sqplanar

Sqplanar is a term used in coordination chemistry to describe a molecular geometry where a central atom is bonded to four other atoms or groups, and these five atoms lie in a single plane. This arrangement is a specific type of square planar geometry, which is one of the fundamental geometries for molecules with a coordination number of four. In this geometry, the four ligands are positioned at the corners of a square, with the central atom at the center of the square. The bond angles between the central atom and any two adjacent ligands are 90 degrees, and the bond angles between the central atom and opposite ligands are 180 degrees.

Sqplanar complexes are common for transition metal ions with d8 electron configurations, such as platinum(II), palladium(II), and nickel(II). These complexes often exhibit distinct chemical properties compared to their tetrahedral counterparts, including different reactivity and spectroscopic features. For example, square planar complexes are known to undergo substitution reactions, where one ligand is replaced by another. The rigidity of the planar structure can influence the stereochemistry of these reactions. Examples of sqplanar complexes include cisplatin, a chemotherapy drug, and various catalytic species. The geometry is determined by a balance of electronic and steric factors.