What is a coordination polyhedron?

A coordination polyhedron is the three-dimensional shape formed around a central metal atom or ion in a coordination compound by its surrounding ligands. In coordination chemistry, metals bond with molecules or ions called ligands. The spatial arrangement of these ligands around the central metal atom forms a specific geometry. This geometry is called a coordination polyhedron. It helps in understanding the structure, stability, and properties of coordination compounds.

Examples of Coordination Polyhedra:

• Tetrahedral: 4 ligands arranged around the central atom, e.g., [ZnCl4]²⁻.
• Square Planar: 4 ligands arranged in a square plane, e.g., [Ni(CN)4]²⁻.
• Octahedral: 6 ligands around the central atom, e.g., [Fe(CN)6]³⁻.
• Trigonal Bipyramidal: 5 ligands, e.g., [Fe(CO)5].
• Square Pyramidal: 5 ligands with one at the apex, e.g., [VO(acac)2].

Importance of Coordination Polyhedron:

• Helps predict physical and chemical properties of complexes.
• Explains magnetic behavior of coordination compounds.
• Used in crystal field theory and molecular orbital theory.
• Important in biological systems like hemoglobin and chlorophyll.