[en] Investigations of H₃Ta(C₅H₅)₂ (III), HW₂(CO)₉(NO) (IV), and HW₂(CO)₈(NO) (P(OCH₃)₃) (V) have been completed. Preliminary results are available for HFeCo₃(CO)₉[P(OCH₃)₃]₃ (VII). This work, together with studies of HMo₂(C₅H₅)₂(CO)₄(P(CH₃)₂) (VI) and [(C₂H₅)₄N]⁺ [HCr₂(CO)₁₀]^- carried out at Argonne has led to some general observations on the geometry and the nature of bonding in these compounds. For example, in the structures of IV and V, both of which have bent W--H--W linkages (less than W--H--W in the range 125-130⁰), there is conclusive evidence for the existence of a closed three-center W--H--W bond with significant metal-metal interaction. Such is the case, because extensions of the axial W--C and W--N bonds trans to the hydride intersect at a point near the center of the W--H--W triangle. The geometry of VI, which also contains a bent M--H--M bond, is consistent with that of IV and V. Bridging M--H bonds in these second- and third-row hydrides range in length from 1.85 to 1.89 A, compared to 1.75 A in the first-row polynuclear complex VII. For metals of corresponding rows, bridging M--H bonds are about 0.1 A longer than terminal bonds, which are classified as single covalent bonds

[en] Recent neutron diffraction investigations on terminal, bridging and triply-bridging metal-hydrogen bonds are reviewed

[en] We have collected neutron diffraction data on a large single crystal of the title compound. The most surprising result is an extremely short Rh-H distance of 1.31(8) A, presumably caused by steric interactions involving the bulky triphenyl phosphine ligands. Crystallographic details: HRh[P(C₆H₅)₃]₄ . ¹/₂C₆H₆ crystallizes in the space group Pa3, with a = b = c = 22.776(3) A, Z = 8. Data were collected at the Brookhaven High Flux Beam reactor at a temperature of -23⁰C, λ = 1.15882(7) A^-1. Least-squares refinement (in which the phenyl rings were treated as rigid groups) resulted in an R factor [based on data with f > 4σ(F)] of 0.12 for 914 reflections and 95 parameters. 10 refs

[en] The extended x-ray absorption fine structure analysis of a purple compound derived from the reaction of cis-Pt(cyclopropylamine)₂Cl₂ with uridine and of a blue compound derived from the reaction of cis-[Pt(NH₃)₂(H₂O₂)]²⁺ with uridine were reported. The local platinum coordination of the two compounds involves Pt-X (where X = N or O) bonds of approximately 2.00 A and a partial but distinct Pt--Pt bond of approximately 2.90 A. The coordination sphere is probably cis-Pt(amine)₂XY where X,Y = N₃, O₂, or O₄ of the uridinato ligand

[en] The crystal and molecular structure of H₄Os(PMc₂Ph)₃ has been investigated by x-ray and neutron diffraction technijues. X-ray data collected at 298 K gave the unit cell parameters a = 11.489 (4) A, b = 12.441 (4) A, c = 11.103 (4) A, α = 90.54 (2)⁰, β = 124.63 (2)⁰, γ = 89.93 (2)⁰, Z = 2 in the triclinic space group P anti 1. Neutron data collected at 90 K gave the cell parameters a = 11.409 (2) A, b = 12.388 (2) A, c = 11.098 (2) A, α = 90.36 (5)⁰, β = 125.07 (1)⁰, and γ = 90.06 (4)⁰. Refinement against the x-ray data coverged at R = 0.055 and R/sub w/ = 0.060 with 3486 reflections with 1 greater than or equal to 30. For the neutron study, agreement factors are R = 0.044 and R/sub w/ = 0.042 based on 3381 reflections. The complex is a distorted pentagonal bipyramid, the four hydride ligands, osmium, and one phosphorus atom being essentially coplanar. Important distances and angles in the molecule are as follows: Os-H = 1.663 (3), 1.648, 1.644 (3), 1.681 (3) A; Os-P = 2.317 (2), 2.307 (2), 2.347 (2) A; H-Os-H = 67.9 (2), 69.4 (2), 70.0 (2)⁰; P-Os-P = 166.1 (1), 97.0 (1), 96.9 (1)⁰; H-Os-P(eq) = 73.0 (1), 79.7 (1)⁰

[en] This review article is largely concerned with the efforts to gather structural information on hydrogen bridge bonds with neutron diffraction data. 11 figures, 1 table

[en] Recent neutron diffraction investigations on terminal, bridging and triply-bridging metal-hydrogen bonds are reviewed. (author)

[en] The compound [(Ph₃P)₂N]⁺²[H₂W₂(CO)₈]^2- has been synthesized in 65% yield from the reaction of [(Ph₃P)₂N]⁺[BH₄]^- with [(Ph₃P)₂N]⁺[W(CO)₅(I)]^- in refluxing tetrahydrofuran. The dianion reacts with BH₃THF in THF to produce [(Ph₃P)₂N]⁺[W(CO)₄(BH₄)]^- in 60% yield. The structure of [(Ph₃P)₂N]⁺₂[H₂W₂(CO)₈]^2- has been studied with x-ray and neutron diffraction techniques at room temperature and 28 K, respectively. The [H₂W₂(CO)₈]^2- anion has approximately D_2h symmetry with a planar W(μ-H)₂W bridge, confirming the earlier x-ray results by Churchill and co-workers on (Et₄N]⁺₂[H₂W₂(CO)₈]^2-. In the [(Ph₃P)₂N]⁺ salt, the anions are situated on crystallographic inversion centers, and distances and angles in the W(μ-H)₂W core are as follows: W-H = 1.920 (3) and 1.933 (2) A, W...W = 3.010 (2) A, H...H = 2.405 (3) A, W-H-W = 102.7 (1)⁰, H-W-H = 77.3 (1)⁰, and H-W-W = 38.78 (6) and 38.78 (6)⁰. The two bridging H atoms are displaced slightly from the intersections of the trans CO-metal vectors in the direction of the metal-metal axis. The [(Ph₃P)₂N]⁺ cation has the usual bent P-N-P configuration, but the phenyl rings are in an uncommon staggered conformation. Crystal data from the neutron diffraction analysis of [(Ph₃P)₂N]⁺₂[H₂W₂(CO)₈]^2- at 28 K: space group P anti 1^-; a = 12.949 (1), b = 13.871 (2), c = 11.000 (1) A; α = 110.828 (8), β = 105.788 (9), γ = 69.334 (8)⁰; V = 1703.4 (4) A³; Z = 1. Final agreement factors were R(F) = 0.027 for 5206 neutron reflections with I greater than or equal to sigma(I) and R(F) = 0.040 for 4238 x-ray reflections with I greater than or equal to 3 sigma(I). 5 figures, 7 tables

[en] We wish to report the first accurate neutron diffraction study of a transition metal structure with a triply bridging hydride ligand, the cluster HFeCo₃(CO)₉(P(OCH₃)₃)₃. The compound crystallizes in the space group P2₁/c, Z = 4. The cell constants at 90 K are a = 15.957 (8) A, b = 10.611 (5) A₉ c = 18.383 (9) A, β = 98.70 (2)⁰. The structure was refined, based on the measured intensities of 8229 reflections; the final discrepancy factors for all reflections are R/sub F²/ = 0.087, R/sub wF²/ = 0.066. The four metal atoms form a tetrahedron with the apical Fe atom additionally bonded to three terminal carbonyl groups. Each Co atom is further bonded to one terminal and two bridging carbonyl ligands, as well as one phosphite group and the hydride ligand. The hydride ligand is located outside the metal cluster, 0.978 (3) A from the Co₃ face. This result confirms that of an earlier x-ray investigation by Huie, Knobler, and Kaesz. The Co--H distances are 1.724 (3), 1.731 (3), and 1.728 (3) A, and Co--H--Co angles are 92.1 (1), 91.7 (1), and 91.5 (1)⁰

[en] The structure of H₃Ni₄Cp₄ (Cp=n⁵-C₅H₅), an unusual paramagnetic metal cluster complex, has been analyzed by single-crystal neutron diffraction techniques at low temperature (81 K). As predicted from an earlier x-ray diffraction study, the hydrogen atoms bridge three faces of the Ni₄ tetrahedral core. Although the Ni₄ cluster itself is an essentially undistorted tetrahedron [with Ni-Ni edges of 2.469 (6) A], the individual Ni₃H linkages are unsymmetrical. The H atoms are slightly displaced away from the unique apical Ni atom: Ni-H distances involving the apical Ni atom average to 1.716 (3) A, while those involving the basal Ni atoms average to 1.678 (6) A. The overall mean Ni-H distance is 1.691 (8) A, and the H atoms are situated an average of 0.907 (6) A above the Ni₃ faces. Other average distances and angles in the molecule follow: H-H = 2.316 (6) A, Ni-C = 2.132 (5) A, Ni-H-Ni = 93.9 (3)⁰, H-Ni-H = 86.1 (6)⁰. The title compound crystallizes in space group C2/c with the following cell parameters at 81 K: a = 28.312 (13) A, b = 9.234 (5) A, c = 14.783 (7) A, BETA = 103.35 (2)⁰, V = 3760 (3) A³, Z = 8. The structure has been refined to yield final agreement factors of R/sub f/ reverse arrow 0.107 and R/sub wf/ = 0.067 for 2616 reflections having I > 1.5 sigma (I)