Back donation

Back donation

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  PRESENTED BY: Khondaker AfrinaHoque. ID-1114015, Reg:900048 Department of chemistry. Comilla university 12/14/2018 1
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  PRESENTATION ON BACK-DONATION OFCO - LIGAND 12/14/2018 2
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  Back-donation of CO-ligand Back donation: A description of the bonding ∏-conjugated ligands to a transition metal which involves a synergic process With donation of electrons from the filled ∏ -orbitals or lone pair orbital of the ligand into an empty orbital of the metal, together with release (back donation ) of electrons from an nd orbital of the metal into the empty ∏*-antibonding orbital of the ligand. 12/14/2018 3
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  Molecular orbital descriptionof CO LUMO HOMO 12/14/2018 4
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  METAL-CO BINDING BINGND TOSINGLE METAL BRIDGING MODES OF CO Metal carbonyl binding may occur in two ways: 12/14/2018 5
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  FIGURE: sigma &pi interaction between CO & metal atom Dative bond M←CO(σ) M ←C bond is strengthened. M →CO (∏*) ∏ bond. M-C bond strengthen. C-O bond weakened. HOMO LUMO M-C bond order >1 C-O bond order<3 BINDING TO SINGLE METAL ATOM 12/14/2018 6
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  BRIDGING MODES OFCO Triply bridging CO Further weakens the C-O bond Lower energy to stretch. Infrared band for C-O lower than doubly bridging case. 12/14/2018 7
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  IR study ofmetal-carbonyl bond The stronger the bond between two atoms , the larger the force constant ; consequently , the larger the energy necessary to stretch the bond and the higher the energy to stretch the bond and the higher the energy of the corresponding band in the infrared spectrum. 12/14/2018 8
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  free CO: vco= 2143 cm-1 M C O M C O M M C O MM 1850–2120 cm-1 1750–1850 cm-1 1620–1730 cm-1 IR study of metal-carbonyl bond The more metal , the more electros to donate to C-O bond.. The C-O bond lengthen & weaken, results less stretching frequency. 12/14/2018 9
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  complex v(CO),cm-1 [Ti(CO)6]2- 1748 [V(CO)6]-1859 Cr(CO)6 2000 [Mn(CO)6]+ 2100 [Fe(CO)6]2+ 2204 IR study of metal-carbonyl bond 12/14/2018 10
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  12/14/2018 11 Thanks ToAll
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  QUESTIONS? 12/14/2018 12