S6Structuresofpolyatomicmolecules(ll)Introduction:In chapter 5, we focused on the (localized and delocalized) -and π-bonds within polyatomic molecules in terms of hybridorbital theory (VB) and MO theory as well as the symmetry rulesfor chemical reactions ofpolyatomicmoleculesIn this chapter, we will discuss multi-center bonds in electron-deficient molecules (e.g., boranes and carboranes) and thechemical bonds in coordination compounds
§6 Structures of polyatomic molecules (II) Introduction: • In chapter 5, we focused on the (localized and delocalized) sand p-bonds within polyatomic molecules in terms of hybrid orbital theory (VB) and MO theory as well as the symmetry rules for chemical reactions of polyatomic molecules. • In this chapter, we will discuss multi-center bonds in electrondeficient molecules (e.g., boranes and carboranes) and the chemical bonds in coordination compounds
$6Structures ofpolyatomic molecules (ll)6.1Multi-centerbondsin electron-deficientsystems6.2 Chemical bonds in coordinationcompounds6.3Ligand Field Theory(LFT)6.4 Transition-metal cluster compounds6.5Carbonclustersand nanotubes
6.1 Multi-center bonds in electron-deficient systems 6.2 Chemical bonds in coordination compounds 6.3 Ligand Field Theory (LFT) 6.4 Transition-metal cluster compounds 6.5 Carbon clusters and nanotubes §6 Structures of polyatomic molecules (II)
Qualitative description of Chemicalbonding within a molecule: VB vs. MOVB: Valence AOs or hybridized orbitals of each atom(s)> Forming 2c-2e -/元-bonds with AOs of surrounding atoms> If necessary, resonance of VB structures are used to accountfor electron delocalization (e.g., the II.6 bond in benzene)!MO: LCAO-MO→ Formation of bonding & nonbonding MOs? Both hybridization & electron delocalization (e.g., II,b bond)are inherently taken into account.A molecule/an aggregate of atoms can have several isomers.How to quickly predict its structure/bonding pattern?
Qualitative description of Chemical bonding within a molecule: VB vs. MO • VB: Valence AOs or hybridized orbitals of each atom(s) Forming 2c-2e s-/p-bonds with AOs of surrounding atoms. If necessary, resonance of VB structures are used to account for electron delocalization (e.g., the 6 6 bond in benzene)! • MO: LCAO-MO Formation of bonding & nonbonding MOs. * Both hybridization & electron delocalization (e.g., a b bond) are inherently taken into account. A molecule/an aggregate of atoms can have several isomers. How to quickly predict its structure/bonding pattern?
Qualitative description of Chemicalbonding within a molecule: VB vs. MOA molecule/an aggregate of atoms can have several isomers.How can one quickly predict its structure/bonding pattern?Chemical bondings occur between the valence atomicorbitals (VAOs)(and valence electrons (VEs)) of theconstituent atoms within a molecule2.The more VEs and VAOs involved in chemical bondingsthe more stable is a molecule> A molecule prefers the bonding pattern/structure thatinvolves as many bonding VEs & VAOs as possible
Qualitative description of Chemical bonding within a molecule: VB vs. MO 1. Chemical bondings occur between the valence atomic orbitals (VAOs) (and valence electrons (VEs)) of the constituent atoms within a molecule. 2. The more VEs and VAOs involved in chemical bondings, the more stable is a molecule. A molecule prefers the bonding pattern/structure that involves as many bonding VEs & VAOs as possible! A molecule/an aggregate of atoms can have several isomers. How can one quickly predict its structure/bonding pattern?
A brief summary on the electronic structures ofmolecules we have learnt(MO & VB)A polyatomic molecule with a closed-shell electronicconfiguration has m(=even) VEs and n VAOsIfm=n,VB: n/2 2c-2e (α-/元-) bonds ( first);MO: n/2 bonding MOs (occupied!)& n/2 antibonding MOsThen if necessary can electron delocalization be consideredC,H2: 10 VAOs/VEs = 2x4 (C) + 2x1(H)> VB: 3 o-bonds & 2 π-bond> MO: 3 - & 2 元-bonding MOs
A polyatomic molecule with a closed-shell electronic configuration has m(=even) VEs and n VAOs. 1) If m = n, VB: n/2 2c-2e (s-/p-) bonds (s first!); MO: n/2 bonding MOs (occupied!) & n/2 antibonding MOs. A brief summary on the electronic structures of molecules we have learnt (MO & VB) C2H2 : 10 VAOs/VEs = 2x4 (C) + 2x1(H) VB: 3 s-bonds & 2 p-bond. MO: 3 s- & 2 p-bonding MOs . Then if necessary can electron delocalization be considered