Neliöplanaariset

Neliöplanaariset, also known as square planar complexes, are a type of coordination complex where a central metal atom is bonded to four ligands arranged in a planar square geometry. This arrangement is common for metal ions with d8 electron configurations, such as Ni(II), Pt(II), and Au(III). The ligands lie in the same plane, with bond angles of approximately 90 degrees between adjacent ligands and 180 degrees between opposite ligands.

The electronic structure of square planar complexes is characterized by the splitting of the d orbitals into different energy levels. In an octahedral field, the d orbitals split into a lower t2g set and a higher eg set. However, in a square planar field, this splitting is more complex, leading to a unique arrangement of energy levels that favors the d8 electron configuration. This electronic arrangement influences the chemical properties and spectroscopic behavior of these complexes.

Square planar complexes exhibit characteristic isomerism, including cis-trans isomerism when the ligands are not all identical. The planar geometry restricts the rotational freedom of the ligands, leading to distinct spatial arrangements that can affect the complex's reactivity and physical properties. Many transition metal complexes with square planar geometry are colored due to d-d electronic transitions, which are influenced by the ligand field strength and the specific metal ion.

Examples of square planar complexes include cisplatin, a vital chemotherapy drug, and various catalysts used in organic synthesis. Their distinct geometry and electronic properties make them important subjects in inorganic chemistry and materials science.