Dimerization of A--[SiNb3W9O40]7- by pH-Controlled Formation of Individual Nb-
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- 作者：Gyu-Shik Kim ; Huadong Zeng ; Wade A. Neiwert ; Jennifer J. Cowan ; Donald VanDerveer ; Craig L. Hill ; and Ira A. Weinstock
- 刊名：Inorganic Chemistry
- 出版年：2003
- 出版时间：September 8, 2003
- 年：2003
- 卷：42
- 期：18
- 页码：5537 - 5544
- 全文大小：184K
- 年卷期：v.42,no.18(September 8, 2003)
- ISSN：1520-510X
文摘
The reversible, stepwise formation of individual Nb-
-O-Nb linkages during acid condensation of 2 equiv of A-
-[SiNb3W9O40]7- (1) to the tri--oxo-bridged structure A--[Si2Nb6W18O77]8- (4) is demonstrated by a combinationof X-ray crystallography and variable-pD solution 183W and 29Si NMR spectroscopy. Addition of DCl to a pD 8.4solution of 1 (Li+ salt in D2O) results in formation of a mono-Nb--O-Nb-linked dimer, A--[Si2Nb6W18O79]12- (2;pD = 3.0-1.3). At pD values between 1.6 and 0.3, two isomers (syn and anti) of the di--oxo-bridged dimer,A--[Si2Nb6W18O78]10- (3), are observed by 183W NMR (C2v and C2h symmetry for the syn and anti isomers,respectively; 5 183W NMR signals for each isomer in the ratio 2:2:2:2:1). X-ray-quality crystals of syn-3 were isolatedin 53% yield (syn-A--Cs8H2[Si2Nb6W18O78]·18H2O, orthorhombic, Cmcm, a = 40.847(2), b = 13.2130(7), and c= 16.8179(9) Å at 173K, Z = 4, final R1 = 0.0685). At the low-pD limit of -0.08 (1.2 M DCl), 4 alone is observed.Additional supporting data are provided by variable-pD 29Si NMR spectroscopy. Reversibility of the above processeswas subsequently demonstrated by acquisition of 183W NMR spectra after incremental additions of LiOH to D2Osolutions of 4 to effect its stepwise hydrolysis to 2 equiv of 1.
-O-Nb linkages during acid condensation of 2 equiv of A--[SiNb3W9O40]7- (1) to the tri--oxo-bridged structure A--[Si2Nb6W18O77]8- (4) is demonstrated by a combinationof X-ray crystallography and variable-pD solution 183W and 29Si NMR spectroscopy. Addition of DCl to a pD 8.4solution of 1 (Li+ salt in D2O) results in formation of a mono-Nb--O-Nb-linked dimer, A--[Si2Nb6W18O79]12- (2;pD = 3.0-1.3). At pD values between 1.6 and 0.3, two isomers (syn and anti) of the di--oxo-bridged dimer,A--[Si2Nb6W18O78]10- (3), are observed by 183W NMR (C2v and C2h symmetry for the syn and anti isomers,respectively; 5 183W NMR signals for each isomer in the ratio 2:2:2:2:1). X-ray-quality crystals of syn-3 were isolatedin 53% yield (syn-A--Cs8H2[Si2Nb6W18O78]·18H2O, orthorhombic, Cmcm, a = 40.847(2), b = 13.2130(7), and c= 16.8179(9) Å at 173K, Z = 4, final R1 = 0.0685). At the low-pD limit of -0.08 (1.2 M DCl), 4 alone is observed.Additional supporting data are provided by variable-pD 29Si NMR spectroscopy. Reversibility of the above processeswas subsequently demonstrated by acquisition of 183W NMR spectra after incremental additions of LiOH to D2Osolutions of 4 to effect its stepwise hydrolysis to 2 equiv of 1.