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Synthesis and Crystal Structures of the First Antimony(III) Aziridinides Nicole Harmgarth,† Phil Liebing,† Florian Zörner,† Mindaugas Silinskas,‡ Edmund P. Burte,‡ and Frank T. Edelmann*,† †
Chemisches Institut der Otto-von-Guericke-Universität, Universitätsplatz 2, 39106 Magdeburg, Germany Institut für Mikro- und Sensorsysteme, Otto-von-Guericke-Universität, Universitätsplatz 2, 39106 Magdeburg, Germany
‡
S Supporting Information *
complex [Li3Sb(μ3-Cl)2(μ-Azn)4(THF)2]∞ (1) and homoleptic Sb2(Azn)6 (2). In a first experiment, we attempted to synthesize the hitherto unknown homoleptic Sb(Azn)3 by treatment of anhydrous SbCl3 with 3 equiv of N-lithioaziridine (= Li(Azn)) in THF (Scheme 1). The starting material Li(Azn) is readily prepared
ABSTRACT: The first antimony(III) aziridinyl derivatives are reported. Treatment of anhydrous SbCl3 with Nlithioaziridine Li(Azn) (Azn = NC2H4) afforded the structurally unique heterobimetallic lithium/antimony(III) amide complex [Li3Sb(μ3-Cl)2(μ-Azn)4(THF)2]∞ (1). Homoleptic Sb2(Azn)6 (2) has become available for the first time through an amide group exchange reaction between Sb(NMe2)3 and 3 equiv of aziridine. The lowmelting Sb2(Azn)6 exhibits a “weak dimer” structure in the crystal.
Scheme 1. Preparation of [{Li3Sb(μ3-Cl)2(μAzn)4(THF)2}]∞ (1) and Sb2(Azn)6 (2)
V
olatile antimony precursors play an important role in the production of Sb-based semiconductor thin layers through chemical vapor deposition (CVD). Typical materials fabricated by CVD processes include, e.g., the binaries AlSb, GaSb, and InSb;1−3 antimony chalcogenides such as Sb2Se3 and Sb2Te3;4,5 and the phase-change material germanium−antimony−telluride, Ge2Sb2Te5 (= GST).6−9 One of the most useful volatile antimony(III) precursors for CVD applications is the readily available tris(dimethylamino)antimony(III), Sb(NMe2)3 (= TDMASb).7,10−13 In the course of an ongoing project directed toward the design of new precursors for GST, we reasoned that the replacement of the dimethylamino groups by the somewhat smaller cyclic aziridinyl unit cyclo-NC2H4 could lead to potentially useful additions to the current library of volatile antimony(III) precursors. A literature search revealed that homoleptic aziridine derivatives E(Azn)n (Azn = NC2H4) of main group elements (groups 13−16) are surprisingly rare. In the case of group 13, there is only a single report on incompletely characterized B(Azn)3,14 while the heavier homologues (E = Al−Tl) are all unknown. For group 14, only Si(Azn)415 and (presumably polymeric) Sn(Azn)416,17 have been reported. The preparation and reactivity of the phosphine derivative P(Azn)3 have been more extensively investigated.18,19 This is due to the potential applications of aziridine derivatives of phosphorus in pharmacology and agriculture.20,21 Once again, no heavier congeners (E = As, Sb, Bi) have been mentioned in the literature. In group 16, only S(Azn)2 has been reported.22 In all cases, structural characterization through single-crystal X-ray diffraction studies is lacking. Here, we report the successful synthesis and structural characterization of the first antimony(III) aziridinyl compounds, namely the heterobimetallic “ate” © 2017 American Chemical Society
in situ by treatment of aziridine with n-butyllithium.23 However, separation of the expected byproduct LiCl by solvent exchange from THF to toluene failed, and instead, light yellow crystals of the “ate” complex [{Li3Sb(μ3-Cl)2(μ-Azn)4(THF)2}·THF]∞ (1·THF) were obtained directly from the reaction mixture. After drying in vacuo, [Li3Sb(μ3-Cl)2(μ-Azn)4(THF)2]∞ (1) was isolated in 21% yield. This compound, which can formally be regarded as an adduct of Li[Sb(Azn)4] with LiCl, is moderately soluble in THF and hydrolyses gradually when exposed to air. In the IR spectrum of 1, two bands at 493 and 423 cm−1 can likely be assigned to ν(Sb−N) vibrations.24 Characteristic bands of the Azn moieties appear at 1467 (δ CH2), 1235 (sym. ring breathing), and 877 cm−1 (δ ring + ρ CH2).25 In the NMR spectra, the Azn moieties give only one singlet signal at δH = 1.86 ppm and δC = 21.1 ppm, respectively, indicating that the compound is dissociated in THF solution. This is confirmed by the 7Li NMR shift of −1.41 ppm, giving evidence to the existence of solvent-separated Li+ ions.26 Received: March 1, 2017 Published: March 27, 2017 4267
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approximately 0.05 mbar and a bath temperature of 120 °C (no decomposition under these conditions) of the liquid product mixture afforded the target product 2 as low-melting, colorless crystals in 73% isolated yield. In contrast to 1, compound 2 is readily soluble in aprotic organic solvents and decomposes immediately under deposition of antimony when exposed to air. In the IR spectrum of 2, two ν(Sb−N) bands appear at 479 and 422 cm−1 and therefore at lower wavenumbers compared to Sb(III) amides with open-chain amide residues.27 Just as in the case of 1, the NMR spectra display only one singlet signal at δH = 1.95 ppm and δC = 21.1 ppm, indicating that Sb(Azn)3 monomers are existent in solution. Accordingly, the highest peak in the mass spectrum of 2 (m/z 247) corresponds to the monomeric ion [121Sb(Azn)3]+. Concerning the solid state structure, compound 2 was found to be polymorphic, appearing in a triclinic (space group P1)̅ and a monoclinic modification (space group P21/c; Figure 2). X-ray structure analysis revealed the presence of
The THF solvate 1·THF crystallizes in the triclinic space group P1̅, with one Sb atom, three Li atoms, two Cl atoms, four Azn moieties, and three THF molecules in the asymmetric unit (Figure 1). The Sb atom is surrounded by all four Azn ligands,
Figure 1. Molecular structure of [{Li3Sb(μ3-Cl)2(μ-Azn)4(THF)2}· THF]∞ (1·THF) in the crystal. Displacement ellipsoids drawn at the 50% probability level, H atoms omitted for clarity. Symmetry codes: (′) 1 − x, 1 − y, 1 − z; (″) 2 − x, 2 − y, 2 − z. Selected bond lengths (pm) and angles (deg): Sb−N1 205.9(4), Sb−N2 206.4(4), Sb−N3 222.8(8), Sb−N4 224.0(4), N1−Sb−N2 87.3(2), N3−Sb−N4 162.6(1), Li1−N1 208.9(9), Li1−N2 209.5(9), Li1−Cl1 234.7(8), Li1−Cl2 234.6(8), N1−Li1−N2 85.8(3), Cl1−Li1−Cl2 122.8(3), Li2−N3 203.4(9), Li2−Cl1 236.6(8), Li2−Cl1′ 238.4(8), Li2−O1 196.6(9), N3−Li2−Cl1 120.0(4), N3−Li2−O1 105.7(4), Cl1−Li1− Cl1′ 102.1(3), Li3−N4 201.9(9), Li3−Cl2 237.1(8), Li3−Cl2′ 241.4(8), Li3−O2 198.6(8), N4−Li3−Cl2 120.8(4), N4−Li3−O2 104.5(4), Cl2−Li3−Cl2″ 101.2(3), Sb−N1−Li1 93.6(3), Sb−N2−Li1 93.3(3), Sb−N3−Li2128.9(3), Sb−N4−Li3 127.3(3).
and the lone-pair at Sb is apparently stereoactive. The coordination can be described as pseudotrigonal bipyramidal with N3 and N4 defining the axial positions (N3−Sb−N4 162.6(1)°). The distinct stereoactivity of the lone-pair is typical for antimony(III),27−40 while in the case of the heavier homologue bismuth(III), various structures with a stereochemically inactive lone pair have been described.41,42 One of the Li atoms in 1·THF (Li1) is part of a virtually planar SbLiN2 ring and displays a tetrahedral coordination by the two ring Azn moieties and two Cl atoms. The two remaining Li atoms (Li2, Li3) are each part of a centrosymmetric Li2Cl2 ring, where a tetrahedral coordination is completed by an Azn moiety and a THF ligand. All four Azn moieties are consequently coordinated to Sb and Li in a μ-bridging mode. The Cl atoms are exclusively attached to Li atoms in a μ3-bridging mode. As a result of this connectivity pattern, an infinite ladder structure of repeating SbClLi2N2, SbLiN2, and Li2Cl2 rings is built, which extends along the space-diagonal of the unit cell. Compound 1 is a unique example of a mixed Li/Sb(III) amide complex. Heterobimetallic alkali metal/Sb(III) complexes with nitrogen ligands have been reported earlier, but these are exclusively imides 30,36,37 or mixed amide/imide compounds,34,35 each with cage architectures. In 1·THF, the Sb− N separations within the central SbLiN2 ring are 205.9(4) and 206.4(4) pm and therefore within the range of 198−216 pm in which other Sb−N(amide) bonds have been observed.27−35 In contrast, the remaining two Sb−N contacts to the “exposed” Azn moieties (N3, N4) are markedly elongated to 222.8(8) and 224.0(4) pm, which fits to the trigonal bipyramidal coordination model. With the intention to develop a chloride-free synthetic protocol to obtain the desired binary aziridinyl compound 2, we carried out an amide group exchange reaction of Sb(NMe2)3 with a slight excess of aziridine. Vacuum distillation at
Figure 2. Molecular structure of Sb2(μ-Azn)2(Azn)4 (2) in the crystal (monoclinic modification). Displacement ellipsoids with 50% probability, H atoms omitted for clarity. Symmetry code: (′) 2 − x, −y, 1 − z. Selected bond lengths (pm) and angles (deg): Sb−N1 208.4(1), Sb···N1′ 253.4(2), Sb−N2 209.6(2), Sb−N3 203.9(2), N1− Sb···N1′ 71.08(6), N1−Sb−N2 90.78(6), N1−Sb−N3 100.77(6), N1′···Sb−N2 158.49(5), N1′···Sb−N3 80.38(6), N2−Sb−N3 92.21(6), Sb−N1···Sb′ 108.92(6).
centrosymmetric dimers Sb2(μ-Azn)2(Azn)4 in both modifications, even though only the monoclinic crystals were suitable for a full structure refinement. The coordination environment of the Sb atom in 2 is similar to that in 1·THF, featuring a pseudotrigonal bipyramidal arrrangement with the stereoactive lone pair in an equatorial position (N1′···Sb−N2 158.49(5)°). The nonbridging Azn moieties are attached to Sb with bond lengths of 209.6(2) and 203.9(3) pm, i.e., in the same range as the “short” Sb−N separations compound 1. One of the Sb−N bonds to the μbridging Azn ligand (Sb−N1) is similar in length with 208.4(1) pm, while the other one (Sb−N1′) is strongly elongated to 253.4(2) pm. The molecular structure of compound 2 can consequently be regarded as an intermediate case between Sb2(Azn)6 dimers and Sb(Azn)3 monomers. The same phenomenon has been observed in structurally related antimony(III) alkoxides and siloxides, Sb2(OR3)6, where the difference in Sb−E separations within the Sb2E4 core (E = N, O) is even larger than in 2.39,40 The so far only structurally characterized binary Sb(III) amide without additional donor groups within the amide groups, Sb[N(SiMe3)2]3, exhibits a monomeric structure in the solid state.32 It can therefore be assumed that the dimerization tendency in the heavy group 15 amides is remarkably low, as in compound 2, dimerization should most likely be supported in view of the sterically very 4268
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precursor design and substrate selectivity. J. Mater. Chem. C 2015, 3, 423−430. (6) Tompa, G. S.; Sun, S.; Rice, C. E.; Cuchiaro, J.; Dons, E. Metalorganic chemical vapor deposition (MOCVD) of GeSbTe-based chalcogenide thin films. MRS Online Proc. Libr. 2007, 997, 275−280. (7) Abrutis, A.; Plausinaitiene, V.; Skapas, M.; Wiemer, C.; Salicio, O.; Longo, M.; Pirovano, A.; Siegel, J.; Gawelda, W.; Rushworth, S.; Giesen, C. Chemical vapor deposition of chalcogenide materials for phase-change memories. Microelectron. Eng. 2008, 85, 2338−2341. (8) Reso, D.; Silinskas, M.; Gewalt, A.; Burte, E. P.; Lisker, M. The role of hydrogen in hot wire chemical vapor deposition of Ge-Sb-Te thin films. Thin Solid Films 2011, 519, 2150−2154. (9) Schuck, M.; Rieß, S.; Schreiber, M.; Mussler, G.; Grützmacher, D.; Hardtdegen, H. Metal organic vapor phase epitaxy of hexagonal Ge−Sb−Te (GST). J. Cryst. Growth 2016, 420, 37−41. (10) Yamamoto, K.; Asahi, H.; Hayashi, T.; Asami, K.; Gonda, S. Metalorganic molecular beam epitaxy growth and etching of GaSb on flat and high-index surfaces using trisdimethylaminoantimony. J. Cryst. Growth 1996, 164, 117−221. (11) Yamamoto, K.; Asahi, H.; Miki, K.; Gonda, S. Etching of GaSb with trisdimethylaminoantimony and triisopropylantimony in a metalorganic molecular beam epitaxy chamber. J. Cryst. Growth 1997, 173, 21−26. (12) Suhandi, A.; Feranie, S.; Arifin, P. Study of electrical properties of GaAs1‑xSbx thin film grown by vertical-MOCVD using TMGa, TDMAAs, and TDMASb. J. Mater. Sci. Eng. A 2011, 1, 199−203. (13) Jeong, J. H.; Choi, D. J. Investigation on the atomic layer deposition of the Se doped Sb−Te phase change films using an alkylsilyl precursor. Mater. Sci. Semicond. Process. 2016, 54, 42−50. (14) Nö th, H.; Wrackmeyer, B. 1lB- und 14N-Kernresonanzmessungen an Alkoxy-, Alkylthio- und 1-Pyrrolylboranen. Chem. Ber. 1973, 106, 1145−1164. (15) Huber, G.; Jockisch, A.; Schmidbaur, H. The Structural Chemistry of Aziridino- and Azetidinosilanes. Eur. J. Inorg. Chem. 1998, 1998, 107−112. (16) Bishop, M. E.; Zuckerman, J. J. N-Organotin Aziridines and Other Cyclic Amines and Their Adducts. Inorg. Chem. 1977, 16, 1749−1762. (17) Molloy, K. C.; Bigwood, M. P.; Herber, R. H.; Zuckerman, J. J. Variable-Temperature Tin-119m Moessbauer Study of Tin(II) and Tin(IV) Amines. Inorg. Chem. 1982, 21, 3709−3712. (18) Socol, S. M.; Jacobson, R. A.; Verkade, J. G. Ligation of Phosphorus Ligands to Silver(I). 1. Coordination of One to Four P(NR2)3 Ligands and the Structure of a Nonlinear Two-Coordinate Complex. Inorg. Chem. 1984, 23, 88−94. (19) Sosnovsky, G.; Konieczny, M. Introduction of Selenium into Organophosphorus Compounds Containing the Aziridinyl and Stable Nitroxyl Groups. Synthesis 1978, 1978, 583−585. (20) Corbridge, D. E. C. Studies in Inorganic Chemistry 20, Phosphorus, An Outline of Its Chemistry. Biochemistry and Uses, 5th ed.; Elsevier: Amsterdam, 1995; p 452. (21) Comprehensive Heterocyclic Chemistry II, A Review of the Literature 1982−1995, 1st ed.; Elsevier: Oxford, 1996; Vol 1A, pp 58−60. (22) Fehér, F.; Degen, B. Darstellung von Diimidazolylsulfanen und Diaziridinylsulfanen. Angew. Chem. 1967, 79, 690. (23) Graefe, A. F.; Meyer, R. E. The synthesis of 1,1′-biaziridine. A new bicyclic system. J. Am. Chem. Soc. 1958, 80, 3939−3941. (24) Kiennemann, A.; Levy, G.; Schué, F.; Taniélian, C. Sur la Préparation de quelques Tris(dialcoylamino)stibines et sur quelques unes de leurs Propriétés. J. Organomet. Chem. 1972, 35, 143−148. (25) Spell, H. L. The Infrared Spectra of N-Substituted Aziridine Compounds. Anal. Chem. 1967, 39, 185−193. (26) Cahen, Y. M.; Handy, P. R.; Roach, E. T.; Popov, A. I. Spectroscopic Studies of Ionic Solvation. XVI. Lithium-7 and Chlorine-35 Nuclear Magnetic Resonance Studies in Various Solvents. J. Phys. Chem. 1975, 79, 80−85. (27) Hu, S.-Z.; Chen, M.-D.; Robertson, B. E. Study on the secondary bonding and coordination polyhedra in crystal of
low demanding aziridinyl moieties. This hypothesis is impressively confirmed by the likewise sterically low-demanding Bi(NMe2)3, where monomeric molecules are aggregated only by very weak Bi···N interactions in the crystal.43 Distinct dimeric structures have been observed in some mixed antimony(III) amide/imide compounds with μ-bridging imide ligands, where the Sb−N separations within the cyclic Sb2N2 core are much more similar than in 2.28−30 In summarizing the results reported here, we succeeded in the synthesis and full characterization of the first aziridinyl derivatives of antimony. A salt-metathesis reaction of SbCl3 with N-lithioaziridine Li(Azn) (Azn = NC2H4) afforded the structurally unique heterobimetallic lithium/antimony(III) amide complex [Li3Sb(μ3-Cl)2(μ-Azn)4(THF)2]∞ (1), whereas homoleptic Sb2(Azn)6 (2) was isolated in good yield (73% after distillation) from a transamination reaction between Sb(NMe2)3 and 3 equiv of aziridine. An X-ray diffraction study of low-melting Sb2(Azn)6 revealed a “weak dimer” structure in the crystal. A future study will show if 2 might rival Sb(NMe2)3 as an antimony precursor in the ALD and MOCVD production of antimony chalcogenide materials.
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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.7b00523. General information, experimental procedures, and full characterization of the compounds (PDF) Crystallographic data for 1 (CIF) Crystallographic data for 2 (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Frank T. Edelmann: 0000-0001-5209-0018 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was generously supported by the German science foundation DFG (grants no. ED 29/29-1 and BU 978/65-1). General financial support by the Otto-von-Guericke Universität Magdeburg is also gratefully acknowledged.
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REFERENCES
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