014. 3c-2e Bonds.pdf

.- The correct shapes. wrrr~~pondin:! to the polyhedra and polyhedraltraementi oredictc.d tw Wade's rules (61. natumll\.Figure 3 (left) Dewar n complex for Clz-CzHnFigure 4. (right) Olah complex for CHI-NO2+-/result fro; "inflaiing" these-styx structures, each boroni having an approximately tetrahedral arrangement of bonds1 and the flexibility of the bonding components allowing forconsiderable distortion from the deal angles if necessarv. Useof any one of the many possible resonance styx structures forthe higher boranes also gives the proper geometry for eachspecies, the choice of the styx structure used being dictatedby the absence of open 3c-2e bonds and (for aesthetic reasons)the symmetry of the components (7). Finally, Figure 6 showsa model for the carborane 2.4-C~BsH7 based on the structure@&$&(71'8QJFigure 5. (left) (a) BIHlo (b) BsHxFigure 6. (right) 2.4-C&H7recently proposed by Lipscomb (2) on the basis of localizedMO calculations.It is apparent from the above examples that commercialproduction of 3c-2e bonding components (and possibly otherlocalized multicentered components such as the 4c-2e bondsin Pt4(CH3)16 and Lid(CH&) would substantially enhancethe value of molecular model kits for the inorganic and organicchemist alike.The author would like to thank Mr. Russ Riley for his helpin making the necessary bonding components and Dr. GlennDirreen for photographing the models.also replaced by straight sections of polyethylene tubing togive a uniform representation of all bonding components. The3c-2e components were cut so that each arch of the Y roughlyspanned a distance equivalent to the longest straight linebonding component (about 1% in.). The tubing was slightlylarger than the holes in the balls and trimming of the ends witha razor insured a secure fit for the bonding components.Some example models are shown in Figures 1 through 6.Figure 1 shows a model of Ala(CH&j, Figure 2 the Ag+-henzenecomplex in eqn. 2, Figure 3 the Dewar a complex in eqn.3, and Figure 4 the CH4-N02+ intermediate in eqn. 4. Figure5 shows models of B4H10 and BeH10 corresponding to thestyxstructures(-21('-21-1 1 4- (6)w 5-411) An extended survey of currently svailablecnmmercial model kits har- recently been givenhy Wailon, A.,"Mc,lecular and Crystel Stmeture Mdels," Halbted Prescr, Chichenter.England. 1978.(2) Reade* interested in the theoretical jurtifieafinn nElncalized hundingeomlwnenfs landconsequently uf ball and stick mudelr in general) and in the distinction between de-Incalined, lueaiired, and multicentered should conult the review by England, w.,Salmon,L.S.,andRuedenberg,K..Furbrhr. Chem Forsch.. 23.31 l1971l.Areview01 localized Mo results for multieenteied bonds in boranes and carboranes can hefound by consultine Lip%cumb. W. N.. Arc. (7,nrn Res, 6.257 119731. ABBRIY~~ dthis work Lipscnmb has suggested ceitain modifications ui the eonventianal sly=picttms:see Eprtein. I. R. and Lipscomb. W. N..lnon. Chem.. 10,1921 l19711.I31 Dpwar. M. J. S.. "The Elec~onieThpowofO~gsnicChemirfw."Oxford Univemity Press.oxford, ,949.I41 Oiah. G.. "Carhorationn and Eleetrophilie Reactions: Wilev, New York, 1974.151 The only malecular modeis 1 nm aware of which attemptto represent 3e-2e bond3 arebardon the tangent-sphere malelpopularized by Bent IseeBent, H.,Forischr. Chsm.Forsch.. 14, 1 119701! and commonly used to represent Gillespie's VSEPR. rules forpredicting molecular geometry. Model kit3 based 0" the use "f pla~tie sphere. andrubber bands have heen extensively used by King lkee King. L. C., Ch~misliy. 37 121,12 I19641l U represent such tangent-3pheredomains.and Sunderwfrth IseeSunderuirth.S.G., J. CHEM. EDUC.. 47.728 119701) hasgiven sometangent-sphere malelrof 3e-2e bonded fritermediates in organic chemistry.Ifii Wade, K..Chrm. Rrit., 11.177 (1976).171 Lipscomb. W. N., "Boron Hydrides," Benjamin. NewYork. 1963.