Chapter 22 Transition Metals week 2 2009

Chapter 22 Transition Metals week 2 2009 - Section 22.5...

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Section 22.5. Bonding in Coordination Complexes: Ligand Field Theory. The most modern theory, an amalgamation of the older ‘crystal field theory’ and molecular  orbital theory. It explains well the observed properties of coordination complexes. The theory assumes that the attraction between M x+  and L is largely (but not completely) ionic/ electrostatic i.e. that the M-L bond is primarily due to an electrostatic (charge) attraction  between the positive charge of M n+  and negative (or partial negative) charge of L -  or L - δ , e.g.  Cl - , Br - , CN - , NH 3 , H 2 O, etc. The great thing about Ligand Field Theory is that it considers the change in energy of the metal  d-orbitals caused by the approach of the L to the M.  This explains the observed colors and many other props. As the ligands L approach the M x+  positions that they will occupy for that coordination  geometry, they destabilize (raise the energy of) those d-orbitals occupying that region of space  more than they destabilize those orbitals that do not, i.e. all d-orbitals are destabilized, but  some more than others. Thus, the d-orbitals do not all have the same energy anymore  (they do in  the free M x+  ion). The shapes of the five d orbitals are shown in blue in figures B-F. Only the d z2 and d x2-y2 point towards the L (orange balls).
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Chapter 22 Transition Metals week 2 2009 - Section 22.5...

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