A zeolite-like zinc phosphonocarboxylate framework and its transformation into two- and three-dimensional structures

Three zinc phosphonocarboxylates, Zn2(pbc)2 x Hdma x H3O x 2 H2O (1), Zn(pbc) x Hdma (2), and Zn4.5(pbc)3(OH)(H2O)0.5 x Hdma (3) (H3pbc = 4-phosphonobenzoic acid, dma = dimethylamine) were synthesized by the mixed solvothermal reaction of Zn(Ac)2 x 2 H2O and 4-phosphonobenzoic acid in N,N-dimethylformamide (DMF) and water. The zigzag and ladderlike chains completely constructed by triply fused 4-membered rings (denoted SBU-1) are linked by the organic moieties to form the 3D zeolite-like structure 1 and the layered structure 2, respectively. As for structure 3, a new second building unit (SBU-2) formed by the inset of the [Zn3O12] trimer into the 4-membered ring as well as SBU-1 is observed. The connections between the two types of SBUs lead to a "zinc phosphate" layer, which is linked by the organic groups to generate a 3D pillar-layered structure. Both solution-mediated and solid-state transformations of 1 to 2 and 3 were observed. A possible mechanism for the transformation is proposed. Gas sorption studies show that 1 has accessible pores for methanol and water and exhibits size selectivity for alcohols.