Physical Chemistry Chapter V Polyatomic Molecular Structure 2019/4/10 Chemistry Department of Fudan University

§5-1. Saturated Polyatomic Molecules §5-1-1. Delocalized Molecular Orbital Molecular Orbital Theory 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University B-O approximate single electronic approximate LCAO-MO Secular equation 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Taking CH4 as an example H 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Taking the four H 1s orbitals as bases Td E 8C3 3C2 6S4 6σd 4 1 2 Reduce to the irreducible components 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University orthonormal 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University four symmetry matched molecular orbitals are: 2019/4/10 Chemistry Department of Fudan University

§5-1-2. Localized Molecular Orbital Valence Bond Theory 1 2 3 x z y 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University C: sp3 hybridization Hybrid Orbitals 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University four molecular orbitals are: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-1-3. Connection & Conversion 1. VB theory is an approximate method, whereas MO theory is quite accurate Localized orbital  No constant Energy Delocalized orbital  Energy Eigenvalue 2019/4/10 Chemistry Department of Fudan University

VB MO 2. Conversion between the two kinds of orbitals 2019/4/10 Chemistry Department of Fudan University

Localized Molecular Orbital Delocalized Molecular Orbital Bond length, Binding energy, Charge density, etc. Delocalized Molecular Orbital Spectrum 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-2.Conjugate Molecules The particular characters of the conjugate molecules: The length of the bond is between the double bond and the single bond; Reactivity The stability to the heat 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-2-1.Hückel Molecular Orbital Theory (HMO) The main idea of HMO 1.Take σ-πorbitals Apart 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2.To the π orbitals, HMO assumes: 2019/4/10 Chemistry Department of Fudan University

§5-2-2.Illustrative Examples of HMO Straight chain alkene---butadiene 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Delocalization Energy The four πelectrons fill two lowest orbitals, the total energy of the  system is: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University For isolated double bond system, the total energy of the four π electrons will be: The energy difference is called delocalization energy (DE) 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-2-3. Graphic Theory 1. Conjugate straight chain alkene Number of C atom: n n order secular determinant: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University The general solution of in (m=1, 2, ……, n) 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2. Conjugate Carbocyclic Alkene The general solution of in (m=1, 2, ……, n) 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

§5-2-4. Conjugate Inorganic Molecule 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University CO2 molecule 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University For CO2: Therefore: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-2-5. The Form of Conjugate  Bonding 1. Conjugate atoms must be in the same plane and they both have a p obital perpendicular to the plane. 2. 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Normal m=n Electron sufficient m>n Electron defficient m<n 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Exercise Work out the energy levels and molecular orbitals of propene radical using HMO method. Show the electronic configurations, bondings and delocalization energies of the propene radical, cation and anion. 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-3. Electron-deficient Molecules Structure of B2H6 2019/4/10 Chemistry Department of Fudan University

1. Open three-center bonding Chemistry Department of Fudan University 3c-2e bonding in B2H6 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

2. Closed three-center bonding 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Structure and 3c-2e bonding in Al2(CH3)6 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-4. Coordination Compounds A coordination compound is composed of An electron donor (ligand or Lewis base), an individual atom or molecule which possesses non-bonding lone-pair electrons; An electron acceptor (metal atom, cation or Lewis acid) which possesses a low-lying empty orbital. 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Donor Atom Ligand Central Atom [Ag(NH3)2]+ Coordination Number 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-4-1. Crystal Field Theory(CFT) A complex is regarded as consisting of a central metal cation surrounded by ionic or dipolar ligands which are electrostatically attracted by the cation. 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 1. The splitting of the d orbitals 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Octahedral Field Taking 5 d orbitals of metal as bases E 8C3 6C2 6C4 3C2 i 6S4 8S6 3 σh 6σd 5 -1 1 2 3 The d orbitals split into two sets 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Characteristic Symmetry Element 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University sphere d Free atom Octahedral Splitting energy: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Tetrahedral Field E 8C3 3C2 6S4 6σd 5 -1 1 2 3 Td E T2 2019/4/10 Chemistry Department of Fudan University

Characteristic Symmetry Chemistry Department of Fudan University 1 2 3 x z 4 Characteristic Symmetry Element y 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Square Planar Field 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

2. Spectrochemical Series I- < Br- < Cl- < SCN- < NO3- < F- < OH- < H2O < NCS- < gly < Py < NH3 < en < NO2- < PPH3 < CN- < CO 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 3. Crystal field stabilization energy The crystal field stabilization energy is defined as the energy by which a complex is stabilized due to the splitting of the d-orbitals. It is determined by Pairing Energy(P) and Splitting Energy( ) 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Weak field complexes:   P (high spin) Strong field complexes:   P (low spin) 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Electron Arrangement d1 d2 d3 d8 d9 2019/4/10 Chemistry Department of Fudan University

high spin for d4-d7 octahedral complex 2019/4/10 Chemistry Department of Fudan University

Low spin for d4-d7 octahedral complex 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 4. Jahn-Teller Effect Any non-linear ion or molecule which is in an orbitally degenerate term will distort to relieve this degeneracy. 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University For octahedral coordination High Spin Low Spin 2019/4/10 Chemistry Department of Fudan University

5. The Applications of CFT Chemistry Department of Fudan University ￭The model can be used to understand, interpret and predict the magnetic behavior, colors and some structures of coordination complexes. ￭ But does not explain the bonding in coordination complexes. 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University The most serious defect of the CFT model is that it does not recognize the existence of overlap, and hence the existence of specific bonding interactions, between the ligands and the metal orbitals. 2019/4/10 Chemistry Department of Fudan University

§5-4-2. Molecule Orbital Theory (MOT) LCAO-MO 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 1. Metal-ligand  interactions Orbital of Central Metal Atom dxy, dyz, dxz T2g 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Taking 6 -type orbitals of the ligands as bases: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Ligand Orbitals 2019/4/10 Chemistry Department of Fudan University

The metal-ligand  bonding in an octahedral complex 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2. Metal-ligand  interactions Taking 12 -type orbitals of the ligands as bases: 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Ligand Orbitals 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Case a 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Case b 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-4-3. - bonding complexes 1. Carbonyl Complex 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University 2. Unsaturated Hydrocarbon Complex 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Exercises Use the molecular orbital theory to explain the spectrochemical series (Taking the Cl-, NH3 and CO for example). Work out which coordination compounds listed below show Jahn-Teller distortion: [Co(NH3)6]3+, (2) [MnCl6]4-; (3) TiCl4, (4) Fe(CO)4 (tetrahedral) 2019/4/10 Chemistry Department of Fudan University

§5-5-1. Ab initio methods §5-5-2. Density functional theory §5-5. Quantum Chemical Computational Methods and Molecular Property Calculations §5-5-1. Ab initio methods §5-5-2. Density functional theory 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University §5-5-3. Molecular property calculations 1. Ionization energy and total energy Koopmans rule: 2019/4/10 Chemistry Department of Fudan University

2. Bond energy and dissociation energy 2019/4/10 Chemistry Department of Fudan University

3. Geometry and dipole moment Chemistry Department of Fudan University 2019/4/10 Chemistry Department of Fudan University

4. Charge density, bond order and free valence 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Example:cyclopropene 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University (2)Bond order Example:cyclopropene 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University Note (A) (B)Conjugate molecule (CH2)3C can show the biggest bonding capacity of C atom,that is 2019/4/10 Chemistry Department of Fudan University

Chemistry Department of Fudan University (3)Free Valence Example:C atom 2019/4/10 Chemistry Department of Fudan University