Thorium-Based Iron Arsenide with Fe-Fe Bonding

This work presents a study on a new thorium iron arsenide, Th₂Fe₁₂As₇, a second discovered compound in the ternary system. It crystallizes in the noncentrosymmetric hexagonal Zr₂Fe₁₂P₇ structure type (space group P6, a = 9.5506(4) Å and c = 3.8645(2) Å). The bonding analysis of Th₂Fe₁₂As₇ reveals that the structure can be represented by a trigonal prismatic environment of the As atoms, which are the geometric locations of anionic components of the structure. The cationic components of the structure are represented by the Th species. Furthermore, the bonding analysis revealed a new feature─a three-dimensional framework of two-atomic bonds between the Fe atoms, which─in the sense of effective charges─is essentially neutral. It plays the role of a bonding mediator within the [Fe-As] framework. Th₂Fe₁₂As₇ is a metallic paramagnet down to the lowest measured temperature, 0.4 K.