title: pH-dependent assembly of two polyoxometalate host-guest structural isomers based on Keggin polyoxoanion templates.
abstract: Two interesting polyoxometalate-templated host–guest compounds 1 and 2 with the same chemical formulae of [Ag6(tpt)4(SiW12O40)Cl2]·2H2O have been obtained by hydrothermal reactions of monolacunary Keggin-type K8[α-SiW11O39]·13H2O with CH3COOAg and tpt ligands under different pH conditions. Compounds 1 and 2 are structural isomers. In 1, the novel chair-like tetranuclear [Ag4(μ3-Cl)2]2+ clusters and additional Ag+ ions are linked by tpt ligands to form a 2D double-layered structure featured with two different types of voids in the layer, and the double-layers are stacked into a 3D host supramolecular framework with 1D channels filled with Keggin [SiW12O40]4− polyoxoanions and water molecules as guests. In 2, Ag+ ions are linked by tpt ligands into a 3D framework of 10(3)-ths topology. The most outstanding structural feature of 2 is that upon six-fold interpenetration among 10(3)-ths nets there are still nanosized channels along the a axis to accommodate Keggin polyoxoanions and water molecules as guests. Compound 2 represents the first example of six-fold interpenetrating cationic networks templated with polyoxoanions. In this work, the obvious differences in structure between 1 and 2 show that hydrochloric acid solution conditions, which offer not only H+ to regulate the pH value but also Cl− to coordinate with Ag+ ions, play an important role in the formation of host frameworks templated by Keggin-type polyoxoanions. The photoluminescence properties of 1 and 2 have been investigated in the solid state.
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China. czlu@fjirsm.ac.cn.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Wenbin
authors.initials: W
authors.lastname: Yang
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Kuang
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Wu
authors.forename: Canzhong
authors.initials: C
authors.lastname: Lu