and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Nanoscaled metal borides and phosphides: recent developments and perspectives

This review highlights the use and great potential of liquid metals as exotic and powerful solvents (i.e. fluxes) for the synthesis of intermetallic phases. The results presented demonstrate that considerable advances in the discovery of novel and complex phases are achievable utilizing molten metals as solvents. A wide cross-section of examples of flux-grown intermetallic phases and related solids are discussed and a brief history of the origins of flux chemistry is given. The most commonly used metal fluxes are surveyed and where possible, the underlying principal reasons that make the flux reaction work are discussed.

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The metal flux: a preparative tool for the exploration of intermetallic compounds.

Recent progresses in exploring the rare earth based intermetallic compounds for cryogenic magnetic refrigeration

Review of the structural, magnetic and magnetocaloric properties in ternary rare earth RE2T2X type intermetallic compounds

Back in black: All metastable and stable phases can be identified for the solid solution arsenic/phosphorus by a combination of quantum-chemical calculations and investigations of the phase formation. Reaction paths for phase formations and transitions in situ were also evaluated. The results show that orthorhombic black arsenic (o-As) is metastable in pure form and has only been previously obtained by stabilizing impurities.

Synthesis and Identification of Metastable Compounds: Black Arsenic—Science or Fiction?

Au2PbP2, Au2TlP2, and Au2HgP2: Ternary Gold Polyphosphides with Lead, Thallium, and Mercury in the Oxidation State Zero

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 YbNi x Sb. 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 YbPt 0 . 9 6 9 ( 7 ) Sb for the investigated crystal. A new, high-temperature 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 F 2 values, 20 variables. The antimonides YbTSb (T= Ni, Pd, Pt, Cu, Ag, Au) show single 1 2 1 Sb Mossbauer signals at isomer shifts ranging from -7.34 to -7.82 mm/s. The crystal chemistry and chemical bonding of these antimonides is discussed.

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Ternary antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au): Synthesis, structure, homogeneity ranges, and 121Sb Mössbauer spectroscopy

The crystal structure of the known compound HgSnP14 (HgPbP14-type, Pnma, Z = 4) was refined from single-crystal X-ray diffractometer data to a residual of R = 0.067 for 1470 structure factors and 83 variable parameters. This polyphosphide has a smaller cell volume than the isotypic compound CdSnP14. For that reason it had been suggested earlier that the mercury atoms in HgSnP14 will show a tendency for linear P—Hg—P 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 CdSnP14. 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 HgSnP14 can be rationalized on the basis of the Zintl-Klemm concept, resulting in the formula Hg+2Sn+2(P14)—4. Accordingly, the environment of the tin atoms shows the lone pair effect. Reactions of the elemental components aiming for the isotypic compounds CuSnP14, CuPbP14, AgSnP14, AgPbP14, AuSnP14, and AuPbP14 resulted in microcrystalline samples. The fibrous habit and the energy dispersive X-ray fluorescence analyses of the products indicate the formation of these polyphosphides. Only for the gold-tin compound was it possible to isolate a single crystal suitable for a structure refinement, which confirmed its HgPbP14-type structure: a = 1259.5(3) pm, b = 982.0(2) pm, c = 1056.2(3) pm, R = 0.046 for 1520 F values and 87 variables. The gold position was found with a lower occupancy, thus resulting in the two possible extreme formulas Au0.852(4)SnP14 and Au0.64(1)Sn1.36(1)P14, depending of whether vacancies or a mixed Au/Sn occupancy is assumed for this position. An analysis of interatomic distances suggests the latter formula to be correct with tetravalent tin on the gold sites corresponding to the formula [(Au+1)0.64(1)(Sn+4)0.36(1)]+2.08(3)[SnP14]—2.



Darstellung und Kristallstruktur von Au1—xSn1+yP14 und anderer Polyphosphide mit HgPbP14-Struktur



Die Kristallstruktur der bekannten Verbindung HgSnP14 (HgPbP14-Typ, Pnma, Z = 4) wurde aus Einkristall-Rontgen-Diffraktometerdaten zu einem Restwert von R = 0, 067 fur 1470 Strukturfaktoren und 83 variable Parameter verfeinert. Dieses Polyphosphid hat ein kleineres Zellvolumen als die isotype Verbindung CdSnP14. Deshalb ist fruher vermutet worden, dass die Quecksilberatome in HgSnP14 eine Tendenz in Richtung einer linearen P—Hg—P-Koordination haben sollten. Die hier vorliegende Strukturverfeinerung hingegen zeigt eine verzerrt-tetraedrische Phosphorumgebung der Quecksilberatome, sehr ahnlich wie die der Cadmiumatome in CdSnP14. Eine Durchsicht der Literatur zeigt, dass ganz allgemein Quecksilber in intermetallischen und mehr oder weniger kovalenten Verbindungen ein kleineres Volumen beansprucht als Cadmium, im Gegensatz zu ionischen Verbindungen, wo das umgekehrte Verhaltnis beobachtet wird. Die chemische Bindung in HgSnP14 kann auf der Basis des Zintl-Klemm-Konzeptes verstanden werden, woraus sich die Formel Hg+2Sn+2(P14)—4 ergibt. Dementsprechend zeigt die Umgebung der Zinnatome die Raumbeanspruchung des nichtbindenden Elektronenpaares. Reaktionen der elementaren Komponenten zur Darstellung der isotypen Verbindungen CuSnP14, CuPbP14, AgSnP14, AgPbP14, AuSnP14 und AuPbP14, ergaben lediglich mikroskristalline Produkte. Deren nadelformiger Habitus und die energiedispersiven Rontgenfluoreszenzanalysen deuten auf die Bildung dieser Polyphosphide. Nur von der Gold-Zinn-Verbindung konnten Einkristalle von ausreichender Grose fur eine Strukturbestimmung erhalten werden, welche die HgPbP14-Struktur bestatigte: a = 1259, 5(3) pm, b = 982, 0(2) pm, c = 1056, 2(2) pm, R = 0, 046 fur 1520 Strukturfaktoren und 87 Variablen. Die Goldposition zeigte eine Unterbesetzung, woraus sich die zwei moglichen (extremen) Formeln Au0, 852(4)SnP14 und Au0, 64(1)Sn1, 36(1)P14 ergeben, je nachdem ob Leerstellen oder eine Au/Sn-Mischbesetzung fur diese Position angenommen wird. Ein Vergleich der interatomaren Abstande mit Literaturdaten legt nahe, dass das Modell mit gemischter Au/Sn-Besetzung richtig ist, mit vierwertigem Zinn auf den Goldlagen entsprechend der Formel [(Au+1)0.64(1)(Sn+4)0.36(1)]+2.08(3)[SnP14]—2.

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

The rare earth metal (RE)-nickel-cadmium intermetallics RE 2 Ni 2 Cd (RE = La, Pr, Nd, Sm, Tb, Dy) were prepared from the elements in sealed niobium or tantalum tubes in a water-cooled sample chamber of a high-frequency furnace. They crystallize with a tetragonal Mo 2 FeB 2 type low-temperature modification, space group P4/mbm, and an orthorhombic Mn 2 AlB 2 type high-temperature modification, space group Cmmm. The cadmium compounds were characterized through their X-ray powder patterns. Five structures of the low-temperature modifications were refined from X-ray single crystal diffractometer data: a = 763.76(9), c = 387.26(8) pm, wR2 = 0.046, 205 F 2 for La 2 Ni 1 . 6 7 ( 1 ) Cd; a = 752.93(7), c = 380.95(6) pm, wR2 = 0.061, 260 F 2 for Pr 2 Ni 2 Cd; a = 750.88(9), c = 378.33(7) pm, wR2 = 0.051, 195 F 2 for Nd 2 Ni 2 Cd; a = 743.6(1), c = 374.0(1) pm, wR2 = 0.036, 386 F 2 for Sm 2 Ni 1 . 9 3 ( 1 ) Cd; a = 734.9(1), c = 366.1(2) pm, wR2 = 0.030, 252 F 2 for Dy 2 Ni 1 . 9 4 ( 1 ) Cd, with 13(12) variables per refinement. The 4g nickel site is only fully occupied in the neodymium and the praseodymium compound. Both modifications can be considered as inter-growths of distorted AlB 2 and CsCl related slabs. In both modification the nickel and cadmium atoms build up two-dimensional [Ni 2 Cd] networks. In the low-temperature modifications the nickel atoms form pairs, while nickel zig-zag chains occur in the high-temperature modifications. These nickel fragments are condensed via the cadmium atoms. The crystal chemistry and the chemical bonding in these intermetallics is discussed.

The Mo2FeB2- and Mn2AlB2-Type Modifications of RE2Ni2Cd (Re = La, Pr, Nd, Sm, Tb, Dy)

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 X-ray 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 foul-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.

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Marcus Eschen

Papers

Au2PbP2, Au2TlP2, and Au2HgP2: Ternary Gold Polyphosphides with Lead, Thallium, and Mercury in the Oxidation State Zero

Ternary antimonides YbTSb (T = Ni, Pd, Pt, Cu, Ag, Au): Synthesis, structure, homogeneity ranges, and 121Sb Mössbauer spectroscopy

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

The Mo2FeB2- and Mn2AlB2-Type Modifications of RE2Ni2Cd (Re = La, Pr, Nd, Sm, Tb, Dy)

Preparation and crystal structures of ternary rare earth silver and gold arsenides LnAgAs2 and LnAuAs2 with Ln = La-Nd, Sm, Gd, and Tb