title: Four new actinide chalcogenides Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5: crystal structures and physical properties.
abstract: Four new actinide chalcogenides—namely, Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5—were synthesized via solid-state methods at 1173 K. Single-crystal X-ray diffraction studies show that Ba2Cu4USe6 crystallizes in a new structure type in space group C2h5–P21/c of the monoclinic system, whereas the three other compounds are isostructural and adopt the Ba2Cu2US5 structure type in space group C2h3–C2/m, also of the monoclinic system. These Ak/Cu/An/Q structures (Ak = alkaline-earth metal; An = actinide; Q = chalcogen) have no short Q–Q interactions and, hence, are charge-balanced with Ak2+, Cu1+, An4+, and Q2–. Crystal structures of all these compounds are two-dimensional and feature layers that are separated by Ba2+ cations. The compositions of these layers differ. In the structure of Ba2Cu4USe6, the ∞2[Cu4USe64–] layers comprising USe6 octahedra and CuSe4 tetrahedra stack perpendicular to the a-axis. These ∞2[Cu4USe64–] layers show short Cu–Cu interactions. In the three isostructural Ak2Cu2AnQ5 compounds, AnQ6 octahedra and CuQ4 tetrahedra are connected along the c-axis in the sequence “...oct tet tet oct tet tet...” to form the ∞2[Cu2AnQ54–] layers. Resistivity, optical, and DFT calculations show semiconducting behavior for these compounds.
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.|ICSM, UMR 5257 CEA/CNRS/UM2/ENSCM, Site de Marcoule-Bât. 426, BP 17171, 30207 Bagnols-sur-Cèze cedex, France.
authors.forename: Adel
authors.initials: A
authors.lastname: Mesbah
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
authors.forename: Jai
authors.initials: J
authors.lastname: Prakash
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
authors.forename: Jessica C
authors.initials: JC
authors.lastname: Beard
authors.affiliation: Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036), Institut Jean Barriol, Université de Lorraine , BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre-lès-Nancy, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Lebègue
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
authors.forename: Christos D
authors.initials: CD
authors.lastname: Malliakas
authors.affiliation: Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States.
authors.forename: James A
authors.initials: JA
authors.lastname: Ibers