Edward J. Barrelt H u n t e r College of the
City University of New York New York, N. Y. 10021
Models Mustrating d Orbitals Involved in Multiple Bonding
In addition to the overall geometry of molecules definrd by their 0 bonds and covalent and van der Waal's radii, Framework Molecular Orbital Models' and Framework Alolecular Models2 have been used to show a bonding involving p orbitals. This was accomplished by using the trigonal bipyramidal metal valence cluster to attain the sp2-hybrid bonding geometry. The octahedral metal valence cluster represcnts the geometry of the sp-hybrid state and has been used to show the orbital overlap involved in the formation of two a bonds. Figure 1 shows Framework Molecular Models (hereafter referred to as FMM) of ethylene, formaldehyde, and acetylene.
This new valence cluster is shown with the thrce metal ones in Figure 3. This mult,iplc valence cluster3 was constructed from readily available ooc-inch plastic spheres4and the linear fasteners supplied with the FAIM set. The sphere was drilled using a drill press wit11 a 90' rotating head to give the geometry which would allow each linear fastener to represent the symmetry L' lence axis of a lobe of a d orbital. The nlultiplc v.
Figure 1. Framework Molecubr Modeir; left, ethylene; center, formddehyde; right, acetylene.
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Figure 3. FMM components and the mulllple valence cluster. Top, left to ,ight: tetrahedral, trigonal bipyromidd octahedral, and multiple valence clurterr Bottom; The right m g l e ond lineor fasteners supplied with the FMM set.
Elements after the second pried have available d orbitals which can participate in bond formation. Sigma bonds involving d orhitals or the various hybrid d-, s-, and porbital combinations can be constructed with the metal valence clusters of the FYIhl Student Set as shown in Figure 2. This paper will describe the use of a new valence cluster to depict the orientation of the symmctry axes of the five d orbitals and the construction of models to show pa-da, drr-da, and 6 bonding. I
BRUMLIK, G . C., BARRETT,E . J.,
J. CHEM.EDUC.,41,
AND
BAUMGARTEN, R . L.,
221 (1964).
BARRETT, E. J., A N D H.kRwEI.L, J. G., Chemistly, 39, (October, 1966): 1967). Available from Prentice-Hall, Inc., ., 40.. (March. . Englcwood Cliffs, N. J. Patents Pending. a Inquiries should be sddl.essed to the author. Available from Are Plastic Co., Jamaica. 35, New York
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Figure 4. The five d orbitals as 9hown by the multiple valence clu.ter. Left: The d Z 2(brown1 and d,~-vz(greyl orbitals. Right: The d,, (yellowl, d,, (orongel, and d., lpurplel orbitals.
cluster representation of the d orbitals is sho~vilin Figure 4. Different colored plastic tubing supplied with the set is used to emphasize each d orbital. This multiple valence cluster can be used to construct models showing the d orbitals involved in a and 6 bond formation. prr-drr Bonding The overlapping orbitals involved in pa-da bond formation and the FAlM interpretation are shown in Figure 5. The bonds are constructed from colored
Figure 2. Left: FMM structure of F e l C N I F . The octahedral valence cluster i3 used to repyesent the metal. Right: FMM strudure of a rquore complex ond o tetrohedrol complex. The octahedral and tetmhedml volence cluster$are used to represent the metal.
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Figure 5. Left: The orbit01 overlap in forming o d*-ps The FMM interpretation showing both the c and r bonds.
bond.
Right:
Figure 6. (Left). The FMM shvcture of the phosphorus-to-oxygen double bond in phosphorus oxytrichloride. CbP =O.
Figure 11. NilPClph.
Figure 8. (Leh). The FMM structure of the metal-to-carbonyl bond.
plastic tubing (colored for atom identification according to the accepted convention) cut at the appropriate covalent radius of each atom and joined by either a linear or angular fastener supplied with the FMM set. Figure G shows a model of the phosphorus-to-oxygen double bond in compounds like phosphorus oxytrichloride. CI,P=O. The multiple valence cluster represents the phosphorus atom. The a hond portion corresponds to donation of an electron pair from phosphorus to oxygen, and the prr-ds bondportion corresponds to donation of an electron pair from oxygen to an d orbital of phosFigure 9. t he FMM ~ t ~ of~ ~ empty t v ~ ~ nickel corbonyl, Ni(CO)c phorus. Figure 7 shows a model of trisilylamine, N(SiH&. The incorporation (delocalization) of the electron pair p orbital of nitrogen into empty d orbitals of the silicon atoms explains the very weal< basic character of the structure and the fact that the molecule is planar rather than pyramidal. Figures 8 and 9 show models of the metal to carbonyl bondsi in nickel carbonyl, Ni(CO)+ The a bond is of thc ligand to metal type, L PI;the drr-pa bond is of the metal to ligand type, PI- L (back bonding). It is this M L ?r bond which alleviates the a c c u m u l ~ tion of negative charge on the metal atom which would
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C.~RTMEI.I., E., AND FOWLES, G. W. A,, "Vsleney and MolecnInr Stntetnre," 2nd ed., Butterworth, London, 1961, p. 240. 'COTTON,F. A., AND WILKINSON, G., "Advanced Inorganic Chernist,ry," Interscience, New York, 1962, p. 754.
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Figure 7. (Right). The FMM ~trvctureof tririlylomine. N(SiHaja.
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result from a bond formation only. This multiple bonding would correspond to the valence bond structure M=C=O.
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Figure 10. Left: Overlapping orbit& involved in dr-drr bond formotion Right: The FMM interpretation of the d*-dr bond.
drr-drr Bonding
The FMM structure of
The overlapping orhitals involved i n drr-da bond formation and the FMM interpretation are shown in Figure 10. An example of this type of bonding is found in metals which have ligands with empty d orbitals such as phosphorus in hTi(PCl&. A model of this structure is shown in Figure 11.
Figure 12. Lefh The overlapping orbitoh involved in S band formation. Right: The FMM interpretotion of the S bond.
Delta Bonding
This type of bonding involves the lateral overlap of properly oriented d orbitals. The overlapping orbitals involved and the FRIIM interpretation are shown in Figure 12. Delta bonding is seen in compounds such as the hydrated copper(I1) acetate salt [Cu(OCOCH3)2]v 2Hz0. The model of this salt is shown in Figure 13. The copper(11) ionelectron configuration (d9)in thesnlid state shows extensive auenchina of un~airedsuins. This and the short Cu-Cu internuclear distance can be accounted for by 6 hond formation involving lateral overla^ of the comer d,.-,. nrwlws." The multiple valence cluster therefore permits a ready visualization of the d orbitals available for all types of bonding in different molecular geometries. The author wishes to thank Mr. Richard Krol for his Figure 13. The FMM structure of [Cuassistance. (OCOCHsh] 2.2H20.
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