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Co-ordination chemistry (CH2207)

Aims

To illustrate the nature of complex ions in solution and the methods used to study them.

General description

This module will look more closely at the nature of co-ordination complexes of the d-block elements, their structure, bonding and reactivity. Topics such as stability, isomerisations and various preferences in geometries will be discussed with reference to the electronic origins of complex geometries. The spectroscopic (electronic and magnetic) properties of complexes will be highlighted with examples.

Oh and Td complexes and the influence of ligand field stabilisation energy and the idea of formation constants. Magnetics and UV spectroscopy (spectrochemical series and p bonding). Crystal field theory for lower symmetry and Jahn-Teller distortions. Square planar complexes.

A basic introduction to the nature of organometallic compounds will be given. Methods of electron counting will be introduced and the 18 electron rule defined. Reference will be made to examples in bio-inorganic systems.

Practical work will reinforce the synthesis of co-ordination compounds and organometallic species as well as their spectroscopic properties. Explanations of different geometrical preferences and use of chelating ligands will also be highlighted.

Syllabus content

Energy levels in transition metal complexes (Oh, Td and D4h geometries), comparison of molecular orbital & crystal field approaches.

Effects of π-bonding. π-acceptor and π-donor ligands, perturbation of t2g MOs in Oh symmetry.

Simple magnetics, spin only formula and its limitations, high and low spin states.

Spectrochemical series, spectra - d-d and charge-transfer, selection rules, extinction coefficients. Hole formalism. Examples of d1, d4, d6 & d9 complex spectra.

Crystal field stabilisation energy and its effects on thermodynamic and kinetic properties of complex ions (introduction, kinetic inertness, lability, ΔHhyd)

Jahn-Teller distortions. Geometries of lower symmetry.

Formation of complex ions in aqueous solutions, introducing equilibrium constants (stepwise and overall stability constants). The chelate and macrocyclic effects.

Isomerism in coordination complexes (geometric, optical, linkage etc.), spectroscopic identification of isomers.

Organometallics introduction. Types of ligand, notations (ηn & μn), electron counting.

Origins of the 18e- rule (related to MO scheme) and its limitations.

Influences of s and p bonding on spectroscopic properties (CO, CN-, NO etc.).

Practical work :

Will involve the synthesis and elucidation of structure/bonding of a variety of transition metal complexes. In conjunction with lecture material examples will include Td. Oh and square planar complexes whose geometry will be proven by spectroscopic and magnetic measurements.

In addition, syntheses will highlight phenomena such as the chelate effect and template synthesis of ligands.