Planar Tetracoordination Chemistry of Carbon Compounds

The concept of planar tetracoordinate carbon (ptC) challenges the long-standing notion that carbon’s preferred geometry is tetrahedral. In ptC species, a central carbon atom engages in four covalent interactions within a single plane, defying classic hybridisation rules. Computational advances have guided the design of ligand environments that balance electronic donation and back-bonding to the carbon centre, stabilising planar arrangements. Key stabilisation strategies include the use of electron-rich peripheral atoms or delocalised ring frameworks that confer σ- and π-aromatic character, often governed by an 18-valence-electron count. Theoretical screening, employing density functional theory and high-level ab initio methods, has identified global-minimum clusters featuring ptC motifs embedded in mixed element rings or star-shaped architectures. These studies have not only expanded the family of conceivable carbon-centred planar hypercoordinate species but have also revealed potential avenues towards isolable complexes. The emergence of ptC chemistry holds promise for novel materials with unique optical and electronic properties and enriches our fundamental understanding of chemical bonding beyond conventional valence paradigms.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Planar Tetracoordination Chemistry of Carbon Compounds publication trend

The graph below shows the total number of articles in planar tetracoordination chemistry of carbon compounds across all publications each year (not limited to Nature Index journals).

Technical terms

Planar tetracoordinate carbon: A carbon atom bonded to four surrounding atoms arranged in a single plane, defying the typical tetrahedral geometry.

Global minimum: The lowest-energy structure on a potential energy surface, representing the most thermodynamically stable configuration of a molecule.

Aromaticity: A stabilisation arising from cyclic delocalisation of electrons, often following Hückel’s rule for π-systems or analogous σ-frameworks.

Valence electron count: The total number of electrons available for bonding within a molecule, frequently used to predict stability according to electron-counting rules.

Density functional theory (DFT): A quantum-chemical computational method that models electronic structure by treating electron density as the central variable.

References

1. Structure and Bonding in Planar Hypercoordinate Carbon Compounds. Chemistry (2022).
2. Persistent Planar Tetracoordinate Carbon in Global Minima Structures of Silicon-Carbon Clusters. Atoms (2022).
3. CAl4X4 (X = Te, Po): Double Aromatic Molecular Stars Containing Planar Tetracoordinate Carbon Atoms. Molecules (2023).