Coordination complex

A coordination complex contains a central atom, often a metal ion, bound to surrounding ligands in coordination chemistry. The metal oxidation state and the ligand donor types are separate pieces of its description.

A complex with an accessible coordination site or low electron count that permits coordination ligand capture. electron deficiency and geometric accessibility must both be assessed.

A complex with a cyclobutenyl ligand. Eta-three binding of its allylic portion can stabilize the ring formed by closure of an appropriately folded metal-dienyl chain.

A four-coordinate complex whose donor atoms lie approximately at the corners of a square. Many low-spin d-eight metal complexes adopt this geometry.

A complex with a face-bound cyclic pi ligand as the seat and several other ligands as the legs. In $\mathrm{CpFe}(\mathrm{CO}{)}_2\mathrm{X}$ the two carbonyls and X form three legs.

A complex in which a ligand binds the same metal through at least two distinct donor atoms, closing a coordination ring.

The idealized eclipsed ion $[\mathrm{M}{\mathrm{o}}_2\mathrm{C}{\mathrm{l}}_8{]}^{4-}$ has two formally Mo(II), d${}^4$ centres and a quadruple bond. Each metal has four chloride ligands arranged approximately in a square.