Syntheses, Structures And Properties Of Molybdenum (Vanadium) Metal-oxygen Clusters

In this paper, by the applications of hydrothermal technique, through the use of a metal element (Mo, W, V etc.) acid (salt) or oxides, selecting the appropriate organic ligands as well as the second transition metal salts, controlling the temperature and pH of reaction system, we synthesized a series of polyoxometalates with novel structures and interesting properties. The structures of all the compounds have been characterized by elemental analyses, IR spectra and X-ray diffraction analyses, some compounds have been characterized by UV-Vis, XPS spectra, TG, XRD, EPRanalyses and magnetic property studies.In this paper, 17 new metal oxygen clusters were synthesized.I. Vanadium oxygen clusters and molybdenum- oxygen clusters By the applycation of hydrothermal synthesis technology, we synthesized two vanadium oxygen clusters and two molybdenum oxygen clusters. [Fe(2,2`-bipy)<sub>3</sub>]<sub>2</sub>[HV<sub>6</sub><sup>V</sup>V<sub>10</sub><sup>IV</sup>O<sub>38</sub>(Cl)]·4.67H<sub>2</sub>O 1; [Ni(enMe)<sub>3</sub>]<sub>2</sub>[H<sub>4</sub>V<sub>5</sub><sup>V</sup>V<sub>10</sub><sup>IV</sup>O<sub>36</sub> (Cl)]·2H<sub>2</sub>O 2; [HN(C<sub>2</sub>H<sub>5</sub>)<sub>3</sub>]<sub>3</sub>[PMo<sub>12</sub>O<sub>40</sub>] 3; [NH<sub>2</sub>(C<sub>2</sub>H<sub>4</sub>NH<sub>2</sub>)<sub>2</sub>][Mo<sub>5</sub>P<sub>2</sub>O<sub>23</sub>]<sub>4</sub>. Compound 1 is composed of the [HV<sub>6</sub><sup>V</sup>V<sub>10</sub><sup>IV</sup>O<sub>38</sub>(Cl)]6- and transition metal complex [Fe(2,2`-bipy)₃]³⁺, Compound 2 is composed of an [H₄V₅^VV₁₀^IVO₃₆(Cl)]4- cluster and [Ni(enMe)₃]₂+. Both compounds are further linked into a novel two dimensional structure through hydrogen bonds. Compound 3 is composed of a pseudo-Keggin [PMo₁₂O₍40_]^3- anions and the protonated TEA cations. Compound 4 is composed of the [Mo₅P₂O²³]^6- anions and the protonated DETA moieties. Compound 3 and Compound 4 all exhibit an unusual 3-D supramolecular network structure through N-H···O hydrogen bonding interactions.II. AsIII-VIV Polyoxometalates oxygen clustersBy the applycation of hydrothermal synthesis technology, we synthesized two AsIII-VIV polyoxometalates. [HAs₆V₁₅O₄₂(H₂O)][Cu(enMe)₂]₂.5·2H₂O 5;[H₂enMe]₂ [As₈V₁₄O₄₂ (H₂O)]·3H₂O 6. The two compounds have been firstly hydrothermally synthesized. X-ray crystallographic studies reveal that compound 5 represents the first example of 2-D structure constructed from [HAs₆V₁₅O₄₂(H₂O)]5- anions and TMCs. The anions [HAs₆V₁₅O₄₂(H₂O)]5- are connected by two different types of double-bridges into a novel chain structure. Moreover, there exits the"orientation"of the anions in chains, it exhibits an unprecedented -A-B↑-C-B↓-A-B↑-C-B↓- linking mode. And the chains are further connected into a brick-wall-like two-dimensional layer structure constructed from POMs and TMCs. Compound 6 exhibits very interesting stacking mode. The trimers are stacked along the c axis into a novel -A-B-A-B- stacking mode.III. Keggin-structure molybdenum-vanadium oxygen clustersBy the applycation of hydrothermal synthesis technology, we synthesized seven Keggin-structure tungsten oxygen clusters. [PMo₈V₆O₄₂][Co(Phen)₂(H₂O)]₂ [TEA]₂A·H₃O·3H₂O 7; [PMo₈V₆O₄₂][Ni(Phen)₂(H₂O)]₂[TEA]₂·H₃O·3H₂O 8; [PMo₈V₆O₄₂][Zn(Phen)₂]₂[4,4′-bpy]·H₃O·3H₂O9; [PMo₈V₆O₄₂][Co(Phen)₂][py]·4H₂O 10; [PMo₈V₆O₄₂][Co(Phen)₂][Him]₂·2H₃O·3H₂O 11; {[PMo^VI₁₀V^IV₄O₄₂][Co(Phen)₂ (H₂O)]₂}{[PMo^VI₁₀V^IV₄O₄₂][Co(Phen)₂]₂}·2OH-·4,4′-bpy 12; [H₂NC₄H₈NH₂]₆ [ Mo^VI₁₆V^V₁₂ P₂O₈₄]·4H₂O 13The seven compounds all were first synthesized. Compounds 7-11 all contain [PMo₈V₆O₄₂]5- anion, transition metal complex, organic amine, protonated water molecule, and water molecules. Compound 7, 8 and 9 are POM supported coordination complexes, while the compound 10 and compound 11 exhibit 1-D extended structures. In addition, the POMs, TMCs and the organic amines construct a supramolecular structure through hydrogen bonds between the oxygen atoms of the water molecules and the oxygen atoms of the anions and the weak van der Waals interactions. Among compounds 10, 11 and 12, there exit a mass of phenol rings between organic amine and transition metal complex, however, there did not exist strongπ···πinteractions between the rings for the steric hindrance.Compound 12 contains two half of crystallographically different anions [PMo^VI₁₀V^IV₄O₄₂]^3-, named as POM 1 and POM 2, respectively. The POM 1 supports two [Co(Phen)₂(H₂O)]²⁺ TMCs with the Co-O bond forming a novel bi-supported coordination complex. POM 2 interconnect [Co(Phen)₂]²⁺ via the Co-O bonds to yield an unusual infinite 2-D {[PMo₁₀V₄O₄₂][Co(Phen)₂]²⁺} positive layer. Moreover, the discrete POM is sandwiched by two adjacent layers into a novel–ABAB- stacking fashion. According to the synthesis of Compound 7-12, we can get an interesting conclusion: different building blocks will build different structures. This approach using different building blocks to build different structures is quite attractive and appears to hold the key to the development of rational approaches for tailor-making materials based on polyoxometalates with desirable features. Compound 13 is composed of [Mo^VI₁₆V^V₁₂P₂O₈₄]^14- by polymerization of two basic unit { Mo8V6P O42}, containing six piperazines and five water molecules around. The every four dimers and the seven piperazines along a certain direction are formed wind model like units through the hydrogen bonds, and the sub-unit repeats expansion to form a beautiful two-dimensional polymer layer, and then stacks into a three-dimensional network structure.V. Keggin-structure molybdenum- antimony oxygen clustersBy the applycation of hydrothermal synthesis technology, we synthesized four Keggin-structure molybdenum- antimony oxygen clusters. [PMo₁₂Sb₂O₄₀][Cu (enMe)₂]·4H₂O14;[PMo₁₂Sb₂O₄₀][Ni(enMe)₂]·4H₂O15;[PMo₁₂Sb₂O₄₀][Cu(en)₂]·H₃O·H₂O 16; [SiMo^VI₉MoV₃O₄₀Sb₂][SiMo^VI₇MoV₅O₄₀Sb₂](H₂en)₂ (en)0.5·(H₂O)8 17.Since our group prepared the first Sb capped Pseudo-Keggin POM {PMo₁₂O₄₀Sb₂} in 2006, Compounds 14-17 were prepared first time for extended structures containing antimony. Compounds 14-16 all exhibit the well-known Pseudo-Keggin core {PMo12O40} with two antimony atoms capping two opposite pits. The most remarkable feature of compound 14-16 are that the novel anion [PMo12O40Sb2]₂- is utilized as a multidentate chelating ligand, coordinating to the transition metal complex via the terminal oxygen atoms to yield an unprecedented 1-D chain. The linking mode of the chain is -A-A-A among compounds 14-16. For compound 17, it contains the first two types of Sb capped Keggin anions. The Si1, Si2 and Si3 POMs are connected together into a 2-D supramolecular layer (layer A) structure through the O···O interactions of the terminal oxygen atoms of the adjacent Si1, Si2 and Si2 POMs. The linking mode of the layer based on Si1 and Si2 POMs is -A-B-A-, while the linking mode of the layer based on Si3 is -A-A-A-. The most interesting feature is that the two different type layers are stacked together alternately. There still exit very complex hydrogen bonding interactions between the oxygen atoms of the anions and the water molecules into a novel supramolecular structure.