CRYSTAL GROWTH & DESIGN
Synthesis and Structure of [C2H10N2][B5O8(OH)]: A Nonmetal Pentaborate with Nonlinear Optical Properties Sihai Yang, Guobao Li,* Shujian Tian, Fuhui Liao, and Jianhua Lin Beijing National Laboratory for Molecular Sciences (BNLMS), State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking UniVersity, Beijing 100871, P. R. China
2007 VOL. 7, NO. 7 1246-1250
ReceiVed October 4, 2006; ReVised Manuscript ReceiVed January 17, 2007
ABSTRACT: A nonmetal pentaborate [C2H10N2][B5O8(OH)] (I) was synthesized by a solvothermal method at 150 °C and characterized by elemental analysis, IR, thermogravimetric analysis, and X-ray diffraction. The structure of I was determined by a single-crystal technique. It crystallizes in the monoclinic system with space group Cc, a ) 6.7085 (13) Å, b ) 11.437(2) Å, c ) 12.530(3) Å, and β ) 95.41(3)°. Powder second-harmonic generation (SHG) efficiency measurements with Nd:YAG laser (1064 nm) radiation show that [C2H10N2][B5O8(OH)] has a SHG efficiency approximately 1.2 times of that of potassium dihydrogen phosphate (KDP). Introduction Borate is one of the large resources for nonlinear optical (NLO) materials.1 Many borate crystals, including β-BaB2O4 (BBO),2 LiB3O5 (LBO),3 CsLiB6O10 (CLBO),4 ReCOB (ReCa4O(BO3)3, Re ) La, Nd, Sm, Gd, Er, Tb, Lu, Y),5 BiB3O6 (BiBO),6 La2CaB10O19 (LCB),7 and Bi3[B6O13(OH)],8 have been widely studied, which show promising nonlinear optical properties. Although most of the known NLO borates contain metal ions as counter cations, it is known9 that the overall second harmonic generation (SHG) coefficient is the geometrical superposition of the microscopic second-order susceptibility of the anionic groups; the contribution from the essentially spherical cations is negligible, except for a few cases in which a large ansymmetric metal cation, such as Bi3+, has a significant contribution to NLO properties.10 Therefore, metal ions may not be an essential component for the NLO borates. There are many NLO materials, such as organic and semiorganic NLO materials, without metal ions.11-13 In recent years, many nonmetal borates have been reported,14 but no NLO property has been mentioned except for a few tetrafluoroborates showing NLO properies.15,16 It is believed that exploring the NLO properties of nonmetal borates is significant for understanding the NLO effect and searching for new NLO materials. Here, we report a new nonmetal pentaborate [C2H10N2][B5O8(OH)] that exhibits the NLO effect. Experimental Section Synthesis. [C2H10N2][B5O8(OH)] was synthesized by the solvothermal method. A typical example for synthesizing [C 2H10N2][B5O8(OH)] was to charge a mixture of H3BO3 (323 mmol), C2H8N2 (88.8 mmol), WO3 (4.31 mmol), and HOCH2CH2OH (215 mmol) in a 50 mL Teflonlined stainless steel autoclave. The autoclave was sealed, heated to 150 °C under autogenous pressure for 120 h, and then cooled to room temperature at a rate of 4 °C/h. The colorless platelet crystalline product was filtered, washed with hot distilled water, and dried at ambient temperature to give about 13.8 g of [C2H10N2][B5O8(OH)] (yield 82% based on H3BO3). The title compound is stable and insoluble in water and most organic solvents. Characterization. Thermogravimetric (TG) analysis was performed using a Netzsch STA 449C simultaneous analyzer utilizing Al2O3 crucibles and type S thermocouples with a heating rate of 10 K/min in * Correspondence author. E-mail:
[email protected]. Tel: (8610)62750342. Fax: (8610)62753541.
Table 1. Crystallographic and Structure Refinement Parameters for [C2H10N2][B5O8(OH)] formula fw crystal system space group a, Å b, Å c, Å β
[C2H10N2][B5O8(OH)] 261.18 monoclinic Cc 6.7085(13) 11.437(2) 12.530(3) 95.41(3)
volume, Å3 Z dcalcd, g‚cm-3 T, K λ(Mo, KR), Å µ, mm-1 R1 (I > 2δ(I))a wR2 (all data) a
957.1(3) 4 1.813 298 0.71073 0.165 0.0325 0.0821
a R ) ∑(||F | - |F ||)/∑|F |. wR )[∑(F 2 - F 2)2/∑(F 2)2]1/2. w )1/ 1 0 c 0 2 0 c 0 [σ2(F02) + (0.0790P)2 + 0.2450P], where P ) (F02 + 2Fc2)/3.
a dynamic argon atmosphere (gas flow 0.03 L/min). IR spectra were recorded in the 400-4000 cm-1 range using a Magna-IR 750 FTIR spectrometer. Elemental analyses were carried out on an Elementar Vario EL III microanalyzer for C, H, and N. Elemental analysis data are as follows: Anal. Calc. for [C2H10N2][B5O8(OH)]: C, 9.20; H, 4.24; N, 10.73. Found: C, 9.14; H, 4.24; N, 10.74. Single-Crystal X-ray Crystallography. Intensity data were collected on a Rigaku AFC6S diffractometer with graphite-monochromated Mo KR(λ ) 0.71073 Å) radiation by using the ω-2θ scan method at room temperature. The structure was solved with direct methods and refined on F2 with full-matrix least-squares methods using SHELXS-97 and SHELXL-97 programs, respectively.17 All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were added in the riding model and refined isotropically with O-H ) 0.82 Å, C-H ) 0.97 Å, N-H ) 0.89 Å. The crystallographic data are summarized in Table 1. X-ray diffraction (XRD) powder patterns calculated from single-crystal data using GSAS18 software closely matched that obtained from a bulk sample as shown in Figure 1.
Results and Discussion [C2H10N2][B5O8(OH)] is a layered compound composed of [B5O8(OH)]n2n- layers intercalated with [C2H10N2]2+ ions. The fundamental building block (FBB) of the structure is a double B3O3-ring unit [B5O10(OH)] consisting of two BO4 tetrahedra, two BO3, and one BO2(OH) triangle (Figure 2). There are five terminal oxygen atoms (O3, O4, O3′, O4′, and O9), four of which are linked to the neighboring FBB to form an extended layer with nine-member ring windows as shown in Figure 3. Another terminal oxygen (O9) is bonded to a proton. In addition to the nine-member rings, there are also two different threemember rings; the three-member ring within the plane consists of two BO3 and one BO4, while the three-member ring perpendicular to the plane contains one BO3 and two BO4. The
10.1021/cg0606794 CCC: $37.00 © 2007 American Chemical Society Published on Web 05/31/2007
Synthesis and Structure of [C2H10N2][B5O8(OH)]
Crystal Growth & Design, Vol. 7, No. 7, 2007 1247 Table 2. Selected Distances That Are Influenced by Hydrogen Bond in [C2H10N2][B5O8(OH)]
Figure 1. Rietveld plot of X-ray diffraction patterns of [C2H10N2][B5O8(OH)].
Figure 2. The [C2H10N2]2+ ion and the fundamental building block [B5O10(OH)]4- of [C2H10N2][B5O8(OH)].
[B5O8(OH)]n2n- borate layer can be considered as a primary flat borate layer plus a side borate chain (BO3), and therefore, the [B5O8(OH)]n2n- layer is noncentrosymmetric. Noncentrosymmetric layers may not neccesarily lead to a noncentrosymmetric crystal. In fact, the same [B5O8(OH)]n2nborate layers have also been observed in Ca[B5O8(OH)]‚H2O19 and Ba[B5O8(OH)]‚H2O.20 In Figure 4a, we illustrate the
D-H‚‚‚A
D‚‚‚H (Å)
H‚‚‚A (Å)
D-H‚‚‚A (Å)
O9-H9‚‚‚O8 N10-H10A‚‚‚O4 N10-H10A‚‚‚O6 N10-H10B‚‚‚O3 N10-H10B‚‚‚O1 N10-H10C‚‚‚O8 N10-H10C‚‚‚O7 N13-H13A‚‚‚O5 N13-H13B‚‚‚O7 N13-H13B‚‚‚O3 N13-H13C‚‚‚O2
0.82 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89 0.89
2.06 2.20 2.54 1.97 2.33 2.10 2.28 1.90 2.24 2.43 1.88
2.807(2) 3.034(3) 3.006(3) 2.785(3) 2.833(3) 2.926(3) 2.788(3) 2.779(3) 3.056(3) 3.208(3) 2.745(3)
stacking of the borate layers in the structure of Ca[B5O8(OH)]‚ H2O. It can be seen that due to the antiparallel stacking of the borate layers, the crystal structure is centrosymmetric. On the contrary, the borate layers in [C2H10N2][B5O8(OH)] are parallel stacked along the b-axis (Figure 5), where the side chains all point to one direction, which leads to a noncentrosymmetric (Cc) structure. This stacking fashion is stablized by counter [C2H10N2]2+ cations and extensive hydrogen bonds as listed in Table 2. As shown in Figure 5, the [C2H10N2]2+ cations are located in the cavities between the layers. In addition to the Coulomb interaction, the [C2H10N2]2+ ions also contribute greatly to the hydrogen bonding interaction with the borate layers. Of course, the hydroxyl groups in the borate layers (O9) also show quite strong hydrogen bonding interaction with O8 in the neighboring layers. Another polymorphic layer of [B5O8(OH)]n2n- was observed in Ce[B5O8(OH)]NO3‚3H2O,21 [H3N(C6H10)NH3][B5O8(OH)],22 and Na2[B5O8(OH)]‚2H2O.23 The polyborate anions in these compounds have exactly the same composition as that in [C2H10N2][B5O8(OH)] but with a different structure. Figure 4b shows the stacking of the polyborate layers in Ce[B5O8(OH)]NO3‚3H2O. One can see that the side-chains are distributed in both sides of the primary borate layer, which leads to zigzag deformation of the primary borate layer. The difference of these two polymorphic layers is the orientation of the tetrahedral BO 4 in the primary layer. In [C2H10N2][B5O8(OH)], BO4 all points to one side, while in Ce[B5O8(OH)]-NO3‚3H2O the orientation of BO4 alternates. The SHG effect was measured by the quasi Kurtz method24 on the powder sample of the title compound. The YAG:Nd3+ laser (1064 nm) was used as incident light, and the frequency-
Figure 3. An overview along the c-direction of the [B5O8(OH)]n2n- layer; cations have been omitted for clarity.
1248 Crystal Growth & Design, Vol. 7, No. 7, 2007
Yang et al.
Figure 4. Different [B5O8(OH)]n2n- layers and their stacks: (a) Ca[B5O8(OH)]‚H2O;20 (b) Ce[B5O8(OH)]NO3‚3H2O.21 O, black circles; B, white circles.
Figure 7. FTIR spectrum of [C2H10N2][B5O8(OH)].
Figure 5. A view of [C2H10N2][B5O8(OH)] to show the layer structure. O, large black spheres; B, small white spheres; N, large white spheres; C, small black spheres; H, small gray spheres.
Figure 8. Absorbance-wavelength curve of [C2H10N2][B5O8(OH)].
Figure 6. TG curve of [C2H10N2][B5O8(OH)].
doubled outputs (λ ) 532 nm) were recorded by using potassium dihydrogen phosphate (KDP) as a reference. Preliminary experimental results show that the compound [C2H10N2][B5O8(OH)]
displays a modest powder SHG efficiency approximately 1.2 times of that of KDP. This compound also exhibits reasonably good thermal stability. The TGA analysis indicates an onset above 300 °C of the decomposition temperature as shown in Figure 6. The weight loss of 23.0% may correspond to the loss of C2H10N2 (calc. loss, 23.0%), and 10.5% may be attributed to the loss of three OH groups in the form of water (calc. loss, 10.35%).
Synthesis and Structure of [C2H10N2][B5O8(OH)]
Crystal Growth & Design, Vol. 7, No. 7, 2007 1249
Figure 9. (a) The asymmetric unit, (b) the chain structure, and (c) the packed structure of WO3(NH2CH2CH2NH2). Table 3. Crystallographic and Structure Refinement Parameters for WO3(NH2CH2CH2NH2) formula fw crystal system space group a, Å b, Å c, Å β
WO3(NH2CH2CH2NH2) 291.95 monoclinic C2 11.101(2) 7.2843(15) 7.5086(15) 94.49(3)
volume, Å3 Z dcalcd, g‚cm-3 T, K λ(Mo, KR), Å µ, mm-1 R1(I > 2δ(I))a wR2 (all data) a
605.3(2) 4 3.204 298 0.71073 19.008 0.0785 0.1949
a R ) ∑(||F | - |F ||)/∑|F | . wR )[∑(F 2 - F 2)2/∑(F 2)2]1/2. w )1/ 1 0 c 0 2 0 c 0 [σ2(F02) + (0.1910P)2 + 10.00P}, where P ) (F02 + 2Fc2)/3.
The FTIR spectrum of [C2H10N2][B5O8(OH)] is shown in Figure 7. The recorded FTIR spectrum was compared with the standard spectrum of the functional groups. The stretching vibrations of the O-H, C-H, and N-H bands are observed at 3227, 3107, 2924, 2761 cm-1. The bands at 1628 and 1569 cm-1 are related to [C2H10N2]2+. The strong bands at ∼1387, 1359, and 940 cm-1 in the spectra are characteristic of BO3,25 and the band at 1256 cm-1 is related to the B-O-H group,25 while the bands around 1068, 989, 862, and 757 cm-1 are characteristic of BO4,25 and the stretching vibrations of the C-N band are also located around 1068 cm-1. UV absorption spectrum of [C2H10N2][B5O8(OH)] was recorded on an UV-3100 UV-VIS-NIR spectrophotometer in the range 200-2400 nm covering the entire near-UV, visible, and NIR regions (Figure 8). Several single crystals about 2 × 1 × 0.5 mm were used for this study. No absorption was found in the visible region. The absorbance increases rapidly around 260 nm due to electronic excitation in this region. The absorbance in the range between 1600 and 2400 nm is related to the multiplication or sum of the vibration of NH3, CH2, and OH groups. The absence of absorption in the region between 320 and 1600 nm shows that this compound could be used for optical window applications. It needs to be mentioned that although the ratio of the raw materials is not critical for the reaction, the existence of WO3 is essential. There will be no solid-state production without WO3, and a new compound WO3(NH2CH2CH2NH2) (II) is formed as a second phase in many cases. When the amount of WO3 is increased to about 8.6 mmol, the major insoluble phase obtained is II. The single crystals of II are needle-shaped. Its crystallographic data are summarized in Table 3, which was determined by a single-crystal technique. The elemental analysis results agree well with the formula supposed as follows: Anal. Calc. for WO3(NH2CH2CH2NH2): C, 8.23; H, 2.76; N, 9.60. Found: C, 8.38; H, 2.85; N,9.63. As shown in Figure 9a, the asymmetric unit of II consists of one W atom, one NH2CH2CH2NH2
molecule, two terminal oxygen atoms, and one bridged oxygen atoms. The asymmetric units link to zigzag chains by corner sharing the bridged oxygen atoms (see Figure 9b). These chains are further connected by the hydrogen bond to form the twodimensional structure of II, and the packed patterns are shown in Figure 9c. The experimental result on the SHG effect shows that the compound WO3(NH2CH2CH2NH2) gives a weak nonlinear optical response, which is lower than 0.1 times of that of KDP. Conclusions In summary, we are trying to explore an approach to new NLO materials by using nonmetal polyborates. As an example, [C2H10N2][B5O8(OH)], obtained by using solvothermal synthesis, consists of a layered borate anion and [C2H10N2]2+ counter cations. The polyborate layer itself is noncentrosymmetric that stacks in a nonsymmetric fashion, and thus the compound does show moderate SHG effects. The counter cation in this compound is only a simple diamine. It might be interesting to introduce more ansymmetic amines, especially those with more delocalized configurations. Acknowledgment. This work was supported by the National Natural Science Foundation of China (Grant 20471003 and 20221101). We are grateful to Dr. GuiLin Wang (Institute of Physics, Chinese Academy of Science) for getting the data on the SHG of the title compound. Supporting Information Available: Crystallographic data in CIF format for compounds I and II. This material is available free of charge via the Internet at http//pubs.acs.org.
References (1) Becker, P. AdV. Mater. 1998, 10, 979. (2) Chen, C.; Wu, B.; Jiang, A.; You, G. Sci. Sin. B 1985, 28, 235. (3) Chen, C.; Wu, Y.; Jiang, A.; Wu, B.; You, G.; Li, R.; Lin, S. J. Opt. Soc. Am. B. 1989, 6, 616. (4) Mori, Y.; Kuroda, I.; Nakajima, S.; Sasaki, T.; Nakai, S. Appl. Phys. Lett. 1995, 67, 1818. (5) (a) Khamaganova, T. N.; Trunov, V. K.; Dzhurinskii, B. F. Zh. Neorg. Khimii 1991, 36, 855. (b) Norrestam, R.; Nygren, M.; Bovin, J. O. Chem. Mater. 1992, 4, 737. (c) Ilyukhin, A. B.; Dzhurinskii, B. F. Zh. Neorg. Khimii 1993, 38, 917. (6) Hellwig, H.; Liebertz, J.; Bohaty, L. J. Appl. Phys. 2000, 88, 240. (7) Wu, Y. C.; Liu, J. G.; Fu, P. Z.; Wang, J. X.; Zhou, H. Y.; Wang, G. F.; Chen, C. T. Chem. Mater. 2001, 13, 753. (8) Li, L. Y.; Li, G. B.; Wang, Y. X.; Liao, F. H. and Lin, J. H. Chem. Mater. 2005, 17, 4174. (9) Chen, C. T. Sci. Sin. 1979, 22, 756.
1250 Crystal Growth & Design, Vol. 7, No. 7, 2007 (10) Lin, Z. S.; Wang, Z. Z.; Chen, C. T.; Lee, M. H. J. Appl. Phys. 2001, 90, 5585. (11) Williams, D. J. Angew. Chem., Int. Ed. Engl. 1984, 23, 690. (12) Long, N. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 21. (13) Jiang, M. H.; Fang, Q. AdV. Mater. 1999, 11, 1147. (14) (a) Visi, M. Z.; Knobler, C. B.; Owen, J. J.; Khan, M. I.; Schubert, D. M. Cryst. Growth Des. 2006, 6, 538. (b) Schubert, D. M.; Visi, M. Z.; Knobler, C. B. Inorg. Chem. 2000, 39, 2250. (c) Liu, Z. H.; Li, L. Q.; Zhang, W. J. Inorg. Chem. 2006, 45, 1430. (d) Li, Q.; Xue, F.; Mak, T. C. W. Inorg. Chem. 1999, 38, 4142. (15) Guieu, V.; Payrastre, C.; Madaule, Y.; Garcia-Alonso, S.; Lacroix, P. G.; Nakatani, K. Chem. Mater. 2006, 18, 3674. (16) Ramajothi, J.; Dhanuskodi, S. Cryst. Res. Technol. 2003, 38, 986. (17) (a) Sheldrick, G. M. SHELXS97, Program for Crystal Structure Solution, University of Go¨ttingen: Go¨ttingen, Germany, 1997. (b) Sheldrick, G. M. SHELXL97, Program for Crystal Structure Refinement, University of Go¨ttingen: Go¨ttingen, Germany, 1997.
Yang et al. (18) (a) Larson, A. C.; von Dreele, R. B. Report LAUR 86-748, Los Alamos National Laboratory, 1985. (b) Rietveld, H. M. J. Appl. Crystallogr. 1969, 2, 65. (19) Yamnova, N. A.; Egorov-Tismenko, Y. K.; Zubkova, N. V.; Dimitrova, O. V.; Kantor, A. P.; Ye, D. N.; Xiong, M. Cryst. Rep. 2003, 48, 557. (20) Pushcharovsky, D. Yu.; Merlino, S.; Ferro, O.; Vinogradova, S. A.; Dimitrova, O. V. J. Alloy Compd. 2000, 306, 163. (21) Li, L. Y.; Jin, X. L.; Li, G. B.; Wang, Y. X.; Liao, F. H.; Yao, G. Q.; Lin, J. H. Chem. Mater. 2003, 15, 2253. (22) Wang, G. M.; Sun, Y. Q.; Yang, G. Y. J. Solid State Chem. 2004, 177, 4648. (23) Corazza, E.; Menchetti, S.; Sabelli, C. Acta. Crystallogr. B 1975, 31, 2405. (24) Kurtz, S. K.; Perry, T. T. J. Appl. Phys. 1968, 39, 37. (25) Li, J.; Xia, S. P.; Gao, S. Y. Spectrochim. Acta 1995, 51, 519.
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