Novel Rare Earth Polyborates. 2. Syntheses and Structures
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- 作者：Linyan Li ; Xianglin Jin ; Guobao Li ; Yingxia Wang ; Fuhui Liao ; Guangqin Yao ; and Jianhua Lin
- 刊名：Chemistry of Materials
- 出版年：2003
- 出版时间：June 3, 2003
- 年：2003
- 卷：15
- 期：11
- 页码：2253 - 2260
- 全文大小：317K
- 年卷期：v.15,no.11(June 3, 2003)
- ISSN：1520-5002
文摘
Three novel hydrated rare earth polyborates, Ln[B8O11(OH)5] (Ln = La-Nd) (1), Ln[B9O13(OH)4]·H2O (Ln = Pr - Eu) (2), and Ce[B5O8(OH)]NO3·3H2O (3) have been synthesized byusing boric acid as a flux at 240 
C, starting from rare earth oxides or nitrates and an excessof boric acid. All these polyborates crystallize in monoclinic structures (P21/n) and consist ofborate sheets as the fundamental unit, that is, [LnB6O11] sheet in 1 and 2 and [CeB5O9]sheet in 3. The borate sheets all contain a nine-membered borate ring, of which the rareearth cations are located around the center. The borate frameworks in 1 and 3 are two-dimensional, which are interlinked via ionic Ln-O bonds forming 3D structures. While in2 the borate framework is three-dimensional with small channels filled by water molecules.Annealing the hydrated polyborates 1 and 2 at moderate temperature leads to two anhydrouspentaborates, 
-LnB5O9 (4) for Ln = Pr-Eu and 
-LnB5O9 (5) for Ln = La, Ce. The structureof -LaB5O9 has been determined by an ab initio method using powder X-ray diffractiondata. It crystallizes in a monoclinic structure in the space group P21/c with a = 6.4418(1) Å,b = 11.6888(3) Å, c = 8.1706(2) Å, and = 105.167(1). The structure of -LnB5O9 containsbuckled nine-membered ring borate sheets that are interlinked by BO3 groups forming athree-dimensional framework. The Eu3+-doped -LaB5O9 materials show dominant 5D0 
7F2 emission and a low quenching concentration (0.6 at. %).
C, starting from rare earth oxides or nitrates and an excessof boric acid. All these polyborates crystallize in monoclinic structures (P21/n) and consist ofborate sheets as the fundamental unit, that is, [LnB6O11] sheet in 1 and 2 and [CeB5O9]sheet in 3. The borate sheets all contain a nine-membered borate ring, of which the rareearth cations are located around the center. The borate frameworks in 1 and 3 are two-dimensional, which are interlinked via ionic Ln-O bonds forming 3D structures. While in2 the borate framework is three-dimensional with small channels filled by water molecules.Annealing the hydrated polyborates 1 and 2 at moderate temperature leads to two anhydrouspentaborates, -LnB5O9 (4) for Ln = Pr-Eu and -LnB5O9 (5) for Ln = La, Ce. The structureof -LaB5O9 has been determined by an ab initio method using powder X-ray diffractiondata. It crystallizes in a monoclinic structure in the space group P21/c with a = 6.4418(1) Å,b = 11.6888(3) Å, c = 8.1706(2) Å, and = 105.167(1). The structure of -LnB5O9 containsbuckled nine-membered ring borate sheets that are interlinked by BO3 groups forming athree-dimensional framework. The Eu3+-doped -LaB5O9 materials show dominant 5D0 7F2 emission and a low quenching concentration (0.6 at. %).