However., in MOT, the 3d orbitals of P is not involved in theP-X bonds in PX,(X = Cl, F)An alternative model to describe the axial bonding insuchbipyramidal molecules as PXs:Key points:The equatorial P-F bonds are normal -bondTheaxialF-P-Fbond:a3-center4-electronbondPs,antibondingP+-F-FEquivalentVBmodel2,nonbondingresonanceofVBstructuresAxialP-Fbondorder,bonding= 1/2MO model
However, in MOT, the 3d orbitals of P is not involved in the P-X bonds in PX5 (X = Cl, F) . An alternative model to describe the axial bonding in such bipyramidal molecules as PX5 : Key points： • The equatorial P-F bonds are normal -bond. • The axial F-P-F bond: a 3-center 4-electron bond. Equivalent VB model: resonance of VB structures MO model Axial P-F bond order = 1/2
dsp2hybridization(square planar)e. dSquareplanar:D4hd2-v2,S,Px,P,e.g., Ni(CN)42-, AuCl4Equivalent case (α=/)Φh3IIQQdO-2-2J2pr111dh1dn23d0dn2十aSV2px22X111Φn40bCD-2Ph3V2py2X11dD20h4py22X2
Square planar: D4h 2 2 2 2 2 2 2 2 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 4 3 2 1 p y x y h s p y x y h s p x x y h s p x x y h s d d d d x y px py d 2 2 ,s, , h1 x y h3 h2 h4 e.g., Ni(CN)4 2 , AuCl4 e. dsp2 hybridization (square planar) • Equivalent case ( = ¼)
f. d?sp3(sp3d2)hybridization (Octahedral)2,d,2-y2,S,Px,Py,P,172一Q07123d2OC121OC321612福入OCEquivalentcase2120C5OC6336
2 3 1 2 1 6 1 5 z oc s pz d 2 2 2 12 1 2 1 2 1 6 1 1 x y z oc s px d d 2 2 2 12 1 2 1 2 1 6 1 2 x y z oc s py d d 2 2 2 12 1 2 1 2 1 6 1 3 x y z oc s px d d 2 2 2 12 1 2 1 2 1 6 1 4 x y z oc s py d d 2 3 1 2 1 6 1 6 z oc s pz d x y x y z z d 2 ,d 2 2 ,s, p , p , p f. d2sp3 (sp3d 2 ) hybridization (Octahedral) F S F F F F F 1 3 2 4 6 x y z 5 • Equivalent case sp3d2
Hybridization schemesspndm gives a“complete"set of hybrid orbitals for"any"geometrylinearspsp2trigonal planarsp3tetrahedralsp3d (d,2)trigonal bipyramidalsp3d(dx2-y2)square pyramidalSp2d2square pyramidalp3d2octahedralsp2dsquareplanar
Hybridization schemes • spndm gives a “complete” set of hybrid orbitals for “any” geometry. sp linear sp2 trigonal planar sp3 tetrahedral sp3d (dz 2 ) trigonal bipyramidal sp3d(dx 2 -y 2 ) square pyramidal sp2d 2 square pyramidal sp3d 2 octahedral sp2d square planar
3. The angle between two hybrid orbitals1)spnhybridizationLet's define = Vαd, + /1-αd,gh = /α,Φ, + /1-α,Φpdijm, = a,, +/1-α,pwhere?D=x,ppx + y,dp, + z,d,Note the angle between the two vectors dp; and dp, is the angle 9jbetween the two hybrid orbitals dh: and hj , i.e.cos, = J pipp,dt
3. The angle between two hybrid orbitals 1) spn hybridization h s 1p hj j s 1 j pj pi h i i s 1i p i px i py i pz x y z i where pi is d i j p i p j cos hi hj ij Note the angle between the two vectors pi and pj is the angle ij between the two hybrid orbitals hi and hj , i.e., Let’s define