3736
Inorg. Chem. 2000, 39, 3736-3737
Synthesis and Magnetic and Structural Characterization of the First Homoleptic Lanthanide β-Ketoiminate William S. Rees, Jr.,*,†,‡,§ Oliver Just,†,§ Stephanie L. Castro,† and Jason S. Matthews†,§ School of Chemistry and Biochemistry, School of Materials Science and Engineering, and Molecular Design Institute, Georgia Institute of Technology, Atlanta, Georgia 30332-0400
ReceiVed February 24, 2000 Introduction One challenge in electronic materials is precise control over both dopant atom concentration and location. Several systems being explored involve lanthanide elements as the dopant, including Si:Er,1 SrS:Ce,2 and (Al, Ga)As:Er.3 Chemical vapor deposition (CVD) of metal oxides often relies on β-diketonates,4 although amides recently have emerged as versatile alternatives for several compositions.1-3,5 Hybrid ligands between these two categories, β-ketoiminates, have been appended to numerous transition elements6 and were evaluated recently for barium.7 Homoleptic compounds generally are preferred for CVD utilization,4 so it was desired to prepare examples from this group for further evaluation as potential dopant sources for electronic materials. Thus, the synthesis and magnetic and structural characterization of the first homoleptic lanthanide β-ketoiminate is described. Previous examples of molecules containing a lanthanide β-ketoiminate interaction8 include a crypt-type compound9 and one heteroleptic cyclopentadienide case.10 Results and Discussion The homoleptic ytterbium tris(β-ketoiminate), 1, was prepared as given in Scheme 1 and shown to be monomeric and solvent-free in the solid state (Figure 1). Ytterbium adopts a nearly perfect octahedral coordination sphere with a meridinal O3 and N3 arrangement. The Yb-N interatomic distances in 1 (2.38, 2.44, 2.44 Å) compare favorably with those determined for Yb[N(TMS)2]3- (2.38, 2.44, 2.47 Å),11 indicating that the * To whom correspondence should be addressed. Phone: 404-894-4049. Fax: 404-894-1144. E-mail:
[email protected]. † School of Chemistry and Biochemistry. ‡ School of Materials Science and Engineering. § Molecular Design Institute. (1) (a) Zheng, B.; Michel, J.; Ren, F. Y. G.; Kimmerling, L. C.; Jacobson, D. C.; Poate, J. M. Appl. Phys. Lett. 1994, 64, 2842. (b) Just, O.; Kimmerling, L. C.; Rees, W. S., Jr. Proc. SPIE 1999, 3469. (2) (a) Rack, P. D.; Holloway, P. H.; Pham, L.; Wager, J.; Sun, S.-S.; Dickey, E.; King, C. N. SID 95 Digest 1995, 480. (b) Rees, W. S., Jr.; Just, O.; VanDerveer, D. G. J. Mater. Chem. 1999, 9, 249. (3) (a) Ennen, H.; Schneider, J.; Pomrenke, G.; Axmann, A. Appl. Phys. Lett. 1983, 43, 943. (b) Greenwald, A. C.; Rees, W. S., Jr.; Lay, U. W. Mater. Res. Soc. Symp. Proc. 1993, 301, 21. (c) Rees, W. S., Jr.; Lay, U. W.; Greenwald, A. C. Mater. Res. Soc. Symp. Proc. 1994, 334, 207. (d) Just, O.; Greenwald, A. C.; Rees, W. S., Jr. Mater. Res. Soc. Symp. Proc. 1996, 415, 111. (e) Greenwald, A. C.; Linden, K.; Rees, W. S., Jr.; Just, O.; Haegal, N. M.; Donder, S. Mater. Res. Soc. Symp. Proc. 1996, 422, 63. (4) Schulz, D. L.; Marks, T. J. In CVD of Nonmetals; Rees, W. S., Jr., Ed.; VCH: New York, 1996; p 37. (5) Rees, W. S., Jr.; Just, O.; Weimann, R.; Schumann, H. Angew. Chem., Int. Ed. Engl. 1996, 35, 419. (6) (a) Parks, J. E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408. (b) Bastianini, A.; Battiston, G. A.; Benetollo, F.; Gerbasi, R.; Porchia, M. Polyhedron 1997, 7, 1105. (c) Bradbury, J. R.; Hampton, J. L.; Martone, D. P.; Maverick, A. W. Inorg. Chem. 1989, 28, 2392 and references therein. (7) (a) Schultz, D. L.; Hinds, B. J.; Neumayer, D. A.; Stern, C. L.; Marks, T. J. Chem. Mater. 1993, 5, 1605. (b) Schultz, D. L.; Hinds, B. J.; Stern, C. L.; Marks, T. J. Inorg. Chem. 1993, 32, 249. (8) Andrienko, I. V.; Martynenko, L. I.; Murav’eva, I. A.; Spitsyn, V. I. Dokl. Akad. Nauk SSSR 1988, 298, 46. (9) Berg, D. J.; Rettig, S. J.; Orvig, C. J. Am. Chem. Soc. 1991, 113, 2528. (10) Thiele, K.-H.; Scholz, A.; Scholz, J.; Bohme, U. Z. Naturforsch. 1993, 486, 1753.
Figure 1. complex 1.
ORTEP representation with numbering scheme for
Scheme 1. Synthetic Route Leading to the Formation of Complex 1
metal-nitrogen interactions in both compounds are similar. Likewise, Yb-O distances present in 1 (2.15, 2.16, 2.16 Å) agree well with those found in Yb(acac)3 (2.20-2.22 Å).12 Both, inter13 and intramolecular14 Lewis base coordination of tertiary amines to ytterbium results in 0.1-0.2 Å longer distances, further indicating the ionic nature of the Yb-N interaction in 1. Previously reported interatomic distances in a heptacoordinated ytterbium β-ketoiminate crypt9 track well with those determined for 1, confirming evident π-electron delocalization present within (11) Tilley, T. D.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1984, 23, 2271. (12) Batsanov, A. S.; Struchkov, Y. T.; Trembovetskii, G. V.; Murav’eva, I. A.; Martynenko, L. I.; Spitsin, V. I. Dokl. Akad. Nauk SSSR 1986, 289, 683. (13) (a) Tilley, T. D.; Andersen, R. A.; Spencer, B.; Zalkin, A. Inorg. Chem. 1982, 21, 2647. (b) Baker, E. C.; Raymond, K. N. Inorg. Chem. 1977, 16, 2710. (c) Brewer, M.; Khasnis, D.; Buretea, M.; Berardini, M.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 1994, 33, 2743. (d) Benetollo, P.; Bombieri, G.; Depaoli, G.; Truter, M. R. Inorg. Chim. Acta 1996, 245, 223. (14) (a) Nassimbeni, L. R.; Wright, M. R. W.; van Niekerk, J. C.; McCallum, P. A. Acta Crystallogr., Sect. B 1979, 35, 1341. (b) van den Hende, J. R.; Hitchcock, P. B.; Lappert, M. F.; Nile, T. A. J. Organomet. Chem. 1994, 472, 79. (c) Baraniak, E.; Bruce, R. S. L.; Freeman, H. C.; Hair, N. J.; James, J. Inorg. Chem. 1976, 15, 2226. (d) Gornitzka, H.; Steiner, A.; Stalke, D.; Kiliman, U.; Edelman, F. T.; Jacob, K.; Thiele, K.-H. J. Organomet. Chem. 1992, 439, C6. (e) Yang, L.-W.; Liu, S.; Wong, E.; Retig, S. J.; Orvig, C. Inorg. Chem. 1995, 34, 2164. (f) Evans, W. J.; Anwander, R.; Berlekamp, U. H.; Ziller, J. W. Inorg. Chem. 1995, 34, 3583.
10.1021/ic000203o CCC: $19.00 © 2000 American Chemical Society Published on Web 07/28/2000
Communications
Figure 2. TGA analysis of complex 1, carried out under an argon atmosphere (15 sccm, 10 °C/min).
the chelating ring. A similar trend has been observed for other non-lanthanide β-ketoiminate complexes.6,7 Compound 1 is volatile and thermally stable in both the vapor and condensed phases, up to the sublimation temperature. The solid-vapor transition appears to be a single-step event (Figure 2), which remarkably occurs at 600 °C (1 atm). This portrayal of thermal robustness is unique among Ln-N interactions, which generally are unstable at such elevated temperature. To our knowledge, no other molecular lanthanide compound displays this degree of thermal stability. The great thermal robustness of 1 may be comparable to that shown previously by metal complexes with intramolecular coordination of Lewis base bearing pendant arms on anionic ligands.15 The magnetic susceptibility of 1 was measured, and diamagnetic corrections were calculated using Pascal’s constants. A plot of µeff vs T (Supporting Information) shows nearly temperatureindependent behavior, decreasing gradually from µeff ) 4.41 µB at 295 K to µeff ) 3.51 µB at 5.17 K. The value at 295 K is comparable to the 4.5 µB predicted by Van Vleck. Deviation from anticipated behavior in rare earth compounds is not unusual and may arise in part from the effects of a weak crystal field in the ground state.16 Summary A new β-ketoiminate ligand platform was prepared and employed in the formation of a lanthanide compound, which possesses unprecedented thermal stability. Additionally, it has reduced oxidative sensitivity compared to other lanthanide examples, being able to be handled in the open atmosphere for brief exposures without any measurable decomposition. The magnetic characterization is consistent with that proposed for an f 13 example. The pseudooctahedral metal center portrays a meridinal N3 and O3 ligand arrangement between the defined planes. Perhaps the most remarkable feature of this first example of a new class of compounds is the extreme thermal robustness that is displayed. This is in marked contrast to reported barium bis(β-ketoiminate) examples,7 and the origin of this unexpected stability currently is undergoing further exploration. Experimental Section General Comments. Manipulations were performed under a dried Ar atmosphere, employing standard Schlenk techniques, or (15) (a) Rees, W. S., Jr.; Caballero, C. R.; Hesse, W. Angew. Chem. 1992, 104, 786. (b) Rees, W. S., Jr.; Moreno, D. A. J. Chem. Soc., Chem. Commun. 1991, 1759. (c) Rees, W. S., Jr.; Lay, U. W.; Dippel, K. A. J. Organomet. Chem. 1994, 483, 27. (d) Kra¨uter, G.; Rees, W. S., Jr. Main Group Chem. 1997, 2, 9. (16) Andruh, M.; Bakalbassis, E.; Kahn, O.; Trombe, J. C.; Porcher, P. Inorg. Chem. 1993, 32, 1616.
Inorganic Chemistry, Vol. 39, No. 17, 2000 3737 in an inert gas-filled glovebox. The solvents were degassed and freshly distilled from sodium or potassium/benzophenone prior to use. Handling and mounting of crystals on the diffractometer were carried out in a 77 K Ar stream.17 Physical Measurements. See Supporting Information for Physical Measurements and X-ray Measurements details. Preparation of 5-N-(n-Pr)-2,2,6,6-tetramethyl-3-heptanone (2). Under an argon atmosphere, 34.4 g (134 mmol) of 2,2,6,6tetramethyl-5-(trimethylsiloxy)hept-4-en-3-one18 and 8.26 g (140 mmol) of n-Pr amine were heated in a Schlenk flask with vigorous stirring for 3 h at 46-48 °C. The reaction mixture was distilled to afford 11.76 g (39% yield) of 5-N-(n-Pr)-2,2,6,6-tetramethyl3-heptanone as a colorless liquid; bp ) 267 °C/760 Torr. 1H NMR [300 MHz, C6D6, δ, ppm]: 0.79 (t, 3H, CH3), 1.05 (s, 9H, (CH3)3CCN), 1.31 (s, 9H, (CH3)3CCO), 1.33 (m, 2H, CH2), 2.99 (m, 2H, NCH2), 5.47 (s, 1H, CH), 12.30 (br s, 1H, NH). 13C NMR [300 MHz, C6D6, δ, ppm]: 11.26 (s, CH3CH2), 23.89 (s, CH3CH2), 28.35 (s, NC(CH3)3), 28.96 (s, COC(CH3)3), 35.80 (s, NC(CH3)3), 41.81 (s, OC(CH3)3), 47.03 (s, NCH2), 85.95 (s, CH), 173.18 (s, CN), 203.10 (s, CO). 14N NMR [400 MHz, C6D6, δ, ppm]: 269.99. IR [cm-1]: 1612, 2365. MS (EI, 70 eV): 225, 210, 182, 168, 57. Anal. Calcd for C14H27NO: C, 74.61; H, 12.08. Found: C, 74.55; H, 12.64. Preparation of Yb Tris(β-ketoiminate) (1). Under an Ar atmosphere 2.80 g (12.45 mmol) of 2 was dissolved in 50 mL of Et2O and added dropwise to a suspension of 0.49 g (12.45 mmol) of KH in 50 mL of Et2O. During the addition the KH slowly disappeared and the reaction mixture became transparent. This solution was added to a suspension of 1.16 g (4.15 mmol) of anhydrous YbCl3 in 50 mL of Et2O at ambient temperature. After the solution was stirred overnight, the solvent was removed, the product was extracted with hexane, and after filtration, the obtained yellow solution was evaporated. The residue was redissolved in 20 mL of toluene and the volume gradually reduced until precipitation set in. X-ray-suitable, air-stable yellow crystals were grown from toluene solution at ambient temperature. Prior to mounting in the X-ray beam, the yellow solid was washed with a small amount of cold toluene. Yield, 2.63 g (75%); mp ) 120 °C. Sublimation conditions: 160-170 °C/10-4 Torr. MS (EI, 70 eV, m/z, 185 °C): 846 [M+], 789, 623, 523, 398, 366, 297 168. IR [Nujol, cm-1]: 2940, 2867, 1570, 1556, 1481, 1419, 1348, 1270, 1222, 1156, 1108, 1054, 1028, 914, 879, 843, 817, 787, 707, 620, 593, 511, 491, 453, 411. Anal. Calcd for C42H78Yb1N3O3: C, 59.61; H, 9.29. Found: C, 59.24; H, 9.46. Acknowledgment. DARPA’s financial support and Dr. Z. J. Zhang’s aid with magnetic measurements are appreciated. W.S.R. was the recipient of an Alexander von Humboldt Award during 1998-1999 with Professor Dr. H. Schumann at the Technische Universita¨t Berlin. Supporting Information Available: Listings of atomic coordinates, anisotropic displacement parameters, full interatomic angles and bond distances, physical measurements, and a plot of µeff vs T. This material is available free of charge via the Internet at http://pubs.acs.org.
IC000203O (17) Single-crystal X-ray analysis of 1 was performed utilizing a Siemens SMART CCD diffractometer at 173 K. Crystal data: Yb1N3O3C42H78, Mr ) 846.11 g mol-1, irregularly shaped yellow, transparent crystal, dimensions 0.25 mm × 0.30 mm × 0.35 mm, triclinic, space group P1h, a ) 10.4591(2) Å, b ) 12.8775(3) Å, c ) 18.3311(3) Å, R ) 100.5610(10)°, β ) 92.6470(10)°, χ ) 110.48°; V ) 2257.42(8) Å3, Z ) 2, Fcalcd ) 1.245 g cm-3, µ ) 2.108 mm-1, F(000) ) 890, 1.14 < φ < 23.23°, -11 < h < 11, -7 < k < 14, -20 < l < 20, R1 ) 0.0182, wR2 ) 0.0502, GOF ) 1.106 for 488 parameters, largest diffr peak and hole ) 0.708 and -0.497 e Å-3. (18) Shin, H.-K.; Hampden-Smith, M. J.; Kodas, T. T.; Rheingold, A. L. J. Chem. Soc., Chem. Commun. 1992, 217.
