Octahedral

Octahedral describes something related to the octahedron, a polyhedron with eight triangular faces, six vertices, and twelve edges. It is one of the five Platonic solids and the dual of the cube. In a regular octahedron, opposite vertices lie along three mutually perpendicular axes; a common coordinate model places the vertices at (±1,0,0), (0,±1,0), and (0,0,±1). The figure exhibits high symmetry, described by the Oh symmetry group with 48 elements.

In chemistry, octahedral refers to a common coordination geometry in which a central atom or ion is surrounded by six ligands arranged at the corners of an octahedron. This arrangement arises frequently with transition metals and gives rise to characteristic ligand-field splitting of d-orbitals (typically into a lower-energy t2g set and a higher-energy eg set). Many complexes are near-ideal octahedra, though distortions can occur due to electronic effects, ligand sizes, or Jahn-Teller distortions. Examples include [Fe(CN)6]3−/4−, [Co(NH3)6]3+, and [Cu(H2O)6]2+.

In solid-state chemistry and mineralogy, octahedral motifs occur in crystal structures: cations may occupy octahedral interstices formed by surrounding atoms, and octahedral tilting is a common distortion mode in perovskites and related materials. The term also appears in crystallography when describing sites in a crystal lattice that coordinate six neighbors in an approximately octahedral geometry.