natureARTICLESchemistryPUBLISHEDONLINE:29JANUARY2012DOI:10.1038/NCHEM.1263QuadruplebondinginC,andanalogouseight-valenceelectronspeciesSasonShaiki*,DavidDanovich,WeiWu2,Peifeng Su2,HenryS.RzepaandPhilippeC.HibertyTriple bonding is conventionally considered to be the limit for multiply bonded main group elements,despite highermetal-metal bondorders beingfrequentlyobservedfortransitionmetalsand lanthanides/actinides.Here,usinghigh-levetheoretical methods,we show that C2 and its isoelectronic molecules CNBN and CB(each having eight valenceelectrons)areboundbyaquadruplebond.Thebondingcomprisesnotonlyone(randtwo-bonds,butalsooneweakinverted'bond, which canbe characterized bythe interaction of electrons intwo outwardlypointing sphybrid orbitals.Asimpleway of assessingtheenergy of the fourth bond is proposed and is foundto be ~12-17kcalmol-1fortheisoelectronic species studied,and thus stronger than a hydrogen bond. In contrast, the analogues of C that containhigher-rowelements, suchas Si,andGez,exhibitonlydoublebonding.b:C=C:1ECC2三CC31
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1367April,1931THENATUREOFTHECHEMICALBOND[CONTRIBUTION FROM GATES CHEMICAL LABORATORY, CALIFORNIA INSTITUTE OFTECHNOLOGY,NO.280]THE NATURE OFTHE CHEMICALBONDAPPLICATIONOFRESULTSOBTAINEDFROMTHEQUANTUMMECHANICSANDFROMATHEORYOFPARAMAGNETIC SUSCEPTIBILITYTO THE STRUCTUREOFMOLECULESBY LINUS PAULINGPUBLISHEDAPRIL6,1931RBCEIVEDFEBRUARY17,I931During the last four years the problem of the nature of the chemicalbond has been attacked by theoretical physicists, especially Heitler andLondon, by the application of the quantum mechanics. This work hasled to an approximate theoretical calculation of the energy of formation andof other properties of very simple molecules, such as Ha, and has also pro.vided a formal justification of the rules set up in 1916 by G.N. Lewis forhis electron-pair bond.In the following paper it will be shown that manymore results of chemical significance can be obtained from the quantummechanical equations, permitting the formulation of an extensive andpowerful set of rules for the electron-pair bond supplementing those ofLewis. These rules provide information regarding the relative strengths2
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Statement byLinus Pauling about themanuscript on thenatureof thechemical bond6August1979During my early years as a scientist, beginning in i919,I had a special interestintheproblem of the natureof the chemicalbond; that is, the nature of the forces that hold atoms together inmolecules,crystals, and other substances,Much of my work duringthis early period was directed toward a solution of this problem, byapplication of both experimental and theoretical methods,Assoon asquantum mechanics was discovered, in 1925,I began striving to applythis powerful theory to the problem.I published several theoreticalpapers in this field during the next few years, without, however,having been ableto answeranumber of important questions.Thenone evening.inDecember,1930,whileIwas sitting atmydeskinmy study at our home on Arden Road and California Street, in Pasadena,California,I had an idea about a way to simplifythe quantum-mechanicalequations in such a manner as to permit their easy approximate solution.I was so excited about this idea that I stayed up most of the night,applying theideatovariousproblems,During the next two months I continued to work on this ideaand to write a paper communicating the results of its application tothe problem of the nature of the chemical bond.As I recall, themanuscript to which this is an introduction was written in early February.1931.A typescriptwas prepared from it,and the manuscript was putinthe wastepaper basket, presumably by me, although I do not have a clearmemory of this matter.Forty-seven years later the manuscript wasgiven to mebyProfessor Ralph Hultgren,In193l Ralph Hultgren wasone of mygraduate students,working for his Ph.D.in chemistry.Hestated, when he gave me themanuscript, that he had removed it fromthe wastepaper basket and had kept it for the intervening forty-sevenyears.I made some changes in the typescript, and the revisedtypescript was submitted to the editor of the Journal of the AmericanChemical Societyon17February193l,Itwas published in theApril3issue,whichappearedon6April1931,onpages1367to1400of theJournal of the American Chemical Society.Volume 53.The short
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time that elapsed between receipt of the article and publication in theJournal indicates thatthe Editor of the Journal,Professor Arthur B, Lambof Harvard University,did not go through the usual process of submittingthe paper to referees for criticism,but instead decided that itwasproper for itto be sent immediately to the printer.There are a few differences between the manuscript andthe published paper.The only major ditference is that I removed thesection on the single-electron bond, pages 4 to 7 of the manuscript,before submitting the typescript for publication,This section on thesingle-electron bond was later expanded, and was published as aseparate paper, with the title The Nature of the Chemical Bond. IL. TheOne-Electron Bond and the Three-Electron Bond. Journal of the AmericanChemicalSociety53,3225-(a931).Duringthefollowingtwoyearsfive more papers were published with the title "The Nature of theChemical Bond, IIl, IV, V, I, and VII, in the Journal of the AmericanChemical Society and the Journal of Chemical PhysicsThese seven papers, and especially the first one, for whichthe original manuscript has been preserved, constituted the principalbasis of knowledge for my bookTheNature of the Chemical Bond,thefirstedition of which was published by Cornell University Press in lssg(secondedition1940,third edition1960).This193lpapermightwellbeconsideredthemost importantpart of the workforwhichI was awardedtheNobel Prizein Chemistryin1954
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