Hydrides crystal structures

There is a lively controversy concerning the interpretation of these and other properties, and cogent arguments have been advanced both for the presence of hydride ions H" and for the presence of protons H+ in the d-block and f-block hydride phases.These difficulties emphasize again the problems attending any classification based on presumed bond type, and a phenomenological approach which describes the observed properties is a sounder initial basis for discussion. Thus the predominantly ionic nature of a phase cannot safely be inferred either from crystal structure or from calculated lattice energies since many metallic alloys adopt the NaCl-type or CsCl-type structures (e.g. LaBi, )S-brass) and enthalpy calculations are notoriously insensitive to bond type. 

The crystal structure of the K(18-crown-6) salt shows a fac-octahedral structure (Ru—H 1.59-1.71 A, Ru—P 2.312-2.331 A) with a large distortion from regular octahedral geometry (H-Ru-H 70-88° P-Ru-P 102-111°) owing to the disparate steric demands of the hydride and tertiary phosphine ligands [95]. 

Determination of this crystal structure of the complex did not locate the hydride ligand but its position can be deduced from the distortion from... 

The most remarkable pentammine is the hydride [Rh(NH3)5H]2+ [91], produced by zinc (powder) reduction of the chloropentammine salt. It shows u(Rh-H) at 2079 cm-1 in the IR spectrum (of the sulphate) and the low-frequency hydride NMR resonance at S = -17.1 ppm as a doublet showing Rh-H coupling (14.5 Hz). Its crystal structure shows the pronounced rraus-influence of hydride, with the Rh-N bond tram to H some 0.17 A longer than the cis Rh-N bond (Figure 2.45) [92]. 

Both these hydrides insert alkenes and alkynes the crystal structure of [Rh(NH3)5(C2H5)]2+Br2 shows the ethyl group has a trans-influence comparable to that of the hydride [93]. 

The saline hydrides are white, high-melting-point solids with crystal structures that resemble those of the corresponding halides. The alkali metal hydrides, for instance, have the rock-salt structure (Fig. 5.39). 

The bisphosphonate - upon reduction with lithiumaluminum hydride in ether at 0°C - produced the amide functionalized primary bisphosphine (1) in good yields [45]. This reaction proceeded to reduce the amide group in 1 to produce the amine functionaUzed primary bisphosphine (2) in <5% yields. The amido bisprimary phosphine 1 is an air stable crystalline solid whereas the amine compound 2 is an oxidatively stable liquid. Separation of 1 and 2 in pure forms was achieved using coliunn chromatography. The amidic bisprimary phosphine 1 was crystallized from chloroform and exhibits remarkable stability not only in the solid state but also in solution as well. The crystal structure of the air stable primary his-phosphine 1 as shown in Fig. 1 is unprecedented to date. 

Rh(OEP)H reacts with CNR (R = Me, n-Bu,) to give the adduct Rh(OEP)-(H)CNR (which has no parallel in CO chemistry) which then slowly transforms to the formimidoyl insertion product, Rh(OEP)C(H)=NR. The dimer Rh(OEP))2 reacts with CNAr (Ar = 2.6-Cf,H3Mc2) in aqueous benzene to give the carbamoyl product. Rh(OEP)C(0)NHAr (characterized by an X-ray crystal structure) together with the hydride, which it.self reacts further with the isocyanide. This is suggc.sted to form via a cationic carbene intermediate, formed by attack of HiO on coordinated CNAr in concert with disproportionation to Rh(III) and Rh(l). 

Fig. 1 The first X-ray crystal structures of three types of the iron hydride complexes...

Interstitial Solid Solutions Interstitial solid solutions involve occupation of a site by introduced ions or atoms, which is normally empty in the crystal structure, and no ions or atoms are left out. Many metals form interstitial solid solutions in which small atoms (e.g., hydrogen, carbon, boron, nitrogen) enter empty interstitial sites within the host structure of the metal. Palladium metal is well known for its ability to absorb an enormous volume of hydrogen gas, and the product hydride is an interstitial sohd solution of formula PdH, 0 0.7, in which hydrogen atoms occupy... 

Palenih, G. ]. The Crystal Structure of the Aluminium Hydride-N,N,N N -Tetramethylethylenediamine Adduct. Acta Cryst. 17, 1573 (1964). 

Although the formation of ionic hydrides is usually exothermic, the formation of interstitial hydrides may have positive enthalpy values. Physical characteristics of interstitial hydrides are determined by the fact that hydrogen atoms in interstitial positions cause some expansion of the lattice but contribute very little mass. Consequently, the interstitial hydrides always have lower densities than the metal itself, even though the crystal structure is normally the same. When interstitial positions contain hydrogen atoms, the flow of electrons in conduction bands within the metal is impeded, so the... 

Hagg, G. 1931. Regularity in crystal structure in hydrides, borides, carbides and nitrides of transition elements. Z. Physik. Chem. 12B 33-56. 

The dimeric complex [RhClL2 L>, present in varying amounts according to the conditions, is also an effective catalyst via a similar hydride route involving complex 1. An originally proposed (80) dimeric tetrahydride was not detected. Detailed crystal structures of both the red and orange forms of RhCl(PPh3)3 have appeared (81). 

Hydrides of variable composition are not only formed with pure metals as solvents. A large number of the binary metal hydrides are non-stoichiometric compounds. Non-stoichiometric compounds are in general common for d,f and some p block metals in combination with soft anions such as sulfur, selenium and hydrogen, and also for somewhat harder anions like oxygen. Hard anions such as the halides, sulfates and nitrides form few non-stoichiometric compounds. Two factors are important the crystal structures must allow changes in composition, and the transition metal must have accessible oxidation states. These factors are partly related. FeO,... 

Recently, the crystal structure of a nickel(II) complex with a tridentate silyl ligand has been reported [20]. The structure in the solid state shows an //2-(Si-H) binding to nickel, with a Ni-H distance of 1.47 A NMR spectra of the complex in solution at -80 °C suggest the formation of a nickel(IV) hydride species through oxidative addition of the silyl-hydrogen to nickel [20]. 

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