Semiconducting La2AuP3, the Metallic Conductor Ce2AuP3, and other Rare-Earth Gold PhosphidesLn2AuP3 with Two Closely Related Crystal Structures

Abstract

The compounds Ln 2 AuP 3 were synthesized by reaction of the elemental components in evacuated silica tubes. Their crystal structures were determined from singlecrystal diffractometer data. The compounds with Ln = La, Ce, and Pr crystallize with an orthorhombic U 2 NiC 3 type structure (Pnma, Z = 4). The structure refinement for Ce 2 AuP 3 resulted in a = 774.14(6) pm, b = 421.11(4) pm, c = 1612.3(1) pm, R = 0.019 for 1410 structure factors and 38 variable parameters. For Pr 2 AuP 3 a residual of R = 0.024 was obtained. Nd 2 AuP 3 crystallizes with a monoclinic distortion of this structure: P2 1 /c, Z = 4, a = 416.14(4) pm, b = 768.87(6) pm, c = 1647.1(2) pm, b = 104.06(1)°, R = 0.022 for 1361 F values and 56 variables. The near-neighbor coordinations of the two structures are nearly the same. In both structures the gold and phosphorus atoms form two-dimensionally infinite nets, where the gold atoms are tetrahedrally coordinated by phosphorus atoms with Au±P distances varying between 245.8 and 284.2 pm. Two thirds of the phosphorus atoms form pairs with single-bond distances varying between 217.7 and 218.9 pm. Thus, using oxidation numbers the structures can be rationalized with the formulas (Ln +3 ) 2 [AuP 3 ] ±6 and (Ln +3 ) 2 Au +1 (P 2 ) ±4 P ±3 . Accordingly, La 2 AuP 3 is a diamagnetic semiconductor. Pr 2 AuP 3 is semiconducting with an antiferromagnetic ground state, showing metamagnetism with a critical field of B c = 0.5(± 0.1) T. In contrast, the cerium compound is a metallic conductor, even though its cell volume indicates that the cerium atoms are essentially trivalent, as is also suggested by the ferro-or ferrimagnetic behavior of the compound.Goldatome von Phosphoratomen tetraedrisch umgeben sind, mit Au±P-Absta È nden von 245,8 bis 284,2 pm. Zwei Drittel der Phosphoratome bilden jeweils Paare mit Einfachbindungsabsta È nden zwischen 217,7 und 218,9 pm. Unter Verwendung von Oxidationszahlen ko È nnen die Strukturen somit durch die Formeln (Ln +3 ) 2 [AuP 3 ] ±6 und (Ln +3 ) 2 Au +1 (P 2 ) ±4 P ±3 beschrieben werden. Dementsprechend ist La 2 AuP 3 ein diamagnetischer Halbleiter. Pr 2 AuP 3 ist halbleitend mit einem antiferromagnetischen Grundzustand, welcher Metamagnetismus mit einer kritischen Feldsta È rke von B c = 0,5(± 0,1) T zeigt. Im Gegensatz dazu hat die Cer-Verbindung metallische Leitfa È higkeit, obwohl ihr Zellvolumen im wesentlichen dreiwertigem Cer entspricht, was auch durch das ferro-oder ferrimagnetische Verhalten der Verbindung nahegelegt wird.

In this issue

“…no P–P bonding), whereas the P2 atoms form pairs with P2–P2 distances of 223 pm, in very good agreement with the average P–P single bond length16 of 223 pm. Similar to the structure of Ce 2 AuP 3 10 also in La 2 AuP 2 O we observe slightly longer Au–P distances to the P 2 unit.…”

“…The sample was heated in a resistance furnace to 773 K, held at this temperature for 12 h, afterwards heated to 1473 K and held at this temperature for 48 h. The sample was cooled by radiative heat loss by shutting off the furnace. When using finely dispersed gold an increased formation of the ternary compound La 2 AuP 3 10 as a by‐product could be observed. Using Au 2 P 3 4 as a precursor, synthesized from gold powder and ground red phosphorus, did not result in the desired product.…”

“…Depending on the cation, the Au–P distances range from 245 to 254 pm. More complex is the two‐dimensional network in R 2 [AuP 3 ] 10. The gold atoms have distorted tetrahedral phosphorus coordination with a broader range of Au–P distances (246–284 pm in Ce 2 AuP 3 ).…”

Preparation and Crystal Structure of Au1—xSn1+yP14 and other Polyphosphides with HgPbP14-Type Structure

“…In the course of our search for new ternary polyphosphides, e.g., RZn 3 P 3 (R ϭ rare earth elements) and PrCd 3 P 3 [6], R 2 AuP 3 (R ϭ LaϪNd) [7], Au 2 PbP 2 [8,9], Au 2 TlP 2 and Au 2 HgP 2 [9] we encountered HgPbP 14 -type polyphosphides containing coppet, silver, and gold, which are reported here. The single-crystal X-ray investigation of the gold tin polyphosphide resulted in a considerable deviation from the ideal composition, corresponding to the general formula Au 1Ϫx Sn 1ϩy P 14 .…”

Hill Plot Focusing on Ce Compounds with High Magnetic Ordering Temperatures and Consequent Study of Ce2AuP3

“…Because the Ce-compounds investigated by Koelling are restricted to pure metal and binary compounds, we have reinvestigated Hill plot, surveying also ternary compounds. Employing CRYSTMET: a commercial database of the structural and powder patterns of metals and intermetallics, a correlation between Through the crystallographic consideration of many Ce-compounds, we focused on Ce 2 AuP 3 with T C of 31 K [5]. Although Ce 2 AuP 3 is metallic, the La counterpart shows a semiconducting behavior [5].…”