Article pubs.acs.org/IC
Two Zeolitic Open-Framework Aluminoborates Directed by Similar Zn-Complexes Qi Wei,† Jia-Jia Wang,† Jie Zhang,*,† and Guo-Yu Yang*,†,‡ †
MOE Key Laboratory of Cluster Science, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China ‡ Department of Chemistry, Key Laboratory for Preparation and Application of Ordered Structural Materials of Guangdong Province, Shantou University, Shantou, Guangdong 515063, China S Supporting Information *
ABSTRACT: Two three-dimensional (3D) zeolitic open-framework aluminoborates (ABOs) [Zn(ma)(en)2][AlB5O10] (1) and [Zn(ma)(en)2][AlB6O11(OH)] (2) (ma = methylamine, en = ethylenediamine) were successfully made under solvothermal conditions, which represent the first examples using similar metal complex (MC) with mixed amines as the structure-directing agents in ABOs. Notice that the central atom in the MC is coordinated by mixed amines is uncommon. However, they exhibit distinctly different structures: 1 crystallizes in a centrosymmetric [Al(B5O10)]n2n− zeolitic framework built by pentaborate (B5O10) clusters and AlO4 tetrahedra, exhibiting a 4-connected cag topology, while 2 contains hexaborate (B6O11(OH)) clusters and AlO4 groups, further alternately joined to form a noncentrosymmetric [AlB6O11(OH)]n2n− zeolitic framework with 7-/9-, 8-/10-ring helical channels and large 13-ring channels, showing a dia topology. Nonlinear optical (NLO) determination showed that 2 exhibits good second-harmonic generation response of ∼1.9 × KH2PO4 and is phase-matchable, combining the short UV cutoff edge, making 2 a potential UV NLO material.
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INTRODUCTION Zeolites are of current interest because of their wide applications ranging from conventional catalysis, separation, and ion exchange to modern microlasers, high-capacity gas storage.1 These functions are mainly determined by properties related to their unique structural features. With the development of the synthetic strategies, great effort has been made in exploring novel zeotype materials by substituting Al and/or Si with other polyatomic building units, which was termed “decoration” by the scale chemistry theory.2 During the past several decades, a large number of exciting phosphate− germanate-based zeolite-type structures have been made and characterized,3 notable examples being UCSB-7/15,3c ND-1,3d PKU-16,3e and ITQ-37.3f Recently, incorporating boron atoms into zeolite structures has been of particular interest, since these compounds may integrate zeolitic porosity with extraordinary optical properties of borate materials. Unlike silicon, boron can be coordinated by oxygen atoms to form either trigonal planar BO3 or tetrahedral BO4 units, both of which lack of an inversion center and favor polymerization into various types of oxoboron clusters.4 Moreover, it is well-known that the planar BO3 triangle with a π-conjugated system has large microscopic second-order susceptibility. These unique structural characteristics make borates an ideal candidate for designing materials with desired nonlinear optical (NLO) activity. The famous examples of β-BaB2O4 (BBO)5 and LiB3O5 (LBO)6 crystals have been widely used in NLO devices. Recently, study on that four-connected polyborate clusters act as the main structural building units (SBUs) to join in © 2017 American Chemical Society
formation of zeolitic aluminoborates (ABOs) has made some progress.7 For example, [Zn(dap)2][AlB5O10] (dap = 1,3diaminopropane),7c which contains the features of both zeolitic inorganic framework and metal−organic coordination network, shows 4-connected dia topology. Another example, BIT-1,7d features a rare zeolite CAN type net and represents the largest pores in ABOs. The two examples display moderate secondharmonic generation (SHG) efficiency of ∼1/3 and 1.1 times of KH2PO4 (KDP), respectively. In addition, it is noteworthy that the reported ABOs directed by metal complexes (MCs) are very limited. MCs as the templates not only have various spatial configurations, different flexibilities, and H-bonding sites but also can imprint their chiral characters into the inorganic host by H-bonding interactions. Furthermore, the central metal atoms of MCs in the known ABOs are all coordinated by homogeneous ligands except the zinc atom in [Zn(en) (dien)][AlB5O10] (en = ethylenediamine; dien = diethylenetriamine),7e in which the dien molecule was formed in situ from condensation of original en reagent. Here, using an amine alcohol solution as solvent and ligand, and combining with an additional amine that cooperatively acts as the mixed ligands for the central metal atoms, we successfully made two zeolitic open-framework ABOs, namely, [Zn(ma)(en)2][AlB5O10] (1) and [Zn(ma)(en)2][AlB6O11(OH)] (2) (ma = methylamine). Interestingly, though 1 and 2 direct by similar SDAs of [Zn(ma)(en)2] complexes, they exhibit distinctly different Received: March 21, 2017 Published: May 19, 2017 6630
DOI: 10.1021/acs.inorgchem.7b00690 Inorg. Chem. 2017, 56, 6630−6637
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Inorganic Chemistry structures: 1 features centrosymmetric (CS) [Al(B5O10)]n2n− framework with cag topology, while 2 crystallizes in noncentrosymmetric (NCS) [AlB6O11(OH)]n2n− framework with dia topology.
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Table 1. Crystallographic Data and Structure Refinements for 1 and 2 compound Fw crystal system space group T/K λ/Å a/Å b/Å c/Å β/deg V/Å3 Z Dcalcd/g·cm−3 μ(Mo Kα)/mm−1 F(000) Completeness GOF on F2 R1, wR2 (I > 2σ(I))a R1, wR2 (all data) Flack parameter
EXPERIMENTAL SECTION
Materials and Methods. All reagents are analytical grade and used without further purification. Elemental analyses of C, H, and N were performed with a Vario EL III elemental analyzer. Powder X-ray diffraction (XRD) patterns were collected on a Rigaku MiniFlex II diffractometer using Cu Kα radiation (λ = 1.540 598 Å) in the angular range of 2θ = 5−50°. Thermogravimetric analyses were measured in a dynamic oxygen atmosphere with a heating rate of 10 °C min−1 using a Mettler TGA/SDTA 851e thermal analyzer. IR spectra were performed on an ABB Bomen MB 102 series FTIR spectrophotometer with pure KBr pellets as a measure for the baseline correction over the scope of 4000−400 cm−1. Photoluminescence spectra were performed on a PerkinElmer LS55 fluorescence spectrometer. The optical diffuse reflectance spectra were measured at room temperature using a PerkinElmer Lamda-950 UV−vis−NIR spectrophotometer equipped with an integrating sphere attachment. BaSO4 plate was used as a standard (100% reflectance). The absorption spectra were converted using the Kubelka−Munk function:8 F(R) = α/S = (1 − R)2/2R. SHG response for 2 was performed on a Q-switched Nd:YAG solid-state laser on powder samples with a wavelength of 1064 nm as the fundamental frequency light.9 As the response is known to strongly depend on the particle size, the samples were ground and sieved into seven distinct particle size ranges: 0−45, 45−58, 58−75, 75−109, 109−150, 150−212, and 212−270 μm. Sieved of the standard NLO material KDP was used as the reference in identical fashion. Synthesis of [Zn(ma)(en)2][AlB5O10] (1). A total of H3BO3 (5.0 mmol, 0.310 g), Al(i-PrO)3 (0.8 mmol, 0.169 g), and Zn powder (1.0 mmol, 0.065 g) was added to methylamine alcohol solution (MAS, 5.0 mL). The mixture was stirred for ∼2 h, and then 1.5 mL of en was added. The final solution was sealed in a 30 mL Teflon-lined stainless steel autoclave, heated at 180 °C for 7 d under autogenous pressure, and then cooled to room temperature. Colorless prismatic-like crystals were obtained in a yield of ∼70% based on Al(i-PrO)3. Anal. calcd (%) for C5N5H21AlB5ZnO10 (1): C 13.11, N 15.30, H 4.59; found: C 12.95, N 15.09, H 4.72. Synthesis of [Zn(ma)(en)2][AlB6O11(OH)] (2). A total of H3BO3 (6.0 mmol, 0.379 g), Al(i-PrO)3 (0.8 mmol, 0.172 g), and Zn powder (1.2 mmol, 0.078 g) was added to MAS 4.0 mL. Then, 1.0 mL en was slowly added under constant stirring. The final solution was sealed in a 30 mL Teflon-lined stainless steel autoclave, heated at 160 °C for 7 d, and then cooled to room temperature. Colorless long prismatic-like crystals were obtained with the yield up to 86% based on Al(i-PrO)3. Anal. calcd (%) for C5N5H22AlB6ZnO12 (2): C 11.97, N 13.96, H 4.39; found: C 11.88, N 13.80, H 4.48. The purities of 1 and 2 were confirmed by powder XRD diffraction study (Figure S1), the patterns were in accordance with the calculated ones simulated from the single-crystal data. Structural Determination. Single-crystal XRD data were collected on an Agilent Technologies SuperNova dual wavelength CCD diffractometer for 1 and Saturn 724 CCD diffractometer for 2 with Mo Kα radiation (λ = 0.710 73 Å) at 293 K. Multiscan method was used for the absorption correction.10 Both structures were solved by direct methods and refined by full-matrix least-squares fitting on F2 using SHELXTL-97 program.11 Anisotropic displacement parameters were refined for all atomic sites except those of H atoms. The H atoms were geometrically placed and refined using a riding model. For 2, the Flack parameter was refined to be 0.00(2), statistically indicating the correctness of the absolute structure.12 The structures were verified using the ADDSYM algorithm from PLATON,13 and no higher symmetry was found. Crystallographic data and structure refinement information are summarized in Table 1. In Supporting Information, the crucial bond lengths are given in Table S1 and Table S2. CCDC: 1040999 for 1 and 1041000 for 2.
C5N5H21Zn AlB5O10 (1) 457.67 orthorhombic Pbca (No. 61) 293(2) 0.71073 13.5496(9) 14.9899(10) 16.8615(8) 3424.7(4) 8 1.775 1.545 1872 99.9% 1.050 0.0351, 0.0982 0.0410, 0.1021
C5N5H22Zn AlB6O12 (2) 501.49 monoclinic P21 (No. 4) 293(2) 0.71073 7.369(3) 15.823(6) 8.152(3) 104.314(6) 921.0(6) 2 1.808 1.452 512 99.5% 1.001 0.0512, 0.1294 0.0711, 0.1840 0.00(2)
R1 = ∑∥F 0| − |Fc ∥/∑|F 0|, wR2 = {∑w[(F 0)2 − (Fc )2] 2 / ∑w[(F0)2]2}1/2.
a
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RESULTS AND DISCUSSION Solvothermal reactions with the same starting material, whereas different reactant composition and crystallization time, afforded two ABOs, namely, [Zn(ma)(en)2][AlB5O10] (1) and [Zn(ma)(en)2][AlB6O11(OH)] (2). The structures of 1 and 2 feature two types of three-dimensional (3D) anionic open frameworks based on different oxoboron clusters, B5O10 and B6O11(OH), interconnected by AlO4 groups, respectively. On the basis of the result from our experiments, the H3BO3/en/ MAS molar ratio, that is, the pH value in the reaction system, has a strong effect on the product crystals. When the pH value of the reaction system is adjusted to ∼9.8, prismatic-like crystals of 1 were obtained, while in the final mixture with a pH value of ∼8.8, long prismatic-like crystals of 2 were made. Presumably, the higher basicity of the reaction system prevents the protonation of the oxoboron cluster, B5O10 in 1 (pH = 9.8) and B6O11(OH) in 2 (pH = 8.8). But the exact crystallization mechanism, which determines the self-assembly processes of symmetry, remains poorly understood. The work reported here represents that the subtle changes in solvothermal synthetic conditions can significantly influence the formation of borates. In addition, replacing MAS with pyridine as solvent was fruitless indicating the importance of MAS, not only as the solvent but also as the ligands. Both 1 and 2 were also obtained when Zn powder was replaced by Zn(CH3COO)2·2H2O. To investigate the influence of different amines on the structural construction of the products, the synthetic procedure was modified by replacing en with 1,3-dap under similar conditions, which obtained another compound of Zn(1,3-dap)[B4O7].14 Structure of [Zn(ma)(en)2][AlB5O10] (1). Single-crystal Xray structure analysis reveals that [Zn(ma)(en)2][AlB5O10] crystallizes in the CS space group Pbca. The structure of 1 has a 3D anionic framework and discrete guest cations. Its asymmetric unit contains one B5O10 (B5) cluster, one Al3+ ion, and a [Zn(ma)(en)2]2+ cation (Figure 1a). In detail, Al atom adopts tetrahedral geometry with Al−O bond lengths in the range of 1.718(2)−1.740(2) Å, and O−Al−O angles vary 6631
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Figure 1. (a) The asymmetric unit of 1 and the coordination environment of Al atom. Symmetry operation: (i) −x, −y, 1 − z; (ii) 0.5 + x, 0.5 − y, 1 − z; (iii) 0.5 + x, y, 1.5 − z. (b) View of the B5 polyborate cluster with fictitious tetrahedral geometry.
from 105.4(4) to 112.5(4)°. The B atoms exhibit dual coordination modes, that is, both trigonal (Δ) and tetrahedral (T). Four BO3 (B1−4) triangles and one BO4 (B5) tetrahedron are linked via bridging μ-O atoms to give a pentaborate cluster, in which two planar B3O3 rings are nearly perpendicular to each other. On the basis of classification of polyborates proposed by Christ, Clark,15 and Hawthorne et al.,16 B5 cluster can be expressed as the shorthand notation of 4Δ1T: ⟨2ΔT⟩ − ⟨2ΔT⟩. BO3 and BO4 units have an average B−O distance of 1.364(4) and 1.471(4) Å, respectively. And the bond angles span from 117.1(3) to 123.6(3)° and from 107.3(2) to 111.0(2)°, respectively. These values are consistent with those in the reported borates.7c,17 The conformation of B5 cluster that with four potential linking O atoms corresponds to four corners of a fictitious (B5O6)O4 tetrahedron (Figure 1b). The strict alternation of the (B5O6)O4 and AlO4 tetrahedra through the vertices gives rise to a 3D anionic [Al(B5O10)]n2n− zeolitic framework (Figure 2). In detail, each B5 cluster connects 11 others via 4 bridging AlO4
tetrahedra and vice versa (Figure S2). Therefore, there is no Al−O−Al connection in the structure. To illustrate more clearly, the framework could be reduced into a CaGaO2 (cag) topology with the total Schläfli symbol of {4·65} when (B5O6)O4 and AlO4 groups act as 4-connected nodes. A PLATON program analysis suggests that there is ∼60.9% (2086.1 Å3 per unit cell) of the solvent-accessible volume by excluding the guest molecules. The 3D framework can be expressed by different types of inorganic layers. The layer containing 11-member rings (MRs) with approximate dimensions of 8.32 × 10.04 Å2 can be found in the bc plane (Figure 2a,b). Adjacent layers are stacked in an −AA′A− sequence. Thus, the channels along the [100] direction are interruptive owing to the reversion and the translation of adjacent layers. A view down the [001] direction exposes the layers with 8- and 14-MR, and their dimensions are ∼6.35 × 6.46 and 7.58 × 11.90 Å2, respectively (Figure 2c,d). Because of the related symmetry operation, the layers are packed in a −CC′C− sequence along the [001] direction. Interestingly, two types of layers with 11-MRs and 8-/14-MRs are alternately arranged along the [010] direction in an -L1-L2L1- sequence (Figure S3a,b). The [Zn(ma)(en)2]2+ cations compensate for the negative charge of the anionic framework and interact with the inorganic framework through extensive H bonds (Figure S3c). The Zn2+ ion is five-coordinated by mixed ligands of two en and one ma molecules to form [ZnN5] distorted tetrahedral geometry (the Zn−N distances: 2.034(3)−2.225(3) Å). Moreover, according to a literature search, there is only one example of [Zn(en)(dien)][AlB5O10]7e in ABOs, where the central atom is chelated with different organic amines. Thus, we predict that study performed on utilizing different organic ligands in the synthetic system may get novel borates with interesting structural features and desired properties. The structure of 1 is closely related to those of other ABOs of K2 Al[B5 O 10 ]·4H 2 O (1a), 7a [Zn(en)(dien)][AlB 5 O 10 ] (1b),7e and [Zn(1,3-dap)2][AlB5O10] (1c);7c they all have the same structural building units (SBUs) of B5O10 and AlO4 groups. However, owing to they are governed by different structure-directing agents (SDAs), the linkage modes of the SBUs are totally different, resulting in two types of 3D frameworks. Different is the CS cag-type framework of 1; in 1a−c, each B5O10 group links to 12 others through 4 bridging
Figure 2. (a, c) Polyhedral view of the single building layer, and (b, d) the topological view of the stacking of layers along the [100] and [001] directions in 1, respectively. 6632
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Figure 3. (a) The asymmetric unit of 2 and the coordination environment of Al atom. Symmetry operation: (i) 1 − x, 0.5 + y, 1 − z; (ii) x, y, −1 + z; (iii) −x, 0.5 + y, 1 − z. (b) View of the B6 polyborate cluster with fictitious tetrahedral geometry.
Figure 4. Polyhedral view of the 3D framework with 13- (a) and 11-MR (b) channels along the [100] and [001] directions, respectively, in 2. (c) Topological view of the 3D framework of 2.
the framework of 2 could be simplified in a dia topology. PLATON program suggested a solvent-accessible volume of ∼52.4% by excluding the guest molecules. In addition, the overall framework possesses muti-dimensional channels system running along the [100], [001], [010], and [101] directions with 13-, 11-, 8-/10-, and 7-/9-MR openings, respectively, in which the 8-/10- and 7-/9-MR channels are helical (Figure 5a,b). In detail, all helices are formed by repeated −B6−AlO4− linkages. Interestingly, the 8- and 10-MR helical channels contain two types of helices with opposite chirality, and the left (L)- and right (R)-handed helical chains are arranged alternately along the [010] direction, respectively (Figure 5d,e). However, all the 7- or 9-MR channels exhibit one type of chirality of helices along the [101] direction, respectively: the L-handed helices of 7-MR and the R-handed helices of 9-MR (Figure 5c). The complex [Zn(ma)(en)2]2+ cations as guests site at the 13-MR channels and connected with the framework with H-bonding interactions from the N atoms to O atoms (Figure S5a). The composition of the B6 (B6−I) cluster in 2 is same as the [B6O11(OH)] (B6−II) cluster in [Zn(dien)2][AlB6O11(OH)] (2a),7b which can be seen as an additional BO2(OH) triangle attaching in a typical B5O10 unit. Interestingly, we can refer to the decorated B6−I and B6−II clusters as cis and trans types, respectively, based on the placement of the “grafted” B6 atom with respect to the O8 atom (Figure 6), showing the structural diversity and flexibility of oxo-borates. The distinct linkage modes of B6 clusters make 2 and 2a have many obvious differences in their extended structures. First, the compositions of the 13-MR opening are different. The openings of the 13ring channels in 2 are delimited by −AlO4-3BO3−AlO44BO3/4-AlO4-3BO3/4- linkages with free diameter of ∼8.2 ×
AlO4 units and vice versa, forming chiral or asymmetric frameworks with intersecting channels. Such arrangements make the frameworks of 1a−c exhibit the diamond-type (dia) topology. The formation of 1 and 1a−c clearly shows that different SDAs can direct the same SBUs into different framework structures. Structure of [Zn(ma)(en)2][AlB6O11(OH)] (2). Compound 2 crystallizes in polar space group P21. The asymmetric unit contains one B6O11(OH) (B6) cluster, one Al3+ ion, and a [Zn(ma)(en)2]2+ cation; all the atoms occupy general sites (Figure 3a). The structure features a 3D anionic framework composed of Al3+ ions and B6 clusters with voids filled by [Zn(ma)(en)2]2+ cations. The Al3+ ion is also tetrahedrally coordinated with Al−O bond lengths in the range of 1.723(5)− 1.750(6) Å and the O−Al−O bond angles varying from 105.7(3) to 112.8(3)°. On the basis of classification of polyborates, the B6 cluster can be written as the shorthand notation of 5Δ1T: ⟨2ΔT⟩ − ⟨2ΔT⟩ Δ. The B−O distances span from 1.299(10) to 1.506(9) Å. O−B−O bond angles fall in the range from 106.3(7) to 122.6(8)°. The B6 cluster can be regarded as one of the terminal O atoms in the B5O10 cluster replaced by a BO2(OH) unit. Hence, the B6 cluster also has four potential linking O atoms that similar to four corners of a fictitious [B 6 O 7 (OH)]O 4 tetrahedron (Figure 3b). As a result, each B6 cluster as tetradentate bridging unit coordinates to four AlO4 tetrahedra, further generating a 3D inorganic [AlB6O11(OH)]n2n− zeolitic framework (Figure 4). Both the B6 in 2 and B5 in 1 can be regarded as fictitious tetrahedra, but their linkage modes are distinctly different; each B6 cluster in 2 is connected to 12 others via 4 bridging AlO4 groups and vice versa (Figure S4). Thus, by regarding B6 and AlO4 groups as 4-connected nodes, 6633
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totally different. The 7-MR (9-MR) helical channel contains one type of chirality of helices in 2 and two types of helices with opposite chirality in 2a. The terminal −OH groups of the “grafted” BO2(OH) triangles point into the 7-MR channels in 2. Each 7-MR channel is surrounded by four 9-MR and two 7MR channels, and vice versa. The channels are arrayed with −7L-9R-7L- sequence along [010] direction. In 2a, the terminal −OH groups exist in 9-MR channels, and each 7-MR channel is surrounded by six 9-MR and adjacent two 7-MR channels, and vice versa. Each pair of the L and R helical channels are strictly arranged alternately along [001] direction and with −9R(L)7L(R)-9R(L)- sequence along [010] direction (Figure S5c,d). Third, the most important issue, 2 crystallizes in chiral space group P21 (∼1.9 × KDP) with framework templated by 5coordinated [Zn(ma)(en)2]2+ cations, while 2a crystallizes in NCS space group Pc (∼1.3 × KDP) with templates of 6coordinated [Zn(dien)2]2+ cations. In total, the structural modulations of 2 and 2a are owing to the flexibility of the B6O11(OH) groups and the effect of cation size. To a certain extent, we conclude that the oxoboron clusters are more flexible compared with solely TO4 tetrahedra in conventional zeolites; as expected, more borates would be probably obtained with novel topologies and promising properties. Structure Relations. As we know, different templates or SDAs not only can direct different ABOs but also direct similar frameworks, such as Al[B5O10]·H2dab·2H2O (dab = 1,4diaminobutane)7a and [H2(1,2-dap)][(CH3) 2NH]AlB5O10 (1,2-dap = 1,2-diaminopropane).18 However, it is worthy to note that no ABO frameworks were templated by similar MCs currently. 1 and 2 were directed by the similar SDAs of [Zn(ma)(en)2] complexes, but they display distinctly different structures: 1 is CS [Al(B5O10)]n2n− framework with cag topology, while 2 crystallizes in NCS [AlB6O11(OH)]n2n− framework with dia topology. (1) The guest templates of [Zn(ma)(en)2] complexes in 1 and 2 are identical in their constituents, but the ZnN5 polyhedron in 1 is closer to regular tetrahedral configuration compared to that in 2 (Figure S6). The local dipole moments of the ZnN5 polyhedra are 4.45 and 5.89 D computed using a bond-valence approach.19 Therefore, the higher distorted ZnN5 polyhedron in 2 may be considered
Figure 5. Polyhedral view of the 3D framework with 7L and 9R (a) and 8L/8R and 10L/10R helical channels (b) along the [101] and [010] directions, respectively, in 2. (c) Side views of the 7L (left) and 9R (right) helices along the [101] direction. (d, e) Side views of the 8L/8R and 10L/10R helices along the [010] direction, respectively.
Figure 6. View of the cis (a) and trans (b) type of the B6 clusters in 2 and 2a, respectively.
11.7 Å2, while those are −AlO4-2BO3−AlO4-4BO3/4-AlO44BO3/4- linkages with diameter of ∼8.7 × 10.3 Å2 in 2a (Figure S5a,b). Second, the unclosed 7- and 9-MR helical channels are
Figure 7. View of adjacent inorganic layers and the MCs, which are arranged antiparallelly along [010] direction in 1 (a), while they are arranged parallelly along [100] direction in 2 (b). 6634
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Inorganic Chemistry as one NLO-active unit. (2) The main difference between the structures lies in their different stacking fashions of the MCs. Both the MCs in 1 and 2 are present in a coupled fashion, as shown in Figure 7; the inconsistent orientations of the MCs make the polarization partially cancel with each other. However, as the operation of rotation occurs along the [010] direction, the adjacent MCs in 1 are arranged antiparallelly along the [010] direction. For 2, because of the translation operation, the adjacent MCs are arranged parallelly along the [100] direction. As a result, the arrangements of MCs further transfer their symmetry to the host inorganic frameworks, respectively. Through host−guest hydrogen-bonding interactions (Figures S3b and 5a), adjacent inorganic layers in 1 are oriented in an −MM′M− sequence along the [010] direction (Figure 7a); the polarities between adjacent layers are canceled out, which renders 1 CS [Al(B5O10)]n2n− framework. On the contrary, the inorganic layers in 2 are aligned in the same directions uniformly with -NNN- sequence; local acentric feature is constructively added, which determines the acentricity of the overall extended NCS structure (Figure 7b). Therefore, the detailed structural comparison analysis indicates that there is a good symmetry correspondence between the arrangement of the guest templates or SDAs and the host framework.20 Additionally, it is believed that the H bonding between the MCs template and the host inorganic framework is the origin of the above phenomena. Optical Properties. The optical diffuse reflectance spectra of 1 and 2 in the region of 190−2500 nm are shown in Figure S7. The optical band gaps obtained by extrapolating the linear part of the rising curve to zero for 1 and 2 are 4.95 and 5.05 eV, respectively. And both exhibit short UV cutoff edges that are lower than 190 nm.21 Additionally, the band gaps are comparable to values of other ABOs ([Zn(en) 3 ][AlB7O12(OH)2] (5.60 eV),7e [Ni(dien)2][AlB6O11(OH)] (4.71 eV),7b and K2Al[B5O10]·4 H2O (4.45 eV)7a), which suggests that they are wide-band gap semiconductors. In addition, the solid-state emission spectra reveal that 1 and 2 have similar broad emission bands centered at 423 nm under excitation of 246 nm (Figure S8). Nonlinear Optical Property. Since 2 crystallized in NCS space group of P21, this prompted us to investigate its SHG property. The plots of SHG signals as a function of particle sizes were measured on a 1064 nm Q-switched Nd:YAG laser. For large particle sizes (150−212 and 212−270 μm), the intensities are about independent of particle sizes. The feature is well in agreement with type-I phase-matching behavior according to the rule proposed by Kurtz and Perry.9 Moreover, comparison of the SHG signals produced by powder samples of 2 and KDP in the same particle range of 150−212 μm indicates that compound 2 displays a moderate-to-strong SHG response of ∼1.9 × KDP (Figure 8). The good SHG activity and short cutoff edge make compound 2 a potential UV NLO material.
Figure 8. Particle size vs SHG intensity and oscilloscope traces of SHG signals for the powder of 2 and KDP in the same particle size of 150−212 μm.
zeolitic framework with dia topology, which was formed by B6O11(OH) clusters and AlO4 tetrahedra. To the best of our knowledge, this is the first observation in the family of ABOs that are directed by similar MCs. This work also shows intriguing structural diversity and flexibility of oxoborates, along with the potential applications in optical field, making borates still be a subject of interest in the future. UV−vis−NIR spectroscopy revealed that both compounds are wide-band gap semiconductors and have short UV cutoff edges. NLO determination showed that 2 exhibits good NLO activity with SHG response of ∼1.9 × KDP and is phase-matchable. All the characteristics make 2 a potential UV NLO material. This work offers the potential for making other novel metal borates in the presence of the same SDAs by changing reaction conditions.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00690. Selected bond distances, simulated and measured powder XRD patterns, IR spectra, TGA, fluorescence spectra, UV−vis−NIR optical diffuse reflectance spectra, and additional structures (PDF) Accession Codes
CCDC 1040999−1041000 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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CONCLUSION In summary, two 3D zeolitic open-framework ABOs [Zn(ma)(en)2][AlB5O10] (1) and [Zn(ma)(en)2][AlB6O11(OH)] (2) have been successfully made by adjusting the pH value of the reaction system under solvothermal conditions. Both are directed by [Zn(ma)(en)2] complexes, but they exhibit distinctly different structures. The strict alternation of B5O10 clusters and AlO4 tetrahedra via the vertices gives rise to the CS zeolitic framework of 1, [Al(B5O10)]n2n−, displaying cag topology, while 2 crystallizes in NCS [AlB6O11(OH)]n2n−
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. (J.Z.) *E-mail:
[email protected]. (G.-Y.Y.) ORCID
Jie Zhang: 0000-0002-6195-8525 Guo-Yu Yang: 0000-0002-0911-2805 6635
DOI: 10.1021/acs.inorgchem.7b00690 Inorg. Chem. 2017, 56, 6630−6637
Article
Inorganic Chemistry Notes
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the NSFC (21571016 and 91122028) and the NSFC for Distinguished Young Scholars (No. 20725101).
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DOI: 10.1021/acs.inorgchem.7b00690 Inorg. Chem. 2017, 56, 6630−6637