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Synthesis, structure, and properties of a novel hydrated borate Rb4[B4O5(OH)4]2·3H2O
Solid State Sciences 13 (2011) 82e87
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Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Synthesis, structure, and properties of a novel hydrated borate Rb4[B4O5(OH)4]2$3H2O Yi Zhao a, b, Shilie Pan b, *, Feng Li b, Yongjiang Wang b, Xiaoyun Fan b, Xiaoyu Dong b, Dianzeng Jia a, Jixi Guo a, Zhongxiang Zhou b a
College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, China Xinjiang Key Laboratory of Electronic Information Materials and Devices, Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, 40-1 South Beijing Road, Urumqi 830011, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 April 2010 Received in revised form 29 September 2010 Accepted 21 October 2010 Available online 29 October 2010
Rb4[B4O5(OH)4]2$3H2O has been grown by slow evaporation method with crystal sizes up to 11 mm 7 mm 4 mm. Its crystal structure has been determined by single-crystal X-ray diffraction and further characterized by powder X-ray diffraction (XRD), IR, and TGA. It crystallizes in the orthorhombic space group Pbcn, with a ¼ 16.3984(14) Å, b ¼ 7.7850(7) Å, c ¼ 16.0763(16) Å, and Z ¼ 4. It contains isolated [B4O5(OH)4]2 polyanions, free water molecules and Rb cations. The Rb(1) and Rb(2) atoms are coordinated by nine and ten oxygen atoms, respectively. Connections between isolated [B4O5(OH)4]2 polyanions are provided by Rb polyhedra and the hydrogen-bonding to form a three-dimensional network. Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords: Rb4[B4O5(OH)4]2$3H2O Borate Crystal structure Crystal growth
1. Introduction
2. Experimental section
In the past several decades, much interest has been focused on alkali borate compounds [1e5] because some of these compounds show interesting physical properties, such as nonlinear optical behavior for KB5O8$4H2O (KB5) [2], LiB3O5 (LBO) [3], CsB3O5 (CBO) [4], CsLiB6O10 (CLBO) [5], Na2B5O8(OH)3$2H2O [6], K3[B3O4(OH)4]$ 2H2O [7], Cs[B(OH)4]$2H2O [8]. Unique character of borate structure determines their large nonlinear optical coefficient, a broad transparency range, and high damage threshold [9,10]. In order to synthesize new borates and search for new materials, we studied the system Rb2OeB2O3eH2O. Some researchers have investigated this system and found the compounds Rb[B5O6(OH)4]$2H2O [11], Rb[B5O7(OH)2]$0.5H2O [12], Rb2[B12(OH)12]$2H2O [13], Rb4B10O17$6H2O [14], Rb3[B3O4(OH)4]$ 2H2O [15], Rb2[B4O5(OH)4]$3.6H2O [16]. The extensive exploration on this system led us to find the new compound Rb4[B4O5(OH)4]2$3H2O (RBOH). In the paper, the crystal structure, powder XRD, IR, and TGA curves of the title compound were reported.
2.1. Compound synthesis
* Corresponding author. Tel.: þ86 991 3674558; fax: þ86 991 3838957. E-mail address: [email protected] (S. Pan). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.10.013
Single crystals of RBOH were synthesized via slow evaporation at room temperature. The starting materials used in the preparation were Rb2CO3 (99.0%, Xinjiang Chemical Co. Ltd.), H3BO3 (99.5%, Tianjin Baishi Chemical Co. Ltd.). The powder mixture of Rb2CO3 and H3BO3 with a molar ratio of 1:1 was used as received and then dissolved in deionized water. The obtained solution was allowed to evaporate slowly at room temperature. Single crystals of a new compound, RBOH, were obtained with sizes up to 11 mm 7 mm 4 mm (Fig. 1). The experimental XRD pattern of RBOH is in agreement with the calculated one based on its single-crystal data, suggesting that the synthesized phase is pure (Fig. 2). 2.2. X-ray crystallography Powder XRD analysis for RBOH was performed at room temperature on an automated Bruker D8 ADVANCE X-ray diffractometer equipped with graphite monochromatized Cu Ka radiation in the angular range from 10 to 70 (2q) with a scanning step width of 0.02 and a fixed counting time of 1 s/step. A colorless and transparent
Y. Zhao et al. / Solid State Sciences 13 (2011) 82e87
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Table 1 Crystal data and structure refinement for RBOH. Empirical formula Formula weight Temperature [K] Wavelength [Å] Crystal system Space group Unit cell dimensions
Fig. 1. Photograph of RBOH crystal. (The minimum scale of the ruler is 1 mm).
crystal of RBOH with dimensions 0.26 mm 0.18 mm 0.12 mm was chosen for the structure determination. Unit cell parameters were derived from a least-squares analysis of 14,169 reflections in the range of 3.16 < q < 25.00 . The data collection was done by Rigaku R-axis Spider IP diffractometer. All calculations were performed with the SHELXTL-97 crystallographic software package [17]. The crystal structure was solved in space group Pbcn. Final least-squares refinement is on Fo2 with data having Fo2 > 2s(Fo2). The final difference Fourier synthesis gave maximum and minimum peaks at 0.867 and 0.767 e Å3, respectively. The structure was checked for missing symmetry elements with PLATON [18]. Crystal data and structure refinement information are summarized in Table 1. Final atomic coordinates and equivalent isotropic displacement parameters of the title compound are listed in Table 2. Selected interatomic distances and angles are given in Table 3. 2.3. IR spectroscopy The IR absorption spectroscopy of RBOH was recorded on a Bruker EQUINOX 55 Fourier transform infrared spectrometer. The sample was mixed thoroughly with dried KBr (5 mg of the sample and 500 mg of KBr), and the spectrum was collected in a range from 400 to 4000 cm1 with a resolution of 2 cm1.
Volume [Å3] Z Density (calculated) [Mg/m3] Absorption coefficient [mm1] F(000) Crystal size [mm3] Limiting indices Reflections collected/unique Completeness to theta ¼ 25.00 [%] Refinement method Data/restraints/parameters Goodness-of-fit on F2o Final R indices[F2o>2s( F2o)]a R indices (all data)a Extinction coefficient Largest diff. peak and hole [e$Å3] P P a R1 ¼ kFo j jFc k= jFo jand wR2
H14B8O21Rb4 778.47 293(2) 0.71073 Orthorhombic Pbcn a ¼ 16.3984(14) Å b ¼ 7.7850(7) Å c ¼ 16.0763(16) Å 2052.3(3) 4 2.519 9.578 1480 0.26 0.18 0.12 19 h 18, 9 k 9, 19 l 19 14,169/1792 [R(int) ¼ 0.1309] 99.1 Full-matrix least-squares on F2o 1792/0/179 1.045 R1 ¼ 0.0383, wR2 ¼ 0.0842 R1 ¼ 0.0465, wR2 ¼ 0.0885 0.0027(5) 0.867 and 0.767 P P ¼ ½ wðF2o F2c Þ= wF4o 1=2 for F2o > 2sðF2o Þ
2.4. TGA The TGA for RBOH was carried out on a NETZSCH STA 449F3 simultaneous analyzer with a heating rate of 20 C/min in an atmosphere of flowing Ar from 40 C to 970 C. 2.5. UV-vis-NIR diffuse-reflectance spectroscopy UV-vis-NIR diffuse-reflectance data for RBOH samples were collected with a SHIMADZU SolidSpec-3700DUV UV-vis-NIR spectrophotometer in the wavelength range from 190 to 1500 nm, shown in Fig. 3. It was found that its UV absorption edge is about 190 nm. 3. Results and discussions 3.1. Crystal structure X-Ray analysis revealed that the compound RBOH is crystallized in the orthorhombic system with space group Pbcn. It contains Table 2 Atomic coordinates ( 104) and equivalent isotropic displacement parameters (Å2 103) for RBOH. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
Fig. 2. Experimental and calculated XRD patterns of RBOH. The red curve is its experimental pattern, the black one is its calculated one. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Atom
x
y
z
Ueq
Rb(1) Rb(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) B(1) B(2) B(3) B(4)
3168(1) 3641(1) 4039(2) 2530(2) 4882(2) 1470(1) 1169(2) 3007(2) 4597(2) 3064(2) 1309(2) 4754(2) 5000 4253(3) 1805(3) 370(3) 3387(3)
722(1) 1944(1) 5826(4) 3240(4) 7218(3) 1239(3) 4279(3) 7937(3) 4200(3) 6506(4) 1301(5) 19(5) 2673(7) 5866(5) 2922(6) 3832(6) 6768(5)
2239(1) 5036(1) 5033(2) 3410(2) 3993(2) 3645(2) 3732(2) 4798(2) 3911(2) 6074(2) 1925(3) 1307(3) 2500 4130(3) 3891(3) 3796(4) 5296(3)
36(1) 31(1) 24(1) 26(1) 26(1) 20(1) 25(1) 25(1) 24(1) 31(1) 41(1) 56(1) 70(2) 20(1) 22(1) 28(1) 21(1)
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Table 3 Selected bond distances (Å) and angles (deg) for RBOH. 2.863(3) 2.864(3) 2.912(3) 2.930(3) 3.051(4) 3.256(3) 3.583(4) 3.123(4) 3.392(2) 3.342(3) 2.836(3) 2.955(3) 2.966(3) 2.970(3) 3.092(3) 3.139(4) 3.273(3) 150.09(9) 83.91(9) 81.90(8) 153.38(9) 49.57(8) 83.60(8) 82.24(11) 91.00(10) 138.12(9) 122.01(10) 74.17(10) 124.23(10) 69.92(10) 79.48(10) 141.14(12) 89.31(9) 120.56(8) 120.50(9) 77.03(9) 98.68(10) 51.53(10) 130.26(10) 69.53(9) 145.47(10) 63.29(10) 63.53(10) 110.45(10) 63.62(8) 142.39(8) 101.28(8) 116.21(8) 105.07(8) 76.02(8) 85.84(8) 86.26(7) 67.15(7) 131.34(7) 46.33(7) 140.81(10) 44.45(8) 93.35(10) 112.17(9) 110.72(9) 44.26(8) 116.97(8) 112.17(8)
Rb(2)eO(6)#7 Rb(2)eO(9)#8 B(1)eO(4)#10 B(1)eO(7)(H(7)) B(1)eO(1) B(1)eO(3) B(2)eO(2)(H(6)) B(2)eO(4) B(2)eO(6)#2 B(2)eO(5) B(3)eO(5) B(3)eO(3)#2 B(3)eO(10)#11(H(3)) B(4)eO(6) B(4)eO(1) B(4)eO(8)(H(1)) O(7)eRb(2)eO(8)#2 O(1)eRb(2)eO(8)#2 O(10)#6eRb(2)eO(8)#2 O(6)#2eRb(2)eO(6)#7 O(3)#5eRb(2)eO(6)#7 O(5)#2eRb(2)eO(6)#7 O(7)eRb(2)eO(6)#7 O(1)eRb(2)eO(6)#7 O(10)#6eRb(2)eO(6)#7 O(8)#2eRb(2)eO(6)#7 O(6)#2eRb(2)eO(9)#8 O(3)#5eRb(2)eO(9)#8 O(5)#2eRb(2)eO(9)#8 O(7)eRb(2)eO(9)#8 O(1)eRb(2)eO(9)#8 O(10)#6eRb(2)eO(9)#8 O(8)#2eRb(2)eO(9)#8 O(6)#7eRb(2)eO(9)#8 O(6)#2eRb(2)eO(2) O(3)#5eRb(2)eO(2) O(5)#2eRb(2)eO(2) O(7)eRb(2)eO(2) O(1)eRb(2)eO(2) O(10)#6eRb(2)eO(2) O(8)#2eRb(2)eO(2) O(6)#7eRb(2)eO(2) O(9)#8eRb(2)eO(2) O(4)#10eB(1)eO(7) O(4)#10eB(1)eO(3) O(7)eB(1)eO(3) O(4)#10eB(1)eO(1) O(7)eB(1)eO(1) O(3)eB(1)eO(1) O(2)eB(2)eO(4) O(2)eB(2)eO(6)#2 O(4)eB(2)eO(6)#2 O(2)eB(2)eO(5) O(4)eB(2)eO(5) O(6)#2eB(2)eO(5) O(3)#2eB(3)eO(5) O(3)#2eB(3)eO(10)#11 O(5)eB(3)eO(10)#11 O(1)eB(4)eO(6) O(1)eB(4)eO(8) O(6)eB(4)eO(8)
3.311(3) 3.332(5) 1.449(5) 1.458(5) 1.494(5) 1.490(5) 1.440(5) 1.475(5) 1.491(6) 1.506(5) 1.360(5) 1.359(6) 1.378(6) 1.364(5) 1.363(5) 1.373(6) 145.43(8) 106.45(8) 96.55(10) 86.69(5) 121.76(7) 44.93(7) 130.75(8) 170.86(7) 78.40(9) 72.10(8) 92.01(9) 53.65(9) 158.22(9) 107.44(10) 66.11(9) 65.89(11) 66.37(9) 119.98(9) 45.02(8) 142.51(8) 73.48(8) 68.45(8) 79.58(7) 166.80(11) 88.00(8) 91.32(8) 127.08(9) 111.4(4) 110.2(3) 108.9(3) 109.6(3) 107.9(3) 108.8(3) 108.5(4) 110.7(3) 110.3(3) 111.1(3) 108.6(3) 107.7(3) 123.1(4) 115.2(4) 121.6(4) 122.4(4) 120.3(4) 117.2(4)
90 80 70
Reflectance(%)
Rb(1)eO(8)#1 Rb(1)eO(5)#2 Rb(1)eO(2) Rb(1)eO(2)#2 Rb(1)eO(10) Rb(1)eO(8)#3 Rb(1)eO(9)#2 Rb(1)eO(9) Rb(1)eO(11) Rb(2)eO(2) Rb(2)eO(6)#2 Rb(2)eO(3)#5 Rb(2)eO(5)#2 Rb(2)eO(7) Rb(2)eO(1) Rb(2)eO(10)#6 Rb(2)eO(8)#2 O(8)#1eRb(1)eO(5)#2 O(8)#1eRb(1)eO(2) O(5)#2eRb(1)eO(2) O(8)#1eRb(1)eO(2)#2 O(5)#2eRb(1)eO(2)#2 O(2)eRb(1)eO(2)#2 O(8)#1eRb(1)eO(10) O(5)#2eRb(1)eO(10) O(2)eRb(1)eO(10) O(2)#2eRb(1)eO(10) O(8)#1eRb(1)eO(9) O(5)#2eRb(1)eO(9) O(2)eRb(1)eO(9) O(2)#2eRb(1)eO(9) O(10)eRb(1)eO(9) O(8)#1eRb(1)eO(8)#3 O(5)#2eRb(1)eO(8)#3 O(2)eRb(1)eO(8)#3 O(2)#2eRb(1)eO(8)#3 O(10)eRb(1)eO(8)#3 O(9)eRb(1)eO(8)#3 O(8)#1eRb(1)eO(9)#2 O(5)#2eRb(1)eO(9)#2 O(2)eRb(1)eO(9)#2 O(2)#2eRb(1)eO(9)#2 O(10)eRb(1)eO(9)#2 O(9)eRb(1)eO(9)#2 O(8)#3eRb(1)eO(9)#2 O(6)#2eRb(2)eO(3)#5 O(6)#2eRb(2)eO(5)#2 O(3)#5eRb(2)eO(5)#2 O(6)#2eRb(2)eO(7) O(3)#5eRb(2)eO(7) O(5)#2eRb(2)eO(7) O(6)#2eRb(2)eO(1) O(3)#5eRb(2)eO(1) O(5)#2eRb(2)eO(1) O(7)eRb(2)eO(1) O(6)#2eRb(2)eO(10)#6 O(3)#5eRb(2)eO(10)#6 O(5)#2eRb(2)eO(10)#6 O(7)eRb(2)eO(10)#6 O(1)eRb(2)eO(10)#6 O(6)#2eRb(2)eO(8)#2 O(3)#5eRb(2)eO(8)#2 O(5)#2eRb(2)eO(8)#2
60 50 40 30 20 10 0 200
400
600
800
1000
1200
1400
Wavelength(nm) Fig. 3. The UV-vis-NIR diffuse-reflectance spectrum of the RBOH compound.
the [B4O5(OH)4]2 unit (Fig. 6). The isolated [B4O5(OH)4]2 polyanions have previously been observed in serials of similar hydrated borates, such as Rb2[B4O5(OH)4]$3.6H2O [16], K2[B4O5(OH)4]$2H2O [19] and Cs2[B4O5(OH)4]$3H2O [19]. As usually happen, there are variations in the individual BeO bond lengths from 1.449(5) to 1.506(5) Å in tetrahedra and from 1.359(6) to 1.364(5) Å in triangles. The BeO(H) bonds of tetrahedral borates, which are 1.440(5) and
Symmetry transformations used to generate equivalent atoms: #1 x,y þ 1,z 1/2; #2 x þ 1/2,y 1/2,z; #3 x þ 1/2,y þ 1/2,z 1/2; #4 x,y,z 1/2; #5 x þ 1,y þ 1,z þ 1; #6 x,y,z þ 1/2; #7 x,y 1,z; #8 x þ 1/2,y þ 1/2,z þ 1/2; #9 x þ 1/2,y þ 1/2,z þ 1; #10 x þ 1/2,y þ 1/2,z; #11 x 1/2,y þ 1/2,z þ 1/2; #12 x 1/2,y þ 1/2,z þ 1; #13 x,y þ 1,z þ 1/2; #14 x,y þ 1,z; #15 x þ 1/2,y 1/ 2,z þ 1/2; #16 x þ 1,y,z þ 1/2.
isolated [B4O5(OH)4]2 polyanions, free water molecules and Rb cations (Fig. 4). The isolated [B4O5(OH)4]2 polyanions in the title compound are connected by H-bonding interaction and the Rb polyhedra to form three-dimensional structure (Fig. 5). There are two tetrahedral BO3(OH) units and two trigonal BO2(OH) units in
Fig. 4. The unit cell of RBOH. The green ellipsoids are Rb atoms; the blue ellipsoids are B atoms; the red ellipsoids are O atoms; the orange ellipsoids are H atoms. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Y. Zhao et al. / Solid State Sciences 13 (2011) 82e87
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Fig. 5. The packing diagram of RBOH. The green spheres are Rb atoms; the red spheres are O atoms; the orange spheres are H atoms; BO4 tetrahedra are shown in light blue, BO3 triangles are shown in light red, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
1.458(5) Å, tend to be on the shorter end of all the bond lengths reported [20e27]. The BeO (H) bond lengths are 1.373(6) and 1.378 (6) Å in triangles (Table 3). The Rb(1) and Rb(2) atoms are characterized by high coordination numbers typical of alkali metals with large ionic radii and large irregular polyhedra. The Rb(1) atom is surrounded by nine oxygen atoms (Fig. 7a), in which two oxygen atoms [O(2), O(2)] are from BO3(OH), three oxygen atoms [O(8), O(8),O(10)] from
Fig. 7. a. The coordination of Rb(1) cation. The H atoms have been removed for clarity. b. The coordination of Rb(2) cation. The H atoms have been removed for clarity.
BO2(OH), one oxygen atom [O(5)] from the BeOeB bridge and three oxygen atoms [O(9), O(9), O(11)] from water molecules. The Rb(2) atom is surrounded by ten oxygen atoms (Fig. 7b), in which two oxygen atoms [O(2), O(7)] is from BO3(OH), two oxygen atoms [O (8), O(10)] from BO2(OH), five oxygen atoms [O(1), O(3), O(5), O(6),
Table 4 Geometrical characteristics of hydrogen bonds in the RBOH structure.
Fig. 6. Polyborate anion [B4O5(OH)4]2-.
Interaction
d(DeH)(Å)
d(H/A)(Å)
d(D/$A)(Å)
DeH/A( )
O(8)eH(1)/O(9) O(9)eH(2)/O(3) O(10)eH(3)/O(11) O(9)eH(4)/O(4) O(11)eH(5)/O(7) O(2)eH(6)/O(4) O(7)eH(7)/O(1)
0.83(4) 0.69(6) 0.69(7) 0.78(6) 0.87(6) 0.69(8) 0.82(7)
1.96(4) 2.23(6) 2.18(6) 2.01(6) 1.78(6) 2.27(7) 1.99(7)
2.776(5) 2.857(5) 2.848(6) 2.778(6) 2.645(4) 2.878(4) 2.807(4)
169(5) 152(7) 165(7) 168(5) 175(7) 150(9) 172(7)
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asymmetric stretching, the symmetric and asymmetric bending modes, respectively [20]. The bands at 760e852,1013e1100, 556 cm1 are assigned as the characteristic peaks of the BO4 [20,22]. Obviously, the RbBOH crystal contains characteristic OeH, BO3, and BO4 groups as its basic structural units, which is consistent with the above crystal structure results.
40
3.3. TGA
100
Transmittance (%)
80
20
0
-20 4000
3500
3000
2500
2000
1500
1000
500
The TGA curve of RBOH displayed in Fig. 9 shows a weight loss of about 16.5% from 40 C to 330 C, which corresponds to the loss of three crystal water molecules and the loss of four structural water molecules from RBOH (theoretical water loss: 16.9%). In the next stage, occurring between 330 and 970 C, the weight loss might be attributed to the gradual volatilization of boron oxide and rubidium oxide.
-1
wavenumber
cm
4. Conclusion
Fig. 8. IR spectrum of the RBOH compound.
O(6)] from the BeOeB bridge and one oxygen atom [O(9)] from water molecule. The Rb(1)eO distances range from 2.863(3) to 3.583(4) Å with an average value of 3.108 Å, while the Rb(2)eO distances range from 2.836(3) to 3.342(3) Å with an average value of 3.122 Å (Table 3). There are four OH groups in the [B4O5(OH)4]2 unit (Fig. 6) and two water molecules in the structure (Fig. 5), all of which participate in hydrogen-bonding (Table 4). Hydrogen bond lengths in the structure lie in the range of values found for hydrogen bonds, which are the cases with the distance between two oxygen atoms smaller than 3.40 Å, the length of the HdO bond smaller than 2.60 Å [28e32].
3.2. IR spectroscopy Seen from Fig. 8, the characteristic peaks of the RBOH compound can be described as follows: The bands at about 3361 and 1648 cm1 are assigned as the stretching and bending modes of OeH [20]. The present study is in agreement with the results obtained for other borates showing that the wave numbers of fundamental vibrations of the BO3 group are divided into three distinct regions, i.e. 931, 1336e1430, 640e713 cm1, assigned as the symmetric and
RbBOH was synthesized by slow evaporation method and structurally characterized by the single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Pbcn, with a ¼ 16.3984(14) Å, b ¼ 7.7850(7) Å, c ¼ 16.0763(16) Å, Z ¼ 4. Its basic unit is represented with isolated tetraborate groups [B4O5(OH)4]2, in which there are two BO4 tetrahedra and two BO3 triangles. The Rb(1) and Rb(2) atoms are coordinated by nine and ten oxygen atoms, respectively. The Rb polyhedra and the hydrogen-bonding system make the isolated [B4O5(OH)4]2 polyanions connect to form a three-dimensional network. Acknowledgments We gratefully acknowledge the support from the “National Natural Science Foundation of China” (Grant No. 50802110), the “One Hundred Talents Project Foundation Program” of Chinese Academe of Sciences, the “Western Light Joint Scholar Foundation” Program of Chinese Academe of Sciences, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry(Grant No. 20091001), the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (Grant No. 200821159, 2009211B33) and the “High Technology Research and Development Program” of Xinjiang Uygur Autonomous Region of China (Grant No. 200816120). References
100
Weight (%)
90
80
70
60
50
200
400
600
800
Temperature Fig. 9. The TGA curve of the RBOH compound.
1000
[1] P. Becker, Adv. Mater. 10 (1998) 979. [2] (a) C.F. Dewey Jr., W.R. Cook Jr., R.T. Hodgson, J.J. Wynne, Appl. Phys. Lett. 26 (1975) 714; (b) J. Harry, H.J. Dewey, IEEE J. Quant. Electron. 12 (1976) 303.(c) C.T. Chen, Sci. Sin. 8 (1977) 579. [3] C.T. Chen, Y.C. Wu, R.K. Li, J. Opt. Soc. Am. B 6 (1989) 616. [4] Y.C. Wu, T. Sasaki, S. Nakai, A. Yokotani, H.G. Tang, C.T. Chen, Appl. Phys. Lett. 62 (1993) 2614. [5] Y. Mori, I. Kuroda, S. Nakajima, T. Sasaki, S. Nakai, Appl. Phys. Lett. 67 (1995) 1818. [6] Y.J. Wang, S.L. Pan, X.L. Tian, Z.X. Zhou, G. Liu, J.D. Wang, D.Z. Jia, Inorg. Chem. 48 (2009) 7800. [7] J.R. Clark, C.L. Christ, Acta Crystallogr. B33 (1977) 3272. [8] I.I. Zviedre, A. F. Ievin’sh, Latv. PSR Zinat, Akad. Vestis, Kim. Ser (1974) 401. [9] Z.G. Hu, M. Yoshimura, Y. Mori, T. Sasaki, J. Cryst. Growth 260 (2004) 287. [10] (a) P.S. Halasyamani, D. O’Hare, Chem. Mater. 10 (1998) 646; (b) M.E. Hagerman, K.R. Poeppelmeier, Chem. Mater. 7 (1995) 602; (c) J.G. Mao, H.L. Jiang, K. Fang, Inorg. Chem. 47 (2008) 8498; (d) A.J. Norquist, K.R. Heier, P.S. Halasyamani, C.L. Stern, K.R. Poeppelmeier, Inorg. Chem. 40 (2001) 2015; (e) G.C. Zhang, Y.C. Wu, Y.G. Li, F. Chang, S.L. Pan, P.Z. Fu, C.T. Chen, J. Cryst. Growth 275 (2005) 1997. [11] H.R. Behm, Acta Crystallogr. C 40 (1984) 217. [12] E.L. Belokoneva, T.A. Borisova, O.V. Dimitrova, Crystallogr. Rep. 48 (4) (2003) 583.
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Synthesis, structure, and properties of a novel hydrated borate Rb4[B4O5(OH)4]2$3H2O Yi Zhao a, b, Shilie Pan b, *, Feng Li b, Yongjiang Wang b, Xiaoyun Fan b, Xiaoyu Dong b, Dianzeng Jia a, Jixi Guo a, Zhongxiang Zhou b a
College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, China Xinjiang Key Laboratory of Electronic Information Materials and Devices, Xinjiang Technical Institute of Physics & Chemistry, Chinese Academy of Sciences, 40-1 South Beijing Road, Urumqi 830011, China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 April 2010 Received in revised form 29 September 2010 Accepted 21 October 2010 Available online 29 October 2010
Rb4[B4O5(OH)4]2$3H2O has been grown by slow evaporation method with crystal sizes up to 11 mm 7 mm 4 mm. Its crystal structure has been determined by single-crystal X-ray diffraction and further characterized by powder X-ray diffraction (XRD), IR, and TGA. It crystallizes in the orthorhombic space group Pbcn, with a ¼ 16.3984(14) Å, b ¼ 7.7850(7) Å, c ¼ 16.0763(16) Å, and Z ¼ 4. It contains isolated [B4O5(OH)4]2 polyanions, free water molecules and Rb cations. The Rb(1) and Rb(2) atoms are coordinated by nine and ten oxygen atoms, respectively. Connections between isolated [B4O5(OH)4]2 polyanions are provided by Rb polyhedra and the hydrogen-bonding to form a three-dimensional network. Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords: Rb4[B4O5(OH)4]2$3H2O Borate Crystal structure Crystal growth
1. Introduction
2. Experimental section
In the past several decades, much interest has been focused on alkali borate compounds [1e5] because some of these compounds show interesting physical properties, such as nonlinear optical behavior for KB5O8$4H2O (KB5) [2], LiB3O5 (LBO) [3], CsB3O5 (CBO) [4], CsLiB6O10 (CLBO) [5], Na2B5O8(OH)3$2H2O [6], K3[B3O4(OH)4]$ 2H2O [7], Cs[B(OH)4]$2H2O [8]. Unique character of borate structure determines their large nonlinear optical coefficient, a broad transparency range, and high damage threshold [9,10]. In order to synthesize new borates and search for new materials, we studied the system Rb2OeB2O3eH2O. Some researchers have investigated this system and found the compounds Rb[B5O6(OH)4]$2H2O [11], Rb[B5O7(OH)2]$0.5H2O [12], Rb2[B12(OH)12]$2H2O [13], Rb4B10O17$6H2O [14], Rb3[B3O4(OH)4]$ 2H2O [15], Rb2[B4O5(OH)4]$3.6H2O [16]. The extensive exploration on this system led us to find the new compound Rb4[B4O5(OH)4]2$3H2O (RBOH). In the paper, the crystal structure, powder XRD, IR, and TGA curves of the title compound were reported.
2.1. Compound synthesis
* Corresponding author. Tel.: þ86 991 3674558; fax: þ86 991 3838957. E-mail address: [email protected] (S. Pan). 1293-2558/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2010.10.013
Single crystals of RBOH were synthesized via slow evaporation at room temperature. The starting materials used in the preparation were Rb2CO3 (99.0%, Xinjiang Chemical Co. Ltd.), H3BO3 (99.5%, Tianjin Baishi Chemical Co. Ltd.). The powder mixture of Rb2CO3 and H3BO3 with a molar ratio of 1:1 was used as received and then dissolved in deionized water. The obtained solution was allowed to evaporate slowly at room temperature. Single crystals of a new compound, RBOH, were obtained with sizes up to 11 mm 7 mm 4 mm (Fig. 1). The experimental XRD pattern of RBOH is in agreement with the calculated one based on its single-crystal data, suggesting that the synthesized phase is pure (Fig. 2). 2.2. X-ray crystallography Powder XRD analysis for RBOH was performed at room temperature on an automated Bruker D8 ADVANCE X-ray diffractometer equipped with graphite monochromatized Cu Ka radiation in the angular range from 10 to 70 (2q) with a scanning step width of 0.02 and a fixed counting time of 1 s/step. A colorless and transparent
Y. Zhao et al. / Solid State Sciences 13 (2011) 82e87
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Table 1 Crystal data and structure refinement for RBOH. Empirical formula Formula weight Temperature [K] Wavelength [Å] Crystal system Space group Unit cell dimensions
Fig. 1. Photograph of RBOH crystal. (The minimum scale of the ruler is 1 mm).
crystal of RBOH with dimensions 0.26 mm 0.18 mm 0.12 mm was chosen for the structure determination. Unit cell parameters were derived from a least-squares analysis of 14,169 reflections in the range of 3.16 < q < 25.00 . The data collection was done by Rigaku R-axis Spider IP diffractometer. All calculations were performed with the SHELXTL-97 crystallographic software package [17]. The crystal structure was solved in space group Pbcn. Final least-squares refinement is on Fo2 with data having Fo2 > 2s(Fo2). The final difference Fourier synthesis gave maximum and minimum peaks at 0.867 and 0.767 e Å3, respectively. The structure was checked for missing symmetry elements with PLATON [18]. Crystal data and structure refinement information are summarized in Table 1. Final atomic coordinates and equivalent isotropic displacement parameters of the title compound are listed in Table 2. Selected interatomic distances and angles are given in Table 3. 2.3. IR spectroscopy The IR absorption spectroscopy of RBOH was recorded on a Bruker EQUINOX 55 Fourier transform infrared spectrometer. The sample was mixed thoroughly with dried KBr (5 mg of the sample and 500 mg of KBr), and the spectrum was collected in a range from 400 to 4000 cm1 with a resolution of 2 cm1.
Volume [Å3] Z Density (calculated) [Mg/m3] Absorption coefficient [mm1] F(000) Crystal size [mm3] Limiting indices Reflections collected/unique Completeness to theta ¼ 25.00 [%] Refinement method Data/restraints/parameters Goodness-of-fit on F2o Final R indices[F2o>2s( F2o)]a R indices (all data)a Extinction coefficient Largest diff. peak and hole [e$Å3] P P a R1 ¼ kFo j jFc k= jFo jand wR2
H14B8O21Rb4 778.47 293(2) 0.71073 Orthorhombic Pbcn a ¼ 16.3984(14) Å b ¼ 7.7850(7) Å c ¼ 16.0763(16) Å 2052.3(3) 4 2.519 9.578 1480 0.26 0.18 0.12 19 h 18, 9 k 9, 19 l 19 14,169/1792 [R(int) ¼ 0.1309] 99.1 Full-matrix least-squares on F2o 1792/0/179 1.045 R1 ¼ 0.0383, wR2 ¼ 0.0842 R1 ¼ 0.0465, wR2 ¼ 0.0885 0.0027(5) 0.867 and 0.767 P P ¼ ½ wðF2o F2c Þ= wF4o 1=2 for F2o > 2sðF2o Þ
2.4. TGA The TGA for RBOH was carried out on a NETZSCH STA 449F3 simultaneous analyzer with a heating rate of 20 C/min in an atmosphere of flowing Ar from 40 C to 970 C. 2.5. UV-vis-NIR diffuse-reflectance spectroscopy UV-vis-NIR diffuse-reflectance data for RBOH samples were collected with a SHIMADZU SolidSpec-3700DUV UV-vis-NIR spectrophotometer in the wavelength range from 190 to 1500 nm, shown in Fig. 3. It was found that its UV absorption edge is about 190 nm. 3. Results and discussions 3.1. Crystal structure X-Ray analysis revealed that the compound RBOH is crystallized in the orthorhombic system with space group Pbcn. It contains Table 2 Atomic coordinates ( 104) and equivalent isotropic displacement parameters (Å2 103) for RBOH. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
Fig. 2. Experimental and calculated XRD patterns of RBOH. The red curve is its experimental pattern, the black one is its calculated one. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Atom
x
y
z
Ueq
Rb(1) Rb(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) O(10) O(11) B(1) B(2) B(3) B(4)
3168(1) 3641(1) 4039(2) 2530(2) 4882(2) 1470(1) 1169(2) 3007(2) 4597(2) 3064(2) 1309(2) 4754(2) 5000 4253(3) 1805(3) 370(3) 3387(3)
722(1) 1944(1) 5826(4) 3240(4) 7218(3) 1239(3) 4279(3) 7937(3) 4200(3) 6506(4) 1301(5) 19(5) 2673(7) 5866(5) 2922(6) 3832(6) 6768(5)
2239(1) 5036(1) 5033(2) 3410(2) 3993(2) 3645(2) 3732(2) 4798(2) 3911(2) 6074(2) 1925(3) 1307(3) 2500 4130(3) 3891(3) 3796(4) 5296(3)
36(1) 31(1) 24(1) 26(1) 26(1) 20(1) 25(1) 25(1) 24(1) 31(1) 41(1) 56(1) 70(2) 20(1) 22(1) 28(1) 21(1)
84
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Table 3 Selected bond distances (Å) and angles (deg) for RBOH. 2.863(3) 2.864(3) 2.912(3) 2.930(3) 3.051(4) 3.256(3) 3.583(4) 3.123(4) 3.392(2) 3.342(3) 2.836(3) 2.955(3) 2.966(3) 2.970(3) 3.092(3) 3.139(4) 3.273(3) 150.09(9) 83.91(9) 81.90(8) 153.38(9) 49.57(8) 83.60(8) 82.24(11) 91.00(10) 138.12(9) 122.01(10) 74.17(10) 124.23(10) 69.92(10) 79.48(10) 141.14(12) 89.31(9) 120.56(8) 120.50(9) 77.03(9) 98.68(10) 51.53(10) 130.26(10) 69.53(9) 145.47(10) 63.29(10) 63.53(10) 110.45(10) 63.62(8) 142.39(8) 101.28(8) 116.21(8) 105.07(8) 76.02(8) 85.84(8) 86.26(7) 67.15(7) 131.34(7) 46.33(7) 140.81(10) 44.45(8) 93.35(10) 112.17(9) 110.72(9) 44.26(8) 116.97(8) 112.17(8)
Rb(2)eO(6)#7 Rb(2)eO(9)#8 B(1)eO(4)#10 B(1)eO(7)(H(7)) B(1)eO(1) B(1)eO(3) B(2)eO(2)(H(6)) B(2)eO(4) B(2)eO(6)#2 B(2)eO(5) B(3)eO(5) B(3)eO(3)#2 B(3)eO(10)#11(H(3)) B(4)eO(6) B(4)eO(1) B(4)eO(8)(H(1)) O(7)eRb(2)eO(8)#2 O(1)eRb(2)eO(8)#2 O(10)#6eRb(2)eO(8)#2 O(6)#2eRb(2)eO(6)#7 O(3)#5eRb(2)eO(6)#7 O(5)#2eRb(2)eO(6)#7 O(7)eRb(2)eO(6)#7 O(1)eRb(2)eO(6)#7 O(10)#6eRb(2)eO(6)#7 O(8)#2eRb(2)eO(6)#7 O(6)#2eRb(2)eO(9)#8 O(3)#5eRb(2)eO(9)#8 O(5)#2eRb(2)eO(9)#8 O(7)eRb(2)eO(9)#8 O(1)eRb(2)eO(9)#8 O(10)#6eRb(2)eO(9)#8 O(8)#2eRb(2)eO(9)#8 O(6)#7eRb(2)eO(9)#8 O(6)#2eRb(2)eO(2) O(3)#5eRb(2)eO(2) O(5)#2eRb(2)eO(2) O(7)eRb(2)eO(2) O(1)eRb(2)eO(2) O(10)#6eRb(2)eO(2) O(8)#2eRb(2)eO(2) O(6)#7eRb(2)eO(2) O(9)#8eRb(2)eO(2) O(4)#10eB(1)eO(7) O(4)#10eB(1)eO(3) O(7)eB(1)eO(3) O(4)#10eB(1)eO(1) O(7)eB(1)eO(1) O(3)eB(1)eO(1) O(2)eB(2)eO(4) O(2)eB(2)eO(6)#2 O(4)eB(2)eO(6)#2 O(2)eB(2)eO(5) O(4)eB(2)eO(5) O(6)#2eB(2)eO(5) O(3)#2eB(3)eO(5) O(3)#2eB(3)eO(10)#11 O(5)eB(3)eO(10)#11 O(1)eB(4)eO(6) O(1)eB(4)eO(8) O(6)eB(4)eO(8)
3.311(3) 3.332(5) 1.449(5) 1.458(5) 1.494(5) 1.490(5) 1.440(5) 1.475(5) 1.491(6) 1.506(5) 1.360(5) 1.359(6) 1.378(6) 1.364(5) 1.363(5) 1.373(6) 145.43(8) 106.45(8) 96.55(10) 86.69(5) 121.76(7) 44.93(7) 130.75(8) 170.86(7) 78.40(9) 72.10(8) 92.01(9) 53.65(9) 158.22(9) 107.44(10) 66.11(9) 65.89(11) 66.37(9) 119.98(9) 45.02(8) 142.51(8) 73.48(8) 68.45(8) 79.58(7) 166.80(11) 88.00(8) 91.32(8) 127.08(9) 111.4(4) 110.2(3) 108.9(3) 109.6(3) 107.9(3) 108.8(3) 108.5(4) 110.7(3) 110.3(3) 111.1(3) 108.6(3) 107.7(3) 123.1(4) 115.2(4) 121.6(4) 122.4(4) 120.3(4) 117.2(4)
90 80 70
Reflectance(%)
Rb(1)eO(8)#1 Rb(1)eO(5)#2 Rb(1)eO(2) Rb(1)eO(2)#2 Rb(1)eO(10) Rb(1)eO(8)#3 Rb(1)eO(9)#2 Rb(1)eO(9) Rb(1)eO(11) Rb(2)eO(2) Rb(2)eO(6)#2 Rb(2)eO(3)#5 Rb(2)eO(5)#2 Rb(2)eO(7) Rb(2)eO(1) Rb(2)eO(10)#6 Rb(2)eO(8)#2 O(8)#1eRb(1)eO(5)#2 O(8)#1eRb(1)eO(2) O(5)#2eRb(1)eO(2) O(8)#1eRb(1)eO(2)#2 O(5)#2eRb(1)eO(2)#2 O(2)eRb(1)eO(2)#2 O(8)#1eRb(1)eO(10) O(5)#2eRb(1)eO(10) O(2)eRb(1)eO(10) O(2)#2eRb(1)eO(10) O(8)#1eRb(1)eO(9) O(5)#2eRb(1)eO(9) O(2)eRb(1)eO(9) O(2)#2eRb(1)eO(9) O(10)eRb(1)eO(9) O(8)#1eRb(1)eO(8)#3 O(5)#2eRb(1)eO(8)#3 O(2)eRb(1)eO(8)#3 O(2)#2eRb(1)eO(8)#3 O(10)eRb(1)eO(8)#3 O(9)eRb(1)eO(8)#3 O(8)#1eRb(1)eO(9)#2 O(5)#2eRb(1)eO(9)#2 O(2)eRb(1)eO(9)#2 O(2)#2eRb(1)eO(9)#2 O(10)eRb(1)eO(9)#2 O(9)eRb(1)eO(9)#2 O(8)#3eRb(1)eO(9)#2 O(6)#2eRb(2)eO(3)#5 O(6)#2eRb(2)eO(5)#2 O(3)#5eRb(2)eO(5)#2 O(6)#2eRb(2)eO(7) O(3)#5eRb(2)eO(7) O(5)#2eRb(2)eO(7) O(6)#2eRb(2)eO(1) O(3)#5eRb(2)eO(1) O(5)#2eRb(2)eO(1) O(7)eRb(2)eO(1) O(6)#2eRb(2)eO(10)#6 O(3)#5eRb(2)eO(10)#6 O(5)#2eRb(2)eO(10)#6 O(7)eRb(2)eO(10)#6 O(1)eRb(2)eO(10)#6 O(6)#2eRb(2)eO(8)#2 O(3)#5eRb(2)eO(8)#2 O(5)#2eRb(2)eO(8)#2
60 50 40 30 20 10 0 200
400
600
800
1000
1200
1400
Wavelength(nm) Fig. 3. The UV-vis-NIR diffuse-reflectance spectrum of the RBOH compound.
the [B4O5(OH)4]2 unit (Fig. 6). The isolated [B4O5(OH)4]2 polyanions have previously been observed in serials of similar hydrated borates, such as Rb2[B4O5(OH)4]$3.6H2O [16], K2[B4O5(OH)4]$2H2O [19] and Cs2[B4O5(OH)4]$3H2O [19]. As usually happen, there are variations in the individual BeO bond lengths from 1.449(5) to 1.506(5) Å in tetrahedra and from 1.359(6) to 1.364(5) Å in triangles. The BeO(H) bonds of tetrahedral borates, which are 1.440(5) and
Symmetry transformations used to generate equivalent atoms: #1 x,y þ 1,z 1/2; #2 x þ 1/2,y 1/2,z; #3 x þ 1/2,y þ 1/2,z 1/2; #4 x,y,z 1/2; #5 x þ 1,y þ 1,z þ 1; #6 x,y,z þ 1/2; #7 x,y 1,z; #8 x þ 1/2,y þ 1/2,z þ 1/2; #9 x þ 1/2,y þ 1/2,z þ 1; #10 x þ 1/2,y þ 1/2,z; #11 x 1/2,y þ 1/2,z þ 1/2; #12 x 1/2,y þ 1/2,z þ 1; #13 x,y þ 1,z þ 1/2; #14 x,y þ 1,z; #15 x þ 1/2,y 1/ 2,z þ 1/2; #16 x þ 1,y,z þ 1/2.
isolated [B4O5(OH)4]2 polyanions, free water molecules and Rb cations (Fig. 4). The isolated [B4O5(OH)4]2 polyanions in the title compound are connected by H-bonding interaction and the Rb polyhedra to form three-dimensional structure (Fig. 5). There are two tetrahedral BO3(OH) units and two trigonal BO2(OH) units in
Fig. 4. The unit cell of RBOH. The green ellipsoids are Rb atoms; the blue ellipsoids are B atoms; the red ellipsoids are O atoms; the orange ellipsoids are H atoms. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
Y. Zhao et al. / Solid State Sciences 13 (2011) 82e87
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Fig. 5. The packing diagram of RBOH. The green spheres are Rb atoms; the red spheres are O atoms; the orange spheres are H atoms; BO4 tetrahedra are shown in light blue, BO3 triangles are shown in light red, respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).
1.458(5) Å, tend to be on the shorter end of all the bond lengths reported [20e27]. The BeO (H) bond lengths are 1.373(6) and 1.378 (6) Å in triangles (Table 3). The Rb(1) and Rb(2) atoms are characterized by high coordination numbers typical of alkali metals with large ionic radii and large irregular polyhedra. The Rb(1) atom is surrounded by nine oxygen atoms (Fig. 7a), in which two oxygen atoms [O(2), O(2)] are from BO3(OH), three oxygen atoms [O(8), O(8),O(10)] from
Fig. 7. a. The coordination of Rb(1) cation. The H atoms have been removed for clarity. b. The coordination of Rb(2) cation. The H atoms have been removed for clarity.
BO2(OH), one oxygen atom [O(5)] from the BeOeB bridge and three oxygen atoms [O(9), O(9), O(11)] from water molecules. The Rb(2) atom is surrounded by ten oxygen atoms (Fig. 7b), in which two oxygen atoms [O(2), O(7)] is from BO3(OH), two oxygen atoms [O (8), O(10)] from BO2(OH), five oxygen atoms [O(1), O(3), O(5), O(6),
Table 4 Geometrical characteristics of hydrogen bonds in the RBOH structure.
Fig. 6. Polyborate anion [B4O5(OH)4]2-.
Interaction
d(DeH)(Å)
d(H/A)(Å)
d(D/$A)(Å)
DeH/A( )
O(8)eH(1)/O(9) O(9)eH(2)/O(3) O(10)eH(3)/O(11) O(9)eH(4)/O(4) O(11)eH(5)/O(7) O(2)eH(6)/O(4) O(7)eH(7)/O(1)
0.83(4) 0.69(6) 0.69(7) 0.78(6) 0.87(6) 0.69(8) 0.82(7)
1.96(4) 2.23(6) 2.18(6) 2.01(6) 1.78(6) 2.27(7) 1.99(7)
2.776(5) 2.857(5) 2.848(6) 2.778(6) 2.645(4) 2.878(4) 2.807(4)
169(5) 152(7) 165(7) 168(5) 175(7) 150(9) 172(7)
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asymmetric stretching, the symmetric and asymmetric bending modes, respectively [20]. The bands at 760e852,1013e1100, 556 cm1 are assigned as the characteristic peaks of the BO4 [20,22]. Obviously, the RbBOH crystal contains characteristic OeH, BO3, and BO4 groups as its basic structural units, which is consistent with the above crystal structure results.
40
3.3. TGA
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Transmittance (%)
80
20
0
-20 4000
3500
3000
2500
2000
1500
1000
500
The TGA curve of RBOH displayed in Fig. 9 shows a weight loss of about 16.5% from 40 C to 330 C, which corresponds to the loss of three crystal water molecules and the loss of four structural water molecules from RBOH (theoretical water loss: 16.9%). In the next stage, occurring between 330 and 970 C, the weight loss might be attributed to the gradual volatilization of boron oxide and rubidium oxide.
-1
wavenumber
cm
4. Conclusion
Fig. 8. IR spectrum of the RBOH compound.
O(6)] from the BeOeB bridge and one oxygen atom [O(9)] from water molecule. The Rb(1)eO distances range from 2.863(3) to 3.583(4) Å with an average value of 3.108 Å, while the Rb(2)eO distances range from 2.836(3) to 3.342(3) Å with an average value of 3.122 Å (Table 3). There are four OH groups in the [B4O5(OH)4]2 unit (Fig. 6) and two water molecules in the structure (Fig. 5), all of which participate in hydrogen-bonding (Table 4). Hydrogen bond lengths in the structure lie in the range of values found for hydrogen bonds, which are the cases with the distance between two oxygen atoms smaller than 3.40 Å, the length of the HdO bond smaller than 2.60 Å [28e32].
3.2. IR spectroscopy Seen from Fig. 8, the characteristic peaks of the RBOH compound can be described as follows: The bands at about 3361 and 1648 cm1 are assigned as the stretching and bending modes of OeH [20]. The present study is in agreement with the results obtained for other borates showing that the wave numbers of fundamental vibrations of the BO3 group are divided into three distinct regions, i.e. 931, 1336e1430, 640e713 cm1, assigned as the symmetric and
RbBOH was synthesized by slow evaporation method and structurally characterized by the single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Pbcn, with a ¼ 16.3984(14) Å, b ¼ 7.7850(7) Å, c ¼ 16.0763(16) Å, Z ¼ 4. Its basic unit is represented with isolated tetraborate groups [B4O5(OH)4]2, in which there are two BO4 tetrahedra and two BO3 triangles. The Rb(1) and Rb(2) atoms are coordinated by nine and ten oxygen atoms, respectively. The Rb polyhedra and the hydrogen-bonding system make the isolated [B4O5(OH)4]2 polyanions connect to form a three-dimensional network. Acknowledgments We gratefully acknowledge the support from the “National Natural Science Foundation of China” (Grant No. 50802110), the “One Hundred Talents Project Foundation Program” of Chinese Academe of Sciences, the “Western Light Joint Scholar Foundation” Program of Chinese Academe of Sciences, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry(Grant No. 20091001), the Natural Science Foundation of Xinjiang Uygur Autonomous Region of China (Grant No. 200821159, 2009211B33) and the “High Technology Research and Development Program” of Xinjiang Uygur Autonomous Region of China (Grant No. 200816120). References
100
Weight (%)
90
80
70
60
50
200
400
600
800
Temperature Fig. 9. The TGA curve of the RBOH compound.
1000
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