear polyoxomolybdenum-based discrete supermolecules Na x [Mo V 6 O 6 (μ 2 -O) 9 (Htrz) 6- x (trz) x ]· n H 2 O ( x = 0, n = 15, 1; x = 1, n = 12, 2; x = 2, n = 10, 3; x = 2, n = 49, 4; Htrz = 1 H -1,2,3-triazole) have been prepared and fully characterized with different amounts of sodium cations inside and outside the intrinsic holes. Structural analyses demonstrate that they all exist a triangular channel constructed by six molybdenum-oxygen groups with inner diameters of 2.86 (1), 2.48 (2), and 3.04 (3/4) Å, respectively. Zero, one, or two univalent enthetic guest Na + have been hosted around the structural centers, which reflect the expansion and contraction effects at microscopic level. Water-soluble species can serve as crown ether-like metallacycles before and after the sodium binding. Diverse nanoscale pores are further formed through intermolecular accumulations with hydrogen bonding. Gas adsorption studies indicate that 2-4 can selectively adsorb CO 2 and O 2 but have little or even no affinities toward H 2 , N 2 , and CH 4 . Theoretical calculations corroborate the roles of Na + and auxiliary ligand with different states in bond distances, molecular orbitals, electrostatic potentials, and lattice energies in these discrete clusters. The binding orders of sodium cations in 2-4 are similar with the classical crown ethers, where 2 is the strongest one with 2.226(4) av Å for sodium cation bonded to six O atoms.