Thorium copper phosphides: more diverse metal-phosphorus and phosphorus-phosphorus interactions than U analogues.

To explore the chemical analogy between thorium and heavier actinides in soft anionic environments, three new thorium phosphides (ThCuP, β-ThCuP, and ThCuP) have been prepared through solid-state reactions using CuI as a reaction promoter. The structure of ThCuP can be described as a filled UTe-type with both dimeric P and monomeric P anions, in which Th is coordinated by eight P atoms in a bicapped trigonal prismatic arrangement and Cu is tetrahedrally coordinated by four P atoms. β-ThCuP contains only P anions and is isostructural with BaCuS. In this structure, Th is coordinated by seven P atoms in monocapped trigonal prismatic geometry and Cu is tetrahedrally coordinated by four P atoms. ThCuP adopts the YCoP-type structure consisting of P anions. This structure contains Th atoms coordinated by six P atoms in a trigonal prismatic arrangement and Cu atoms that are either tetrahedrally coordinated by four P atoms or square pyramidally coordinated by five P atoms. Electric resistivity measurements and electronic structure calculations on β-ThCuP indicate a metal. These new compounds may be charge-balanced and formulated as ThCu(P)P, Th(Cu)(P), and Th(Cu)(P), respectively. The structural, bonding, and property relationships between these Th compounds and related actinide and rare-earth phases are discussed. Titled compounds display more diverse ion-ion interactions and different electronic structures from those in UCuP and UCuP that were synthesized under similar experimental conditions, suggesting divergence of thorium-phosphide chemistry from uranium-phosphide chemistry.