title: Gold-gold bonding: the key to stabilizing the 19-electron ternary phases LnAuSb (Ln = La-Nd and Sm).
abstract: We report a new family of ternary 111 hexagonal LnAuSb (Ln = La-Nd, Sm) compounds that, with a 19 valence electron count, has one extra electron compared to all other known LnAuZ compounds. LaAuSb, CeAuSb, PrAuSb, NdAuSb, and SmAuSb crystallize in the YPtAs-type structure, and have a doubled unit cell compared to other LnAuZ phases as a result of the buckling of the Au-Sb honeycomb layers to create interlayer Au-Au dimers. The dimers accommodate the one excess electron per Au and thus these new phases can be considered Ln2(3+)(Au-Au)(0)Sb2(3-). Band structure, density of states, and crystal orbital calculations confirm this picture, which results in a nearly complete band gap between full and empty electronic states and stable compounds; we can thus present a structural stability phase diagram for the LnAuZ (Z = Ge, As, Sn, Sb, Pb, Bi) family of phases. Those calculations also show that LaAuSb has a bulk Dirac cone below the Fermi level. The YPtAs-type LnAuSb family reported here is an example of the uniqueness of gold chemistry applied to a rigidly closed shell system in an unconventional way.
authors.affiliation: Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Seibel
authors.forename: Leslie M
authors.initials: LM
authors.lastname: Schoop
authors.forename: Weiwei
authors.initials: W
authors.lastname: Xie
authors.forename: Quinn D
authors.initials: QD
authors.lastname: Gibson
authors.forename: James B
authors.initials: JB
authors.lastname: Webb
authors.forename: Michael K
authors.initials: MK
authors.lastname: Fuccillo
authors.forename: Jason W
authors.initials: JW
authors.lastname: Krizan
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cava