No abstract

The ternary antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au) were synthesized by reaction of the elements in sealed tantalum tubes in a high-frequency furnace. The structures of YbCuSb (NdPtSb type), YbAgSb (TiNiSi type), and YbAuSb (NdPtSb type) were confirmed on the basis of X-ray powder diffraction data. Those of the nickel, palladium, and platinum based antimonides (cubic MgAgAs type) were refined from single crystal X-ray data. The nickel based antimonide has a pronounced homogeneity range YbNixSb. The structures of five crystals have been investigated. The cubic lattice parameter increases with increasing nickel content from 613.13(6) pm(x = 0.17) to 621.25(5) pm (x = 0.63). Full occupancy of the palladium and antimony sites was observed for YbPdSb while the platinum compound shows some platinum vacancies leading to the composition YbPt0.969(7)Sb for the investigated crystal. A new, hightemperature modification of YbPdSb was obtained by rapidly quenching an arc-melted sample: TiNiSi type, Pnma, a = 725.6(2), b = 458.3(1), c = 785.4(2) pm, wR2 = 0.1255, 421 F2 values, 20 variables. The antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au) show single 121Sb Mössbauer signals at isomer shifts ranging from -7.34 to -7.82 mm/s. The crystal chemistry and chemical bonding of these antimonides is discussed.

The 14 arsenides LnAgAs 2 and LnAuAs 2 (Ln = La-Nd, Sm, Gd, Tb) were prepared by reaction of stoichiometric mixtures of the elemental components at high temperatures and characterized by Xray diffractometry. The silver compounds LaAgAs 2 and CeAgAs 2 and the gold compounds LnAuAs 2 (Ln = Ce-Nd, Sm, Gd, Tb) crystallize with HfCuSi 2 type structure (P4/nmm, Z = 2). Of these, the structures of CeAgAs 2 (a = 408.5(1), c = 1048.2(1) pm, conventional residual R = 0.017 for 261 structure factors and 12 variable parameters) and CeAuAs 2 (a = 411.4(1), c = 1015.3(2) pm, R = 0.030 for 428 F values) were refined from four-circle diffractometer data. The silver compounds LnAgAs 2 (Ln = Pr, Nd, Sm, Gd, Tb) are isotypic with the antimonide SrZnSb 2 (Pnma, Z = 4) as demonstrated by a single-crystal structure refinement of PrAgAs 2 (a = 2107.3(4), b = 401.7(1), c = 407.8(1) pm, R = 0.042 for 746 F values and 26 variables). The gold compound LaAuAs 2 (I4/mmm, Z = 4, a = 416.9(1), c = 2059.5(3) pm, R = 0.038 for 303 F values and 13 variables) was found to be isotypic with the bismuthide SrZnBi 2 , again by a refinement from single-crystal diffractometer data. In the structures of CeAgAs 2 , LaAuAs 2 , and CeAuAs 2 large displacement parameters perpendicular to the four-fold axes were found for one of the two arsenic positions. These structures could also be refined with split positions for these arsenic atoms, which allow for considerable As-As bonding, resulting in a formal charge of −1 for these atoms. Chemical bonding in these compounds can thus be rationalized by a simple model corresponding to the formula Ln +3 T +1 As −1 As −3 (T = Ag, Au), where the superscripts indicate oxidation numbers.

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.

The crystal structure of the known compound HgSnP 14 (HgPbP 14 -type, Pnma, Z ϭ 4) was refined from single-crystal X-ray diffractometer data to a residual of R ϭ 0.067 for 1470 structure factors and 83 variable parameters. This polyphosphide has a smaller cell volume than the isotypic compound CdSnP 14 . For that reason it had been suggested earlier that the mercury atoms in HgSnP 14 will show a tendency for linear PϪHgϪP coordination. This is not supported by the present structure refinement, which shows a distorted tetrahedral phosphorus coordination for the mercury atoms, very similar to that of the cadmium atoms in CdSnP 14 . A brief literature survey shows that quite generally the mercury atoms have a smaller volume requirement than the cadmium atoms in intermetallics and more or less covalent compositions, in contrast to more ionic compounds, where the inverse relationship is observed. Chemical bonding in HgSnP 14 can be rationalized on the basis of the Zintl-Klemm concept, resulting in the formula Hg ϩ2 Sn ϩ2 (P 14 ) Ϫ4 . Accordingly, the environment of the tin atoms shows the lone pair effect. Reactions of the elemental components