The square planar
molecular geometry in chemistry
describes the stereochemistry (spatial arrangement of atoms) that is adopted by certain chemical compounds
. As the name suggests, molecules of this geometry have their atoms positioned at the corners of a square on the same plane about a central atom.
Relationship to other geometries
The addition of two ligands to linear compounds, ML<sub>2</sub>, can afford square planar complexes. For example, <sup><nowiki>−</nowiki></sup> adds chlorine to give square planar <sup><nowiki>−</nowiki></sup>.
In principle, square planar geometry can be achieved by flattening a tetrahedron. As such, the interconversion of tetrahedral and square planar geometries provides an intramolecular pathway for the isomerization of tetrahedral compounds. This pathway does not operate readily for hydrocarbons, but tetrahedral nickel(II) complexes, e.g.
)<sub>2</sub>, undergo this change reversibly.
Removal of a pair of ligands
from the z-axis of an octahedron
, leaving four ligands in the x-y plane. For transition metal compounds, the crystal field
splitting diagram for square planar geometry can thus be derived from the octahedral diagram. The removal of the two ligands stabilizes the d<sub>z<sup>2</sup></sub> level,... Read More