Sp d Hybridization

An extreme example of hybidization is the structure proposed for sulphur hexafluoride, SFe. The six S-F bonds are dhected to the apices of a regular octahedron. An aiTangement which would satisfy this number of covalent bonds is sp d hybridization. The ground state of the sulphur atom is s p° and... 

FIGURE 3.17 One of the five sp d hybrid jjj orbitals, and their five directions, that 5 ... 

Thus the bonding in sulfur hexafluoride SF has for a long time been considered to involve two of the 3d orbitals of sulfur, with the sulfur in a sp d hybridized state and... 

We can also generalize the sum rules (3.37) for a general set of inequivalent sp d hybrids. Each of the nine possible hybrids can be expressed as... 

In iodine heptafluoride, IF, the iodine atom uses sp d hybrid orbitals. 

State the number and type of atomic orbitals that mix to form the set of sp d hybrid orbitals. 

The possibility of orbital reorganization in ion-radicals should be taken into account. Thus, organic derivatives of three-valence phosphorus exist in the sp hybrid state and an electron is removed from one of these orbitals. The cation-radical formed can retain the initial orbital configuration, but can also convert into the sp d hybrid state. In the latter case, one additional orbital of the phosphorus atom becomes accessible for the reactant attack. If Y—H bond in the reactant is weak, the reaction R3P+ -f YH proceeds with the participation of an sp frontal orbital according to the radical mechanism. Thiols are typical reactants with the weak Y—H bonds. If anions (A ) react with RjP, the vacant sp d orbital of the phosphorus appears to be a target. Scheme 3.14 illustrates the orbital pictures and the reaction directions. 

A molecule exhibits sp d hybridization in its bonding structure. The most probable geometric shape of this molecule is... 

Which of the following molecules does not exhibit sp d hybridization ... 

Fig, 7.4 A schematic representation of transition metal sp (dashed curve) and d (solid curve) densities of states when sp-d hybridization is neglected. 

The sp-d hybridization energy is the contribution that results from turning on the hybridization matrix elements in eqn (7.25), resulting in the mixing between the NFE sp and d bands. As expected, it is negative, taking the approximately constant value of about 2 eV across the series. 

In octahedral silicon complexes, two AO (d z, d,2 y2, e symmetry) participate simultaneously in the a-bonding (sp d -hybridization). The d,y, d and d, orbitals with tjq symmetry can be used for ii-bonding with the appropriate orbitals of the substituents. It was put forward that an additional donor-acceptor interaction which increases the coordination number of the second row Main Group element involves continuum of the energetic states lying above the ionization potential... 

Binding of Cl- to an aryl iodide may well involve sp d hybridization at iodine to accommodate the ninth electron, but the involvement of a d-oibital in bonding at sulfur is more controversial. Recently it was discovered that even first row elements can form Cl- complexes the evidence indicates that th complexes utilize three-electron bonds, not d-orbitals. Best explored are templates for radical relay chlorination using nitrogen atoms. 

Initially, hypervalent molecules like PCI5 and SFe were described in terms of sp d" hybrid orbitals, in an extension of the sp" orbital description used to characterize molecules that obey the octet rule. However, ab initio calculations have shown that d orbitals play only a minor role in the bonding of hypervalent molecules. An alternative approach proposed by Pauling invoked combinations of resonance stmctures involving four covalent bonds and one or more additional ionic bonds, as shown in Scheme 1 for PF5. 

In an sp d hybridized phosphorus atom in a TBP molecule, will the atom have a greater electronegativity when bonding through eQuatorial or axial orbitals Explain. 

From a valence bond point of view, the formalMMi of both the dodecahedron and the square antiprism can arise ftom sp d hybridization. The necessity of using fbur d... 

Figure 10.6 Geometry of trigonal bipyramidal sp d and octahedral sp d hybrid bonds.

Most sets of hybrid orbitals are equivalent and symmetric, that is, four orbitals directed to the corners of a regular tetrahedron, six (Psp orbitals to the corners of an octahedron, etc. In the case of sp d hybrids the resulting orbitals are not equivalent. In the trigonal bipyramidal arrangement three orbitals directed trigonally form one set of equivalent orbitals (these may be considered sp hybrids) and two orbitals directed linearly (and perpendicular to the plane of the first three) form a second set of two (these may be considered dp hybrids). The former set is known as the equatorial orbitals and the latter as the axial orbitals. Because of the nature of the different orbitals involved, bonds formed from the two are intrinsically different and will have different properties even when bonded to identical atoms. For example, in molecules like PFj bond lengths differ for axial and equatorial bonds (see Chapter 6). 

Phosphorus peniafluoride ( >3/,). A Lewis structure for the PFj molecule requires ten electrons in the valence shell of the phosphorus atom and the use of 3s, 3p, and l>d orbitals and five cr bonds. It is impossible to form five bonds in three dimensions such that they are all equidistant from one another, but the trigonal bipyramidal (Fig. 6.1e) and square pyramidal arrangements tend to minimize repulsions. Almost every five-coordinate molecule (coordination compounds excepted) which has been carefully investigated has been found to have a trigonal bipyramidal structure. The structure of the PF5 molecule is shown in Fig. 6.1e sp d hybrid). The bonds are of two types axial, the linear F—P—F system and equatorial, the three P—F bonds forming a trigonal plane. 

We see that sp d hybridization uses an available d orbital in the outermost occupied shell of the central atom. The heavier Group VA elements—P, As, and Sb—can form five covalent bonds using this hybridization. But nitrogen, also in Group VA, cannot form five covalent bonds, because the valence shell of N has only one t and three orbitals (and no d orbitals). The set of t and orbitals in a given energy level (and therefore any set of hybrids composed only of t and p orbitals) can accommodate a maximum of eight electrons and participate in a maximum of four covalent bonds. The same is true of all elements of the second period, because they have only t and p orbitals in their valence shells. No atoms in the first and second periods can exhibit expanded valence. 

The central atom, S, is bonded to four atoms and has one lone pair. This is an example of the general formula AB U. Sulfur has five regions of high electron density, so we know that the electronic geometry is trigonal bipyramidal and that the bonding orbitals are sp d hybrids. But now a new question arises Is the lone (unshared) pair more stable in an axial ( ) or in an equatorial (e) position If it were in an axial position, it would be 90° from... 

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