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 (ThCuP2 , β-ThCu2 P2 , and ThCu5 P3 ) have been prepared through solid-state reactions using CuI as a reaction promoter. The structure of ThCuP2 can be described as a filled UTe2 -type with both dimeric P2 4- and monomeric P3- 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-ThCu2 P2 contains only P3- anions and is isostructural with BaCu2 S2 . In this structure, Th is coordinated by seven P atoms in monocapped trigonal prismatic geometry and Cu is tetrahedrally coordinated by four P atoms. ThCu5 P3 adopts the YCo5 P3 -type structure consisting of P3- 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-ThCu2 P2 indicate a metal. These new compounds may be charge-balanced and formulated as Th4+ Cu+ (P2 4- )1/2 P3- , Th4+ (Cu+ )2 (P3- )2 , and Th4+ (Cu+ )5 (P3- )3 , 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 UCuP2 and UCu2 P2 that were synthesized under similar experimental conditions, suggesting divergence of thorium-phosphide chemistry from uranium-phosphide chemistry.