Standard bonding numbers hydrides

The names of unsaturated compounds are derived by using appropriate substitutive nomenclature rules. Note that trivial names are also allowed for particular polynuclear species, for example, N2H4, diazane, commonly known as hydrazine. For a discussion of names of hydrides in which elements exhibit non-standard bonding numbers, see the Nomenclature of Inorganic Chemistry, p. 85. Note that for the hydrides of Table 5.1 and their derivatives, substitutive names are generally preferred. 

In the absence of any designator, the ending -ane signifies that the skeletal element exhibits its standard bonding number, namely 3 for boron, 4 for Croup 14 [1VA] elements. 3 for the Croup 15 [VA] dements, and 2 for the Croup 16 [VIA) dements. In cases where bonding numbers other than these are exhibited, they must be indicated in the hydride name by means of an appropriate superscript appended to the Creek letter A.13 these symbols being separated from the name by a hyphen. 

Names cfoligonttclear hydrides derived from elements of standard bonding number. Names are constructed by prefixing the ane names of the corresponding mononuclear hydride with the appropriate multiplicative prefix (di-, tri-.letra-. etc.) corresponding to the number of atoms of the chain bonded in series. 

Where there is a choice of parent hydrides among those listed in Table IR-6.1 (or corresponding hydrides with non-standard bonding numbers, cf. Section IR-6.2.2.2), the name is based on the parent hydride of the element occurring first in the sequence ... 

IR-6.2.1 Mononuclear parent hydrides with standard and non-standard bonding numbers IR-6.2.2 Homopolynuclear parent hydrides (other than boron and carbon hydrides)... 

IR-6.2.2.1 Homonuclear acyclic parent hydrides in which all atoms have their standard bonding number... 

IR-6.2.2.2 Homonuclear acyclic parent hydrides with elements exhibiting non-standard bonding numbers... 

Substitutive nomenclature is recommended only for derivatives of the parent hydrides named in Table IR-6.1 (in Section IR-6.2.1), and derivatives of polynuclear hydrides containing only these elements (see Sections IR-6.2.2 to IR-6.2.4). The bonding numbers of the skeletal atoms are understood to be as in Table IR-6.1 (these bonding numbers, e.g. 4 for Si and 2 for Se, are termed standard bonding numbers). Other bonding numbers must be indicated by an appropriate designator (the X convention , see Section IR-6.2.2.2 and Section P-14.1 of Ref. 1). 

In cases where the skeletal atoms of a hydride chain are the same but one or more has a bonding number different from the standard values defined by Table IR-6.1, the name of the hydride is formed as if all the atoms showed standard bonding numbers, but is preceded by locants, one for each non-standard atom, each locant qualified without a space by Xn, where n is the appropriate bonding number. 

Where there is more than one kind of substituent, the prefixes are cited in alphabetical order before the name of the parent hydride, parentheses being used to avoid ambiguity, and multiplicative prefixes being used as necessary. Non-standard bonding numbers are indicated using the. -convention (see Section IR-6.2.2.2). An overview of the rules for naming substituted derivatives of parent hydrides is given in Section IR-6.3, while a detailed exposition may be found in Ref. 3. 

In cases where the bonding number deviates from the standard number defined above, it must be indicated in the hydride name by means of an appropriate superscript appended to the Greek letter X, this symbol being separated from the name in Table IR-6.1 by a hyphen. 

There are many examples of borohydride compounds of these metals, e.g., Cu, Ag, Zn and Cd-BH as neutral and anionic complexes in which the mode of bonding of BH is dependent on the coordination number of the metaP. Higher borane anions also combine with Cu and Ag, yielding both neutral and anionic complexes. Although no borohydrides of Au are isolated, treatment of Au-halide complexes with, e.g., NaBH, is a standard method for the preparation of Au-cluster compounds Copper(I) hydride, first reported in 1844, has the ZnS structure [d(Cn-H) = 0.173 nm (1.73 A) d(Cu-Cu) = 0.289 nm (2.89 A)] and decomposes to the elements when heated. At >100°C the decomposition is explosive. 

However, making the standard assumption that each bond drawn between two atoms results from the sharing of a pair of electrons, the number of valence electrons available for bonding in B2H6 is insufficient. Thus, the seven B—H and B—B bonds would require 7 electron pairs or 14 electrons, but the total number of valence electrons available is only 12, 3 from each boron atom and 1 from each hydrogen atom. Thus the ethane structure is unreasonable and is not observed. Because of the apparent shortage of valence electrons, boron hydrides are often referred to as electron deficient compounds. 

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