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X-Ray and Neutron Diffraction Studies on p-Hydrido-nonacarbonyl( ni trosyl) di tungs ten [HW,(CO),(NO)]. Evidence for a Closed Three-Center Metal-Hydrogen-Metal Bond' James P. 01sen,2a'bThomas F. Koetzle,*2cStephen W. Kirtley,*Zb Mark Andrews,2bDonald L. Tipton,2band Robert Bau* 2 a , 3
Contributionf r o m the Departments of Chemistry, Unicersity of Southern California, Los Angeles, California 90007, Brookhauen National Laboratory, Upton, New York 11973, and New College, Sarasota, Florida 33578. Received April 25,1974
Abstract: X-Ray and neutron diffraction studies on the complex HW2(C0)9(NO)have been carried out. HW2(C0)9(NO),prepared by the treatment of [HW2(CO),~]with NaNOs-CH3COOH, crystallizes in twq different modi%cations: a triclinic form (a-HW2(CO)g(NO); space group Pi,a = 12.284 (14) A, b = 9.621 ( 5 ) A, c = 6.921 (4) A, cy = 112.84 (2)', p = , 91.31 (5)O, y =097.34 (4)", 2 = 2)aanda monclinic form (p-HW2(CO)g(NO);space group C2/c, a = 14.582 ( 8 ) A, b = 6.771 (4) A, c = 15.627 (9) A, p = 102.336 (6)", Z = 4). X-Ray studies of the acrystals first revealed the unexpected bent nature of the molecule, but did not locate the position of the hydrogen atom. This was accomplished in the subsequent neutron diffraction analyses of both crystalline forms, which showed essentially the same*structure: a molecule held together by a single bent W-H-W linkage, with W-H = 1.873 A, W. . . W = 3.329 A, W-H-W = 125.5', H-W-W = 27.3'. A particularly significant finding is the fact that the axial ligand-metal vector does not point directly at the hydrogen atom but approximately bisects the H-WW angle. This strongly suggests the presence of a closed, three-center two-electron W-H-W bridge bond in which appreciable W-W overlap exists. Refinement of the neutron scattering lengths of the light atoms showed that the nitrosyl group is disordered over the two axial positions. The position of the hydrogen atom in the W-H-W bond appears to be symmetric, but it was not possible to tell if this effect is real or merely an artifact caused by the 5050 nitrosyl-carbonyl packing disorder. Final agreement factors were based on strong reflections ( I > 3 ~: ) aHW,(CO)g(NO) (X-ray data) R = 6.1 for 1932 reflections; cy-HW2(CO)g(NO) (neutron data) R = 6.0% for 2518 reflections; p-HW,(CO)g(NO)(neutron data) R = 6 . 6 % for 919 reflections.
x
x
A
mong the various types of bonds known to exist, the metal-hydrogen-metal bond is perhaps the most poorly characterized and least understood. Although several recent X-ray studies4-'? have succeeded in locating, and in a few cases refining, hydrogen atom positions, it is clear that such studies are on the whole unable to generate hydrogen positions with the precision necessary to answer some of the more fundamental questions about the M-H-M bond. One such question has to d o with symmetry. Are M-H-M bonds inherently asymmetric or can they be symmetric in certain cases? l3l1, Another question (1) This work, performed under the auspices of the Atomic Energy Commission, was presented on March 28, 1974, at the Spring Meeting of the American Crystallographic Association, held at Berkeley, Calif. (2) (a) University of Southern California: (b) New College; (c) Brookhav en National Laboratory. (3) Research Fellow of the Alfred P. Sloan Foundation, 197441976, (4) For pre-1973 X-ray structure determinations of M-H-M bonds, see Table XVI in ref 6. Also see section E of ref 5 for more detailed descriptions. ( 5 ) B. A. Frenz and J. A. Ibers in "Transition Metal Hydrides," E. L. Muetterties, Ed., Marcel Dekker, New York, N. Y., 1971. (6) H . D. Kaesz and R. B. Saillant, Chem. Rec., 72,231 (1972). (7) S . W. IGrtley, J. P. Olsen, and R. Bau, J . Amer. Chem. Soc., 95, 4532 (1973). (8) A. J. P. Domingos, B. F. G. Johnson, J. Lewis, and G. M. ShelChem. Commun., 912 (1973). drick, J . Chem. SOC., (9) L. J. Guggenberger and F. N. Tebbe, J . Amer. Chem. Soc., 95, 7870 (1973). (10) M. R. Churchill and S. W. Y. Ni Chang, J. Amer. Chem. Soc., 95,2150 (1973). (11) M. R. Churchill, S. W. Y . Ni Chang, M. L. Berch, and A. Davison, J . Chem. SOC., Chem. Commuri., 691 (1973). (12) R. Bau, B. Don, R. A. Love, R. D. Wilson, R. Greatrex, and R. J. Haines, manuscript in preparation. (13) The detection of asymmetry in hydrogen bonding is a difficult problem, even with the best neutron diffraction data as evidenced by the
has to d o with the nature of overlap. Are the threecenter two-electron M-H-M bonds of the closed variety (I) with some M-M overlap or are they open (11) with no M-M interaction?
M I
M I1
In this paper, we report X-ray and neutron diffraction analysis on two crystalline forms of HW2(C0)9This work, together with the recently completed studies on HMozCpn(CO)4(PMe),l 9 is the first single-crystal neutron diffraction characterization of the M-H-M bond.?' There were several reasons which made HW,(CO),(NO) particularly suitable for such a n analysis: (a) it readily forms large crystals ambiguity in the interpretation of the [HF?]- anion diffraction data (ref 14-18). (14) W. C. Hamilton and J. A. Ibers, "Hydrogen Bonding i n Solids," W. A. Benjamin, New York, N. Y., 1968, p 108-124. (15) S. W. Petersonand H. A. Levy,J. Chem. P/7j,s.,20, 704(1952). (16) B. L. McGaw and J. A. Ibers, J . Chem. Phj,s., 39, 2677 (1963). (17) J. A. Ibers, J . Chem. Phj,S., 40,402 (1964). (18) J. M. Williams and L. F. Schneemeyer, J . Amer. Chem. SOC.,95, 5780 (1973). (19) Since the completion of our work, it has come to our attention that neutron studies on HMozCp2(CO)r(PMe?)have recently been completed [J. L. Petersen, L. F.Dahl, and J. M. Williams, J. Anzer. Chem. SOC.,96, 6610 (1974)]. In that compound, a symmetric, bent Mo-HMo bond was found. (20) M. Andrew, D. L. Tipton, S. W. Icirtley, and R. Bau, J. Chem. Soc., Chem. Commiin., 181 (1973). (21) It should be pointed out that neutral diffraction studies on a powdered sample of HNb& have been reported. In this study, the hydrogen atom was located in the center of a metal octahedron: A. Simon,Z. Anorg. A l l g . Chem., 355,311 (1967).
Bau, et a/.
X-Ray and Neutron Diffraction Studies on HWdCOjdNO)
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and is completely air-stable in the solid form; (b) it contains the highly unusual feature of a molecule held together solely by a bent M-H-M bond;22 (c) there was the possibility of detecting an asymmetric W-H-W linkage, since the two halves of the molecule, W(CO)5 and U'(CO),(NO), are different; (d) the presence of a c l e a ~ l jdejned ~ axial ligand in an octahedral emironmeiit ~ o z t l dserce as a convenient "pointer" to identify the direction of the metal orbital used in the threecenter orellap.
cu form) and a monoclinic form. X-Ray data were collected on CY-HWZ(CO)~(NO) and neutron data on both forms. Each of these will be described in turn. X-Ray Diffractionona-HW2(CO)9(NO). This work was reported earlier by us in a preliminary communication. *O a-HWz(CO)e(NO) crystallizes as bright red-orange parallelepipeds with well-formed faces. A specimen of dimensions 0.06 X 0.09 X 0.22 mm was mounted in a capillary tube along its long axis. Weissenberg and precession photographs indicated a triclinic crystal system. The unit cell parameters, obtained by measuring the setting angles of 41 reflections on a Nonius CAD-3 automated diffractometer, are given together with other relevant crystal data in Table I.
Experimental Section Preparation of HW,(CO)t,(NO). All manipulations were performed under nitrogen and all solvents degassed before use. [Na-][HW2(CO)lo-]. prepared from W(C0)s (2.51 g, 7.14 mmol) using published methods.23 was dissolved in 200 ml of water, and sodium nitrite (2.02 g. 29.3 mmol) was added. Dropwise addition of acetic acid (3.5 ml; 6 M ) to the stirred solution caused vigorous gas evolution and the formation of a brownish yellow precipitate which, after overnight stirring. was filtered, washed. and dried. Recrystallization from dichloromethane gave orange crystals of H W ? ( C 0 ) 8 N 0 in 4075 yield based on W(CO)6.24 The solid is stable in air (mp 128-129.5") but solutions of HW2(CO)s(NO) in common organic solvents are somewhat air-sensitive. A d . Calcd for HW?(CO),(NO): C , 16.60; H, 0.15; N, 2.15. Found: C. 16.34: H. 0.27; N. 2.28. The mass spectrum26 showed a parent multiplet in agreement with the formula HWZ(CO)e(NO). Additional multiplets were observed corresponding to progressive loss of four C O groups, the NO group. four additional CO groups, and the hydrogen with the final C O group. The retention of the isotope pattern during the entire sequence indicates that the hydrogen is almost always lost with the last CO group. The 'H nnir of HU'?(CO),(NO) showed a single resonance at T 21.77 in acetone and T 21.71 i n tetrahydrofuran (TMS internal standard). N o i b W ' satellites were observed because of the limited solubilits of the compound. The infrared spectrum of the carbonyl and nitrosyl regions shomed the following absorptions26in cyclohexane solution: 2069 (m). 2045 (SI, 201 1 (w), 1989 (w), 1953 (sh), 1944 (s). 175.5 (m. br). 1717 (sh) cm-'. The Raman spectrum of a powdered sample in the Same region showed the following absorptions:?; 2132 (s). 2068 (x)2C51 . (m). 2023 (in), 1986 (s), 1941 (sh). 1923 (m). 1896 (in). 172.5 (nl). 171 5 (sh) cm-'. Absorptions in the 800--12OO-~m-~ region oi' the Raman spectrum were also observed: 1205 (w. br). 1 1 1.5 (111. br). 1045 (m. br). 965 (m. br). 900 (w.hr). 790 ( w , br) cm-I.
Crystallographic Section2b HW,(CO),(NO) crystallizes from acetone in two forms in approximately equal amounts: a triclinic form (hereafter referred to as the -
~
( 2 2 ) In most compounds \\ith !v-H-M bonds, the hydride bridge is either part of ;i structured metal cluster frameaork or exists in conjunction with cthcr bridging ligands such as CO, PR:, or SR groups. (23) (a) U . Anders and W. A . G . Graham, Cheni. Commuli., 499 (19651; (b) R . G. Hnkti'r, J . Amer. Chcm. Soc., 8 8 , 4376 (1966); (c) \V. C . I
