Useful Concepts in Coordination Chemistry

8 Housecroft, C.E. and Sharpe, A.G., Inorganic Chemistry, 3 edn., Prentice Hall Upper Saddle River, 2007. 

The study of supramolecular complexes of metal cations is really nothing more than the coordination chemistry of relatively labile (i.e. ligand substitution is relatively rapid under ambient conditions) metal ions and relatively elaborate, usually chelating or multidentate ligands (see Section 1.5). It is therefore worth spending a little time reviewing some basics of coordination chemistry before looking at specific supramolecular systems. Experts read no further  

A complex compound is compound formed between reactants of which the valencies are already formally saturated, e.g. C0CI2 + 2 Et4N CH (Et4N)2[CoCl4]. All three compounds are stable 

Supramolecular Chemistry, 2nd edition J. W. Steed and J. L. Atwood 2009 John Wiley Sons, Ltd ISBN 978-0-470-51233-3 

From the Latin ligare, to bind. For an interesting discussion of the use and spread of this term see Brock, W. H., Jensen, K. A., Jprgensen, C. K., Kauffman, G. B., The origin and dissemination of the term ligand in chemistry. Polyhedron 1983, 2, 1-7. 

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