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The space between: Neutron diffraction studies reveal multiple hydrogen atom coordination numbers in an anionic dysprosium hydride cluster
Inorganica Chimica Acta 363 (2010) 562–566
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Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
The space between: Neutron diffraction studies reveal multiple hydrogen atom coordination numbers in an anionic dysprosium hydride cluster Timothy Stewart a,*, Masayoshi Nishiura b, Yosuke Konno b, Zhaomin Hou b, Garry J. McIntyre c, Robert Bau a a
Department of Chemistry, University of Southern California, 3620 McClintock Ave., SGM 418, Los Angeles, CA 90089-1062, USA Organometallic Chemistry Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan c Institut Laue-Langevin, 6 rue Jules Horowitz, BP156, 38042 Grenobl, Cedex 9, France b
a r t i c l e
i n f o
Article history: Received 31 October 2008 Received in revised form 12 March 2009 Accepted 22 March 2009 Available online 28 March 2009 Dedicated to Prof. Paul S. Pregosin. Keywords: Single-crystal neutron diffraction structures Four-coordinate hydrogen atom Multiple hydride coordination numbers
a b s t r a c t Our single-crystal neutron diffraction results unambiguously reveal a four-coordinate H atom located in the center of a soluble organometallic tetrahedral complex [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8]. The core of the molecule consists of a tetranuclear cluster with one interstitial, two face-bridging and five edge-bridging hydride ligands. The 0 four Dy–H distances to the interstitial hydride ligand are 2.249(9), 2.255(9), 2.157(12) and 2.160(12) A Å. The compound was prepared via the reaction of [(C5Me4SiMe3)4Dy4(l-H)8(THF)2] with LiCl. Neutron data collected on a 3 mm3 pale-yellow single crystal on the Quasi-Laue diffractometer VIVALDI at I.L.L. (Grenoble) which gave an agreement factor R = 10.1% in the final structure refinement against 6947 reflections. The existence of a four-coordinate hydrogen reinforces previous results observed with a series of high-connectivity hydride ligands located at the interstitial cavities of molecular clusters. Interestingly, this structure allows us to analyze simultaneously three different types of hydride coordination in the same molecule (M2(l2-H), M3(l3-H), and M4(l4-H)). Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction For many years our group and others have utilized single-crystal neutron diffraction to characterize accurately hydride ligands; in particular, hydrogen atoms which are positioned interstitially within heavy-metal lattices. The phenomenon of hydrogen atoms occupying vacant interstitial sites has led to extraordinary coordination numbers (e.g. 2, 3, 4, 5 and 6) [1–6]. Neutron diffraction has greatly improved our ability to characterize accurately hydrogen atoms in the presence of heavy metals which is an infamously weak aspect of X-ray diffraction. Recently reported by our group was a four coordinate hydride ligand (l4-H) in a [Y4H8[C5Me4(SiMe3)]4(THF)] metal complex [3]. Those findings completed a long standing goal to characterize a series of multiple-bonded hydride ligands in an organometallic compound. Curiously, upon refinement of the [Y4H8[C5Me4 (SiMe3)]4(THF)] structure we located further types of H linkage (l2-H and l3-H) in the same molecule in addition to the targeted interstitial (l4-H). We had previously noted that there appears to be a relationship between the number of metal atoms surrounding a hydrogen atom and its corresponding metal (M)–H distance: since there is a decrease in bond order due to the coordination number of hydrogen increasing, the overall M–H distance increases accordingly. This was true in the cases where there is exclusively one type * Corresponding author. Tel.: +1 208 724 9032. E-mail address: [email protected] (T. Stewart). 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.03.024
of linkage in the compound. Introducing different types of linkages in the same molecule disrupts the previously observed M–H bond length trends. Our study set out to elucidate whether this phenomenon was an anomaly of the particular compound or whether it is reproducible in another complex. In 2003, Hou and co-workers proposed the idea of multiple H coordination in the same molecule using X-ray diffraction [7]. They reported the synthesis and X-ray structures of two organolanthanide complexes (the non-solvate form [(C5Me4SiMe3)Lu(l-H)2]4 and the solvated [(C5Me4SiMe3)Lu(l-H)2]4(THF). Although X-ray diffraction is not an accurate technique for such compounds, the hydride atoms near the Lu tetrahedral cluster were located by difference Fourier synthesis and the coordinates and isotropic parameters were allowed to vary in the least-squares refinement (SHELX-97). The remaining hydrogen atoms were placed at the calculated positions appropriate to a riding model. Hou and co-workers’ structural characterization demonstrates three distinct hydride metal bond types in the same molecule. Later on, the analogous yttrium complexes [(C5Me4SiMe3)Y(l-H)2]4 and [(C5Me4SiMe3)Y(lH)2]4(THF) were also reported [8,9]. Our recent publication [3] was the first neutron study to characterize accurately multiple hydride coordinations in the same molecule containing the [(C5Me4SiMe3)4Y4H8](THF) complex. Reported here is a neutron diffraction study on such metal hydride bondings in an anionic dysprosium hydride cluster [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(lH)8], and is the second known study of this type with similarly convincing results.
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2. Experimental 2.1. Preparation of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] The title complex [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was prepared from the neutral compound [(C5Me4SiMe3)4Dy4(l-H)8(THF)2] [10]. To a THF solution (1.0 mL) of [(C5Me4SiMe3)4Dy4(l-H)8(THF)2] (49.4 mg, 0.0313 mmol) was added a THF solution (1.0 mL) of LiCl (1.3 mg, 0.0313 mmol). The colorless solution was stirred at room temperature for 1 h. After removal of the solvent under vacuum, the resulting white residue was dissolved in THF (0.3 mL). Hexane (1.5 mL) was carefully layered on the solution. Crystals were obtained after the mixture was cooled to 30 °C and kept at this temperature overnight to give pale-yellow crystals of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] (38.3 mg, 0.0217 mmol, 69%), some of which were of size and forms suitable for X-ray and neutron diffraction studies. The 1H NMR of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was not informative because of the influence of the paramagnetic Dy(III) ion. Anal. Calc. for C64H124Cl1Dy4Li1O4Si4: C, 43.62; H, 7.09. Found: C, 43.36; H, 6.91%. To delay crystalline decomposition, the single-crystal samples were stored in an inert (Ar) atmosphere in separate quartz glass ampoules. 2.2. X-ray and neutron diffraction studies X-ray analysis on the title compound [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was carried out at 150 K on a SMART APEX CCD diffractometer using fine-focused graphite-monochromated Mo 0 A). The crystal sample was selected unKa radiation (k = 0.71073 Å der streaming nitrogen gas and flash frozen into a nylon loop bathed in mineral oil at the end of a copper pin. The cell parameters for [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] were obtained from the least-squares refinement of the spots (from 60 collected frames) using the SMART program of a rhombohedral pale-yellow single-crystal sample measuring 0.20 0.08 0.05 mm3 in size. 0 A hemisphere of data were collected up to a resolution of 0.77 Å A, the intensity data were processed using the Saint Plus program. All calculations for the structure determination were carried out using the SHELXTL package (version 6.14) [11]. Initial atomic positions were located direct methods and refined by least square using SHELX with 16 519 independent reflections and within the h
range 1.27–26.73° (completeness 99.6%). Empirical absorption corrections were applied by SADABS [12]. Calculated hydrogen positions were input and refined as riding the corresponding carbon atoms. A summary of the refinement details and the resulting agreement factors are given in Table 1. Final X-ray structure refinement for [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] results in Rint = 6.7%, R1 = 4.8% and wR2 = 8.9%. Data to parameter ratio = 22:1. The crystal system is monoclinic with space group P20 1/n, Z = 4 0 and unit-cell dimensions are: 0 A, c = 19.03 Å A and b = 91.2180(10)°. a = 13.86 Å A, b = 29.57 Å Neutron analysis on the title compound [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was carried out at two temperatures, 150 and 10 K on the Very-Intense Vertical-Axis Laue Diffractometer Instrument (VIVALDI) at the Institut Laue-Langevin. The sample was mounted in an inert-argon atmosphere, the pale-yellow rhombohedral shaped single-crystal sample of dimensions 3.25 1.25 0.75 mm3 rested alone at the bottom of a sealed 4 mm diameter quartz glass ampoule. This sample, which is normal size (3 mm3) for neutron studies, was then mounted in a He cryostat on VIVALDI and analyzed with the intense neutron source at ILL. VIVALDI uses an unconventional quasi-Laue geometry for data collection [13]. In this technique the sample is bathed in the full waveband of un-monochromated thermal neutron beam. In addition the diffraction data were recorded using a cylindrical area detector made from Gd2O3-doped BAFBR:Eu2+ image plates and which subtends eight sterad at the sample position [14a]. The combination of the high flux at the sample position and the large-solid angle detector gives a gain in data-collection efficiency of one to two orders of magnitude over conventional monochromatic diffractometers at the same source. At 150 K, a total of 15 Laue diffraction patterns, each accumulated over 2 h were collected at 20° intervals in rotation of the crystal about the vertical detector axis. At 10 K a total number of 13 Laue diffraction patterns, each accumulated over 3 h, were collected, again at 20° rotational intervals. These patterns were indexed using the program LAUEGEN from the Daresbury Laboratory Suite [14b,c] and the reflections were integrated and the background subtracted using the INTEGRATE+, which uses a twodimensional version of the minimum r(I)/I algorithm [14d]. The reflections were normalized to a common incident wavelength, using a curve derived by comparing equivalent reflections and multiple observations via the program LAUENORM [14e].
Table 1 Experimental details for the X-ray and neutron diffraction studies of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8]. See text for discusson of the unit-cell parameters. Empirical formula Source Formula weight Crystal system Z Unit-cell parameters 0 a (Å A0 ) b (Å A0 ) c (Å A) b (°) 0 Volume (Å A3) Temperature (K) 3 ) Crystal size (mm 0 Wavelength (Å A) Data collection time (h) h range (°) Number of reflections Number of unique reflections Number of parameters refined Goodness of fit (GOF) Number of reflections (>4r) Final agreement factors (I > 2r data)
C64H124ClDy4LiO4Si4 X-ray 1752.3 monoclinic, P21/n 4
C64H124ClDy4LiO4Si4 neutron 1754.0 monoclinic, P21/n 4
C64H124ClDy4LiO4Si4 neutron 1754.0 monoclinic, P21/n 4
13.8656(8) 29.5705(17) 19.0368(11) 91.2180(10) 7803.6(8) 150(4) 0.20 0.08 0.05 0.71073 6 1.27–26.73 46 418 16 519 731 0.976 13 042 R1 = 0.0352 wR2 = 0.0891
14.5850(8) 30.2000(17) 19.2870(11) 91.4850 7803.6 150(2) 3.25 1.25 0.75 1.1–2.5 30 1.62–72.00 42 117 6023 1239 1.105 4357 R1 = 0.1302 wR2 = 0.3341
14.5900(8) 29.9700(17) 19.3100(11) 91.260 7803.6 10(2) 3.25 1.25 0.75 1.1–2.5 39 1.62–72.00 57 042 11 343 1819 1.115 6947 R1 = 0.1011 wR2 = 0.2315
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Fig. 1. Molecular structure of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] by neutron diffraction analysis at 10 K. All hydrogen atoms have been omitted for clarity.
Normalization will correct for most small absorption variations arising from the sample shape. Reflections were observed with 0 wavelengths between 1.0 and 3.5 0Å A but only reflections with wavelengths between 1.1 and 2.5 Å A were accepted for scaling, those outside the range were too weak or had too few equivalents to determine the normalization curve with confidence. At 150 K, 42 229 reflections were observed, of which 6023 are unique. At 10 K, 57 133 reflections were observed, of which 28 384 were single reflections with wavelengths between 0.8 0 and 2.6 Å A, to yield 11 343 unique reflections, of those 6947 are 78% of the unique data for d spacing greater than 4r leaving 0 greater than 1.04 Å A, The merged reflections were phased with the isotropic/non-hydrogen positions from the X-ray analysis. The title complex, [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8], crystallizes in space group P21/n with one independent anion/ cation pair in 0 the asymmetric 0unit-cell and has0 the parameters: A, c = 19.287(1) Å A, b = 91.485(1)°. a = 14.585(1) Å A, b = 30.200(1) Å Recall that initially from the X-ray analysis the position of hydride ligands were not constrained in the studies. However, in the present neutron analysis hydrogen atoms appear as negative peaks in the difference Fourier maps. Hydride ligands were found to be on the cluster surfaces at the edge and face bridging sites in addition to the four-coordinated interstitial position. All other H atoms in the 150 and 10 K data sets (116 hydrogen atoms of the C–H groups) were also unambiguously located in this manner. The positional and anisotropic thermal displacement parameters for all atoms in the 10 K data asymmetric unit were refined by a full matrix least-squares procedure [15]. All atoms in the 10 K data set behaved well under anisotropic refinement with a data to parameter ratio 6:1. The refinement successfully converged to give the following agreement factors: R(F) = 10.1% for all 6947 reflections with I > 4r(I), and R(F) = 20.5% for all data. In particular, the Dy4H8Cl core of both 150 and 10 K data sets were anisotropically well behaved with average thermal parameter values of U(aniso) = 0.0037(1) and 0 0.0278(1) Å A2 for the dysprosium and hydrogen atoms, respectively. A summary of the crystal data and refinement parameters is given in Table 1. The overall anion/cation structure is shown in Fig. 1, where all hydrogen atoms have been excluded for clarity. During structural analysis few ill-behaved atoms arose. Some low-level restraints were applied in the early refinements, but all
restraints were released in the final least-squares refinement. Also, only the temperature dependent ratios between the linear unit-cell parameters can be determined in the Laue method. In the analysis of the 150 K neutron data we assumed the X-ray values at the same temperature; in the analysis of the 10 K
Fig. 2. ORTEP plot of the core [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] (figure derived from 10 K results; thermal ellipsoids drawn at 50% probability).
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neutron data these were reduced by 1% to account for the likely thermal contraction.
Table 2 Select key distances and angles in the [Dy4H8Cl] core from 150 and 10 K neutron refinements. The population deviations of the averages are given in parentheses. 150 K
10 K
Bond lengths (Å) Dy–Dy distances Dy(1)–Dy(2) Dy(1)–Dy(3) Dy(1)–Dy(4) Dy(2)–Dy(3) Dy(2)–Dy(4) Dy(3)–Dy(4) Average
3.335(5) 3.554(5) 3.586(5) 3.581(5) 3.597(5) 3.856(5) 3.585
3.310(2) 3.532(2) 3.542(2) 3.549(2) 3.527(2) 3.913(2) 3.562
Dy–Cl distances Dy(3)–Cl(1) Dy(4)–Cl(1) Average
2.803(9) 2.793(9) 2.798
2.778(4) 2.784(2) 2.781
Dy–H (central) distances Dy(1)–H(1) Dy(2)–H(1) Dy(3)–H(1) Dy(4)–H(1) Average
2.264(18) 2.309(19) 2.111(21) 2.187(22) 2.218
2.249(9) 2.255(9) 2.158(12) 2.160(12) 2.205
Dy–H (face-bridging) distances Dy(1)–H(2) Dy(2)–H(2) Dy(3)–H(2) Dy(1)–H(3) Dy(2)–H(3) Dy(4)–H(3) Average
2.442(2) 2.421(2) 2.289(20) 2.429(21) 2.420(22) 2.346(18) 2.391
2.452(11) 2.400(12) 2.228(9) 2.424(11) 2.387(12) 2.282(10) 2.362
Dy–H (edge-bridging) distances Dy(1)–H(4) Dy(2)–H(4) Dy(1)–H(5) Dy(3)–H(5) Dy(1)–H(6) Dy(4)–H(6) Dy(2)–H(7) Dy(3)–H(7) Dy(2)–H(8) Dy(4)–H(8) Average
2.255(19) 2.221(22) 2.232(19) 2.190(22) 2.284(20) 2.160(20) 2.263(24) 2.173(20) 2.254(28) 2.162(22) 2.219
2.209(10) 2.188(9) 2.236(11) 2.148(10) 2.248(10) 2.189(9) 2.254(12) 2.210(9) 2.233(10) 2.161(11) 2.208
Selected bond angles (°) Core-bridging Dy(1)–H(1)–Dy(2) Dy(1)–H(1)–Dy(3) Dy(1)–H(1)–Dy(4) Dy(2)–H(1)–Dy(3) Dy(2)–H(1)–Dy(4) Dy(3)–H(1)–Dy(4) Average
93.6(7) 108.6(9) 107.3(9) 108.2(9) 106.3(8) 127.6(9) 108.6
94.6(4) 106.5(5) 106.9(5) 107.1(5) 106.1(5) 130.0(5) 108.5
Face-bridging Dy(1)–H(2)–Dy(2) Dy(1)–H(2)–Dy(3) Dy(2)–H(2)–Dy(3) Average
86.6(9) 97.4(9) 99.1(9) 94.4
86.0(4) 97.9(4) 100.1(4) 94.7
Dy(1)–H(3)–Dy(2) Dy(1)–H(3)–Dy(4) Dy(2)–H(3)–Dy(4) Average
86.9(8) 97.4(7) 98.0(8) 94.1
86.9(4) 97.6(4) 98.1(4) 94.2
96.4(7) 107.0(9) 107.6(8) 107.7(8) 109.1(11) 105.5 87.1(2)
97.7(4) 107.3(4) 106.0(4) 105.3(5) 106.8(5) 104.6 89.4(11)
Edge-bridging Dy(1)–H(4)–Dy(2) Dy(1)–H(5)–Dy(3) Dy(1)–H(6)–Dy(4) Dy(2)–H(7)–Dy(3) Dy(3)–H(8)–Dy(4) Average Dy(3)–Cl(1)–Dy(3)
3. Results and discussion We have collected two neutron data sets at different temperatures (150 and 10 K) on the same crystal sample with VIVALDI. The 10 K data set result gave a lower final agreement factor then the 150 K data set; due in part to the larger number of unique reflections measured. Despite the differences in agreement factors, the final results for the two temperatures, especially those results concerning the central Dy4H8Cl core (Fig. 2), are remarkably consistent. Table 2 lists the distance and angles in the Dy4H8Cl cores from the two neutron structural determinations. The rational for carrying out the present neutron study was to locate a four-coordinate hydrogen atom interstitially in an anionic tetrahedral dysprosium metal cluster. Our neutron data analysis has revealed that in addition to the four-coordinate hydrogen atom, the Dy4H8Cl core contains one edge-bridging chloride, two face-bridging hydrides and five edge-bridging hydrides. The interstitial hydrogen atom is bonded to the four dyspro0 sium atoms, giving an average Dy–H distance of 2.205(3) Å A (Table 2). The individual angles are, as expected, close to the ideal tetrahedral angle of 109°. The cluster is however slightly distorted from ideal tetrahedral symmetry because of the presence of a chloride atom bridging Dy(3) to Dy(4), a motif which is absent from the remaining Dy atoms in the cluster. The most obvious manifestation of the lowered symmetry is the presence of the two unique facebridging hydrogen atoms H(2) and H(3), which lie above the Dy(1)–Dy(2)–Dy(4) and Dy(1)–Dy(2)–Dy(3) faces of the tetrahedron, respectively, but which is absent from other faces of the cluster. Other, less pronounced manifestations of slightly lowered symmetry are the fact that the Dy(3)–Dy(4) distance, which involves the edge-bridging chloride atom is longer than the Dy(1)–Dy(2) distance (Table 2), thus giving a concomitant larger interstitial Dy(3)–H(1)–Dy(4) angle compared to the Dy(1)–H(1)– Dy(2) angle. In the past, neutron diffraction studies have shown a relationship between the number of metal atoms surrounding a hydrogen atom and its corresponding M–H distance [16]. In these studies the hydride–metal bond distance increases systematically with each addition of metal atom coordination. However, in each structural M–H example each molecule possessed only one type of hydrogen atom coordination [17–19]. Very recently, we found that in the tetrahedral yttrium complex [(C5Me4SiMe3)4Y4(lH)2]4(THF), which possesses three different types of linkages in the same compound: Y2(l2-H), Y3(l3-H), and Y4(l4-H) metal– hydride bonds, the relation between the M–H bond distance and the coordination number is not that straightforward [3]. There is the usual bond length increase as one goes from edgebridging to face-bridging (Y2(l2-H) to Y3(l3-H)), but there is a
Table 3 Key similar average bond lengths between [((C5Me4SiMe3)YH2)4](THF), the first reported tetrahedral cluster with one interstitial, one face-bridging, and six edgebridging hydride ligands and our current [Li(THF)4][(C5Me4SiMe3)4Dy4H8Cl] organometallic cluster with one interstitial, two face-bridging and five edge-bridging hydrides. [((C5Me4SiMe3)YH2)4] (THF)
[Li(THF)4] [(C5Me4SiMe3)4Dy4H8Cl]
Average bond lengths (Å) M–M distances M–M M–(TFH), M–Cl–M
3.459 3.693
3.563 3.781
M–H (central) M–H (face-bridging) M–H (edge-bridging)
2.197 2.344 2.166
2.205 2.362 2.208
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decrease in bond length in the next bonding type, Y3((l3-H) to Y4((l4-H)). Until now, this is the first example of its kind to (a) demonstrate accurately the existence of a four-coordinate hydrogen atom in a soluble organometallic hydride and (b) compare the tightness of the tetrahedral cavity for different metal-coordinated hydride atoms in the same molecule. In our current neutron study on the anionic dysprosium cluster, we observed analogous bonding trends [3]. A comparison of lengths is given in Table 3. The usual (as expected) increase in 0 bond length is A] to Dy3(l3-H) observed0 as one goes from Dy2(l2-H) [2.20(1) Å actually decreases in0 the next [2.36(1) Å A], then, the Dy–H distance 0 A] to Dy4(l4-H) [2.21(5) Å A], due to step, from Dy3(l3-H) [2.36(1) Å the tightness of the tetrahedral cavity. This idea was first proposed in our previous work. In our current work we observe analogous trends as before with different hydrogen atom coordination numbers but we also notice the lengths and angles are almost identical. This is, in part, most likely a result of dysprosium’s 0 0 A) [20]. similar covalent radius (1.59 Å A) to yttrium (1.62 Å Acknowledgment This work was supported by the American Chemical Society (Grant PRF-40715-AC3). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2009.03.024. References [1] F. Lutz, R. Bau, P. Wu, T.F. Koetzle, C. Krueger, J.J. Schneider, Inorg. Chem. 35 (1996) 2698. [2] R.G. Teller, R.D. Wilson, R.K. McMullan, T.F. Koetzle, R. Bau, J. Am. Chem. Soc. 100 (1978) 3071.
[3] M. Yousufuddin, J. Baldamus, O. Tardif, Z. Hou, S.A. Mason, G.J. McIntyre, R. Bau, J. Am. Chem. Soc. 130 (2008) 3888. [4] R. Bau, M.H. Drabnis, L. Garlaschelli, W.T. Klooster, Z. Xie, T.F. Koetzle, S. Martinengo, Science 275 (1997) 1099. [5] (a) D.W. Hart, R.G. Teller, C.Y. Wei, R. Bau, G. Longoni, S. Campanella, P. Chini, T.F. Koetzle, Angew. Chem., Int. Ed. Engl. 18 (1978) 80; (b) D.W. Hart, R.G. Teller, C.Y. Wei, R. Bau, G. Longoni, S. Campanella, P. Chini, T.F. Koetzle, J. Am. Chem. Soc. 103 (1981) 1458. [6] P.F. Jackson, B.F.G. Johnson, J. Lewis, P.R. Raithby, M. McPartlin, W.J.H. Nelson, K.D. Rouse, J. Allibon, S.A. Mason, J. Chem. Soc., Chem. Commun. 7 (1980) 295. [7] O. Tardif, M. Nishiura, Z. Hou, Organometallics 22 (6) (2003) 1171. [8] D. Cui, O. Tardif, Z. Hou, J. Am. Chem. Soc. Commun. 126 (5) (2004) 1312. [9] Y. Luo, J. Baldamus, O. Tardif, Z. Hou, Organometallics 24 (18) (2005) 4362. [10] D. Cui, M. Nishiura, Z. Hou, Macromolecules 38 (2005) 4089. [11] G.M. Sheldrick, SHELXTL, Version 6.14, Bruker Analytical X-ray System Inc., Madison, WI, 1997. [12] R.H. Blessing, Acta Crystallogr. A51 (1995) 33. [13] C. Wilkinson, J.A. Cowan, D.A.A. Myles, F. Cipriani, G.J. McIntyre, Neutron News 13 (2002) 37. [14] (a) F. Capriani, J.C. Castsgna, M.S. Lehmann, C. Wilkinson, Physica B 213 (1995) 975; (b) J.W. Campbell, J. Appl. Crystallogr. 28 (1995) 228; (c) J.W. Campbell, Q. Hao, M.M. Harding, N.D. Nguti, C. Wilkinson, J. Appl. Crystallogr. 31 (1998) 23; (d) C. Wilkinson, H.W. Khamis, R.F.D. Stansfield, G.J. McIntyre, J. Appl Crystallogr. 21 (1988) 471; (e) J.W. Campbell, J. Habash, J.R. Helliwell, K. Moffat, Information Quarterly of Protein Crystallography, vol. 18, SERC Daresbury Laboratory, Warrington, England, 1988. [15] G.M. Sheldrick, SHELX-97, A Computer Program for the Refinement of Crystal Structures, University of Göttingen, Göttingen, Germany, 1997. [16] R. Bau, M.H. Dradnis, L. Garlaschelli, W.T. Klooster, Z. Xie, T.F. Koetzle, S. Martinengo, Science 275 (1997) 1099. [17] D. Hanke, K. Wieghardt, B. Nuber, R.S. Lu, E.L. McMullan, T.F. Koetzle, R. Bau, Inorg. Chem. 32 (1993) 4300. [18] R.K. Brown, J.M. Williams, A.J. Sivak, E.L. Muetterties, Inorg. Chem. 19 (1980) 370. [19] J.S. Ricci, T.F. Koetzle, R.J. Goodfellow, P. Espinet, P.M. Maitlis, Inorg. Chem. 23 (1984) 1828. [20] K. Barbalace, Periodic Table of Elements – Dysprosium – Dy. EnvironmentalChemistry.com, 1995–2008. (accessed 10.08.08).
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The space between: Neutron diffraction studies reveal multiple hydrogen atom coordination numbers in an anionic dysprosium hydride cluster Timothy Stewart a,*, Masayoshi Nishiura b, Yosuke Konno b, Zhaomin Hou b, Garry J. McIntyre c, Robert Bau a a
Department of Chemistry, University of Southern California, 3620 McClintock Ave., SGM 418, Los Angeles, CA 90089-1062, USA Organometallic Chemistry Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan c Institut Laue-Langevin, 6 rue Jules Horowitz, BP156, 38042 Grenobl, Cedex 9, France b
a r t i c l e
i n f o
Article history: Received 31 October 2008 Received in revised form 12 March 2009 Accepted 22 March 2009 Available online 28 March 2009 Dedicated to Prof. Paul S. Pregosin. Keywords: Single-crystal neutron diffraction structures Four-coordinate hydrogen atom Multiple hydride coordination numbers
a b s t r a c t Our single-crystal neutron diffraction results unambiguously reveal a four-coordinate H atom located in the center of a soluble organometallic tetrahedral complex [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8]. The core of the molecule consists of a tetranuclear cluster with one interstitial, two face-bridging and five edge-bridging hydride ligands. The 0 four Dy–H distances to the interstitial hydride ligand are 2.249(9), 2.255(9), 2.157(12) and 2.160(12) A Å. The compound was prepared via the reaction of [(C5Me4SiMe3)4Dy4(l-H)8(THF)2] with LiCl. Neutron data collected on a 3 mm3 pale-yellow single crystal on the Quasi-Laue diffractometer VIVALDI at I.L.L. (Grenoble) which gave an agreement factor R = 10.1% in the final structure refinement against 6947 reflections. The existence of a four-coordinate hydrogen reinforces previous results observed with a series of high-connectivity hydride ligands located at the interstitial cavities of molecular clusters. Interestingly, this structure allows us to analyze simultaneously three different types of hydride coordination in the same molecule (M2(l2-H), M3(l3-H), and M4(l4-H)). Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction For many years our group and others have utilized single-crystal neutron diffraction to characterize accurately hydride ligands; in particular, hydrogen atoms which are positioned interstitially within heavy-metal lattices. The phenomenon of hydrogen atoms occupying vacant interstitial sites has led to extraordinary coordination numbers (e.g. 2, 3, 4, 5 and 6) [1–6]. Neutron diffraction has greatly improved our ability to characterize accurately hydrogen atoms in the presence of heavy metals which is an infamously weak aspect of X-ray diffraction. Recently reported by our group was a four coordinate hydride ligand (l4-H) in a [Y4H8[C5Me4(SiMe3)]4(THF)] metal complex [3]. Those findings completed a long standing goal to characterize a series of multiple-bonded hydride ligands in an organometallic compound. Curiously, upon refinement of the [Y4H8[C5Me4 (SiMe3)]4(THF)] structure we located further types of H linkage (l2-H and l3-H) in the same molecule in addition to the targeted interstitial (l4-H). We had previously noted that there appears to be a relationship between the number of metal atoms surrounding a hydrogen atom and its corresponding metal (M)–H distance: since there is a decrease in bond order due to the coordination number of hydrogen increasing, the overall M–H distance increases accordingly. This was true in the cases where there is exclusively one type * Corresponding author. Tel.: +1 208 724 9032. E-mail address: [email protected] (T. Stewart). 0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2009.03.024
of linkage in the compound. Introducing different types of linkages in the same molecule disrupts the previously observed M–H bond length trends. Our study set out to elucidate whether this phenomenon was an anomaly of the particular compound or whether it is reproducible in another complex. In 2003, Hou and co-workers proposed the idea of multiple H coordination in the same molecule using X-ray diffraction [7]. They reported the synthesis and X-ray structures of two organolanthanide complexes (the non-solvate form [(C5Me4SiMe3)Lu(l-H)2]4 and the solvated [(C5Me4SiMe3)Lu(l-H)2]4(THF). Although X-ray diffraction is not an accurate technique for such compounds, the hydride atoms near the Lu tetrahedral cluster were located by difference Fourier synthesis and the coordinates and isotropic parameters were allowed to vary in the least-squares refinement (SHELX-97). The remaining hydrogen atoms were placed at the calculated positions appropriate to a riding model. Hou and co-workers’ structural characterization demonstrates three distinct hydride metal bond types in the same molecule. Later on, the analogous yttrium complexes [(C5Me4SiMe3)Y(l-H)2]4 and [(C5Me4SiMe3)Y(lH)2]4(THF) were also reported [8,9]. Our recent publication [3] was the first neutron study to characterize accurately multiple hydride coordinations in the same molecule containing the [(C5Me4SiMe3)4Y4H8](THF) complex. Reported here is a neutron diffraction study on such metal hydride bondings in an anionic dysprosium hydride cluster [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(lH)8], and is the second known study of this type with similarly convincing results.
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2. Experimental 2.1. Preparation of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] The title complex [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was prepared from the neutral compound [(C5Me4SiMe3)4Dy4(l-H)8(THF)2] [10]. To a THF solution (1.0 mL) of [(C5Me4SiMe3)4Dy4(l-H)8(THF)2] (49.4 mg, 0.0313 mmol) was added a THF solution (1.0 mL) of LiCl (1.3 mg, 0.0313 mmol). The colorless solution was stirred at room temperature for 1 h. After removal of the solvent under vacuum, the resulting white residue was dissolved in THF (0.3 mL). Hexane (1.5 mL) was carefully layered on the solution. Crystals were obtained after the mixture was cooled to 30 °C and kept at this temperature overnight to give pale-yellow crystals of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] (38.3 mg, 0.0217 mmol, 69%), some of which were of size and forms suitable for X-ray and neutron diffraction studies. The 1H NMR of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was not informative because of the influence of the paramagnetic Dy(III) ion. Anal. Calc. for C64H124Cl1Dy4Li1O4Si4: C, 43.62; H, 7.09. Found: C, 43.36; H, 6.91%. To delay crystalline decomposition, the single-crystal samples were stored in an inert (Ar) atmosphere in separate quartz glass ampoules. 2.2. X-ray and neutron diffraction studies X-ray analysis on the title compound [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was carried out at 150 K on a SMART APEX CCD diffractometer using fine-focused graphite-monochromated Mo 0 A). The crystal sample was selected unKa radiation (k = 0.71073 Å der streaming nitrogen gas and flash frozen into a nylon loop bathed in mineral oil at the end of a copper pin. The cell parameters for [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] were obtained from the least-squares refinement of the spots (from 60 collected frames) using the SMART program of a rhombohedral pale-yellow single-crystal sample measuring 0.20 0.08 0.05 mm3 in size. 0 A hemisphere of data were collected up to a resolution of 0.77 Å A, the intensity data were processed using the Saint Plus program. All calculations for the structure determination were carried out using the SHELXTL package (version 6.14) [11]. Initial atomic positions were located direct methods and refined by least square using SHELX with 16 519 independent reflections and within the h
range 1.27–26.73° (completeness 99.6%). Empirical absorption corrections were applied by SADABS [12]. Calculated hydrogen positions were input and refined as riding the corresponding carbon atoms. A summary of the refinement details and the resulting agreement factors are given in Table 1. Final X-ray structure refinement for [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] results in Rint = 6.7%, R1 = 4.8% and wR2 = 8.9%. Data to parameter ratio = 22:1. The crystal system is monoclinic with space group P20 1/n, Z = 4 0 and unit-cell dimensions are: 0 A, c = 19.03 Å A and b = 91.2180(10)°. a = 13.86 Å A, b = 29.57 Å Neutron analysis on the title compound [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] was carried out at two temperatures, 150 and 10 K on the Very-Intense Vertical-Axis Laue Diffractometer Instrument (VIVALDI) at the Institut Laue-Langevin. The sample was mounted in an inert-argon atmosphere, the pale-yellow rhombohedral shaped single-crystal sample of dimensions 3.25 1.25 0.75 mm3 rested alone at the bottom of a sealed 4 mm diameter quartz glass ampoule. This sample, which is normal size (3 mm3) for neutron studies, was then mounted in a He cryostat on VIVALDI and analyzed with the intense neutron source at ILL. VIVALDI uses an unconventional quasi-Laue geometry for data collection [13]. In this technique the sample is bathed in the full waveband of un-monochromated thermal neutron beam. In addition the diffraction data were recorded using a cylindrical area detector made from Gd2O3-doped BAFBR:Eu2+ image plates and which subtends eight sterad at the sample position [14a]. The combination of the high flux at the sample position and the large-solid angle detector gives a gain in data-collection efficiency of one to two orders of magnitude over conventional monochromatic diffractometers at the same source. At 150 K, a total of 15 Laue diffraction patterns, each accumulated over 2 h were collected at 20° intervals in rotation of the crystal about the vertical detector axis. At 10 K a total number of 13 Laue diffraction patterns, each accumulated over 3 h, were collected, again at 20° rotational intervals. These patterns were indexed using the program LAUEGEN from the Daresbury Laboratory Suite [14b,c] and the reflections were integrated and the background subtracted using the INTEGRATE+, which uses a twodimensional version of the minimum r(I)/I algorithm [14d]. The reflections were normalized to a common incident wavelength, using a curve derived by comparing equivalent reflections and multiple observations via the program LAUENORM [14e].
Table 1 Experimental details for the X-ray and neutron diffraction studies of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8]. See text for discusson of the unit-cell parameters. Empirical formula Source Formula weight Crystal system Z Unit-cell parameters 0 a (Å A0 ) b (Å A0 ) c (Å A) b (°) 0 Volume (Å A3) Temperature (K) 3 ) Crystal size (mm 0 Wavelength (Å A) Data collection time (h) h range (°) Number of reflections Number of unique reflections Number of parameters refined Goodness of fit (GOF) Number of reflections (>4r) Final agreement factors (I > 2r data)
C64H124ClDy4LiO4Si4 X-ray 1752.3 monoclinic, P21/n 4
C64H124ClDy4LiO4Si4 neutron 1754.0 monoclinic, P21/n 4
C64H124ClDy4LiO4Si4 neutron 1754.0 monoclinic, P21/n 4
13.8656(8) 29.5705(17) 19.0368(11) 91.2180(10) 7803.6(8) 150(4) 0.20 0.08 0.05 0.71073 6 1.27–26.73 46 418 16 519 731 0.976 13 042 R1 = 0.0352 wR2 = 0.0891
14.5850(8) 30.2000(17) 19.2870(11) 91.4850 7803.6 150(2) 3.25 1.25 0.75 1.1–2.5 30 1.62–72.00 42 117 6023 1239 1.105 4357 R1 = 0.1302 wR2 = 0.3341
14.5900(8) 29.9700(17) 19.3100(11) 91.260 7803.6 10(2) 3.25 1.25 0.75 1.1–2.5 39 1.62–72.00 57 042 11 343 1819 1.115 6947 R1 = 0.1011 wR2 = 0.2315
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Fig. 1. Molecular structure of [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] by neutron diffraction analysis at 10 K. All hydrogen atoms have been omitted for clarity.
Normalization will correct for most small absorption variations arising from the sample shape. Reflections were observed with 0 wavelengths between 1.0 and 3.5 0Å A but only reflections with wavelengths between 1.1 and 2.5 Å A were accepted for scaling, those outside the range were too weak or had too few equivalents to determine the normalization curve with confidence. At 150 K, 42 229 reflections were observed, of which 6023 are unique. At 10 K, 57 133 reflections were observed, of which 28 384 were single reflections with wavelengths between 0.8 0 and 2.6 Å A, to yield 11 343 unique reflections, of those 6947 are 78% of the unique data for d spacing greater than 4r leaving 0 greater than 1.04 Å A, The merged reflections were phased with the isotropic/non-hydrogen positions from the X-ray analysis. The title complex, [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8], crystallizes in space group P21/n with one independent anion/ cation pair in 0 the asymmetric 0unit-cell and has0 the parameters: A, c = 19.287(1) Å A, b = 91.485(1)°. a = 14.585(1) Å A, b = 30.200(1) Å Recall that initially from the X-ray analysis the position of hydride ligands were not constrained in the studies. However, in the present neutron analysis hydrogen atoms appear as negative peaks in the difference Fourier maps. Hydride ligands were found to be on the cluster surfaces at the edge and face bridging sites in addition to the four-coordinated interstitial position. All other H atoms in the 150 and 10 K data sets (116 hydrogen atoms of the C–H groups) were also unambiguously located in this manner. The positional and anisotropic thermal displacement parameters for all atoms in the 10 K data asymmetric unit were refined by a full matrix least-squares procedure [15]. All atoms in the 10 K data set behaved well under anisotropic refinement with a data to parameter ratio 6:1. The refinement successfully converged to give the following agreement factors: R(F) = 10.1% for all 6947 reflections with I > 4r(I), and R(F) = 20.5% for all data. In particular, the Dy4H8Cl core of both 150 and 10 K data sets were anisotropically well behaved with average thermal parameter values of U(aniso) = 0.0037(1) and 0 0.0278(1) Å A2 for the dysprosium and hydrogen atoms, respectively. A summary of the crystal data and refinement parameters is given in Table 1. The overall anion/cation structure is shown in Fig. 1, where all hydrogen atoms have been excluded for clarity. During structural analysis few ill-behaved atoms arose. Some low-level restraints were applied in the early refinements, but all
restraints were released in the final least-squares refinement. Also, only the temperature dependent ratios between the linear unit-cell parameters can be determined in the Laue method. In the analysis of the 150 K neutron data we assumed the X-ray values at the same temperature; in the analysis of the 10 K
Fig. 2. ORTEP plot of the core [Li(THF)4][(C5Me4SiMe3)4Dy4(l-Cl)(l-H)8] (figure derived from 10 K results; thermal ellipsoids drawn at 50% probability).
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neutron data these were reduced by 1% to account for the likely thermal contraction.
Table 2 Select key distances and angles in the [Dy4H8Cl] core from 150 and 10 K neutron refinements. The population deviations of the averages are given in parentheses. 150 K
10 K
Bond lengths (Å) Dy–Dy distances Dy(1)–Dy(2) Dy(1)–Dy(3) Dy(1)–Dy(4) Dy(2)–Dy(3) Dy(2)–Dy(4) Dy(3)–Dy(4) Average
3.335(5) 3.554(5) 3.586(5) 3.581(5) 3.597(5) 3.856(5) 3.585
3.310(2) 3.532(2) 3.542(2) 3.549(2) 3.527(2) 3.913(2) 3.562
Dy–Cl distances Dy(3)–Cl(1) Dy(4)–Cl(1) Average
2.803(9) 2.793(9) 2.798
2.778(4) 2.784(2) 2.781
Dy–H (central) distances Dy(1)–H(1) Dy(2)–H(1) Dy(3)–H(1) Dy(4)–H(1) Average
2.264(18) 2.309(19) 2.111(21) 2.187(22) 2.218
2.249(9) 2.255(9) 2.158(12) 2.160(12) 2.205
Dy–H (face-bridging) distances Dy(1)–H(2) Dy(2)–H(2) Dy(3)–H(2) Dy(1)–H(3) Dy(2)–H(3) Dy(4)–H(3) Average
2.442(2) 2.421(2) 2.289(20) 2.429(21) 2.420(22) 2.346(18) 2.391
2.452(11) 2.400(12) 2.228(9) 2.424(11) 2.387(12) 2.282(10) 2.362
Dy–H (edge-bridging) distances Dy(1)–H(4) Dy(2)–H(4) Dy(1)–H(5) Dy(3)–H(5) Dy(1)–H(6) Dy(4)–H(6) Dy(2)–H(7) Dy(3)–H(7) Dy(2)–H(8) Dy(4)–H(8) Average
2.255(19) 2.221(22) 2.232(19) 2.190(22) 2.284(20) 2.160(20) 2.263(24) 2.173(20) 2.254(28) 2.162(22) 2.219
2.209(10) 2.188(9) 2.236(11) 2.148(10) 2.248(10) 2.189(9) 2.254(12) 2.210(9) 2.233(10) 2.161(11) 2.208
Selected bond angles (°) Core-bridging Dy(1)–H(1)–Dy(2) Dy(1)–H(1)–Dy(3) Dy(1)–H(1)–Dy(4) Dy(2)–H(1)–Dy(3) Dy(2)–H(1)–Dy(4) Dy(3)–H(1)–Dy(4) Average
93.6(7) 108.6(9) 107.3(9) 108.2(9) 106.3(8) 127.6(9) 108.6
94.6(4) 106.5(5) 106.9(5) 107.1(5) 106.1(5) 130.0(5) 108.5
Face-bridging Dy(1)–H(2)–Dy(2) Dy(1)–H(2)–Dy(3) Dy(2)–H(2)–Dy(3) Average
86.6(9) 97.4(9) 99.1(9) 94.4
86.0(4) 97.9(4) 100.1(4) 94.7
Dy(1)–H(3)–Dy(2) Dy(1)–H(3)–Dy(4) Dy(2)–H(3)–Dy(4) Average
86.9(8) 97.4(7) 98.0(8) 94.1
86.9(4) 97.6(4) 98.1(4) 94.2
96.4(7) 107.0(9) 107.6(8) 107.7(8) 109.1(11) 105.5 87.1(2)
97.7(4) 107.3(4) 106.0(4) 105.3(5) 106.8(5) 104.6 89.4(11)
Edge-bridging Dy(1)–H(4)–Dy(2) Dy(1)–H(5)–Dy(3) Dy(1)–H(6)–Dy(4) Dy(2)–H(7)–Dy(3) Dy(3)–H(8)–Dy(4) Average Dy(3)–Cl(1)–Dy(3)
3. Results and discussion We have collected two neutron data sets at different temperatures (150 and 10 K) on the same crystal sample with VIVALDI. The 10 K data set result gave a lower final agreement factor then the 150 K data set; due in part to the larger number of unique reflections measured. Despite the differences in agreement factors, the final results for the two temperatures, especially those results concerning the central Dy4H8Cl core (Fig. 2), are remarkably consistent. Table 2 lists the distance and angles in the Dy4H8Cl cores from the two neutron structural determinations. The rational for carrying out the present neutron study was to locate a four-coordinate hydrogen atom interstitially in an anionic tetrahedral dysprosium metal cluster. Our neutron data analysis has revealed that in addition to the four-coordinate hydrogen atom, the Dy4H8Cl core contains one edge-bridging chloride, two face-bridging hydrides and five edge-bridging hydrides. The interstitial hydrogen atom is bonded to the four dyspro0 sium atoms, giving an average Dy–H distance of 2.205(3) Å A (Table 2). The individual angles are, as expected, close to the ideal tetrahedral angle of 109°. The cluster is however slightly distorted from ideal tetrahedral symmetry because of the presence of a chloride atom bridging Dy(3) to Dy(4), a motif which is absent from the remaining Dy atoms in the cluster. The most obvious manifestation of the lowered symmetry is the presence of the two unique facebridging hydrogen atoms H(2) and H(3), which lie above the Dy(1)–Dy(2)–Dy(4) and Dy(1)–Dy(2)–Dy(3) faces of the tetrahedron, respectively, but which is absent from other faces of the cluster. Other, less pronounced manifestations of slightly lowered symmetry are the fact that the Dy(3)–Dy(4) distance, which involves the edge-bridging chloride atom is longer than the Dy(1)–Dy(2) distance (Table 2), thus giving a concomitant larger interstitial Dy(3)–H(1)–Dy(4) angle compared to the Dy(1)–H(1)– Dy(2) angle. In the past, neutron diffraction studies have shown a relationship between the number of metal atoms surrounding a hydrogen atom and its corresponding M–H distance [16]. In these studies the hydride–metal bond distance increases systematically with each addition of metal atom coordination. However, in each structural M–H example each molecule possessed only one type of hydrogen atom coordination [17–19]. Very recently, we found that in the tetrahedral yttrium complex [(C5Me4SiMe3)4Y4(lH)2]4(THF), which possesses three different types of linkages in the same compound: Y2(l2-H), Y3(l3-H), and Y4(l4-H) metal– hydride bonds, the relation between the M–H bond distance and the coordination number is not that straightforward [3]. There is the usual bond length increase as one goes from edgebridging to face-bridging (Y2(l2-H) to Y3(l3-H)), but there is a
Table 3 Key similar average bond lengths between [((C5Me4SiMe3)YH2)4](THF), the first reported tetrahedral cluster with one interstitial, one face-bridging, and six edgebridging hydride ligands and our current [Li(THF)4][(C5Me4SiMe3)4Dy4H8Cl] organometallic cluster with one interstitial, two face-bridging and five edge-bridging hydrides. [((C5Me4SiMe3)YH2)4] (THF)
[Li(THF)4] [(C5Me4SiMe3)4Dy4H8Cl]
Average bond lengths (Å) M–M distances M–M M–(TFH), M–Cl–M
3.459 3.693
3.563 3.781
M–H (central) M–H (face-bridging) M–H (edge-bridging)
2.197 2.344 2.166
2.205 2.362 2.208
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decrease in bond length in the next bonding type, Y3((l3-H) to Y4((l4-H)). Until now, this is the first example of its kind to (a) demonstrate accurately the existence of a four-coordinate hydrogen atom in a soluble organometallic hydride and (b) compare the tightness of the tetrahedral cavity for different metal-coordinated hydride atoms in the same molecule. In our current neutron study on the anionic dysprosium cluster, we observed analogous bonding trends [3]. A comparison of lengths is given in Table 3. The usual (as expected) increase in 0 bond length is A] to Dy3(l3-H) observed0 as one goes from Dy2(l2-H) [2.20(1) Å actually decreases in0 the next [2.36(1) Å A], then, the Dy–H distance 0 A] to Dy4(l4-H) [2.21(5) Å A], due to step, from Dy3(l3-H) [2.36(1) Å the tightness of the tetrahedral cavity. This idea was first proposed in our previous work. In our current work we observe analogous trends as before with different hydrogen atom coordination numbers but we also notice the lengths and angles are almost identical. This is, in part, most likely a result of dysprosium’s 0 0 A) [20]. similar covalent radius (1.59 Å A) to yttrium (1.62 Å Acknowledgment This work was supported by the American Chemical Society (Grant PRF-40715-AC3). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2009.03.024. References [1] F. Lutz, R. Bau, P. Wu, T.F. Koetzle, C. Krueger, J.J. Schneider, Inorg. Chem. 35 (1996) 2698. [2] R.G. Teller, R.D. Wilson, R.K. McMullan, T.F. Koetzle, R. Bau, J. Am. Chem. Soc. 100 (1978) 3071.
[3] M. Yousufuddin, J. Baldamus, O. Tardif, Z. Hou, S.A. Mason, G.J. McIntyre, R. Bau, J. Am. Chem. Soc. 130 (2008) 3888. [4] R. Bau, M.H. Drabnis, L. Garlaschelli, W.T. Klooster, Z. Xie, T.F. Koetzle, S. Martinengo, Science 275 (1997) 1099. [5] (a) D.W. Hart, R.G. Teller, C.Y. Wei, R. Bau, G. Longoni, S. Campanella, P. Chini, T.F. Koetzle, Angew. Chem., Int. Ed. Engl. 18 (1978) 80; (b) D.W. Hart, R.G. Teller, C.Y. Wei, R. Bau, G. Longoni, S. Campanella, P. Chini, T.F. Koetzle, J. Am. Chem. Soc. 103 (1981) 1458. [6] P.F. Jackson, B.F.G. Johnson, J. Lewis, P.R. Raithby, M. McPartlin, W.J.H. Nelson, K.D. Rouse, J. Allibon, S.A. Mason, J. Chem. Soc., Chem. Commun. 7 (1980) 295. [7] O. Tardif, M. Nishiura, Z. Hou, Organometallics 22 (6) (2003) 1171. [8] D. Cui, O. Tardif, Z. Hou, J. Am. Chem. Soc. Commun. 126 (5) (2004) 1312. [9] Y. Luo, J. Baldamus, O. Tardif, Z. Hou, Organometallics 24 (18) (2005) 4362. [10] D. Cui, M. Nishiura, Z. Hou, Macromolecules 38 (2005) 4089. [11] G.M. Sheldrick, SHELXTL, Version 6.14, Bruker Analytical X-ray System Inc., Madison, WI, 1997. [12] R.H. Blessing, Acta Crystallogr. A51 (1995) 33. [13] C. Wilkinson, J.A. Cowan, D.A.A. Myles, F. Cipriani, G.J. McIntyre, Neutron News 13 (2002) 37. [14] (a) F. Capriani, J.C. Castsgna, M.S. Lehmann, C. Wilkinson, Physica B 213 (1995) 975; (b) J.W. Campbell, J. Appl. Crystallogr. 28 (1995) 228; (c) J.W. Campbell, Q. Hao, M.M. Harding, N.D. Nguti, C. Wilkinson, J. Appl. Crystallogr. 31 (1998) 23; (d) C. Wilkinson, H.W. Khamis, R.F.D. Stansfield, G.J. McIntyre, J. Appl Crystallogr. 21 (1988) 471; (e) J.W. Campbell, J. Habash, J.R. Helliwell, K. Moffat, Information Quarterly of Protein Crystallography, vol. 18, SERC Daresbury Laboratory, Warrington, England, 1988. [15] G.M. Sheldrick, SHELX-97, A Computer Program for the Refinement of Crystal Structures, University of Göttingen, Göttingen, Germany, 1997. [16] R. Bau, M.H. Dradnis, L. Garlaschelli, W.T. Klooster, Z. Xie, T.F. Koetzle, S. Martinengo, Science 275 (1997) 1099. [17] D. Hanke, K. Wieghardt, B. Nuber, R.S. Lu, E.L. McMullan, T.F. Koetzle, R. Bau, Inorg. Chem. 32 (1993) 4300. [18] R.K. Brown, J.M. Williams, A.J. Sivak, E.L. Muetterties, Inorg. Chem. 19 (1980) 370. [19] J.S. Ricci, T.F. Koetzle, R.J. Goodfellow, P. Espinet, P.M. Maitlis, Inorg. Chem. 23 (1984) 1828. [20] K. Barbalace, Periodic Table of Elements – Dysprosium – Dy. EnvironmentalChemistry.com, 1995–2008.