i.B,H11Electron-deficientmulti-centerbondsNido structureVAO= 5x4(B) + 11(H) = 31 (needs 31VE)VE= 15(B) + 11 (H) = 26H一Actually having 8 BH o-bonds, 3 BHB 3cH2e bonds, and 2 BBB 3c-2e bonds!?.HHMO treatmentββEB-Eββ=0Eg-EββE-EsolveseqularequationE =E +2βE, =E, =EB-βBBa+Vb+yaWiTriangularBBBBBBB3c-2ebond3c-2ebond
ii. B5H11 Electron-deficient multi-center bonds Triangular BBB 3c-2e bond • VAO= 5x4(B) + 11(H) = 31 (needs 31VE) • VE= 15(B) + 11 (H) = 26 • Actually having 8 BH s-bonds, 3 BHB 3c- 2e bonds, and 2 BBB 3c-2e bonds! Nido structure 0 E - E E - E E - E B B B ( ) 3 1 E E E 2 seqular equation 1 2 3 1 a b a B B E E solve B B B BBB 3c-2e bond HMO treatment
ili.B,HNido structureElectron-deficient multi-centerbondsVAO=5x4(B) + 9(H) = 29HHHVE=5x3(B) + 9x1(H) = 24eBB-B1) 5 B-H -bonds; (10e)BB2) 4 BHB 3c-2e bonds; (8e)HHH3) a B, 5c-6e bond. (6e)Each peripheral B atomcontributesonesp3-HOandoneelectron.The central B atomcontributes three sp3-HOsand 2e
iii. B5H9 Electron-deficient multi-center bonds • VAO=5x4(B) + 9(H) = 29 • VE=5x3(B) + 9x1(H) = 24e 1) 5 B-H s-bonds; (10e) 2) 4 BHB 3c-2e bonds; (8e) 3) a B5 5c-6e bond. (6e) Nido structure • Each peripheral B atom contributes one sp3 -HO and one electron. • The central B atom contributes three sp3 -HOs and 2e
Types of Chemical bonds in BoranesB-H and B-B(a) Single α-bond (2c-2e):HP(b) 3c-2e bond:BBBB(c)Otherpolycenter-polyelectronbondCBBQuestion arisen:How to determine the geometric and electronicstructures of more complicated boranes?
B-H and B-B (c) Other polycenter-polyelectron bond (b) 3c-2e bond: (a) Single s-bond (2c-2e): Types of Chemical bonds in Boranes Question arisen: How to determine the geometric and electronic structures of more complicated boranes?
6.1.2 B,Hn+m with an open-framework structure (includingnido-andarachno-type)andLipscomb's styxmethod.In mid 1950s, Lipscomb proposed the styx method to predictthe topological structures of boranes B,Hn+m with open-framework structures.Linus Pauling(1954&1962NobelPrizewinner)WilliamLipscomb(1976NobelPrizewinner)一RoaldHoffmann(1981Nobelprize winner)Boranesand their chemical bonding:WilliamLipscombWonNobelprize,1976;PassedawayonApr.14,2011
6.1.2 BnHn+m with an open-framework structure (including nido- and arachno-type) and Lipscomb’s styx method. In mid 1950s, Lipscomb proposed the styx method to predict the topological structures of boranes BnHn+m with openframework structures. Boranes and their chemical bonding: William Lipscomb Won Nobel prize,1976; Passed away on Apr. 14, 2011. Linus Pauling (1954&1962 Nobel Prize winner) William Lipscomb (1976 Nobel Prize winner) Roald Hoffmann (1981 Nobel prize winner)
B,Hn+mwithanopen-frameworkstructurehn:the number of B atoms,thus the minimal number of B-H bondsm:thenumberofextraHatomsTypeBHB3c-2eBBB 3c-2eBB2c-2eExtra B-HBBBHHBBBBNumberTheconditionforastableborane:x=m-sorm=x+st=n-sorn=s+tpsetsofstyxpisomersy =(2s-m)/2Todifferentiate the isomers, eachisomer can be labeled bya set of (styx)
n: the number of B atoms, thus the minimal number of B-H bonds m: the number of extra H atoms. BnHn+m with an open-framework structure B B H B B B B H H B B s t y x Type Number BHB 3c-2e BBB 3c-2e BB 2c-2e Extra B-H The condition for a stable borane: x = m-s or m = x+s t = n-s or n = s+t y = (2s-m)/2 p sets of styx p isomers • To differentiate the isomers, each isomer can be labeled by a set of (styx)