ligands
Ligands - in complex compounds: atoms, molecules or anions that are directly attached to a central atom or central cation, called the coordination center or the core of the complex. The concept of ligand is not clear and in many cases it is a contractual matter. In organic chemistry the term ligand is used interchangeably with the term substitute. The link between addend and atom or central cation is that of the addendum. The ligand atom, which contains the free electron pair, which is built into the free orbitals of the core, or filled with π orbitals, behaving in the same manner. In very rare cases, the connection can take place through free orbital overlapping with the orbits of the central atom. The ligand atom may be a strongly-electronegative element or a non-electronegative element - for example, a carbon atom, by which all organometallic ligands are by definition. Donor groups may be electrically neutral or anionic.