 |
 |
 |
 |
 |
 |
||
 |
 |
 |
 |
 |
| 1 | 1/1 | 返回列表 |
| 查看: 728 | 回復(fù): 0 | ||
kebochen061金蟲 (正式寫手)
|
[求助]
thermodynamic sink
|
|
The title compound 1 was synthesized by the hydrothermal reaction of a mixture of concentrated H 3 PO 4 , V 2 O 5 , hydrous niobium oxide (niobic acid), and TMAOH at 130 8C for 16 h, leading to the formation of a clear, yellow solution. In our previous synthesis of V 3 Nb 12 , we found that low temperatures (110 8C) gave better yields because higher temperatures and longer reaction times lead to the formation of tancolored insoluble byproducts, thus lowering the yields.In that system, the tan precipitate was a thermodynamic sink.However, we found that by incorporating H 3 PO 4 into the reaction, these undesired tan precipitates did not form, even at elevated temperatures and much longer reaction times, for example at 150 8C for 60 h, indicating that phosphate in the reaction system stabilizes the cluster and prevents the formation of insoluble precipitate. We characterized the PV 2 Nb 12 cluster using negativemode ESI-MS, which showed a series of signals of 4,3 and 2 charged ions that match calculated peak positions for PV 2 Nb 12 adducts of protons and TMA cation (Figure 1).The peak separations are differentiated by the number of combined charge-balancing TMA and protons. The peaks of PV 2 Nb 12 were at lower m/z value than the V 3 Nb 12 because of the substitution of the central vanadium atom with a phosphorus atom, which has a lower atomic mass. ESI-MS thus allowed us to easily identify PV 2 Nb 12 in mixtures with V 3 Nb 12 and provided qualitative information about purity and redox state. As we observe that even weakly bound TMA can cause changes in chemical shifts in the 51V NMR signals of the two capping VO 5 in 1, we anticipate that the more strongly coordinating alkali cation analogue of PV 2 Nb 12 will have much greater shifted 51V peak positions if the two capping VO 5 have different populations of locally coordinated alkali cations. The pH-dependent 31P and 51V NMR spectra were collected between pH 3.8 and 13.3. The UV/Vis spectra of PV 2 Nb 12 show no significant pH variations in the stable pH region, with an increase in the absorbance at wavelengths at very low and very high pH, re-spectively, which is consistent with our conclusions that the compound is dissociating (Figure 7). Precipitation at low pH may also be associated with protonation and charge-neutral-ization of the cluster, and we observed some small changes in the UV/Vis spectra near 248 nm that might indicate protonation In the lower-energy region, two isosbestic points at about 250 and 260 nm are observed, which is consistent with pH-dependent speciation changes, such as controlled dissociation. The greater pH stability of PV 2 Nb 12 relative to V 3 Nb 12 is evident both in the NMR spectroscopy and pH variation of the UV/Vis absorbance. Another comparison can be made to the isostructural phosphovanadate ion, [PV 14 O 42 ] 9 which is stable in a narrower pH range, 1.5-pH3, than PV 2 Nb 12 . For this PV 14 O 42 molecule, the 17O,31P, and 51VNMR spectra have all been interpreted to indicate steady changes in protonation state. This effect is consistent with the well-known reduced lability of phosphate to substitution at the oxygen sites. We speculate that the phosphate reduces access to lacunary metastable states in the Keggin ion structure that form by dynamic bond-length modulation (or even breaking) being central to the reactivity and dissociation of large metal-oxide clusters. In our view, the rate of equilibration with lacunary metastable states is faster |
回復(fù)此樓» 猜你喜歡
291求調(diào)劑
已經(jīng)有6人回復(fù)
-
315分求調(diào)劑
已經(jīng)有6人回復(fù)
-
277跪求調(diào)劑
已經(jīng)有8人回復(fù)
-
295求調(diào)劑
已經(jīng)有5人回復(fù)
-
295材料工程專碩求調(diào)劑
已經(jīng)有3人回復(fù)
-
085701環(huán)境工程求調(diào)劑
已經(jīng)有5人回復(fù)
-
083000學(xué)碩274求調(diào)劑
已經(jīng)有4人回復(fù)
-
275求調(diào)劑
已經(jīng)有8人回復(fù)
-
一志愿211院校 344分 東北農(nóng)業(yè)大學(xué)生物學(xué)學(xué)碩，求調(diào)劑
已經(jīng)有8人回復(fù)
-
085602 307分 求調(diào)劑
已經(jīng)有5人回復(fù)
相關(guān)版塊跳轉(zhuǎn)
我要訂閱樓主 kebochen061 的主題更新
| 1 | 1/1 | 返回列表 |
| 最具人氣熱帖推薦 [查看全部] | 作者 | 回/看 | 最后發(fā)表 | |
|---|---|---|---|---|
|
[考研] 295材料工程專碩求調(diào)劑 +3 | 1428151015 2026-03-27 | 3/150 |
|
|---|---|---|---|---|
|
|
[考研] 322求調(diào)劑 +3 | 宋明欣 2026-03-27 | 3/150 |
|
|
[考研] 食品工程專碩一志愿中海洋309求調(diào)劑 +3 | 小張zxy張 2026-03-26 | 5/250 |
|
|
|
[考研] 一志愿北京化工大學(xué) 070300 學(xué)碩 336分 求調(diào)劑 +9 | vv迷 2026-03-22 | 9/450 |
|
|
|
[考研] 材料292調(diào)劑 +12 | 橘頌思美人 2026-03-23 | 12/600 |
|
|
|
[考博] 26申博 +3 | 加油沖��！ 2026-03-26 | 3/150 |
|
|
|
[考研] 307求調(diào)劑 +8 | 超級伊昂大王 2026-03-24 | 9/450 |
|
|
|
[考研] 314求調(diào)劑 +3 | 溪云珂 2026-03-26 | 3/150 |
|
|
|
[考研] 調(diào)劑推薦 +5 | 清酒714 2026-03-26 | 6/300 |
|
|
|
[考研] 材料求調(diào)劑 +5 | .m.. 2026-03-25 | 5/250 |
|
|
|
[考研] 求調(diào)劑323材料與化工 +7 | 1124361 2026-03-24 | 7/350 |
|
|
|
[考研] 325求調(diào)劑 +3 | Aoyijiang 2026-03-23 | 3/150 |
|
|
|
[考研] 生物學(xué) 296 求調(diào)劑 +4 | 朵朵- 2026-03-26 | 6/300 |
|
|
|
[考研] 334分 一志愿武理 材料求調(diào)劑 +4 | 李李不服輸 2026-03-26 | 4/200 |
|
|
|
[考研] 材料277求調(diào)劑 +5 | min3 2026-03-24 | 5/250 |
|
|
|
[考研]
 085404電子信息284分求調(diào)劑
+4
|
13659058978 2026-03-24 | 4/200 |
|
|
|
[考研] 材料/農(nóng)業(yè)專業(yè)，07/08開頭均可，過線就行 +3 | 呵唔哦豁 2026-03-23 | 4/200 |
|
|
|
[論文投稿] 急發(fā)核心期刊論文 +3 | 賢達問津 2026-03-23 | 5/250 |
|
|
|
[考研] 276求調(diào)劑 +3 | YNRYG 2026-03-21 | 4/200 |
|
|
|
[考研]
 一志愿東華大學(xué)控制學(xué)碩320求調(diào)劑
+3
|
Grand777 2026-03-21 | 3/150 |
|