Synthesis,Structures And Properties Of Vanadium-Containing Polyoxoniobate-Based Organic-Inorganic Hybrid Compounds

The Keggin-type polyanion is one of the most thoroughly studied and widely used members in the family of polyoxometalates（POMs）.The incorporation of Keggin POMs with large cations,such as transition-metal（TM）organic units or organic amine cations,not only affords a variety of extended organic-inorganic hybrid compounds,but also provides POMs with wide applications.In this paper,on the basis of molecular design and assembly,we carried on research on reactivity of the vanadium-containing polyoxoniobates with transition metal ions or organic amine cations,by use of baker,hydrothermal or hydrothermal-baker methods,and a series of vanadium-containing Keggin-type polyoxoniobate-based organic-inorganic hybrid compounds,with transition metals complexes or organic amine cations as decorating units or counter ions,were successfully obtained.The compounds were structurally characterized by single crystal X-ray diffractions,elemental analyses,PXRD,IR,UV,XPS,TG analysis.X-ray photoelectronic spectroscopy were used to determine the oxidation state of transition metal centers.1.Using K₇HNb₆O₁₉·8H₂O as niobate precursor,V₂O₂（SO₄）₂（H₂O）₆ as vanadate precursor,in the presence of Co（Ⅱ）salts and ethanediamine（en）,a vanadium-containg S-centred polyoxoniobate-based organic-inorganic hybrid compound,with cobalt complexes as the decorating/bridging units,was hydrothermally isolated.[Co^Ⅱ（H₂O）₆]_0.5[Co^Ⅱ（en）₂]₄SNb₈V₈^ⅣV_1.25^VO_45.25（OH）_2.75·13H₂O（1）Compound 1 contains the first S-centered polyoxoniobate,SNb₈V_9.25O_45.25,also known as the largest oxovanadoniobate cluster hitherto obtained.The polyanion is covalently extended by cobalt complexes into a three-dimensional architecture via terminal oxygen atoms from NbO₆ or VO₅.The magnetic studies show 1 orders as a weak ferromagnet at low temperature.2.Using K₇HNb₆O₁₉·8H₂O as niobate precursor,VOPO₄·2H₂O as vanadate precursor,in the presence of Co（Ⅱ）salts and ethanediamine/1,2-diaminopropane（pn）,four vanadium-contanining P-centered polyoxoniobate-based orgranic-inorganic hybrid compounds,with cobalt complexes as the decorating/bridging units,were hydrothermally isolated.The controllable synthesis of compounds 2 and 3 is realized by changing hydrothermal temperature or adding N-aminoethylpiperazine as additive.[Co^Ⅱ（pn）₂]₄HPNb₁₀V₂^ⅣO₄₀(V^ⅣO)₄·17H₂O（2）[Co^Ⅱ（pn）₂]₅PNb₁₂O₄₀(V^ⅣO)₆（OH）₇·15H₂O（3）[Co^Ⅱ（pn）₃]₄PNb₁₂o₄₀(V^ⅣO)₆（OH）₅·20H₂O（4）[Co^Ⅲ（en）₃]₂[Co^Ⅲ（en）₂（H₂O）₂]_0.5H_2.5PNb₁₂O₄₀ V^VV^ⅣO₂·20H₂O（5）Compound 2 features a new divanadium-substituted Keggin polyoxoniobates capped by four vanadyl groups,PNb₁₀V₂O₄₀（VO）₄,and 3 features a hexa-capped Keggin polyoxoniobates,PNb₁₂O₄₀（VO）₆;those polyanions were covalently extended by cobalt complexes into three-dimensional architectures via terminal oxygen atoms from NbO₆ or VO₅.Compound 4 contains a dicapped Keggin polyoxoniobates,PNb₁₂O₄₀（VO）₂,and 5 contains a hexa-capped Keggin polyoxoniobates,PNb₁₂O₄₀（VO）₆;those polyanions were arranged with cobalt complexes cations via electronic interactions and hydrogen bonding interactions into three-dimensional supramolecular frameworks.In particular,compound 5 showed size-selective uptake over water molecules.3.Using K₇HNb₆O₁₉·8H₂O as niobate precursor,VOPO₄·2H₂O as vanadate precursor,in the presence of Cu（Ⅱ）salts and ethanediamine/1,2-diaminopropane,three vanadium-containing P/V-centered polyoxoniobate-based orgranic-inorganic hybrid compounds,with copper complexes as the decorating/bridging units,were hydrothermally isolated.[Cu^Ⅱ（en）₂]₄[Cu^Ⅱ（en）₂]₂PNb₁₂O₄₀V^VV^VIO₂（OH）₂·11H₂O（6）[Cu^Ⅱ（pn）₂])₄PNb₁₂O₄₀（V^VO）₄（OH）₅·13H₂O（7）[Cu^Ⅱ（en）₂H₂O][Cu^Ⅱ（en）₂]₄V^VNb₁₂O₄₀（V^VO）₄（OH）₇·8H₂O（8）Compound 6 contains a dicapped polyoxoniobate,PNb₁₂O₄₀（VO）₂,which was arranged with copper complexes cations via electronic interactions and hydrogen bonding interactions into three-dimensional supramolecular frameworks.Compounds7-8 both contain a tetracapped polyoxoniboate,XNb₁₂O₄₀（VO）₄,and the heteroatom in 7 is P and that in 8 is V,respectively.Those polyanions were covalently extended by copper complexes into three-dimensional or one-dimensional architectures via terminal oxygen atoms from NbO₆ or VO₅.4.Using[（CH₃）₄N]₉PNb₁₂O₄₀（VO）₂·19H₂O as starting materials,by ion exchange or precipitation reactions,two vanadium-containing P/V-centered polyoxoniobate-based organic-inorganic hybrid layered compounds were obtained.In the presence of K₇HNb₆O₁₉·8H₂O,ethanediamine,a dicapped V-centered Keggin polyoxoniobate-based organic-inorganic compound was isolated.（CH₃）₄N[C₁₆H₃₃（CH₃）₃N)]₈PNb₁₂O₄₀（V^VO）₂·6H₂O（9）[C₁₈H₃₇（CH₃）₃N)]₉PNb₁₂（V^VO）₂·15H₂O（10）（H₂en）_7.5（Hen）VNb₁₂O₄₀（NbONO₃）₂（OH）₅·2CH₃OH·7H₂O（11）Compounds 9-10 were hybrid surfactant compounds as lamllar phases,whereas11 was an interesting Keggin polyoxoniobate-based organic-inorganic compound,with diprotonated 1,2-diaminoethane as the counter ions.Those polyanions were arranged with organic amine cations via electronic interactions and hydrogen bonding interactions into three-dimensional supramolecular structures.