Synthesis 、 Crystalstuctureandproperty Studyof Thewells-dawson Lacunarypolyoxotungstate-Based Polyoxometalates

Polyoxometalates have potential applications in many fields owing to their unique structural variety and interesting physicochemical properties, such as catalysis, medicine, and magnetism. Lacunary polyoxotungstates are one kind of excellent inorganic multidentate O-donor ligands for assembly of novel POM compounds. In this paper, many novel structural polyoxometalate compounds have been synthesized by assembly of the lacunary Wells-Dawson polyoxometalates and transition-metal cations or the Ln cations. Twelve novel compounds have been obtained by the hydrothermal technique and conventional aqueous solution methods, and characterized by IR, elemental analyses, single crystal X-ray diffractions, TG, and UV-vis. The magnetic properties, electrochemical properties and photocatalytic properties of these compounds have been primarily studied.1. Four hexavacant polyoxoanion {P₂W₁₂}-based trimeric crown-like compounds have been synthesized by the reaction of the hexavacant {P₂W₁₂} POM building block with the transition-metal cations and the Ln cations. Compounds 1-4 all contain a trimeric crown-type aggegrates composed of three {P₂W₁₂} subunits and three W linkers. Compounds 1 and 2 are all the isolated trimeric polyoxometalates containing six Co2+ and Ni2+, respectively, which represent the fist trimeric crown-like compounds containing six transition-metal centers; in compound 3, the trimeric crown contains a Mn-Gd3+mixed cluster, and, the 3d-4f mixed metal cluster-containing trimeric crowns are further connected by the 3d and 4f linkers into a two-dimensional porous framework. In compound 4, two Co2+ ions are captured by the trimeric crown, which is linked by the Gd3+ ions into a one-dimensional chain. Compounds 3 and 4 represent the fist example of {P₂W₁₂}-based compounds containing the 3d and 4f metal cations. Magnetic study reveals that the antiferromagnetic interaction exists in these two compounds. Na₁₈[{Co（H₂O）₄}₆{WO（H₂O）}3(P₂W₁₂O48)3]?109H₂O （1） Na₁₈[{Ni（H₂O）₄}₆{WO（H₂O）}3(P₂W₁₂O48)3]?110H₂O （2） K6Na8[{HMn2Gd3（Tart）O2（H₂O）25}{P6W42O151（H₂O）7}]?44H₂O （3） K6Na10[{GdCo（H₂O）11}2{P6W41O148（H₂O）7}]?43H₂O （4）2. Three double-Dawson type polyoxoanions have been synthesized by reaction of the hexavacant Wells-Dawson polyoxoanion {P₂W₁₂} with the transition metal cations under the conventional aqueous solution. Compound 5 is a Mn-substutited dimeric compound, which is further connected by the H-bonding interactions into a one dimensional supermoleculer chain. Compound 6 is the first Co-substituted double-Dawson type polyoxoanion; compound 7 is a mutiferric-containing double-Dawson type polyoxoanion. The electrocatalytic study indicates that species of 5, 6, and 7 have electrocatalytic activity for nitrite reduction. （C4H10NO）12Na2[α1-MnP2W17O61)]2·7H₂O （5） [（CH3）2NH₂]3K2Na11[α1-CoP2W17O61]2·30H₂O （6） Na8K2[Fe2（H₂O）8（Fe2P2W16O60）2]·41H₂O （7）3. A double-Dawson type polyoxoanion-based chain-like compound 8 has been synthesized by reaction of the hexavacant {P₂W₁₂} and Mn2+ with the assistance of the carboxylate and the organic amine ligands; further, a saturated Dawson polyoxoanion-based organic-inorganic hybrid 9 was obtained by increasing the amount of the carboxylate; A hybrid inorganic-metalorganic sandwich-type polyoxometalate 10 was synthesized by reaction of the trivacant Keggin polyoxoanion, the Cu2+, and the organic amine ligands; self assembly of NaVO3, Na2MoO4·2H₂O and NiCl2·6H₂O with the assistance of organic liginds under hydrothermal conditions results in two dumbbell-like polyoxometalates 11 and 12. Na8H₂L（H₂enMe）₄{Mn（H₂O）2[（W4Mn4O12）（P2W14O54）2]}·17H₂O （8） （H₂L）3[P2W₁₈O62]·7.5H₂O （9） [Cu（enMe）2（H₂O）]2{Cu（enMe）2[Cu（enMe）]3[Cu（H₂O）]3（SbW9O33）2}·5H₂O （10） [Ni（enMe）2]4{[Ni（enMe）2（H₂O）]2[Ni（enMe）2][（VVMoVI8V4IVO40）（VIVO）2]2}·10H₂O （11） [Ni（enMe）2]5{[Ni（enMe）2]2[（VVMoVI4MoV4V4IVO40）（VIVO）₄]2}·2H₂O （12）...