Chem. Mater. 1997, 9, 1385-1392
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Preparation and Characterization of a Material of Composition BiP (Bismuth Phosphide) and Other Intergroup 15 Element Phases Geoff C. Allen,*,† Claire J. Carmalt,*,‡,§ Alan H. Cowley,*,§ Andrew L. Hector,⊥ Smuruthi Kamepalli,§ Yvonne G. Lawson,| Nicholas C. Norman,*,‡,| Ivan P. Parkin,⊥ and Laura K. Pickard| The Interface Analysis Centre, The University of Bristol, Oldbury House, Bristol, BS2 8BS, UK; The University of Newcastle upon Tyne, Department of Chemistry, Newcastle upon Tyne, NE1 7RU, UK; The University of Texas at Austin, Department of Chemistry and Biochemistry, Austin, Texas, 78712; University College London, Department of Chemistry, 20 Gordon Street, London, WC1H 0AJ, UK; and The University of Bristol, School of Chemistry, Bristol, BS8 1TS, UK Received November 22, 1996. Revised Manuscript Received April 2, 1997X
The reaction between equimolar quantities of BiCl3 and the silylphosphine P(SiMe3)3 in toluene or THF (tetrahydrofuran) solution affords a black precipitate with the composition of bismuth phosphide, BiP, which has been examined by EDXA, SEM, XPS, powder XRD, solid-state 31P NMR spectroscopy, and elemental analysis. Alternative possible routes to BiP involving the reactions between Na3P and BiCl3 and between Bi(NMe2)3 and P(SiMe3)3 have also been investigated, both of which afford black powders of composition close to BiP, although in the latter case there is some contamination with bismuth metal. Analogous reactions with either SbCl3 or AsCl3 and P(SiMe3)3 afford black and dark brown precipitates, respectively, which are formulated as the materials antimony phosphide, SbP, and arsenic phosphide, AsP, on the basis of similar analyses. Preliminary experiments have also shown that the related arsenides, BiAs and SbAs, can be prepared from reactions between either BiCl3 or SbCl3 and the silylarsine As(SiMe3)3, and that a ternary phase with the composition BiSbP2 is formed in the reaction between BiCl3, SbCl3, and P(SiMe3)3 in a 1:1:2 mole ratio. A material of composition close to elemental phosphorus is obtained from the reaction between PCl3 and P(SiMe3)3.
Introduction Element phosphides, ExPy, constitute an important and structurally diverse class of compound, examples of which are known for almost all elements. There are, however, some conspicuous absences particularly in the case of the heavier group 15 elements. Thus, as noted in the text Chemistry of the Elements by Greenwood and Earnshaw,1 “phosphorus forms binary compounds with all elements except Sb, Bi and the inert gases” and, in a recent and comprehensive review on element phosphides by von Schnering and Ho¨nle,2 it is stated that “Bi, Hg and Pb form no binary phosphides at all”. In fact, with the recent exception of phosphorus(V) nitride, P3N5, reported by Schnick,3 there is very little definitive characterization data for solid-state compounds that involve only the group 15 elements. A survey of the early literature reveals that attempts to prepare binary phosphides of arsenic, antimony, and bismuth have resulted in only poorly characterized †
Interface Analysis Centre, University of Bristol. University of Newcastle upon Tyne. University of Texas at Austin. ⊥ University College London. | School of Chemistry, University of Bristol. X Abstract published in Advance ACS Abstracts, May 15, 1997. (1) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; p 559. (2) von Schnering, H.-G.; Ho¨nle, W. Chem. Rev. 1988, 88, 243. (3) Schnick, W. Angew. Chem., Int. Ed. Engl. 1993, 32, 806. ‡ §
S0897-4756(96)00606-0 CCC: $14.00
materials.4 Arsenic monophosphide is reportedly formed by the action of dry arsine on phosphorus trichloride below 20 °C or via a similar reaction involving phosphine and arsenic trichloride,5 while more recent reports describe phosphorus-arsenic alloys of the type P1-xAsx (x ) 0.05, 0.1-0.5) which adopt an orthorhombic layered structure similar to that of orthorhombic black phosphorus. These alloys were transformed from the orthorhombic phase to one of rhombohedral symmetry and finally to a simple cubic form by increasing the pressure at room temperature (a similar transformation is known for elemental phosphorus); the cubic phase exhibits superconductivity at low temperature.6 Early reports of the existence of an antimony phosphide phase are inconclusive. Antimony monophosphide was reportedly prepared by the action of phosphorus on a solution of antimony tribromide in carbon disulfide, although attempts to repeat this claim were unsuccessful.7 In the case of bismuth monophosphide, only poorly characterized black powders have been obtained, the properties of which resemble those of a (4) Hansen, M. Constitution of Binary Alloys, Metallurgy and Metallurgical Engineering Series; McGraw-Hill: New York, 1958; pp 155-6, 173, 178-9, 324, 1088. (5) Corbridge, D. E. C. Phosphorus: An outline of its Biochemistry and Technology, 3rd ed.; Elsevier: New York, 1958; Chapter 2. (6) Shirotani, I.; Shiba, S.; Takehiko, K.; Shimomura, O.; Yagi, T. Physica B 1993, 190, 169. (7) See: Mellor, J. W. Comprehensive Treatise on Inorganic and Theoretical Chemistry; Longmans, Green & Co. Ltd.: London, 1928; Vol. VIII, pp 851-852 and references therein.
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phosphiferous bismuth. Neither by direct or indirect methods has a bismuth phosphide been prepared with any certainty.7 One of the most general preparative routes to element phosphides is to heat the element in question with an appropriate amount of elemental phosphorus at high temperature either in an inert atmosphere or in an evacuated sealed tube. However, any potential synthesis of bismuth phosphide directly from the elements is thwarted both by the apparent limited solubility of phosphorus in molten bismuth7 and by the fact that these elements are known to crystallize separately from molten mixtures; crystalline orthorhombic black phosphorus has, in fact, been obtained by recrystallization of phosphorus from molten bismuth.8 This problem of restricted mutual solubility in the molten state was also encountered in attempted preparations of antimony phosphide.9 It should be noted, however, that most of the heteronuclear diatomic molecules, such as BiP, SbP, and AsP, have been studied spectroscopically in the gas phase (see, for example, refs 10 and 11 ). The related element arsenides, ExAsy, are also an important and structurally diverse class of materials, examples of which are likewise known for most elements, and many have important electronic properties, such as the group 13 (Al, Ga, In) arsenides. In contrast, the group 15 arsenides, like the phosphides, do not constitute a well-characterized group of compounds, although there are a number of reports of the existence of an alloy of arsenic and antimony (see ref 4 and literature cited therein), and one phase of the mineral allemonite has a composition corresponding to the formula AsSb.4 Early reports of an arsenic-bismuth alloy indicate that two layers form as a result of these elements having only limited mutual solubility in the liquid state, although subsequent investigations revealed that this formation of layers was due to insufficient mixing of the melts. Nevertheless, the solubility of arsenic in bismuth is only slight (see ref 4 and literature cited therein). Our interest in preparing bismuth phosphide, BiP, in particular stemmed from the realization that it is isoelectronic with lead(II) sulfide, PbS,12 which is an intrinsic semiconductor with a bandgap of 0.37 eV. This material has a wide range of applications including use in photoconductive cells and transistors, as an infrared detector, and as a mirror coating. Herein we describe the preparation and characterization of a material of empirical composition BiP, together with the related binary phosphides of antimony and arsenic. Preliminary results on the preparation of the ternary compound, BiSbP2, are also presented together with details on some related arsenides, namely, BiAs and SbAs. A communication of part of this work relating to the preparation of BiP has appeared.13 (8) Brown, A.; Rundqvist, S. Acta Crystallogr. 1965, 19, 684. (9) Klemm, W.; Falkowski, I. V. FIAT Rev. Ger. Sci.; Inorganic Chemistry, 1949, Part I, pp 274. See also: Z. Anorg. Chem. 1948, 256, 343. (10) Gingerich, K. A.; Cocke, D. L.; Kordis, J. J. Phys. Chem. 1974, 78, 603. (11) Kordis, J.; Gingerich, K. A. J. Chem. Phys. 1973, 58, 5141. (12) Greninger, D.; Kollonitsch, V.; Kline, C. H. Lead Chemicals; International Lead Zinc Research Organisation, Inc. (ILZRO): New York; pp 121-156. (13) Carmalt, C. J.; Cowley, A. H.; Hector, A. L.; Norman, N. C.; Parkin, I. P. J. Chem. Soc., Chem. Commun. 1994, 1987.
Allen et al.
Preparation and Properties of Bismuth Phosphide Solution precipitation routes, using a variety of solvents, to III-V (or 13-15) materials involving the elimination of a silyl halide Me3SiX (X ) Cl, Br, I) have previously been described by the groups of Wells,14 Barron,15 Buhro,16 Alivisatos,17 Nozik,18 and Fitzmaurice19 according to eq 1. This method relies on the
EX3 + E′(SiMe3)3 f EE′ + 3Me3SiX
(1)
E ) Al, Ga, In; X ) Cl, Br, I; E′ ) P, As, Sb formation of a strong Si-X bond and has been used in the preparation of solid AlAs,14e GaP,14b,c GaAs,14a,d,17a,19 GaSb,14f InAs14a and InP.15,17b,18 In general, initial reactions occur rapidly at or below room temperature via intermediate species such as the phosphine, arsine, or stibine adducts [X3ErE′(SiMe3)3] and the dimeric, four-membered ring compounds [{EX2E′(SiMe3)2}2], examples of which have been isolated and crystallographically characterized in many cases.14b-d Heating of solid samples of these primary products to temperatures of about 300 °C subsequently results in complete elimination of all remaining Me3SiX with formation of the EE′ phase. In contrast to the group 13-15 chemistry, treatment of a stirred solution of BiCl3 in toluene or THF (tetrahydrofuran) with 1 equiv of P(SiMe3)3 at room temperature led to the immediate formation of an insoluble black precipitate (1a), full elemental analytical data for which were in accord with a material of composition close to BiP with only minor amounts of carbon, hydrogen, silicon, and chlorine present. The observation that the elimination of Me3SiCl is much more facile here than in the case of the analogous 13-15 reactions shown in eq 1 is presumably a consequence of the relative weakness of the Bi-Cl bond. A number of further analyses, described below, were carried out in order to characterize 1a more fully and, more specifically, to determine whether this material was a genuine bismuth phosphide compound or merely an intimate mixture of elemental bismuth and phosphorus. Energy-dispersive X-ray analysis (EDXA) of 1a confirmed the presence of bismuth and phosphorus with only minimal levels of impurities (Figure 1) consistent with the elemental analytical data. No appreciable (14) (a) Wells, R. L.; Pitt, C. G.; McPhail, A. T.; Purdy, A. P.; Shafieezad, S.; Hallock, R. B. Chem. Mater. 1989, 1, 4. (b) Wells, R. L.; Self, M. F.; McPhail, A. T.; Aubuchon, S. R.; Woudenberg, R. C.; Jasinski, J. P. Organometallics 1993, 12, 2832. (c) Aubuchon, S. R.; McPhail, A. T.; Wells, R. L.; Giambra, J. A.; Bowser, J. R. Chem. Mater. 1994, 6, 82. (d) Johansen, J. D.; McPhail, A. T.; Wells, R. L. Adv. Mater. Opt. Electron. 1992, 1, 29. (e) Wells, R. L.; Pitt, C. G.; McPhail, A. T.; Purdy, A. P.; Shafieezad, S.; Hallock, R. B. Mater. Res. Soc. Symp. Proc. 1989, 131, 45. (f) Baldwin, R. A.; Foos, E. E.; Wells, R. L.; Yap, G. P. A.; Rheingold, A. L. Abstracts of Papers, 211th American Chemical Society National Meeting (New Orleans, LA, March 24-29, 1996; INOR 198. (15) Healy, M. D.; Laibinis, P. E.; Stupik, P. D.; Barron, A. R. J. Chem. Soc., Chem. Commun. 1989, 359. (16) Buhro, W. E. Polyhedron 1994, 13, 1131 and references therein. (17) (a) Potter, L. D.; Guzelian, A. A.; Alivisatos, A. P.; Wu, Y. J. Chem. Phys. 1995, 103, 4834. (b) Guzelian, A. A.; Katari, J. E. B.; Kadavanich, A. V.; Banin, U.; Hamad, K.; Juban, E.; Alivasatos, A. P.; Wolters, R. H.; Arnold, C. C.; Heath, J. R. J. Phys. Chem. 1996, 100, 7212. (18) Micic, O. I.; Sprague, J. R.; Curtis, C. J.; Jones, K. M.; Machol, J. L.; Nozik, A. J.; Giessen, B.; Fluegel, B.; Mohs, G.; Peyghambarian, N. J. Phys. Chem. 1995, 99, 7754 and references therein. (19) Butler, L.; Redmond, G.; Fitzmaurice, D. J. Phys. Chem. 1993, 97, 10750.
New Intergroup 15 Element Phases
Figure 1. EDXA spectrum (in keV) for 1a.
Figure 2. SEM of 1a.
quantities of carbon, silicon, or oxygen were observed over a number of surface sites, indicating that any amounts present were less than 1%. Chlorine contamination was more difficult to gauge by this technique since the primary chlorine and bismuth peak energies are nearly coincident, although elemental analytical data showed that
