CHEM321 FILE 15A PI-BONDING DETERMINED from GROUP THEORY

CHEM321 FILE 15A PI-BONDING DETERMINED from GROUP THEORY -...

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Unformatted text preview: -BONDING(CENTRAL ATOM)-LIGAND MULTIPLE BONDINGM. R. ChurchillOctober 2 2009(1) Oxides & Oxy-acids-Bonding in Oxides or Oxy-acidse.g., CO32-, NO2-, NO3-, SO2, SO3, SO42-; PO43-, ClO2-, ClO3-, ClO4-,etc.-Bonding is also possible of other non-metallic atoms:N=N, NN, C=C, CC, C=N, CN, P=S, S=S, As=S and many other multiple bonds exist.(2) Transition-metal complexes with -acceptor ligandsTransition-metal complexes with acceptor ligandsLigand-to-metal bonding is accompanied by metalligand - back donationMetal orbital is full (usually d); donor orbital empty (usually antibonding)e.g. CN-, CO, NO, RNC, SCN-, N=C=S-, PR3, AsR3, SbR3, olefins, alkynes LM -bonding and ML -bonding act synergistically.(3) Transition-metal complexes having -donor ligandsTransition-metal complexes having -donor ligandsMetal orbital is empty (usually d-); donor orbital full (usually non-bonding)e.g. =O, N, =N-R, CH, CR etc. Ligand-to-metal bonding is accompanied by ligand-to-metal bonding. Examples here include such species as MnO4- and CrO42-.SPECTROCHEMICAL SERIESThe effects of items (2) and (3) are indicated by the order of LIGANDS in the SPECTROCHEMICAL SERIES.I-< Br-< F-< OH-< CH3CO2-< C2O42-< H2O < py < NH3< en < SO32-< o-phen < NO2-< CN-< CO PR3< NO -acceptorligands have strong ligand fields and are to the right -donorligands provide very weak ligand fields and would be to the extreme left of this table.Group Theoretical Approach to -bonding THE PROBLEM IN VECTOR FORMLet as define the M-L -bond as the z-axisThe ligand atom (L) is assigned two mutually orthogonal vectors (along x & y), which are orthogonal to the -bond. These vectors correspond to the positive lobe of an atomic orbital (of potential -symmetry) on the ligand atom. These orbitals on the ligand could overlap with orbitals of the same symmetry on the central atom (M).Types of Metal-Ligand -...
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This note was uploaded on 12/01/2009 for the course CHE 321 taught by Professor Churchill during the Spring '09 term at SUNY Buffalo.

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CHEM321 FILE 15A PI-BONDING DETERMINED from GROUP THEORY -...

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