Grown from lithium flux,the ErCo5Si3.17 silicide is a combination of disordered derivatives of the UCo5Si3 and Yb6Co30P19 structure types

A ternary hexaerbium triacontacobalt enneakaidecasilicide, ErCo₅Si_3.17, crystallizes as a combination of disordered variants of the hexagonal UCo₅Si₃ (P6₃/m) and Yb₆Co₃₀P₁₉ (P) structure types and is closely related to the Sc₆Co₃₀Si₁₉ and Ce₆Rh₃₀Si₁₉ types. The Er, Co and three of the Si atoms occupy sites of m.. symmetry and a fourth Si atom occupies a site of .. symmetry. The environment of the Er atom is a 21‐vertex pseudo‐Frank–Kasper polyhedron. Trigonal prismatic coordination is observed for the Si atoms. The Co atoms are enclosed in heavily deformed cuboctahedra and 11‐vertex polyhedra. Crystallochemistry analysis and the data from electronic structure calculations (TB–LMTO–ASA) suggest that the Er atoms form positively charged cations which compensate the negative charge of the [Co₁₂Si₉]^m− polyanions.