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???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^??H₂O?₆]_0.5[Co^??en?₂]₄SNb₈V₈^?V_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???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^??pn?₂]₄HPNb₁₀V₂^?O₄₀(V^?O)₄·17H₂O?2?[Co^??pn?₂]₅PNb₁₂O₄₀(V^?O)₆?OH?₇·15H₂O?3?[Co^??pn?₃]₄PNb₁₂o₄₀(V^?O)₆?OH?₅·20H₂O?4?[Co^??en?₃]₂[Co^??en?₂?H₂O?₂]_0.5H_2.5PNb₁₂O₄₀ V^VV^?O₂·20H₂O?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???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^??en?₂]₄[Cu^??en?₂]₂PNb₁₂O₄₀V^VV^VIO₂?OH?₂·11H₂O?6?[Cu^??pn?₂])₄PNb₁₂O₄₀?V^VO?₄?OH?₅·13H₂O?7?[Cu^??en?₂H₂O][Cu^??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.