Structures of Boranes:Threetypes/seriesB,HgB.H10B4H10Arachno-typeB,Hn+6Nido-typeB,Hn+4B:H12B1oH14(Cage): B.H, 2Closo-type
Structures of Boranes: Three types/series B4H10 B5H9 B6H10 B8H12 B10H14 Arachno-type BnHn+6 Nido-type BnHn+4 Closo-type (Cage): BnHn 2-
6.1.3 Borohydride anions B,H,2-and carboranesCr,B,H(n+n'+m) with closo-structures and the Wade's ruleB,H,2-(closo):· BeHe2-6(octahedral)BsH3(Dan)BgHg(On)B,H"(Dsn)BaHi-zdB:Hg?-(dodecahedral)B12H122(icosahedral)10B,Hg-(C2)BioHioDad)BuH(C2)B12HizUAThere is little tendency to add H+ and form neutral species
6.1.3 Borohydride anions BnHn 2- and carboranes CnBnH(n+n+m) with closo-structures and the Wade’s rule BnHn 2- (closo): • B6H6 2- (octahedral) • B8H8 2- (dodecahedral) • B12H12 2- (icosahedral) There is little tendency to add H+ and form neutral species
polyhedra with n verticestrigonalbipyramidoctahedronpentagonal bipyramidN=5N=6N=7dodecahedrontricappedtrigonal prismN=8N=9bicappedsquareantiprismN=10icosahedronN=12octadecahedron16.8N=11
polyhedra with n vertices
"Closo"series - formula B,H,2Total valenceelectrons:Nye(Total) = 3n (B) + n (H) + 2 (charge) = 4n+2.Total valence atomic orbitals:Nyo(Total) = 4n (B) + n (H) = 5nEach B-H bond uses 2 electrons.(2c-2e o-bond)→ Nye(B-H) = 2n & Nyo(B-H) = 2n.The skeletal VEs (for the polyhedral framework):Nve (skeletal) = (4n + 2) - 2n = 2(n+1) = NFENyo(skeletal) = 5n - 2n = 3n
“Closo” series - formula BnHn 2- • Total valence electrons: NVE(Total) = 3n (B) + n (H) + 2 (charge) = 4n+2 •Total valence atomic orbitals: NVO(Total) = 4n (B) + n (H) = 5n • Each B-H bond uses 2 electrons. (2c-2e s-bond) NVE(B-H) = 2n & NVO(B-H) = 2n • The skeletal VEs (for the polyhedral framework): NVE (skeletal) = (4n + 2) - 2n = 2(n+1) = NFE NVO(skeletal) = 5n – 2n = 3n
MOs in “"closo"-series B,H,2-Wade's (n+1)rulesEach B atom is sp-hybridizedforming an exocentric B-H bond.Each B atom contributes aradialhybrid orbital to form a total of nradial skeletal MOs with the onlyonebonding MObeing occupiedradialtangential1bondingnbondingEach B atom has two tangentialn-1antibondingn antibondingAOs. These AOs form 2n3nskeletalAOs/MOstangential skeletal MOs, half ofwhich are bonding orbitals and n+1 bonding skeletalMOsdoublyoccupiedA n-vertice closo-borane2n-1 antibondingskeletalMOsanion or carborane has in totalNFE= 2n + 2of (n+1)bondingskeletalMOs
Wade’s (n+1) rules • 3n skeletal AOs/MOs • n+1 bonding skeletal MOs • 2n-1 antibonding skeletal MOs • NFE= 2n + 2 MOs in “closo”-series BnHn 2- • Each B atom is sp-hybridized, forming an exocentric B-H bond. • Each B atom contributes a radial hybrid orbital to form a total of n radial skeletal MOs with the only one bonding MO being occupied. • Each B atom has two tangential AOs. These AOs form 2n tangential skeletal MOs, half of which are bonding orbitals and doubly occupied. • A n-vertice closo-borane anion or carborane has in total of (n+1) bonding skeletal MOs