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Reactivity of Polyoxoniobates in Acidic Solution: Controllable Assembly and Disassembly Based on Niobium‐Substituted Germanotungstates
Author(s) -
Li ShuJun,
Liu ShuXia,
Li CongCong,
Ma FengJi,
Liang DaDong,
Zhang Wei,
Tan RuiKang,
Zhang YuanYuan,
Xu Lin
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201001963
Subject(s) - reactivity (psychology) , niobium , thermogravimetry , dimer , chemistry , infrared spectroscopy , natural bond orbital , monomer , crystallography , nuclear chemistry , medicinal chemistry , inorganic chemistry , molecule , organic chemistry , polymer , medicine , alternative medicine , pathology
The reactivity of polyoxoniobates has been studied in acidic solution by grafting niobium onto trivacant Keggin‐type germanotungstates. Four niobium‐containing compounds were obtained in the course of this study. Cs 6.5 K 0.5 [GeW 9 (NbO 2 ) 3 O 37 ] ⋅ 6H 2 O (Cs 6.5 K 0.5 ‐ 1 ) synthesized by the reaction of K 7 H[Nb 6 O 19 ] and A‐α‐Na 10 [GeW 9 0 34 ] in H 2 O 2 solution is a tris(peroxoniobium)‐substituted A‐α‐GeW 9 derivative. Cs 6.5 K 0.5 [GeW 9 Nb 3 O 40 ] ⋅ 10H 2 O (Cs 6.5 K 0.5 ‐ 2 ) is a peroxo‐free compound obtained by eliminating the peroxo groups in 1 . Monomers 1 and 2 as precursors can each afford two nanoscale POMs, dimer Cs 5 [H 15 Ge 2 W 18 Nb 8 O 88 ] ⋅ 18H 2 O (Cs 5 ‐ 3 ) and tetramer Cs 8 K 3 H 9 [Ge 4 W 36 Nb 16 O 166 ] ⋅ 27H 2 O (Cs 8 K 3 H 9 ‐ 4 ), through the formation of NbONb bridges. Disassembly through the cleavage of NbONb bonds from 4 to 2 and 1 was achieved by controlling the pH and by adding H 2 O 2 , respectively. The transition from 1 to 2 can be achieved by simply adding H 2 O 2 to a solution of 1 . All four compounds were characterized in the solid state by elemental analysis, infrared spectroscopy, thermogravimetry, and single‐crystal X‐ray diffraction. 183 W NMR analysis proved that the solid‐state structures of polyanions 1 – 4 were retained after dissolution. Disassembly from 4 to 1 and 2 in solution was observed by 183 W NMR spectroscopy. The UV/Vis spectra of 1 at different pH confirmed that it is stable in the pH range of 0.1–14.0 at room temperature.