Article pubs.acs.org/IC
Germanium Compounds Containing GeE Double Bonds (E = S, Se, Te) as Single-Source Precursors for Germanium Chalcogenide Materials Hyo-Suk Kim, Eun Ae Jung, Seong Ho Han, Jeong Hwan Han, Bo Keun Park, Chang Gyoun Kim,* and Taek-Mo Chung* Thin Film Materials Research Center, Korea Research Institute of Chemical Technology, 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea S Supporting Information *
ABSTRACT: New germanium chalcogenide precursors, SGe(dmamp)2 (3), SGe(dmampS)2 (4), SeGe(dmamp)2 (5), SeGe(dmampS)2 (6), TeGe(dmamp)2 (7), and TeGe(dmampS)2 (8), were synthesized from Ge(dmamp)2 (1) and Ge(dmampS)2 (2) using sulfur, selenium, and tellurium powders (dmamp = 1-dimethylamino-2-methyl-2-propanolate, dmampS = 1-dimethylamino-2-methylpropane-2-thiolate). Complexes 1 and 2 were synthesized from metathesis reactions of GeCl2· dioxane with 2 equiv of aminoalkoxide or aminothiolate ligands. Thermogravimetric analysis of complex 1 displayed good thermal stability and volatility. The molecular structures of complexes 2−8 from X-ray single crystallography showed distorted trigonal bipyramidal geometry at the germanium centers. Germanium chalcogenide materials (GeSe and GeTe) were obtained from the thermal decomposition of complexes 5, 6, and 8 in hexadecane. X-ray diffraction patterns exhibited that GeSe and GeTe had orthorhombic and rhombohedral phases, respectively. This study affords a facile method to easily prepare germanium chalcogenide materials using well-designed and stable complexes by thermal decomposition of single-source precursors in solution.
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GeCl2·dioxane), and alkyl germanium reagents are often used as germanium reagents. The most widely used chalcogenide reagents are alkyl chalcogenides and hydrogen chalcogenides (H2S, H2Se, and H2Te). However, germane is a toxic pyrophoric gas, and hydrogen chalcogenides are also highly toxic and flammable. Moreover, germane and hydrogen chalcogenide reagents are not particularly environmentally or production-friendly. Previously, compounds containing a double bond between group 14 and 16 elements have been reported.13−18 In these complexes, the vacant coordination site in divalent Ge(L)2 complex allows the formation of tetravalent germanium chalcogenide complexes EGe(L)2 (E = S, Se, and Te), most of which are considered unstable due to weak pπ−pπ bonding in the germanium−chalcogenide interaction. However, stable germanium chalcogenide complexes have been isolated by employing sterically bulky protecting groups. Recently, Fischer and Power reviewed compounds with multiple bonding
INTRODUCTION Germanium chalcogenides (GeS, GeSe, and GeTe) have drawn increasing attention in a wide range.1 Among them, germanium sulfide (GeS) and germanium selenide (GeSe) have distorted rock-salt structures and are narrow band gap p-type semiconductors with possible light-absorbing layers (Eg = 1.5−1.6 eV for GeS and 1.1−1.2 eV for GeSe). GeS and GeSe have applications in solar cells, photovoltaic device, and lithium ion batteries.2−4 Meanwhile, germanium telluride (GeTe) has received great attention in phase change nonvolatile memory (PCRAM) due to its reversible amorphous-to-crystalline phase transition, which can be triggered thermally or electrically and has high read/write speeds.1,5,6 Germanium chalcogenide materials have been synthesized using a variety of methods such as sol−gel process, solid-state reaction, chemical vapor deposition (CVD), atomic layer deposition (ALD), solution chemistry routes, laser photolysis, and electrodeposition.4,7−12 Single-source precursors for germanium chalcogenides are extremely rare, so chalcogenide materials are obtained from separate germanium and chalcogen sources. Germane, germanium halides (GeCl4, GeI4, and © 2017 American Chemical Society
Received: January 9, 2017 Published: March 22, 2017 4084
DOI: 10.1021/acs.inorgchem.6b02697 Inorg. Chem. 2017, 56, 4084−4092
Article
Inorganic Chemistry
443 (w), 417 (w). Anal. Calcd for C12H28GeN2O2: C, 46.26; H, 9.25; N, 9.19. Found: C, 45.89; H, 9.57; N, 8.56%. Preparation of Ge(dmampS)2 (2). GeCl2·dioxane (0.8 g, 3.6 mmol) was slowly added to a solution of Li(dmampS) (1.0 g, 7.2 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The reaction mixture was then filtered to remove salts, and the filtrate was concentrated in vacuo to afford the product as yellow solid. Pure product (2) was obtained as a white solid by sublimation (60 °C/0.5 torr). Recrystallization from an ether solution gave pure colorless crystals suitable for X-ray crystallography. Yield: 0.9 g (75%); 1 H NMR (C6D6, 300.13 MHz): δ 1.54 (s, 6H, SC(CH3)2), 2.26 (s, 6H, N(CH3)2), 2.36 (s, 2H, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 35.3 (C(CH3)2), 47.5 (N(CH3)2), 49.1 (C(CH3)2), 73.3 (CCH2N); IR (cm−1): 2978 (s), 2950 (s), 2850 (s), 2824 (s), 2779 (m), 1454 (vs), 1400 (w), 1384 (w), 1358 (m), 1290 (m), 1253 (w), 1211 (w), 1195 (w), 1124 (s), 1095 (m), 1024 (s), 963 (m), 852 (w), 826 (vs), 599 (m), 543 (w), 443 (sh), 416 (m). Anal. Calcd for C12H28GeN2S2: C, 42.75; H, 8.37; N, 8.31; S, 19.02. Found: C, 41.82; H, 8.31; N, 9.06; S, 19.60%. Preparation of SGe(dmamp)2 (3). Sulfur powder (0.2 g, 6.2 mmol) was slowly added to a solution of Ge(dmamp)2 (1.9 g, 6.2 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The product was obtained as a white solid by removing all volatiles from the reaction mixture. Recrystallization from an ether solution gave the pure product (3) as colorless crystals. Yield: 1.7 g (82%); 1H NMR (C6D6, 300.13 MHz): δ 1.09 (s, 3H, OC(CH3)2), 1.50 (s, 3H, OC(CH3)2), 1.79 (d, 1H, J = 11.79 Hz, CH2N), 2.24 (s, 3H, N(CH3)2), 2.54 (s, 3H, N(CH3)2), 2.77 (d, 1H, J = 11.79 Hz, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 32.3 (C(CH3)2), 32.7 (C(CH3)2), 46.7 (N(CH3)2), 47.6 (N(CH3)2), 66.7 (C(CH3)2), 69.1 (CCH2N); IR (cm−1): 3022 (w), 2998 (m), 2969 (m), 2917 (m), 1452 (m), 1400 (m), 1383 (m), 1366 (m), 1359 (m), 1295 (w), 1253 (w), 1200 (m), 1149 (S), 1125 (w), 1029 (m), 1017 (w), 979 (m), 945 (s), 915 (m), 836 (s), 803 (s), 680 (s), 668 (s), 557 (w), 477 (m), 469 (m), 428 (m). Anal. Calcd for C12H28GeN2O2S: C, 42.76; H, 8.37; N, 8.31; S, 9.51. Found: C, 42.12; H, 8.37; N, 8.37; S, 9.62%. Preparation of SGe(dmampS)2 (4). Sulfur powder (0.2 g, 6.2 mmol) was slowly added to a solution of Ge(dmampS)2 (2.1 g, 6.2 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The product was obtained as a yellow solid by removing all volatiles from the reaction mixture. Recrystallization from an ether solution gave the pure product (4) as yellow crystals. Yield: 2.0 g (86%); 1H NMR (C6D6, 300.13 MHz): δ 1.16 (s, 3H, SC(CH3)2), 1.42 (d, 1H, J = 11.97 Hz, CH2N), 1.61 (s, 3H, SC(CH3)2), 2.24 (br, 3H, N(CH3)2), 2.58 (br, 3H, N(CH3)2), 3.42 (d, 1H, J = 11.94 Hz, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 34.0 (C(CH3)2), 36.2 (N(CH3)2), 45.3 (C(CH3)2), 66.9 (CCH2N); IR (cm−1): 3001 (m), 2967 (m), 2901 (m), 1453 (s), 1434 (m), 1400 (m), 1374 (m), 1363 (m), 1291 (w), 1245 (m), 1199 (w), 1126 (s), 1101 (w), 1034 (m), 1027 (s), 1011 (s), 972 (w), 862 (w), 830 (s), 600 (m), 553 (w), 475 (s), 460 (s), 418 (m). Anal. Calcd for C12H28GeN2S3: C, 39.04; H, 7.65; N, 7.54; S, 26.05. Found: C, 38.17; H, 7.45; N, 7.00; S, 25.29%. Preparation of SeGe(dmamp)2 (5). Selenium powder (0.2 g, 2.5 mmol) was slowly added to a solution of Ge(dmampS)2 (0.8 g, 2.5 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The product was obtained as a yellow solid by removing all volatiles from the reaction mixture. Recrystallization from an ether solution gave the pure product (5) as yellow crystals. Yield: 0.8 g (79%); 1H NMR (C6D6, 300.13 MHz): δ 1.07 (s, 3H, OC(CH3)2), 1.52 (s, 3H, OC(CH3)2), 1.71 (d, 1H, J = 11.82 Hz, CH2N), 2.23 (s, 3H, N(CH3)2), 2.50 (s, 3H, N(CH3)2), 2.82 (d, 1H, J = 11.79 Hz, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 32.5 (C(CH3)2), 32.8 (C(CH3)2), 46.5 (N(CH3)2), 47.8 (N(CH3)2), 66.4 (C(CH3)2), 69.4 (CCH2N); 77Se NMR (C6D6, 76.58 MHz): δ −391.0; IR (cm−1): 3022 (w), 2998 (m), 2968 (m), 2915 (m), 1478 (m), 1463 (m), 1451 (m), 1400 (m), 1383 (m), 1366 (m), 1360 (m), 1293 (w), 1252 (w), 1199 (m), 1147 (s), 1125 (m), 1028 (m), 1016 (m), 978 (m), 945 (s), 914 (m), 834 (s), 803 (s), 678 (s), 666 (s), 555
between group 14 and 16 elements. Many of the stable and structurally characterized compounds in this class also involve nitrogen donor ligands, which stabilize the multiple bonded species through electron donation, by a nitrogen atom either from a β-diketiminato ligand or a neighboring N-donor functionality.19 However, this weakens the multiple bond by disruption of the 14/16 elements π-overlap. In this study, we demonstrate the synthesis of stable germanium complexes as single-source precursors for germanium chalcogenide materials. The steric influence of the aminoalkoxide ligand is shown to stabilize the metal center by providing desirable chelate interactions, thus forming a fully saturated coordination environment around the metal cation, which facilitates the donor reactivity of the germanium center. Herein, we report the synthesis of new germanium complexes, SGe(dmamp) 2 (3), SGe(dmampS) 2 (4), SeGe(dmamp)2 (5), SeGe(dmampS)2 (6), TeGe(dmamp)2 (7), and TeGe(dmampS)2 (8) from the reactions of Ge(dmamp)2 (1) and Ge(dmampS)2 (2) with elemental chalcogens (E = S, Se, and Te) (dmamp = 1-dimethylamino2-methyl-2-propanolate, dmampS = 1-dimethylamino-2-methylpropane-2-thiolate). Germanium chalcogenide materials GeSe and GeTe were obtained by the thermal decomposition of complexes 5, 6, and 8 in solution.
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EXPERIMENTAL SECTION
General. All manipulations were performed under dry, oxygen-free nitrogen or argon atmospheres using Schlenk techniques or a glovebox. All solvents were purified by Innovative Technology PSMD-4 solvent purification system. GeCl2·dioxane, KSeCN, n-BuLi (2.5 M in hexane), dimethylamine (2.0 M in tetrahydrofuran (THF)), and sulfur, selenium, and tellurium powders were purchased from Aldrich. Lithium 1-(dimethylanimo)-2-methylpropane-2-thiolate (Li(dmampS)) was synthesized using a modified literature method.20,21 Functionalized bidentate aminoalcohol, 1-dimethylamino-2-methyl-2propanol (dmampH), (CH3)2NCH2C(CH3)2OH, and sodium (1dimethylamino-2-methyl-2-propoxide) (Na(dmamp)) were prepared according to literature procedures.22,23 Ge(dmamp)2 was synthesized using a modified literature method.24 1H NMR and 13C NMR spectra were recorded on a Bruker DPX 300 MHz FT−NMR spectrometer. All samples for NMR analysis were contained in sealed NMR tubes and referenced using benzene-d6 as standard. 77Se and 125Te NMR spectra were recorded on a Bruker Avance III HD Nano bay 400 MHz FT−NMR spectrometers, and diphenyl diselenide and diphenyl ditelluride were externally used as reference. Infrared spectra were obtained with a Nicolet NEXUS FT-IR spectrometer using a 4 mm KBr window or KBr pellet. Elemental analyses were performed using a Thermoquest EA-1110 CHNS analyzer. The materials obtained from complex decomposition were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD pattern was obtained on a Rigaku D/Max-2200 V X-ray diffractometer operating at 40 kV and 40 nA, using Cu Kα target. SEM images were obtained on TESCAN Mira 3 LMU FEG FE-SEM operating at 10 kV. Preparation of Ge(dmamp)2 (1). GeCl2·dioxane (0.8 g, 3.6 mmol) was slowly added to a solution of Na(dmamp) (1.0 g, 7.2 mmol) in THF. The reaction mixture was allowed to stir overnight at room temperature. The mixture was then filtered to remove salts, and the filtrate was concentrated in vacuo to afford crude product. Pure product (1) was obtained as a colorless liquid by distillation (90 °C/ 0.5 torr). Yield: 0.9 g (81%); 1H NMR (C6D6, 300.13 MHz): δ 1.37 (s, 6H, OC(CH3)2), 2.25 (s, 6H, N(CH3)2), 2.31 (s, 2H, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 33.4 (C(CH3)2), 46.6 (N(CH3)2), 69.5 (C(CH3)2), 75.0 (CCH2N); IR (cm−1): 2964 (s), 2855 (s), 2827 (s), 2788 (s), 1455 (s), 1402 (w), 1378 (m), 1352 (s), 1292 (m), 1259 (w), 1187 (m), 1150 (s), 1124 (s), 1094 (w), 1037 (s), 983 (s), 941 (s), 906 (m), 831 (s), 798 (m), 787 (m), 619 (s), 532 (m), 488 (w), 4085
DOI: 10.1021/acs.inorgchem.6b02697 Inorg. Chem. 2017, 56, 4084−4092
Article
Inorganic Chemistry Scheme 1. Synthetic Scheme for Complexes 1−8
for 2 h, the solution was heated at 350 °C for 1 h under a nitrogen atmosphere. The reaction mixture was cooled to room temperature and centrifuged at 15 000 rpm for 20 min. The obtained black precipitates were washed with toluene three times. Thermal Decomposition of SeGe(dmampS)2 (6). SeGe(dmampS)2 (0.5 g, 1.2 mmol) was dissolved in oleylamine (50 mL) at room temperature. After it was degassed under vacuum at 100 °C for 2 h, the solution was heated at 320 °C for 1 h under a nitrogen atmosphere. The reaction mixture was cooled to room temperature and centrifuged at 15 000 rpm for 20 min. The obtained black precipitates were washed with toluene three times. Thermal Decomposition of TeGe(dmampS)2 (8). TeGe(dmampS)2 (0.3 g, 0.6 mmol) was slowly dissolved in hexadecane (19 mL, 64.6 mmol) and oleylamine (2 mL), used as a capping agent, at room temperature. After it was degassed under vacuum at 120 °C for 2 h, the solution was heated at 270 °C for 1 h under a nitrogen atmosphere. The reaction mixture was cooled to room temperature and centrifuged at 12 000 rpm for 10 min. The obtained black precipitates were washed with ethanol three times. Thermal Analyses. Thermogravimetric analysis (TGA) and differential thermal analysis of the newly synthesized complexes were investigated using a PerkinElmer TGA7 apparatus. TGA data were obtained up to 800 °C at a heating rate of 10 °C/min at atmospheric pressure with N2 as carrier gas. TG sampling was performed inside an argon-filled glovebox to avoid contact with air. X-ray Crystallography. Single crystals of 2−8 were grown from a diethyl ether solution at room temperature. A specimen of suitable size and quality was coated with mineral oil and mounted onto a glass capillary. Reflection data were collected on a Bruker Apex II-CCD area detector diffractometer, using graphite-monochromated Mo Kα radiation (λ = 0.710 73 Å). The hemisphere of reflection data was collected as ω-scan frames of 0.3°/frame at an exposure time of 10 s/ frame. Cell parameters were determined and refined by the SMART program.25 Data reduction was performed using SAINT software.26 Data were corrected for Lorentz and polarization effects. An empirical absorption correction was applied using the SADABS program.27 The structure was solved by direct methods, and all non-hydrogen atoms were subjected to anisotropic refinement by full-matrix least-squares on F2 using the SHELXTL/PC package.28 Hydrogen atoms were placed at their geometrically calculated positions and refined riding on the corresponding carbon atoms with isotropic thermal parameters. Additional crystallographic information is available in the Supporting Information.
(m), 494 (w), 473 (w), 453 (m), 427 (m). Anal. Calcd for C12H28GeN2O2Se: C, 37.54; H, 7.35; N, 7.30. Found: C, 37.81; H, 7.36; N, 7.12%. Preparation of SeGe(dmampS)2 (6). Selenium powder (0.2 g, 2.5 mmol) was slowly added to a solution of Ge(dmampS)2 (0.9 g, 2.5 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The product was obtained as a yellow solid by removing all volatiles from the reaction mixture. Recrystallization from an ether solution gave the pure product (6) as yellow crystals. Yield: 0.9 g (89%); 1H NMR (C6D6, 300.13 MHz): δ 1.14 (s, 3H, SC(CH3)2), 1.33 (d, 1H, J = 12.03 Hz, CH2N), 1.62 (s, 3H, SC(CH3)2), 2.27 (br, 3H, N(CH3)2), 2.52 (br, 3H, N(CH3)2), 3.49 (d, 1H, J = 12.00 Hz, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 34.4 (C(CH3)2), 36.0 (N(CH3)2), 45.5 (C(CH3)2), 66.5 (CCH2N); 77Se NMR (C6D6, 76.58 MHz): δ −129.1; IR (cm−1): 2998 (m), 2966 (m), 2900 (m), 1452 (s), 1432 (m), 1400 (m), 1373 (m), 1363 (m), 1290 (w), 1244 (w), 1187 (w), 1125 (s), 1099 (w), 1027 (m), 1010 (s), 975 (w), 829 (s), 598 (m), 551 (w), 471 (m), 450 (w), 417 (m). Anal. Calcd for C12H28GeN2S2Se: C, 34.64; H, 6.78; N, 6.73; S, 15.41. Found: C, 34.70; H, 6.88; N, 6.74; S, 15.13%. Preparation of TeGe(dmamp)2 (7). Tellurium powder (0.08 g, 0.7 mmol) was slowly added to a solution of Ge(dmamp)2 (0.2 g, 0.7 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The product was obtained as a yellow solid by removing all volatiles from the reaction mixture. Recrystallization from an ether solution gave the pure product (7) as yellow needle-shaped crystals. Yield: 0.2 g (68%); 1H NMR (C6D6, 300.13 MHz): δ 1.01 (s, 3H, OC(CH3)2), 1.51 (s, 3H, OC(CH3)2), 1.60 (d, 1H, J = 11.76 Hz, CH2N), 2.19 (s, 3H, N(CH3)2), 2.37 (s, 3H, N(CH3)2), 2.82 (d, 1H, J = 11.61 Hz, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 32.7 (C(CH3)2), 33.1 (C(CH3)2), 45.9 (N(CH3)2), 48.2 (N(CH3)2), 65.7 (C(CH3)2), 69.9 (CCH2N); 125Te NMR (C6D6, 127.23 MHz): δ −943.0; IR (cm−1): 2965 (m), 2921 (m), 2851 (s), 2827 (m), 1455 (s), 1384 (w), 1361 (m), 1297 (w), 1205 (m), 1149 (s), 1125 (m), 1025 (m), 984 (s), 947 (s), 913 (m), 833 (s), 804 (s), 673 (s), 662 (m), 554 (w), 492 (w), 433 (w). Anal. Calcd for C12H28GeN2O2Te: C, 33.32; H, 6.52; N, 6.48. Found: C, 33.26; H, 6.60; N, 6.48%. Preparation of TeGe(dmampS)2 (8). Tellurium (0.03 g, 0.3 mmol) was slowly added to a solution of Ge(dmampS)2 (0.1 g, 0.3 mmol) in toluene. The reaction mixture was allowed to stir at room temperature overnight. The product was obtained as an orange solid by removing all volatiles from the reaction mixture. Recrystallization from an ether solution gave the pure product (8) as orange crystals. Yield: 0.1 g (65%); 1H NMR (C6D6, 300.13 MHz): δ 1.45 (s, 6H, SC(CH3)2), 2.31 (s, 8H, N(CH3)2, CH2N); 13C NMR (C6D6, 75.04 MHz): δ 35.2 (C(CH3)2), 46.4 (N(CH3)2), 47.6 (C(CH3)2), 70.1 (CCH2N); 125Te NMR (C6D6, 127.23 MHz): δ −471.6; IR (cm−1): 2960 (s), 2949 (s), 2901 (s), 2851 (s), 2827 (m), 1455 (vs), 1399 (m), 1362 (m), 1290 (m), 1213 (w), 1199 (w), 1184 (w), 1124 (s), 1095 (m), 1026 (s), 1009 (s), 966 (m), 827 (vs), 667 (m), 597 (m), 547 (w), 467 (sh), 418 (m). Anal. Calcd for C12H28GeN2S2Te: C, 31.01; H, 6.07; N, 6.03; S, 13.80. Found: C, 29.38; H, 5.89; N, 5.44; S, 13.26%. Thermal Decomposition of SeGe(dmamp)2 (5). SeGe(dmamp)2 (0.5 g, 1.3 mmol) was dissolved in oleylamine (50 mL) at room temperature. After it was degassed under vacuum at 100 °C
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RESULTS AND DISCUSSION Complexes 1−8 were synthesized as shown in Scheme 1. Treatment of GeCl2·dioxane with 2 equiv of sodium 1dimethylamino-2-methyl-2-propoxide (Na(dmamp)) afforded a colorless liquid, Ge(dmamp)2 (1), which was purified by distillation under vacuum (90 °C/0.5 torr) to give an 81% yield.24 Lithium 1-dimethylamino-2-methylpropane-2-thiolate (Li(dmampS)) was synthesized from the reaction of 2,2dimethylthiirane with lithium dimethylamide. GeCl2·dioxane was reacted with 2 equiv of Li(dmampS) to give a yellow solid, Ge(dmampS)2 (2), which was purified by sublimation under 4086
DOI: 10.1021/acs.inorgchem.6b02697 Inorg. Chem. 2017, 56, 4084−4092
Article
Inorganic Chemistry vacuum (60 °C/0.5 torr) to give a 75% yield. Germanium chalcogenide complexes such as SGe(dmamp)2 (3), S Ge(dmampS)2 (4), SeGe(dmamp)2 (5), SeGe(dmampS)2 (6), TeGe(dmamp)2 (7), and TeGe(dmampS)2 (8) were prepared in moderate-to-good yields by treating 1 equiv of sulfur, selenium, or tellurium powder with complexes 1 or 2 in toluene at room temperature and stirring the reaction mixture until the chalcogen powders were completely consumed. The products were obtained as white or yellow solids and purified by recrystallization from saturated diethyl ether solution. Elemental analysis of the complexes demonstrated their highly air-sensitive and hygroscopic characters. Single crystals of complexes 2−8 were grown from a saturated diethyl ether solution of the corresponding complexes at room temperature. The crystallographic data for 2−8 are summarized in Table S1. The selected bond lengths and angles are shown in Tables 1−3, and perspective views of 2−8 are presented in Figures 1−3.
of the two dmampS ligands occupied the axial positions with a N(1)−Ge(1)−N(11) bond angle of 158.91(5)°. Sulfur atoms S(1) and S(11) of two dmampS ligands and lone-pair electrons occupied equatorial position. The S(1)−Ge(1)−S(11) bond angle was 103.757(16)°, which was less than the ideal bond angle of 120° due to the lone-pair electrons of germanium metal. The structures of tin(II) and germanium(II) compounds similar to that of complex 2 have been reported,29 wherein bis[2-(dimethylamino)ethoxy]tin and bis[2-(dimethylamino)ethoxy]germanium had distorted trigonal bipyramidal geometries with lone-pair electrons in the equatorial positions to minimize lone-pair−bond-pair repulsion. In complex 2, S(11)− Ge(1)−N(11), N(1)−Ge(1)−S(1), S(1)−Ge(1)−N(11), and N(1)−Ge(1)−S(11) bond angles were 78.61(3)°, 80.14(3)°, 86.09(4)°, and 89.18(4)°, respectively. The nitrogen−germanium bond lengths were 2.3052(13) Å (Ge(1)−N(1)) and 2.3596(14) Å (Ge(1)−N(11)), while sulfur−germanium bond lengths were 2.3279(4) Å (Ge(1)−S(1)) and 2.3282(4) Å (Ge(1)−S(11)). Complexes 3−8 were crystallized in a monoclinic crystal system and space group P2(1)/n. The molecular structures of 3−8 appeared to be isostructural. The molecular structures of 3, 5, and 7, in which each of the germanium centers was bonded to two dmamp ligands and chalcogen atoms (S, Se, and Te), exhibited a distorted trigonal bipyramidal geometry (Figure 2). N1 and N2 atoms in the two dmamp ligands were in axial positions, with N(1)−Ge−N(2) bond angles of 154.65(6)°, 154.60(7)°, and 147.4(6)° in complexes 3, 5, and 7, respectively. The N(1)−Ge−N(2) bond angle in complex 7 was smaller than those in 3 and 5. O1 and O2 atoms in the two dmamp ligands and chalcogen atoms (S, Se, and Te) occupied equatorial positions around the germanium center. The sum of bond angles in the equatorial plane was 360° in complexes 3, 5, and 7. The O(1)−Ge(1)−O(2) bond angle of 121.6(5)° in complex 7 was larger than those in 3 (117.06(6)°, O(1)− Ge(1)−O(2)) and 5 (116.80(7)°, O(1)−Ge(1)−O(2)). The bond lengths between dmamp ligand oxygen atoms and germanium were 1.7973(12) Å (Ge(1)−O(1)) and 1.8021(12) Å (Ge(1)−O(2)) in 3, 1.8010(13) Å (Ge(1)− O(1)) and 1.8025(13) Å (Ge(1)−O(2)) in 5, and 1.804(11) Å (Ge−O(1)) and 1.790(11) Å (Ge−O(2)) in 7, respectively.
Table 1. Selected Bond Lengths (Å) and Bond Angles (deg) of Complex 2 complex 2 bond lengths (Å) Ge(1)−N(1) Ge(1)−N(11) Ge(1)−S(1) Ge(1)−S(11) bond angles (deg) N(1)−Ge(1)−S(1) N(1)−Ge(1)−S(11) N(1)−Ge(1)−N(11) S(1)−Ge(1)−S(11) S(1)−Ge(1)−N(11) S(11)−Ge(1)−N(11)
2.3052(13) 2.3596(14) 2.3279(4) 2.3282(4) 80.14(3) 89.18(4) 158.91(5) 103.757(16) 86.09(4) 78.61(3)
Single-crystal X-ray analysis of 2, crystallized in the orthorhombic crystal system and Pbca space group, showed a distorted trigonal bipyramidal geometry (including a lone pair of electrons) about the central germanium atom with two dmampS ligands (Figure 1). Nitrogen atoms N(1) and N(11)
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 3, 5, and 7 complex 3 bond lengths Ge(1)−O(1) Ge(1)−O(2) Ge(1)−N(1) Ge(1)−N(2) Ge(1)−S(1) bond angles O(1)−Ge(1)−O(2) O(1)−Ge(1)−S(1) O(2)−Ge(1)−S(1) N(2)−Ge(1)−N(1) O(1)−Ge(1)−N(2) O(2)−Ge(1)−N(2) S(1)−Ge(1)−N(2) O(1)−Ge(1)−N(1) O(2)−Ge(1)−N(1) S(1)−Ge(1)−N(1)
complex 5
complex 7
1.7973(12) 1.8021(12) 2.1732(15) 2.1284(15) 2.1000(6)
Ge(1)−O(1) Ge(1)−O(2) Ge(1)−N(1) Ge(1)−N(2) Se(1)−Ge(1)
1.8010(13) 1.8025(13) 2.1774(17) 2.1390(17) 2.2369(3)
Ge−O(1) Ge−O(2) Ge−N(1) Ge−N(2) Ge−Te
1.804(11) 1.790(11) 2.139(15) 2.153(16) 2.463(2)
117.06(6) 121.20(5) 121.71(5) 154.65(6) 86.53(6) 81.53(6) 103.13(5) 79.88(6) 85.73(6) 102.22(5)
O(1)−Ge(1)−O(2) O(1)−Ge(1)−Se(1) O(2)−Ge(1)−Se(1) N(2)−Ge(1)−N(1) O(1)−Ge(1)−N(2) O(2)−Ge(1)−N(2) O(1)−Ge(1)−N(1) O(2)−Ge(1)−N(1) N(2)−Ge(1)−Se(1) N(1)−Ge(1)−Se(1)
116.80(7) 121.28(5) 121.92(5) 154.60(7) 86.48(6) 81.25(6) 79.94(7) 85.84(6) 102.84(5) 102.55(5)
O(2)−Ge−O(1) O(2)−Ge−Te O(1)−Ge−Te N(1)−Ge−N(2) O(2)−Ge−N(1) O(1)−Ge−N(1) O(2)−Ge−N(2) O(1)−Ge−N(2) N(1)−Ge−Te N(2)−Ge−Te
121.6(5) 118.6(3) 119.8(4) 147.4(6) 83.9(5) 80.6(6) 80.7(5) 83.4(6) 106.4(5) 106.2(4)
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Inorganic Chemistry Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) of Complexes 4, 6, and 8 complex 4 bond lengths Ge(1)−N(1) Ge(1)−N(2) Ge(1)−S(1) Ge(1)−S(2) Ge(1)−S(3) bond angles S(3)−Ge(1)−S(1) S(3)−Ge(1)−S(2) S(1)−Ge(1)−S(2) N(1)−Ge(1)−N(2) S(3)−Ge(1)−N(1) N(1)−Ge(1)−S(1) N(1)−Ge(1)−S(2) S(3)−Ge(1)−N(2) S(1)−Ge(1)−N(2) S(2)−Ge(1)−N(2)
complex 6
complex 8
2.2052(13) 2.3101(13) 2.2373(4) 2.2411(4) 2.1094(5)
Ge(1)−N(1) Ge(1)−N(2) Ge(1)−S(1) Ge(1)−S(2) Se(1)−Ge(1)
2.2095(12) 2.3096(12) 2.2373(4) 2.2405(4) 2.2460(2)
Ge−N(1) Ge−N(2) Ge−S(1) Ge−S(2) Ge−Te
2.315(4) 2.236(4) 2.2469(14) 2.2457(12) 2.4802(6)
120.95(2) 120.36(2) 118.545(19) 160.30(5) 100.90(4) 83.25(4) 89.48(4) 98.79(4) 86.17(4) 81.04(4)
S(1)−Ge(1)−S(2) S(1)−Ge(1)−Se(1) S(2)−Ge(1)−Se(1) N(1)−Ge(1)−N(2) N(1)−Ge(1)−S(1) N(1)−Ge(1)−S(2) N(1)−Ge(1)−Se(1) S(1)−Ge(1)−N(2) S(2)−Ge(1)−N(2) Se(1)−Ge(1)−N(2)
118.298(18) 121.364(15) 120.218(14) 160.39(5) 83.09(4) 89.65(4) 100.49(4) 86.21(3) 81.01(3) 99.11(3)
S(2)−Ge−S(1) S(2)−Ge−Te S(1)−Ge−Te N(2)−Ge−N(1) N(2)−Ge−S(2) N(2)−Ge−S(1) N(2)−Ge−Te S(2)−Ge−N(1) S(1)−Ge−N(1) N(1)−Ge−Te
117.83(5) 122.17(4) 119.94(4) 160.40(14) 82.40(10) 90.02(11) 99.83(10) 86.38(10) 81.07(10) 99.74(9)
(103.757(16)°), which had lone-pair electrons in an equatorial site. Additionally, S(1)−Ge(1)−S(2) bond angles were slightly smaller when the chalcogen atom was larger. The bond lengths between sulfur atoms of the dmampS ligand and germanium were 2.2373(4) Å (Ge(1)−S(1)) and 2.2411(4) Å (Ge(1)− S(2)) in complex 4, 2.2373(4) Å (Ge(1)−S(1)) and 2.2405(4) Å (Ge(1)−S(2)) in 6, and 2.2469(14) Å (Ge−S(1)) and 2.2457(12) Å (Ge−S(2)) in 8. The Ge−S single bond lengths of complexes 4, 6, and 8 are similar to those of Ge(SAr)2 compounds (2.24−2.29 Å)30 and shorter than those of complex 2. Unsurprisingly, the Ge−N bond lengths in complexes 4, 6, and 8 were shorter than those in the starting complex 2 (2.3279(4) and 2.3282(4) Å). The bond distances between nitrogen atoms of dmampS ligand and germanium were 2.2052(13) Å (Ge(1)−N(1)) and 2.3101(13) Å (Ge(1)− N(2)) in complex 4, 2.2095(12) Å (Ge(1)−N(1)) and 2.3096(12) Å (Ge(1)−N(2)) in 6, and 2.315(4) Å (Ge− N(1)) and 2.236(4) Å (Ge−N(2)) in 8, with slight exception, which were slightly shorter than those in 2 (2.3052(13) and 2.3596(14) Å). The Ge(1)−S(1) distances of 2.100(6) Å in complex 3 and 2.1094(5) Å in complex 4 were longer than those of 2.056(2) Å in [Ge(S){N(SiMe3)C(Ph)C(SiMe3)(C5H4N-2)}Cl]31 and 2.069(1) Å in (Bui2ATI)Ge(S)NC4H4.32 The Ge(1)−Se(1) distances of 2.2369(3) Å in complex 5 and 2.2460(2) Å in complex 6 were longer than those of 2.191(1) Å in [Ge(Se){N(SiMe 3 )C(Ph)C(SiMe 3 )(C 5 H 4 N-2)}Cl] 31 and 2.202(1) Å in (Bui2ATI)Ge(Se)SPh.32 The Ge−Te bond lengths of 2.463(2) Å in complex 7 and 2.4802(6) Å in complex 8 were longer than that of 2.424(2) Å in L(Cp)GeTe (L = HC[C(Me)N-2,6-iPr2C6H3]2).33 The lengths of the germanium−chalcogenide double bonds such as GeS, Ge = Se, and GeTe in complexes containing the same chalcogenide were similar regardless of the ligand (dmamp or dmampS) and increased as the chalcogenide atom size increased (S → Se → Te). In addition, the bond length between germanium and chalcogen atoms explains the property of the germanium−chalcogenide atom interaction, showing the existence of Ge+−E− ↔ GeE resonance structures. The bond lengths of Ge−S, Ge−Se, and Ge−Te in complexes 3−8 exhibited the average values between Ge−E single bonds (Ge− S = 2.26 Å, Ge−Se = 2.39 Å, and Ge−Te = 2.59 Å) and GeE
Figure 1. Crystal structure of complex 2.
Nitrogen−germanium bond lengths were 2.1732(15) Å (Ge(1)−N(1)) and 2.1284(15) Å (Ge(1)−N(2)) in 3, 2.1774(17) Å (Ge(1)−N(1)) and 2.1390(17) Å (Ge(1)− N(2)) in 5, and 2.139(15) Å (Ge−N(1)) and 2.153(16) Å (Ge−N(2)) in 7, respectively. The distorted trigonal bipyramidal coordination geometry exhibited by complexes 4, 6, and 8, in which each germanium center was bonded to two dmampS ligands and chalcogen atoms (S, Se, and Te), was similar to that of the starting complex 2 (Figure 3). The N1 and N2 atoms in the two dmampS ligands in complexes 4, 6, and 8 were in axial positions, with N(1)−Ge−N(2) bond angles of 160.30(5)°, 160.39(5)°, and 160.40(14)°, respectively, which were larger than that of complex 2 (158.91(5)°). The S1 and S2 atoms in the two dmampS ligands and chalcogen atoms (S, Se, and Te) occupied equatorial positions around the germanium center. The bond angles in complex 4 were 120.95(2)° (S(3)−Ge(1)− S(1)), 120.36(2)° (S(3)−Ge(1)−S(2)) and 118.545(19)° (S(1)−Ge(1)−S(2)) showing an ideal value of 120°. The S(1)−Ge(1)−S(2), S(1)−Ge(1)−Se(1), and S(2)−Ge(1)− Se(1) bond angles in complex 6 were 118.298(18)°, 121.364(15)°, and 120.218(14)°, respectively, while those of S(2)−Ge−S(1), S(2)−Ge−Te, and S(1)−Ge−Te in complex 8 were 117.83(5)°, 122.17(4)°, and 119.94(4)°, respectively. The sums of equatorial bond angles in complexes 4, 6, and 8 were 359.8°, 359.88°, and 359.94°, respectively, which were almost equal to the ideal equatorial plane (360°). The S(1)− Ge(1)−S(2) bond angles in complexes 4, 6, and 8 were 118.545(19)°, 118.298(18)°, and 117.83(5)°, respectively, which were larger than that of the starting compound 2 4088
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Figure 3. Crystal structures of complexes 4, 6, and 8.
proton peaks for the dmamp ligand appeared as two doublets at δ = 1.79 (J = 11.79 Hz) and 2.77 (J = 11.79 Hz) in complex 3, δ = 1.71 (J = 11.82 Hz) and 2.82 (J = 11.79 Hz) in 5, and δ = 1.60 (J = 11.76 Hz) and 2.82 (J = 11.61 Hz) in 7, respectively, which were comparable with that in complex 1 (δ = 2.31 ppm). The 1H NMR spectra of complexes 4 and 6 showed dmampS ligand SC(CH3)2 protons as two singlets at δ = 1.16/1.61 and 1.14/1.62 ppm, respectively, which were comparable with that in complex 2 (δ = 1.54 ppm). The dmampS ligand N(CH3)2 peaks for complexes 4 and 6 appeared as two broad peaks at δ = 2.24/2.58 and 2.27/2.52 ppm, respectively, which were comparable to the corresponding singlet in complex 2 (δ = 2.26 ppm). Furthermore, the dmampS ligand CCH2N proton peaks appeared as two doublets, at δ = 1.42 (J = 11.97 Hz) and 3.42 (J = 11.94 Hz) in complex 4 and δ = 1.33 (J = 12.03 Hz) and 3.49 (J = 12.00 Hz) in complex 6, and were comparable to that in complex 2 (δ = 2.59 ppm). The 1H NMR spectra of complexes 1 and 2 showed ligand peaks as one singlet, while in complexes 3−7, containing chalcogenide atoms (S, Se, and Te), peak splitting occurred. In complex 8, the dmampS ligand
Figure 2. Crystal structures of complexes 3, 5, and 7.
double bonds (GeS = 2.06 Å, Ge = Se = 2.19 Å, and GeTe = 2.39 Å).14 The 1H NMR spectrum of complex 1, recorded in benzened6, showed three singlets at δ = 1.37 ppm (OC(CH3)2), δ = 2.25 ppm (N(CH3)2), and δ = 2.31 ppm (CH2), respectively, which were in downfield positions with respect to Na(dmamp) (δH = 1.23 ppm (OC(CH3)2), 2.24 ppm (N(CH3)2, CH2)). The 1H NMR peaks of the dmampS ligand in complex 2 appeared at δ = 1.54 ppm for SC(CH3)2, δ = 2.26 ppm for N(CH3)2, and δ = 2.36 ppm for CH2, respectively. The 1H NMR spectra of complexes 3, 5, and 7, recorded in benzene-d6, showed peaks for alkoxy CH3 protons in the dmamp ligand as two singlets at δ = 1.09/1.50, 1.07/1.52, and 1.01/1.51 ppm, respectively, which were comparable to that in complex 1 (δ = 1.37 ppm) as one singlet. The N(CH3)2 peaks of the dmamp ligand in complexes 3, 5, and 7 appeared as two singlets at δ = 2.24/2.54, 2.23/2.50, and 2.19/2.37 ppm, respectively, which were comparable to that in complex 1 (δ = 2.25 ppm). CCH2N 4089
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Inorganic Chemistry SC(CH3)2 peak appeared at δ = 1.45 ppm, while N(CH3)2 and CH2 peaks appeared at δ = 2.31 ppm as singlets, respectively. The 77Se NMR spectra for 5 and 6 displayed one signal at δ = −391.0 and −129.1, respectively, which were upfield-shifted comparable to the Tbt(Tip)Ge = Se complex (Tbt = 2,4,6tris[bis(trimethylsilyl)methyl]-phenyl, Tip = 2,4,6-tris(isopropy)phenyl) at δ = 940.6.34 The 125Te NMR spectra for 7 and 8 exhibited one signal at δ = −943.0 and −471.6, respectively. Note that the signals of complexes 5 and 7 containing dmamp ligand showed more upfield shift than those of the complexes 6 and 8 containing dmampS ligand. Thermogravimetric analysis (TGA) of complexes 1 and 2 was conducted from room temperature to 800 °C (Figure 4).
Figure 6. XRD pattern of GeSe obtained by thermal decomposition of germanium complex 6.
Figure 4. TGA of complexes 1 (solid line) and 2 (dot line).
Complex 1 exhibited good volatility with a clean single-step mass loss of 92% in the 160−270 °C region and a final residue mass of 8%. In contrast, complex 2 showed a first weight loss (of ∼47%) at 240 °C and a second loss (of ∼17%) was complete at ∼590 °C. The final residue was 19% at 720 °C. TGA data suggested that residual materials of complex 2 might be germanium, where the calculated percentage of residual germanium was 21%. Differential thermal analysis (DTA) of 2 showed an endothermic peak at 223 °C, accompanied by a weight loss in TGA, regarded as evaporation temperatures of the decomposition materials, and an endothermic peak at 60 °C attributed to the sublimation of complex 2. Complexes 5, 6, and 8 were investigated as single-molecule precursors to synthesize germanium chalcogenide materials. XRD patterns of the materials resulting from thermal decomposition of 5, 6, and 8 are shown in Figures 5−7. Complex 5 was allowed to thermally decompose in oleylamine at 350 °C. The XRD pattern revealed that the decomposed
Figure 7. XRD pattern of GeTe obtained by thermal decomposition of germanium complex 8.
products were orthorhombic phase GeSe (JCPDS Card No. 00−048−1226), while energy-dispersive spectrometry (EDS) results for the materials were expressed as GeSe (Ge/Se = 34:37). The atomic percentage of oxygen from compound 5 containing dmamp ligand was confirmed to be a very small amount of the remaining 3%, as found in the EDS data. Complex 6 was thermally decomposed in oleylamine at 320 °C. The XRD pattern showed that the decomposed products were orthorhombic phase GeSe (JCPDS Card No. 01−072−1468), and EDS data for the resulting materials were expressed as GeSe (Ge/Se = 35:37). The atomic percentage of sulfur from compound 6 containing dmampS ligand was confirmed to be a very small amount of the remaining less than1%, as found in the EDS data. Finally, complex 8 was thermally decomposed in hexadecane solvent, with oleylamine as a capping reagent, at 270 °C. The XRD pattern showed that the resulting materials were rhombohedral phase GeTe (JCPDS Card No. 01−071− 4852), while EDS results for the materials were expressed as GeTe (Ge/Te = 40:57). The results obtained confirmed that the thermal decomposition products of complex 8 were GeTe with small amounts of tellurium. Sulfur was confirmed to be present as a small amount in the remaining 3%, as found in the EDS data. However, the obtained results demonstrated that the thermal decomposition product of complex 7 was not made of nanoparticles. SEM images of GeSe and GeTe, obtained by the thermal decompositions of germanium complexes 6 and 8, respectively, displayed micrometer-sized aggregation, as shown in Figures S1 and S2.
Figure 5. XRD pattern of GeSe obtained by thermal decomposition of germanium complex 5 (* = selenium). 4090
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Inorganic Chemistry Furthermore, thermal decomposition results for complexes 5 and 6 in oleylamine were compared at 250, 300, and 350 °C, respectively. At 250 °C, the XRD pattern showed that the thermal decomposition product of complex 5 was only hexagonal phase Se (JCPDS Card No. 01−073−0465) and that the thermal decomposition product of complex 6 did not form nanoparticles. At both 300 and 350 °C, the XRD patterns revealed that the decomposed products of complex 5 were orthorhombic phase GeSe (JCPDS Card No. 00−032−0411). Furthermore, the XRD pattern of thermally decomposed materials from complex 6 showed orthorhombic-phase GeSe (JCPDS Card No. 01−075−1802) at 300 and 350 °C. However, at 300 °C, the thermally decomposed product of complex 6 was GeSe, with a selenium peak in XRD data (Figures S3−S7).
Notes
CONCLUSION Germanium chalcogenide complexes 3−8, with a germanium− chalcogenide double bond, were designed and synthesized from the reaction of Ge(dmamp)2 (1) and Ge(dmampS)2 (2) with elemental chalcogens (E = S, Se, and Te). Moreover, the germanium center was stabilized by desirable chelate interactions due to formation of a fully saturated coordination environment around the metal cation. X-ray crystallographic studies showed that the molecular structures of 2−8 appeared to be isostructural, adopting distorted trigonal bipyramidal geometries. Using germanium chalcogenide complexes 5, 6, and 8, GeSe and GeTe were prepared by thermal decomposition in solution. XRD patterns showed that GeSe and GeTe were orthorhombic and rhombohedral phases, respectively. Compounds 5, 6, and 8 showed satisfactory potential as single-source precursors for germanium chalcogenides. Furthermore, complex 1 could be applied as a precursor to germanium thin films using chemical vapor deposition/ atomic layer deposition (CVD/ALD) due to its stable and volatile characteristics.
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The authors declare no competing financial interest. Supplementary crystallographic data for this paper can be found in CCDC-1497273 (for 2), CCDC-1497274 (for 3), CCDC1498276 (for 4), CCDC-1498279 (for 5), CCDC-1498278 (for 6), CCDC-1498277 (for 7), and CCDC-1498275 (for 8). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif.
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ACKNOWLEDGMENTS This research was supported by a Grant from the Development of Organometallics and Device Fabrication for IT.ET Convergence Project through the Korea Research Institute of Chemical Technology (KRICT) of Republic of Korea (SI160302).
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S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02697. Tabulated crystallographic data and data collection parameters, SEM images, thermal decompositions, XRD patterns (PDF) X-ray crystallographic information (CIF) X-ray crystallographic information (CIF) X-ray crystallographic information (CIF) X-ray crystallographic information (CIF) X-ray crystallographic information (CIF) X-ray crystallographic information (CIF) X-ray crystallographic information (CIF)
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REFERENCES
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Corresponding Authors
*E-mail:
[email protected]. Phone: +82-42-860-7359. Fax: +82-42-861-7151. (T.-M.C.) *E-mail:
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Taek-Mo Chung: 0000-0002-5169-2671 4091
DOI: 10.1021/acs.inorgchem.6b02697 Inorg. Chem. 2017, 56, 4084−4092
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Inorganic Chemistry
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DOI: 10.1021/acs.inorgchem.6b02697 Inorg. Chem. 2017, 56, 4084−4092
