SO2d

SO2d is a hypothetical two-dimensional allotrope of sulfur dioxide described in theoretical studies as a possible 2D phase derived from the chemistry of sulfur oxides. It should not be confused with gaseous SO2 or with bulk solid sulfur dioxide; in this context SO2d refers to an atomically thin sheet with a defined in-plane structure.

In proposed models, SO2d would form a planar lattice consisting of sulfur and oxygen atoms arranged in a porous network. The bonding is described as predominantly covalent, with S–O–S connections yielding a sheet with potential hexagonal or distorted honeycomb symmetry. The structure is anticipated to exhibit high in-plane stiffness and a notable surface area.

Theoretical studies using density functional theory and phonon calculations have explored its stability. Some simulations predict dynamic stability under certain chemical potentials, suggesting the phase could be metastable relative to decomposition into SO2 gas or oxide components. Other models warn of possible instabilities linked to oxide volatility or reconstruction.

Predicted electronic properties vary by calculation method, with reports ranging from semiconducting to metallic behavior and a wide span of band-gap estimates. Computational work typically emphasizes sensitivity to functional choice and external factors such as substrate interaction and strain. Mechanical properties are often described as strong in-plane but with low thickness.

No experimental synthesis or characterization of SO2d has been reported. If realized, synthesis would likely require precise control of growth conditions, possibly employing bottom-up deposition or epitaxial strategies on suitable substrates, with stabilization provided by substrate effects or chemical passivation. Research remains speculative, with ongoing assessments of feasibility and potential applications in catalysis, sensing, or nanoelectronics.