Bicapped

Bicapped is an adjective used in geometry, crystallography, and chemistry to describe a structure in which two caps are added to opposite faces of a polyhedron, producing a two-capped form. The term is commonly applied to describe coordination environments around a central atom, where two additional ligands occupy positions related to two faces of a core polyhedron.

In practice, a cap is typically a pyramidal arrangement of atoms or ligands that attaches to a face of the base polyhedron. The specific geometry of a bicapped shape depends on which faces are capped and how the caps connect to the core, giving rise to variations used to model real-world molecular and crystal structures.

Examples frequently encountered in the literature include bicapped trigonal prisms and bicapped octahedra. These descriptors appear in inorganic and solid-state chemistry as a compact way to convey the arrangement of surrounding atoms around a central atom, particularly for higher coordination numbers. Other bicapped forms, such as bicapped cube-like geometries, are described in crystallographic studies to capture the diversity of local environments found in materials.

Usage notes: Bicapped is typically part of longer polyhedral descriptors that specify both the core geometry and the capped faces. The exact interpretation can vary with context, so accompanying information about the core polyhedron and the nature of the caps is common in formal descriptions.

See also: polyhedron, coordination geometry, Johnson solids, capping.