Syntheses, Structures And Properties Of Molybdenum (Tungsten) Oxygen Organic-Inorganic Hybrid Materials

Polyoxometalates (POMs) represent a fascinating class of inorganic chemistry with a structural variety and interesting properties, which are of use in fields as diverse as catalysis, sorption, molecular electronics, medicine, etc. As the applications of hydrothermal technique on the syntheses, various organic-inorganic hybrid materials of particular properties emerges constantly and much attention has been caused on the performances studies of various materials. In this field, an important advance is to decorate well-known polyoxoanions with various organic and/or transition metal complex moieties and then to link them up into one-, two-, even three-dimensional extended solid materials in appropriate ways. The introduction of metal complex can not only enrich the frameworks of polyoxometalates but also ameliorate their electronic and mangnetic properties. Based on this mechanism, we synthesized metal-oxygen clusters or cluster-polymers based on molybdenum, tungsten and arsenic-molybdenum oxygen clusters. On the bases of X-ray structural analyses, some central compounds have been characterized by IR, XPS, EPR, XRD spectra. The thermal analyses and magnetic properties of some compounds have been studied, which would take an important role in the explorations of structures and functions for the compounds.I. Molybdenum-oxygen clusters and molybdenum-oxygen organic -inorganci hybrid meterials.Applying in hydrothermal synthesis reactions, we synthesized six molybdenum- oxygen clusters and molybdenum-oxygen organic-inorganci hybrid meterials. (H₂bipy)₂[β-Mo₈O₂₆] 1,(Hbipy)₃(bipy)₂[K(β-Mo₈O₂₆)]·2H₂O 2,(Hbipy)₃(bipy)₂ [K(β-Mo₈O₂₆)]·H₂O 3 , (nBu)₄[α-Mo₈O₂₆] 4 , [Cu(4,4'-bipy)]₂Mo2O7 5 ,MoO3(2-2'-bipy) 6. Compounds 1-4 are composed of the well-known [Mo₈O₂₆], cluster anion, in which compounds 1-3 are the (β-Mo₈O₂₆) isomer, while the compound 4 is [α-Mo₈O₂₆] isomer. Compounds 1-4 are linked into novel 3D layer through hydrogen bonding interactions, respectively. The same 1D [K(β-Mo₈O₂₆)] chains are contained in both of compounds 2 and 3. compounds 5 and 6 exhibit the novel 3-D network structure and 1-D chain-like structure, respectively. The X-ray single crystal analysis, elemental analysis, IR, XPS, and TG etc., have been performed on these compounds.II Arsenic-molybdenum oxygen clustersApplying in hydrothermal synthesis reactions, we synthesized eight arsenic- molybdenum oxygen clusters. K₂[H₂(As₃O₃)₂(Mo₆O₁₈)(NiO₆)]·H₂O₇, K₂[H₂ (As₃O₃)₂(Mo₆O₁₈)(CoO6)] 8, [Zn(H₄,4'-bipy)₂(H₂O)₄][(As₃O₃)₂(Mo₆O₁₈) (ZnO₆)]·4H₂O 9, (H₂4,4'-bipy)₃[As₂Mo₁₈O₆₂]10, [Cu(2,2'-bipy)₂H₂O]{(As₂Mo₁₈O₆₂) [Cu(2,2'-bipy)]₃}·2OH·6H₂O 11, [(4,4'-bipy)]₃[As^IV₂Mo₁₈O₅₆ (AsIIIO₃)₂]·4H₂O 12, (H₂4,4'-bipy)₂[Co(2,2'-bipy)₃]₂K[As₂Mo₁₈O₆₂][As₂Mo₁₈O₅₉(AsIIIO₃)]·1.5H₂O 13, K₅Mo₈O₂₄(OH)₂AsO₄·2H₂O 14. These compounds can be grouped into three systems based on the difference of structure types. The compounds 7-9 belonging to the modified Anderson system: In the compounds 7-9, two ring-link (As₃O₃) units cap on the face of Anderson cluster anions which has the plane arrangement to construct a novel capped-Anderson types. Compounds 7 and 8 almost has the same structure, and the differences are the number of lattice water and the center metal atoms. As we known, compound 7 represents the first capped-Anderson complex with the Ni atom resides in the center site. The unusual feature of compounds 7 and 8 is that the [(As₃O₃)₂(Mo₆O₁₈)(NiO₆)]4- units are not discrete but are linked to the potassium cations via terminal oxo atoms, giving rise to a 3-D framework. To best of our knowledge, although the similar cluster anions with that in compound 7-9 have been reported, all of those exhibit discrete structure or further connect to form multi-dimensional supramolecular structure via hydrogen-bonding interactions. Compounds 7 and 8 are the first example of 3-D complex which use [(As₃O₃)₂(Mo₆O₁₈)(MO₆)]4- (M=Ni or Co)cluster as building units to connect to the bridge sites (potassium ions). Compound 9 represents a new 3-D network structure constructed from transition metal coordination cations [Zn(H₄,4'-bipy)₂(H₂O)₄]4+, lattice water molecules and polyoxoanions [(As₃O₃)₂(Mo₆O₁₈)(ZnO₆)]4- via multi-point N-H···O and O-H···O hydrogen bonding interactions. All of the compounds are characterized by IR, elemental analyses, XPS and single crystal X-ray diffraction analyses, respectively. In addition, the magnetic behaviors for compounds 7 and 8 have been investigated.Compounds 10-13 (H₂4,4'-bipy)₃[As₂Mo₁₈O₆₂] 10, [Cu(2,2'-bipy)₂H₂O] {(As₂Mo₁₈O₆₂)[Cu(2,2'-bipy)]₃}·2OH·6H₂O 11, [(4,4'-bipy)]₃[As^IV₂Mo₁₈O₅₆ (AsIIIO₃)₂]·4H₂O 12, (H₂4,4'-bipy)₂[Co(2,2'-bipy)₃]₂K[As₂Mo₁₈O₆₂][As₂Mo₁₈O₅₉ (AsIIIO₃)]·1.5H₂O 13) exhibit a new type modified polyoxometal complex constructed from the [α-As₂Mo₁₈O₆₂]6- polyoxoanion: compound 10 exhibits a novel 3-D supramolecular structure linked by the protoned 4,4'-bipy groups. Compounds 10-13 are capped-Dawson type polyoxometalates. The neutral cluster [As₂Mo₁₈O₆₂{Cu(2,2'-bipy)}₃] in 10 exhibits a modified Dawson type structure, which is capped by three transition metal coordination fragments [Cu(2,2'-bipy)]₂+ on the hole sites of the Dawson polyoxoanion. While 12 exhibits the first structurally characterized bi-capped Dawson cluster which is also derived from [α-As₂Mo₁₈O₆₂]6- polyoxoanion and capped by two main group atoms As. Additionally, both of these two capped Dawson complex further connect to form fascinating 2-D supramolecular layer through hydrogen-bonding interactions. In the cluster unit of 13, there are two types of cluster anions. One is the well-known Dawson type polyoxoanion and the other is mono-capped Dawson type polyoxoanion, and the mono-capped Dawson type polyoxoanion almost has the same capped-structure with 12, which is also derived from [α-As₂Mo₁₈O₆₂]6- polyoxoanion and capped by one main group atoms As on the hole of the cluster. All of the compounds are characterized by IR, elemental analyses, XPS and single crystal X-ray diffraction analyses, respectively. In addition, the magnetic behavior for compound 11 has been investigated.Compound K₅Mo₈O₂₄(OH)₂AsO₄·2H₂O 14 exhibit a novel 3D extend structure based on AsMo8 cluster units. Adjacent cluster anions [AsMo8O₃₀H₂]₅- are maninly linked through O-K-O bonds and further connected to form a 3D networ with the lattice water molecules reside in the hole.III Tungsten oxygen clustersApplying in hydrothermal synthesis reactions, we synthesized four tungsten oxygen clusters. :Compound (en)₃Co3P4W4O28 15 represents a 3D structural orgnaic-inorganic hybrid materialm, and the protoned en molecules reside in the hole.compound H₃(4,4'-bipy)₄[PW₁₂O₄0]·6H₂O 16 is a 3-D supramolecular network constructed from [PW₁₂O₄0] cluster, organic groups 4,4'-bipy molecules and lattice waters. compound [Cu(O-2,2'-bipy)]8[PW₁₂O₄0 {Cu(4,4'-bipy)₂}2]·2H₂O 17 was synthesized by PW₁₂O₄0 as the origin materials,and exhibits a novel 2-D layer-like structure which is linked by the TMCs, the insitu-hydroxy 2,2'-bipy coordinated units [Cu(O-2,2'-bipy)] occupy the interbedded of adjacent layer;compound (H₂4,4'-bipy)₃[AsW11ZnO₃₉]·H₃O 18 is a 1-D chain-like structure,and the cluster unit is [AsW11ZnO₃₉] polyoxoanion,All of the compounds are characterized by IR, elemental analyses, XPS and single crystal X-ray diffraction analyses, respectively. In addition, the magnetic behavior for compound 15 has been investigated.IV Mixed molybdemum-tungsten oxygen clusterThe compound 19 exhibits a mixed molybdenum-tungsten polyoxometal complex which is capped with four Co(dien) fragments and with main group element As occupying the center site. As shown in Fig. 1, the title compound consists of the highly reducedε-Keggin structure of [(AsVO₄)MoV8WVI4 O33(μ2-OH)₃]8- obtained from the rotation of all four M3O13 groups of theα-Keggin isomer by 60o. All of the compounds are characterized by IR, elemental analyses, XPS and single crystal X-ray diffraction analyses, respectively. In addition, the magnetic behavior for compound 19 has been investigated.