Hydrogen binary hydrides

Binary Compounds of Hydrogen. Binary compounds of hydrogen with the more electropositive elements are designated hydrides (NaH, sodium hydride). 

The metallic monohaHdes zirconium chloride [14989-34-5] ZrCl, and zirconium bromide [31483-18-8] ZrBr, reversibly absorb hydrogen up to a limiting composition of ZrXH (131). These hydrides are less stable than the binary hydride ZrH2, and begin to disproportionate above 400°C to ZrH2 and ZrX in a hydrogen atmosphere (see also Hydrides). 

Hydrogen combines with many elements to form binary hydrides MH (or M H ). All the main-group elements except the noble gases and perhaps indium and thallium form hydrides, as do all the lanthanoids and actinoids that have been studied. Hydrides are also formed by the more electropositive transition elements, notably Sc, Y, La, Ac Ti, Zr, Hf and to a lesser... 

Hydrido complexes are well-known bui simple binary hydrides are noi. which is iti keeping wiih ihe posinon nf ihese melals in Ihe hydrogen gap" portion of ihe periodic lable ip, 67. ... 

In order for an intermetallic compound to react directly and reversibly with hydrogen to form a distinct hydride phase, it is necessary that at least one of the metal components be capable of reacting directly and reversibly with hydrogen to form a stable binary hydride. 

No binary hydrides have been characterized, but reactions of the metal powders with alkali metal hydrides in a hydrogen atmosphere lead to Li3RhH4 (planar RhH4 ) and M3MH6 (M = Li, Na M = Rh, Ir) with octahedral MHj [34],... 

The nature of a binary hydride is related to the characteristics of the element bonded to hydrogen (Fig. 14.8). Strongly electropositive metallic elements form ionic compounds with hydrogen in which the latter is present as a hydride ion, H. These ionic compounds are called saline hydrides (or saltlike hydrides). They are formed by all members of the s block, with the exception of beryllium, and are made by heating the metal in hydrogen ... 

You can see the effect of hydrogen bonding clearly in the boiling point data of the binary hydrides of Groups 14 to 17 (IVA to VIIA), shown in Figure 4.16. In Group 14, the trend in boiling point is as expected. 

Figure 5.20 Table of the binary hydrides and the Allred-Rochow electronegativity [26], Most elements react with hydrogen to form ionic, covalent or metallic binary hydrides.

According to the rule of imaginary binary hydrides, the stability of hydrogen on an interstitial site is the weighted average of the stability of the corresponding binary hydrides of the neighboring metallic atoms [35]. 

The semiempirical models mentioned above allow an estimation of the stability of binary hydrides provided that the rigid band theory can be applied. However, the interaction of hydrogen with the electronic structure of the host metal in some binary hydrides and especially in the ternary hydrides is often more complicated. In many cases, the crystal structure of the host metal and therefore also the electronic structure... 

A hydride formed in the reaction of a binary solid-solution alloy with hydrogen can be considered as a solid solution of two binary hydrides and will have properties related to the properties of the constituent binary hydrides. An intermetallic-compound hydride, however, formed in accordance with Reaction... 

This chapter commences with a review of a limited number of ternary hydride systems that have two common features. First, at least one of the two metal constituents is an alkali or alkaline earth element which independently forms a binary hydride with a metal hydrogen bond that is characterized as saline or ionic. The second metal, for the most part, is near the end of the d-electron series and with the exception of palladium, is not known to form binary hydrides that are stable at room temperature. This review stems from our own more specific interest in preparing and characterizing ternary hydrides where one of the metals is europium or ytterbium and the other is a rarer platinum metal. The similarity between the crystal chemistry of these di-valent rare earths and Ca2+ and Sr2+ is well known so that in our systems, europium and ytterbium in their di-valent oxidation states are viewed as pseudoalkaline earth elements. 

The periodic trends in main-group elements become apparent when we compare the binary compounds they form with one specific element. All the main-group elements, with the exception of the noble gases and, possibly, indium and thallium, form binary compounds with hydrogen, so these hydrides can be examined to look for periodic trends. We meet the binary hydrides several times in this chapter and the next, so, at this stage, we confine the discussion to a brief survey and see how their properties reveal periodic behavior. 

The binary hydrides are compounds that contain hydrogen and just one other element. Formulas and melting points of the simplest hydrides of the main-group elements are listed in Figure 14.2. Binary hydrides can be classified as ionic, covalent, or metallic. 

Hydrogen forms three types of binary hydrides. Active metals give ionic hydrides, such as LiH and CaFF nonmetals give covalent hydrides, such as NH3, H2O, and HF and transition metals give metallic, or interstitial, hydrides, such as PdH,.. Interstitial hydrides are often nonstoichiometric compounds. 

Hydrogen combines with many metals to form binary hydrides MHX. The hydride ion H has two electrons with the noble gas configuration of He. Binary metal hydrides have the following characteristics ... 

Generally chemists recognize three broad types of binary hydrides (that is, compounds containing hydrogen and one additional element). These are molecular hydrides, saltlike hydrides, and interstitial hydrides. 

From binary hydrides and Pt(Pd) sponge at 593-693 K nnder 0.8 bar (Pd componnds 20 bar) hydrogen pressure ... 

From reactions of binary hydrides MH with T at 753 K and 10 bar hydrogen pressure no compound formation with KH and Fe up to 1073 K and 100 bar Ru does not react with KH, and Os not with NaH and KH under experimental conditions powders either white (Li) or green (Na) all ah sensitive ordered stmctures (Figure 11) from npd at room temperature on deuterides R3c,Z = 6 (hex setting), KtCdCh type stmcture octahedral [THe] " 18-electron complex with T site synunetry 3 surrounded by two M sites in nearly cubic configuration one D site lif 4M+ [THe] " T = Ru, Os, d . Interatomic distances are given in Table 8. 

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