Article pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Variable Asymmetric Chains in Transition Metal Oxyfluorides: Structure−Second-Harmonic-Generation Property Relationships Belal Ahmed, Hongil Jo, Seung-Jin Oh, and Kang Min Ok* Department of Chemistry, Chung-Ang University, 84 Heukseok-ro, Dongjak-gu, Seoul 06974, Republic of Korea S Supporting Information *
ABSTRACT: Four novel transition metal oxyfluorides, [Zn(pz)3][MoO2F4]· 0.1H 2 O (1), [Zn(pz) 2 F 2 ][Zn(pz) 3 ] 2 [WO 2 F 4 ] 2 (2), [Cd(pz) 4 ][Cd(pz)4(H2O)][MoO2F4]2·0.625H2O (3), and [Zn(mpz)3]2[MoO2F4]2 (4) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized. Compounds 1 and 4 contain helical chains. Compound 2 accommodates zigzag chains, and compound 3 has quasi-one-dimensional linear chains. The variable chain structures are found to be attributable to the different structure-directing anionic groups and hydrogen bonding interactions. Compound 4 crystallized in the noncentrosymmetric (NCS) polar space group, Pna21, is nonphasematchable (Type I), and reveals a moderate second-harmonic-generation (SHG) efficiency (10 × α-SiO2). The observed SHG efficiency of compound 4 is due to the small net polarization occurring from the arrangement of ZnN3F2 trigonal bipyramids. Spectroscopic and thermal characterizations along with calculations for the title materials are reported.
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(Zn2+ and Cd2+), and heterocyclic ligands [pyrazole (pz) and 3methylpyrazole (mpz)]. Synthesis, structural description, spectroscopic characterization, and thermal properties for the title compounds are provided. Detailed second-harmonicgeneration (SHG) properties and the origin of the SHG for the helical chains with NCS structure are also presented.
INTRODUCTION Rational design and construction of compounds crystallizing in noncentrosymmetric (NCS) space groups have been of great interest attributed to their intriguing physical properties.1−10 The interesting characteristics expected from crystalline compounds with NCS structures may be utilized in various functional application fields, i.e., lasers, detectors, memories, energy systems, and photolithography. 11 Among many approaches toward the functional materials containing NCS structures, combining the basic building units (BBUs) exhibiting specific moments have drawn huge attentions. Specifically, the combination of distortive octahedra containing early transition metals (ETM), polarizable polyhedra with late transition metals (LTMs), and organic ligands through solvothermal reactions have been extensively explored. In fact, the individual net dipole moments arising from the asymmetric BBUs were key factors for the polarity engineering.12−14 In addition, the combination of unsymmetrical BBUs resulted in interesting structures such as isolated molecules, chains, layers, and frameworks.15−17 The structural diversity found from mixed metal oxyfluoride compounds has been intimately related to the hard−soft acid−base chemistry: The hard ETM acids with high oxidation states tend to be coordinated by the hard bases such as F− and O2−, whereas the soft LTM with low oxidation states tend to be connected by the soft organic bases. Several mixed metal oxyfluoride materials have successfully suggested important clues for the asymmetric environment including the structure-directing properties.18,19 Here, we discovered four new mixed transition metal oxyfluorides revealing various chain structures by combining distorted ETM octahedra (Mo6+ and W6+), polarizable LTM cations © XXXX American Chemical Society
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EXPERIMENTAL SECTION
Caution: Hydrof luoric acid is toxic and corrosive! Synthesis. ZnO (99.0%, Waco), CdO (99.5%, Aldrich), MoO3 (99.5%, Alfa Aesar), WO3 (99.5%, Daejung), C3H4N2 (pyrazole) (98%, Alfa Aesar), C4H6N2 (3-methypyrazole) (97%, Alfa Aesar), and HF (aq. 48 wt %, J.T Baker) were used as received. Crystals of all the reported compounds were grown via hydrothermal reactions. For [Zn(pz)3][MoO2F4]·0.1H2O (1), 4.00 × 10−3 mol (0.326 g) of ZnO, 4.00 × 10−3 mol (0.576 g) of MoO3, 2.40 × 10−2 mol (1.630 g) of pyrazole, 2.00 × 10−2 mol (0.834 g) of aqueous HF (48%), and 0.324 mL of water were combined. For [Zn(pz)2F2][Zn(pz)3]2[WO2F4]2 (2), 5.00 × 10−3 mol (0.407 g) of ZnO, 5.00 × 10−3 mol (1.159 g) of WO3, 1.00 × 10−2 mol (0.681 g) of pyrazole, 2.50 × 10−2 mol (1.042 g) of aqueous HF (48%), and 0.811 mL of water were combined. For [Cd(pz)4][Cd(pz)4(H2O)][MoO2F4]2·0.625H2O (3), 5.00 × 10−3 mol (0.642 g) of CdO, 5.00 × 10−3 mol (0.720 g) of MoO3, 3.00 × 10−2 mol (2.042 g) of pyrazole, 2.50 × 10−2 mol (1.042 g) of aqueous HF (48%), and 1.621 mL of water were combined. For [Zn(mpz)3]2[MoO2F4]2 (4), 1.00 × 10−3 mol (0.081 g) of ZnO, 1.00 × 10−3 mol (0.144 g) of MoO3, 6.00 × 10−3 mol (0.498 g) of 3methylpyrazole, 5.00 × 10−3 mol (0.208 g) of aqueous HF (48%), and 0.180 mL of water were combined. Each reaction mixture was loaded in autoclaves with 23 mL Teflon cups. After tightly sealing, the Received: April 3, 2018
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DOI: 10.1021/acs.inorgchem.8b00903 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Table 1. Crystallographic Data for Compounds 1−4 formula fw space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z T (K) λ (Å) ρcalcd (g cm−1) Flack parameter R(F0)a Rw(F02)b a
1
2
3
4
ZnMoC9H12F4N6O2.10 475.18 I41/a (No. 88) 20.7523(3) 20.7523(3) 14.9462(3) 90 6436.7(2) 16 298.0(2) 0.71073 1.961 N/A 0.0437 0.0900
Zn3W2C24H32F10N16O4 1362.51 Pnma (No. 62) 34.0224(5) 13.4973(2) 8.74410(10) 90 4015.38(10) 4 298.0(2) 0.71073 2.254 N/A 0.0324 0.0684
Cd2Mo2C24H34F8N16O5.62 1205.35 P21/n (No. 14) 14.627(3) 23.224(5) 25.046(5) 105.15(3) 8212(3) 8 100.0(2) 0.70000 1.950 N/A 0.0327 0.0822
Zn2Mo2C24H36F8N12O4 1031.31 Pna21 (No. 33) 19.8002(3) 10.5826(2) 18.5277(3) 90 3882.25(11) 4 298.0(2) 0.71073 1.765 0.005(5) 0.0272 0.0539
R(F0) = Σ ||F0| − |Fc||/Σ |F0|. bRw(F02) = [Σw(F02 − Fc2)2/Σw(F02)2]1/2.
autoclaves were heated to 150 °C for 72 h (24 h for compound 1) and slowly cooled to room temperature at a rate of 6 °C h−1. Colorless crystals of compounds 1−4 were obtained by vacuum filtration in 84, 28, 62, and 59% yields, respectively, based on ZnO or CdO. Compound 4 crystallizing in a NCS space group was deposited to NCS Materials Bank (http://ncsmb.knrrc.or.kr). Structure Determination. Single crystal X-ray diffraction data for compounds 1−4 were collected on a Bruker SMART BREEZE diffractometer (Mo Kα radiation) with a 1K CCD area detector at room temperature and on a BL2D-SMC at the Pohang Light Source II using 0.65000 Å radiation at 100 K. A colorless block (0.332 mm × 0.440 mm × 0.516 mm) for compound 1, a colorless block (0.335 mm × 0.403 mm × 0.562 mm) for compound 2, a colorless block (0.028 mm × 0.028 mm × 0.063 mm) for compound 3, and a colorless block (0.232 mm × 0.425 mm × 0.440 mm) for compound 4 were selected. The structure solutions and refinements were obtained by SHELXS9720 and SHELXL-97,20 respectively, in the software package WinGX98.21 Crystallographic data for the title compounds are tabulated in Table 1. Characterization. Powder X-ray diffraction (PXRD) data of the reported crystalline materials were obtained on a Bruker D8-Advance diffractometer using Cu Kα radiation with 40 kV and 40 mA in the 2θ range of 5−70° with a step size of 0.02° for 0.1 s. The measured PXRD patterns for the pure polycrystalline samples were in good agreement with the calculated data generated from single crystal X-ray diffraction experiments (see the Supporting Information). Infrared (IR) spectra for the title compounds were collected by a Thermo Scientific Nicolet 6700 FT-IR spectrometer in the range of 400−4000 cm−1 at room temperature. UV−vis diffuse reflectance spectra for the synthesized materials were obtained on a Varian Cary 500 scan UV−vis−NIR spectrophotometer in the spectral range of 200−2000 nm at room temperature. The measured reflectance data were converted to absorbance using the Kubelka−Munk function.22,23 Thermogravimetric analysis (TGA) was carried out on a SCINCO TGA N-1000 thermal analyzer from room temperature to 900 °C heating at a rate of 10 °C min−1 under a constant flowing of Ar gas. Elemental analysis was performed on a Carlo Erba EA1108 analyzer. Elemental microanalysis: compound 1 obsrvd (calcd): C, 24.84% (22.83%); H, 2.58% (2.55%); N, 16.21% (17.75%). compound 2 obsrvd (calcd): C, 21.39% (21.16%); H, 2.47% (2.37%); N, 15.07% (16.45%). compound 3 obsrvd (calcd): C, 23.62% (24.16%); H, 3.05% (2.70%); N, 16.99% (18.78%). compound 4 obsrvd (calcd): C, 27.97% (27.95%); H, 3.58% (3.52%); N, 16.26% (16.30%). SHG measurements were performed by using a modified KurtzNLO measurement system with a DAWA Q-switched Nd:YAG solid state laser (1064 nm radiation operating at 20 Hz).24 Polycrystalline sample of NCS compound 4 was ground and sieved into various
particle size ranges (
