Isoelectronic compounds

We have also examined the reaction of THFBH3 with [0s3(y-H)2(C0)10](4,5). Our purpose was to determine if a reaction analogous to hydroboration would occur to give a compound isoelectronic with the known [0s3(y-H)2(y-CH2)(CO)10](6). The following reaction was observed. 

B. Heterocyclic Compounds Isoelectronic with the Double-Charged Parent... 

The cohesive energy per bond (commonly called bond energy) for the homopolar semiconductors and compounds isoelectronic with them, plotted against covalcncy. The lines represent an extremely simple empirical rule. 

According to Huisgen (1963), a 1,3-dipole is a compound isoelectronic with either propargyl anion, [CH=CH—CH2], or allyl anion, [CH2=CH—CH2] , being linear and bent species, respectively. On the other hand, the dipolarophile is an unsaturated compound. Thus, the above equation can be more explicitly written ... 

Scheme 8.6. Stabilization Energy and Index of Aromaticity for Heteroaromatic Compounds Isoelectronic with Benzene and Naphthalene... 

SOURCES of data Values of V(,(d) were chosen to bring the total cohesive energy into agreement with experiment for the homopolar solid, and held fixed in the compounds isoelectronic with them. The theoretical is predicted by using Eq. (7-3) and the values from the first three columns. Experimental values were obtained by adding the heat of formation (the energy required to separate the compound into elements in the standard state), from Wagman et al. (1968), to the heat of atomization of the elements, from Kittel (1967, p. 98). A correction of about 0.01 eV/bond should be made to compensate for the different temperatures at which the heat was measured. 

In this case the covalency of boron is brought up to four because the donor molecule supplies the necessary electrons. The adduct formed, trimethylamine-borane, is a stable white solid. Other compounds of a similar kind are known, all derived from the simple structure H3N -> BH3. This compound is isoelectronic with ethane, i.e. it contains the same number of electrons and has the same shape. 

There are similar analogues to other aliphatic hydrocarbons, for example HjN BHj, which is isoelectronic with ethene, and a most interesting compound called borazine, B3N3H6, which possesses physical properties remarkably like those of the aromatic analogue ... 

Boron nitride is chemically unreactive, and can be melted at 3000 K by heating under pressure. It is a covalent compound, but the lack of volatility is due to the formation of giant molecules as in graphite or diamond (p. 163). The bond B—N is isoelectronic with C—C. 

Isocyanide is isoelectronic with CO and a reactive compound in the presence of Pd catalysts. The heterobicyclic compound 127 is obtained by the successive insertion of 2.6-xylyl isocyanide (126) into the Pd-hydride bond formed from the hydrosilane[121. Aryl isocyanide inserts into the Si—Si bond in oligo-silanes. For example, 3 mol of 2,6-xylyl isocyanide insert into the tetrasilane 128 to give 129[122],... 

Indole is classified as a 7c-excessive aromatic compound. It is isoelectronic with naphthalene, with the heterocyclic nitrogen atom donating twm of the ten 7t-electrons. 

Boron forms B—N compounds that are isoelectronic with graphite (see Boron compounds, refractoryboron compounds). The small size also has a significant role in the interstitial alloy-type metal borides boron forms. Boron forms borides with metals that are less electronegative than itself including titanium, zirconium, and hafnium. 

The copper(I) ion, electronic stmcture [Ar]3t/ , is diamagnetic and colorless. Certain compounds such as cuprous oxide [1317-39-1] or cuprous sulfide [22205-45 ] are iatensely colored, however, because of metal-to-ligand charge-transfer bands. Copper(I) is isoelectronic with ziac(II) and has similar stereochemistry. The preferred configuration is tetrahedral. Liaear and trigonal planar stmctures are not uncommon, ia part because the stereochemistry about the metal is determined by steric as well as electronic requirements of the ligands (see Coordination compounds). 

Ethylene is another molecule that is similar to formaldehyde. The two compounds are isoelectronic. In the case of ethylene, the oxygen in formaldehyde is replaced by a carbon with two additional hydrogens attached to it. 

The BH4 ion is essentially non-coordinating in its alkali metal salts. However, despite the fact that it is isoelectronic with methane, BH4 has been found to act as a versatile ligand, forming many coordination compounds by means of 3-centre B-H M bonds to somewhat less electropositive metals. " Indeed, BH4 ... 

Two factors have contributed to the special interest that attaches to B-N compounds. First, the B-N unit is isoelectronic with C-C and secondly, the size and electronegativity of the 3 atoms are similar, C being the mean of B and N ... 

The binary compounds of the Group 13 metals with the elements of Group 15 (N, P, As, Sb, Bi) are stmcturally less diverse than the chalcogenides just considered but they have achieved considerable technological application as III-V semiconductors isoelectronic with Si and Ge (cf. BN isoelectronic with C, p. 207). Their stmctures are summarized in Table 7.10 all adopt the cubic ZnS stmcture except the nitrides of Al, Ga and In which are probably more ionic (less covalent or metallic) than the others. Thallium does not form simple compounds... 

Carbon is known with all coordination numbers from 0 to 8 though compounds in which it is 3- or 4-coordinate are the most numerous. Some typical examples are summarized in the Panel (p. 291). Particular mention should also be made of hypercoordinate non-classical carbo-nium ions such as 5-coordinate CHj", square pyramidal CsHs (cf. the isoelectronic cluster B3H9, p. 154), pentagonal pyramidal C6Me6 " (cf. iso-electronic Bf,Hio, p. 154) and the bicyclic cation 2-norbomyl, C7H] 1... 

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