Fabrication of new metal phosphonates from tritopic trisphosphonic acid containing methyl groups and auxiliary ligands: syntheses, structures and gas adsorption properties

Hydrothermal reactions of benzene-1,3,5-triyltris(methylene)triphosphonic acid (H6L1) or (2,4,6- trimethylbenzene-1,3,5-triyl)tris(methylene)triphosphonic acid (H6L2) with metal sulfates, 4,4'-bipyridyl (4,4'-bipy), 2,2'-bipyridyl (2,2'-bipy), 1,10-phenanthroline (1,10-phen) and 1,2-di(4-pyridyl)ethylene (dpe), afforded eight new transition metal trisphosphonates, namely, [Cu-2(H3L1)(2)(H2O)(2)][H(2)dpe][H2O](4) (1), [Ni-1.5(H3L2) (H2O)(2)][H2O] (2), [Ni(H4L2)(1,10-phen)(H2O)(2)] (3), [Ni(H4L2)(2,2'-bipy)(H2O)(2)] (4), [Cu(H4L2)(4,4'-bipy)] (5), [Cu(H4L2)(1,10-phen)][H2O] (6), [Cu(H4L2)(2,2'-bipy)(H2O)][H2O](0.13) (7), and [Mn-1.5(H3L2)(H2O)(2)][H2O](1.1) (8). The single-crystal X-ray diffraction measurements indicate that compounds 2 and 8 are isostructural and feature 3D framework structures with (5,6,8)-net topology; 1, 5 and 6 exhibit 2D layered structures; whereas 3, 4 and 7 have 0D dimer structures. The trisphosphonate ligands (H6L1 and H6L2) in these eight compounds adopt either cis-cis-cis or cis-trans-trans conformation with or without the existence of an auxiliary N-containing ligand. The attachment of methyl groups to the benzene core can enhance the crystallinity and enrich the structure diversity. The introduction of 2,2'-bipy and 1,10-phen usually result in low dimensionality whereas 4,4'-bipy can extend the structure to a higher dimensionality. The activated sample of compound 5 has a permanent 1D nanoporous structure and shows high selective adsorption of CO2 over CH4.