4koordinovaný

4koordinovaný is a term used in coordination chemistry to describe a central atom that is bonded to four ligands, giving a coordination number of four. The designation is commonly applied to transition metal centers, but it can refer to main-group elements as well. Four-coordinate species are found in both inorganic complexes and organometallic compounds.

The two most common geometries for four-coordinate centers are tetrahedral and square planar. Tetrahedral arrangements are typical for many d10 metals (such as Zn2+, Cd2+) and for several early transition metal complexes, where steric and electronic factors favor a structure with bond angles close to 109.5 degrees. Square planar geometries are favored by certain d8 metals (for example Ni2+, Pt2+) and by complexes with strong field ligands, where the ligand field stabilizes a planar arrangement and low-spin electronic configurations. Distorted forms between these geometries can occur due to ligand size, electronic effects, or crystal packing.

Common examples include square-planar [Ni(CN)4]2− and [PtCl4]2−, as well as tetrahedral [ZnCl4]2− and [CdCl4]2−. The geometry influences properties such as reactivity, ligand binding kinetics, and spectroscopic characteristics. Four-coordinate species can exhibit cis/trans isomerism in square-planar systems and, in tetrahedral cases with four different ligands, can possess stereochemical complexity. The concept of 4koordinovaný is a fundamental descriptor in describing the structure and chemistry of such complexes.