Unprecedented Application of Flexible Bis(pyridyl-tetrazole) Ligands To Construct Helix/Loop Subunits To Modify Polyoxometalate Anions

By
introducing the unprecedented and flexible isomeric bis­(pyridyl-tetrazole)
ligands into a polyoxometalates (POMs) system, three POM-based compounds,
{Ag2(4-bptzb)2(H2O)2[H2PMo12O40]2}·4-bptzb·5H2O (1), [Ag4(3-bptzb)2(PMoVMoVI11O40)]·2H2O (2), and Ag3(3-bptzb)2.5(H2O)2[H3P2W18O62] (3) [4-bptzb = 1,4-bis­(5-(4-pyridyl)­tetrazolyl)­butane
and 3-bptzb =1,4-bis­(5-(3-pyridyl)­tetrazolyl)­butane], were synthesized
under hydrothermal conditions and structurally characterized by single-crystal
X-ray diffraction analyses. Compound 1 exhibits a dimeric
structure constructed from two Keggin [PMo12O40]3– anions and a binuclear [Ag2(trans-4-bptzb)2]2+ subunit in which
the trans-4-bptzb acts as a bidentate bridging ligand
with one tetrazolyl group. In 2, the 3-bptzb acts as
a tetradentate bridging ligand with the tetrazolyl and pyridyl groups
linking AgI ions to generate a 3D metal–organic
framework (MOF), which contains charming meso-helix
chains. The Keggin anions acting as bidentate inorganic ligands reside
in the distorted tetragonal channels of the MOF. In compound 3, the 3-bptzb adopts versatile coordination modes linking
AgI ions to first construct loop connecting loop 1D chains,
which are linked by {Ag­[P2W18O62]}n zigzag chains to form a scarce hamburger-style
2D sheet. These adjacent sheets are further fused by 3-bptzb ligands
to construct a 3D framework. The influences of isomeric bptzb ligands
and POMs on the construction of Ag-bptzb subunits and the whole structures
of the title compounds are discussed. The electrochemical behaviors
and electrocatalytic activities of compounds 2 and 3 and their corresponding parent POMs as well as the fluorescent
properties of the title compounds have been studied in detail. In
addition, the photocatalytic activities of compounds 2 and 3 and their corresponding parent POMs for decomposition
of methylene blue, rhodamine B, and methyl orange under UV irradiation
have also been investigated.