chapter6bw

Trigonal bipyramidal square
6.1.2 Crystal Field Model • focuses on the energies of the d orbitals. • • • • • Assumptions 1. Ligands are negative point charges. 2. Metal-ligand bonding is entirely ionic. strong-field (low-spin): large splitting of d orbitals weak-field (high-spin): small splitting of d orbitals
1. spectrochemical series CN– > NO2– > en > NH3 > H2O > C2O42– > OH– > F– > Cl– > Br– > I–
A. Crystal field splitting
2. charge on metal weakest bond smallest ∆
3
“Nido” series – formula BnH(n+4) •Total valence electrons(VEC) = 3n (B) + n(H) + 4 (extra H and/or negative charges) = 4n +4 •Framework electrons (NFE) =2n+4 (n+2 pairs). •The structure of the “nido” compound is based on the “closo” polyhedron with one more vertex than the “nido” compound. “Arachno” series – formula BnH(n+6) •Total valence electrons(VEC) = 4n +6 •Framework electrons (NFE) =2n+4 (n+2 pairs). •The structure of the “nido” compound is based on the “closo” polyhedron with two more vertex than the “nido” compound.
higher E
strongest bond largest ∆
weakest
B : sp 3
β
EH - E
6.1.1 Boranes and their relatives
H
B
3 1.
2Å H
96.5
Å 19 H 1.
B
121.8
β 0
E2 = E B
β
0 β =0 EB - E (bonding ) (anti - bonding ) (anti - bonding )
H
Electron-deficient multi-center bonds
Alkali metals and alkali earth metals
[Li(CH3)]4
H
H B Be H
H B H
H
Li CH3
H
H
6.2 Chemical bonds in the coordination compounds
A. Crystal field splitting
A. Crystal field splitting
dz 2 dx2 - y 2
eg t2g
crystal field splitting, ∆
E
3d
dxy dxz
dyz
"naked" metal
coordination complex
A. Crystal field splitting
B B B B H
p sets of styx
p isomers
H
(b) 3center-2electron bonds s
B B
B H
t
B
y
H B B H B B B H B H H B H H H H
x
H B BH2 H B B H (2402) BH2 H
The topological structure of B6H10
MOs in “closo” series
Wade’s rules
Structure of Carboranes
1,5-C2B3H5 n+1 bonding and nonbonding MOs 2n-1 antibonding
Notes: B-H σ orbital and its electrons are not taken into account
New theories arose to describe bonding. –Valence bond, crystal field, and ligand field.
O O C H2C N CH2 CH2 O C H2C O N
O CH2 C O CH2 C O O
ethylenediaminetetraacetate (EDTA4–) (hexadentate)
Be(CH3) 2
H3 C H3C Be C H3 Be CH3 H3C Be C H3 H3 C Be C H3 H3 C Be CH3 Be C H3 H3 C Be C H3 H3 C Be C H3 H3 C Be
dimer
trimer
polymer
4
Coordination compounds compounds composed of a metal atom or ion and one or more ligands. – Ligands usually donate electrons to the metal – Includes organometallic compounds Typically consists of a complex ion and counter ions (anions or cations as needed to produce a neutral compound). [Fe(en)2(NO2)2]2SO4 [Co(NH3)5Cl]Cl2 [Co(Co(NH3)4(OH2)3]Br6
(4220)
(3311)
Structure of Boranes
6.1.3 For Borohydride ions BnHn2-’s closo structure and carboranes CnBnHn+n’+m
BnHn2-(closo) B4H42-( tetrahedral)
B4H10
B5H9
Three center two electron B-H-B bond:
ψ3
ii.
B5H9
H
Electron-deficient multi-center bonds
H B H B
ψH
ψ1 ψ2
HHLeabharlann B H B HEB - E
B
β
EB - E
ψ B1
ψ B2
H
β β
β
β β =0 EB - E
H
solve seqular equation E1 = EB + 2 β E 2 = E 3 = EB − β
H
H
H
B
H H
B
H
B B B
ψ1 =
1 (ψ a + ψ b + ψ a ) 3
3center-2electron bonds
1
Chemical bonds in Boranes
(a) Single bond B-H B-B
6.1.2 For BnHn+m’s open structure (including to nido and arachno) n equals to number of B-H bonds Its stationary condition: x = m-s t = n-s y = (2s-m)/2
sp sp2 sp3 dsp2 dsp3 d2sp2 d2sp3
pyramid
octahedral tetragonal
Anti-square pyramid
Bicapped square antiprism
icosahedral
5
Crystal-Field Theory
Crystal-Field Theory
6.2.1 Coordination polyhedron
molecualr Ag(NH3)2+ CuCl3Ni(CO)4 PtCl42Fe(CO)5 C.N. 2 3 4 4 5 5 FeF64others 6 8 8 10 12 Ih
hybridization type
Symmetry geometry linear D3h Td D4h D3h C4v Oh D4h D4d triangular tetrahedral square planar
H
E1 = E H + cβ ( E2 > E H ) E3 = E B − c' β
H
H
H
B
H H
B
H
B: 3 valence electrons forms 2 B-H bond
1 ψ 1 = (ψ B1 + 2ψ H + ψ B 2 ) 2 1 ψ2 = (ψ B1 − ψ B 2 ) 2 1 ψ 3 = (ψ B1 − 2ψ H + ψ B 2 ) 2