Reaction of hydrogen with metallic and reduced halides. The requirement of delocalized electrons for reaction

Abstract

The reactions of hydrogen with a number of metallic halides, cluster compounds, and saltlike halides which are strong reducing agents have been investigated. The following new compounds have been identified from reactions of hydrogen with the binary halide utilizing conditions in the ranges 200-475 °C and 250-1900 Torr: ThI2H0.7, ThI2H18, LaI2H0.75, CeI2H0 82, PrI2Ht 2, Scl2 -Hq f). TiL d !q 4. Nb8li; H .3. Mo6C1i2Ho,7, ScCf _íHq88. GdClisHg.go, ZrClj 5H0.7, and CsScCl3Hg 33.On the other hand, TiCl2, Til2, and ZrCl3 do not take up significant H2 while only NdCl2 of the compounds studied decomposes to known binary phases (NdCl3 and NdH2+). Thermodynamic data from equilibrium pressure measurements in the thorium iodide-hydrogen system are reported. The generalization is developed from these studies that hydrogen is taken up only by those halides which contain delocalized electrons, that is, are metallic or contain clusters with delocalized bonding. Structural and bonding implications of these findings are discussed. The general interpretation of the metallic halide hydrides, of the cluster hydrides, and of the binary hydrides of the same elements is considered in terms of multicenter bonding of hydrogen with metal ions via conduction electrons, the hydrogen thereby acquiring a partial negative charge through overlap with the delocalized electrons. This property is reflected in both the rich variety and the often nonstoichiometric character of the hydrides considered.

Adjustment of the Stability of Complex Hydrides by Anion Substitution

“…For intermetallic metal hydrides it has earlier been found that hydrogenation of ThI 2 is possible and that the plateau pressure is different from metal hydride prepared from Th metal. 28 For complex hydrides nothing similar has been reported, even though the compounds K 3 AlH 4 F 2 and NaMgH x F x have been reported to exist. 29,17 It has earlier been reported anomalies in differential scanning calorimety results for TiF 3 -doped Na 3 AlH 6 that are in line with the present work.…”

Characterization of Catalytically Active Octahedral Metal Halide Cluster Complexes

“…Figure 9 plots n-butylamine titers as a function of the Hammett acidity function (H 0 are reported to be +1.3 to +1.5 and +1.5 to −3.0, respectively [27]. The solid-phase synthesis of the well-formed crystalline solid state cluster [Mo 6 [15]. Dihydrogen directly converts double-metal-layered ZrX (X = Cl and Br) to the ZrXH phase [16].…”

“…A diversity of metal atoms and halogen ligands is also an attribute of halide clusters. Studies on the reactivity of halide clusters are quite limited, and have generally been confined to observations of ligand exchange reactions with organic or inorganic reagents, an exception being the report of a simple reaction with hydrogen [15,16]. The applications of these clusters have been explored based on properties such as high temperature superconductivity, metallic conductivity at elevated temperatures, low-dimensional electronic or magnetic properties, and good thermal stability.…”

5d Orbital and electronic localization in rare earth diiodides and praseodymium halides, Pr2X5 (X = Br, I)

“…These investigators have shown that many of the trivalent dihalides take up hydrogen at 400 °C in amounts suggesting possible incorporation into the Ln3 triangles we have discussed. 25 Hydrogenation of Lal2 at higher temperatures seems to lead to products that do not adopt a MoS2-type structure. 26 Finally, we note that, in the synthesis of reduced rare earth compounds, the reducing agent is usually the elemental metals.…”