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Pnictide oxides exhibit a rich crystal chemistry, which is much more than the ZrCuSiAs structure of LaFeAsO, the mother-structure of the 1-1-1-1 materials. The present micro-review focuses on different dimensionalities in the oxidic and the pnictide substructures, largely extending the structural building units. The second part concerns BaAl4/ThCr2Si2 superstructures, which extend the crystal chemistry of BaFe2As2. Key parameters for superstructure formation are either an ordering of the transition metal and p-element atoms ( coloring) or an ordering of vacancies. [ABSTRACT FROM AUTHOR]

The quaternary gold arsenide oxides Ce9Au5− xAs8O6 and Pr9Au5− xAs8O6 were synthesized from the rare earth elements ( RE), rare earth oxides, arsenic and gold powder at maximum annealing temperatures of 1173 K. The structures were refined from single crystal X-ray diffractometer data: Pnnm, a=1321.64(6) pm, b=4073.0(3), c=423.96(2), wR2=0.0842, 3106 F2 values, 160 variables for Ce9Au4.91(4)As8O6 and Pnnm, a=1315.01(4), b=4052.87(8), c=420.68(1) pm, wR2=0.0865, 5313 F2 values, 160 variables for Pr9Au4.75(1)As8O6. They represent a new structure type and show a further extension of pnictide oxide crystal chemistry. A complex polyanionic gold arsenide network [Au5As8]15− (with some disorder in the gold substructure) is charge compensated with polycationic strands of condensed edge-sharing O@ RE4/4 and O@ RE4/3 tetrahedra ([ RE4O3]212+) as well as RE3+ cations in cavities. [ABSTRACT FROM AUTHOR]

The quaternary gold arsenide oxides Ce9Au5− xAs8O6 and Pr9Au5− xAs8O6 were synthesized from the rare earth elements ( RE), rare earth oxides, arsenic and gold powder at maximum annealing temperatures of 1173 K. The structures were refined from single crystal X-ray diffractometer data: Pnnm, a=1321.64(6) pm, b=4073.0(3), c=423.96(2), wR2=0.0842, 3106 F2 values, 160 variables for Ce9Au4.91(4)As8O6 and Pnnm, a=1315.01(4), b=4052.87(8), c=420.68(1) pm, wR2=0.0865, 5313 F2 values, 160 variables for Pr9Au4.75(1)As8O6. They represent a new structure type and show a further extension of pnictide oxide crystal chemistry. A complex polyanionic gold arsenide network [Au5As8]15− (with some disorder in the gold substructure) is charge compensated with polycationic strands of condensed edge-sharing O@ RE4/4 and O@ RE4/3 tetrahedra ([ RE4O3]212+) as well as RE3+ cations in cavities. [ABSTRACT FROM AUTHOR]

New quaternary palladium arsenide oxides Nd10Pd3As8O10 and Sm10Pd3As8O10 were synthesized from the rare earth (RE) elements, appropriate rare earth oxides, arsenic and palladium sponge at maximum annealing temperatures of 1223 K. The structure of the neodymium compound was refined from X-ray single crystal diffractometer data at different temperatures. The samarium compound was found to be isotypic on the basis of Guinier powder diffraction. Both compounds are isotypic with Nd10Au3As8O10 and consist of stacked, formal polycationic [RE10O10]10+ and polyanionic [Pd3(As2)4]10− layers. In contrast to the well-known, tetrahedrally coordinated rare earth oxide layers with basically ionic bonding, the palladium arsenide layers exhibit rather covalent character, which is underlined by XPS data. Electrical resistivity measurements indicate semiconducting properties for Nd10Pd3As8O10 and additionally show an anomaly at approximately 160 K, which results from a structural phase transition, clarified by X-ray single crystal diffractometer data. The phase transition originates from out of plane distortions of the palladium atoms, which show structural order around 160 K. Specific heat measurements and temperature dependent magnetic susceptibility data (including low field measurements) do not show any corresponding anomaly, referring to a very small structural change, which mainly effects electrical conductivity in the present palladium arsenide substructure. Nd10Pd3As8O10 exhibits Curie–Weiss paramagnetism and shows no magnetic order down to 2.5 K. Electronic band structure calculations predict a metallic state – probably due to the very small gap – and confirm the covalent character of the [Pd3As8] layer. [ABSTRACT FROM AUTHOR]

The phosphide oxides La3Cu4P4O2 and La5Cu4 P4O4Cl2 were synthesized from lanthanum, copper(I) oxide, red phosphorus, and lanthanum(III) chloride through a ceramic technique. Single crystals can be grown in a NaCl/KCl flux. Both structures were refined from single crystal X-ray diffractometer data: I4/ mmm, a = 403.89(4), c = 2681.7(3) pm, wR2 = 0.0660, 269 F2 values, 19 variables for La3Cu4P4O2 and a = 407.52(5), c = 4056.8(7) pm, wR2 = 0.0905, 426 F2 values, 27 variables for La5Cu4P4O4Cl2. Refinement of the occupancy parameters revealed full occupancy for the oxygen sites in both compounds. The structures are composed of cationic (La2O2)2+ layers and covalently bonded (Cu4P4)5- polyanionic layers with metallic characteristics, and an additional La3+ between two adjacent (Cu4P4)5- layers. The structure of La5Cu4P4O4Cl2 comprises two additional LaOCl slabs per unit cell. Temperature-dependent magnetic susceptibility studies revealed Pauli paramagnetism. The phosphide substructure of La3Cu4P4O2 was studied by 31P solid state NMR spectroscopy. By using a suitable dipolar re-coupling approach the two distinct resonances belonging to the P24- and the P3- units could be identified. [ABSTRACT FROM AUTHOR]

The quaternary gold(i) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(iii) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10]10+ layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(i)3(As2)4]10− layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1–As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by 197Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(i), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie–Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of the phosphide oxides RE2AuP20 (RE = La, Ce, Pr, Nd) were obtained from mixtures of the rare earth elements, binary rare earth oxides, gold powder, and red phosphorus in sealed silica tubes. Small single crystals were grown in NaCl/KCl fluxes. The samples were studied by powder X-ray diffraction, and the structures were refined from single crystal diffractometer data: La2AuP20 type, space group C2/m, a = 1515.2(4), b = 424.63(8), c = 999.2(2) pm, β = 130.90(2)°, wR2 = 0.0410, 1050 F² values for Ce2AuP2O, and a = 1503.6(4), b = 422.77(8), c = 993.0(2) pm, β = 130.88(2)°, wR2 = 0.0401, 1037 F² values for Pr2AuP20, and a = 1501.87(5), b = 420.85(5), c = 9903(3) pm, β = 131.12(l)°, wR2 = 0.0944, 1143 F² values for Nd2AuP2O with 38 variables per refinement. The structures are composed of [RE20]4+ polycationic chains of cis-edge-sharing ORE4/2 tetrahedra and polyanionic strands [AuP2]4-, which contain gold in almost trigonal--planar phosphorus coordination by P3- and P24- entities. The isolated phosphorus atoms and the P2 pairs in La2AuP20 could clearly be distinguished by 31P solid state NMR spectroscopy and assigned on the basis of a double quantum NMR technique. Also, the two crystallographically inequivalent La sites could be distinguished by static 139La NMR in conjunction with theoretical electric field gradient calculations. Temperature-dependent magnetic susceptibility measurements show diamagnetic behavior for La2AuP20. Ce2AuP20 and Pr2uP2O are Curie--Weiss paramagnets with experimental magnetic moments of 235 and 3.48 µB per rare earth atom, respectively. Their solid state 31P MAS NMR spectra are strongly influenced by paramagnetic interactions. Ce2AuP20 orders antiferromagnetically at 13.1(5) K and shows a metamagnetic transition at 11.5 kOe. Pr2AuP20 orders ferromagnetically at 7.0 K. [ABSTRACT FROM AUTHOR]

Ce23Ru7Zn4 is obtained by melting of the elements in stoichiometric amounts (Nb ampoule, 1500 K, 10 min). [ABSTRACT FROM AUTHOR]

The quaternary gold(I) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(III) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10](10+) layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(I)3(As2)4](10-) layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1-As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by (197)Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(I), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie-Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K.