Framework Structures of Interconnected Layers in Calcium Iron Arsenides

The
new calcium iron arsenide compounds Can(n+1)/2(Fe1–xMx)(2+3n)M′n(n–1)/2As(n+1)(n+2)/2 (n = 1–3; M = Nb, Pd, Pt; M′ = □, Pd,
Pt) were synthesized and their crystal structures determined by single-crystal
X-ray diffraction. The series demonstrates the structural flexibility
of iron arsenide materials, which otherwise prefer layered structures,
as is known from the family of iron-based superconductors. In the
new compounds, iron arsenide tetrahedral layers are bridged by iron-centered
pyramids, giving rise to so far unknown frameworks of interconnected
FeAs layers. Channels within the structures are occupied with calcium
and palladium or platinum, respectively. Common basic building blocks
are identified that lead to a better understanding of the building
principles of these structures and their relation to CaFe4As3.