Coordination Number: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | higher
The concept of a coordination number is a very useful one. It applies to main groups and transition elements in the same way, although coordination compounds in the classical sense include mostly transition metals. Coordination numbers can range from 1 to 16. In general however, coordination numbers will be 6 and lower for the first row transition metals. In the following pages, examples for various coordination numbers are given. Coordination numbers apply to main group element compounds, such as water, but also to transition metal complexes such as TiCl4
Transition metal complexes with the coordination number 1 are rare. In the case of main group elements this coordination number is more common, e.g. in HF, ICl. It can be also observed in the gas phase.
Some of the examples known are the copper(I) complex shown here and the analogous Ag(I) complex made by Strähle et al. They used the bulky 2,4,6-(triphenyl)phenyl ligand to prevent aggregation of the molecules (Reference: Lingnau, R.; Strähle, J. Angew. Chem. Int. Ed. Engl., 27, 1988, 436).