Ca3Au6.61Ga4.39 was synthesized by reacting the elements in a glassy carbon crucible under argon in a water-cooled sample chamber in a high-frequency furnace. The compound crystallizes with a new hexagonal structure type, space group P6(3)/mmc: Z = 2, a = 926.6(2), c = 733.1(2) pm, wR2 = 0.0832, 328 F-0(2) values and 20 variables. This structure type consists of a remarkably complex three-dimensional [Au6.61Ga4.39] network with significant Au-Au, Au-Ga, and Ga-Ga interactions. The calcium atoms are located within slightly distorted hexagonal channels of the gold-gallium network. The structural relations to the AlB2 and Er2RhSi3 type structures are discussed.

New ternary stannide YbPdSn2 was synthesized from the elements in a sealed tantalum tube in a high-frequency furnace. YbPdSn2 was characterized through X-ray powder and single crystal data: Cmcm. a=442.4(2), b = 1108.6(3), c = 738.4(2) pm. wR2 = 0.0450, 317 F-2 values, and 16 variable parameters. YbPdSn2 crystallizes with the MgCuAl2 type structure, a ternary ordered variant of the Re3B type. The tin sublattice of YbPdSn2 corresponds to a distorted lonsdaleite-like arrangement with Sn-Sn distances varying from 303 to 336 pm.

The stannides CaErPt3Sn5, CaTmPt3Sn5, CaYbPt3Sn5, and CaLuPt3Sn5 were prepared from the elements in glassy carbon crucibles under an argon atmosphere in a high-frequency furnace. Their Yb2Pt3Sn5 type structure (space group Pnma) was refined from single-crystal X-ray data: a=736.4(1) pm, b=444.11(9) pm, c=2639.9(4) pm, wR=0.0905, 1403 F2 values, 63 variables for the erbium; a=733.9(2) pm, b=443.0(1) pm, c=2634.8(5) pm, wR2=0.1430, 1372 F2 values, 63 variables for the thulium; a=733.9(1) pm, b=443.3(1) pm, c= 2635.7(6) pm, wR2=0.0734, 2079 F2 values, 64 variables for the ytterbium; and a=735.0(2) pm, b=441.6(2) pm, c= 2634.1(7) pm, wR2=0.1202, 1344 F2 values, 63 variables for the lutetium compound. The Yb2Pt3Sn5 structure is built up from a complex threedimensional [Pt3Sn5] polyanion in which the ytterbium atoms fill distorted hexagonal channels. The two crystallographically different ytterbium sites have coordination numbers (CN) 20 and 18, respectively. In the erbium, thulium, and lutetium compound, the CN 20 position is occupied exclusively by calcium atoms, while a mixed calcium–rare-earth occupancy is observed for the CN 18 position. In the ytterbium compound both positions show mixed occupancy. The refinements resulted in the compositions Ca1.33Er0.67Pt3Sn5, Ca1.45Tm0.55Pt3Sn5, Ca1.28Yb0.72Pt3Sn5, and Ca1.63Lu0.37Pt3Sn5 for the crystals investigated. These results were confirmed by magnetic susceptibility measurements. The erbium and the thulium compound show Curie–Weiss behavior with experimental effective magnetic moments of 9.5(2) and 8.4(2) μB, respectively. At 4.8(1) K, the erbium compound orders ferro- or ferrimagnetically, while antiferromagnetic ordering at TN=5.0(1) K is observed for the thulium compound. CaYbPt3Sn5 shows Curie–Weiss behavior above 100 K with an experimental magnetic moment of 2.8(2) μB and Θ=−71(5) K, indicating mixed-valent behavior. CaLuPt3Sn5 shows a diamagnetic signal of −7.8×10−9 m3/mol.

New compounds Sr2Rh2In3 and Sr3Ir4Sn4 were synthesized by reacting the elements in glassy carbon crucibles under an argon atmosphere in a high-frequency furnace. X-ray diffraction of powders and single crystals yielded C2/m, mC14, a=1101.9(1) pm, b=427.18(5) pm, c=793.01(7) pm, β=115.40(1)°, wR2=0.0480, 708 F2 values and 24 parameters for Sr2Rh2In3 (new structure-type) and I43m, cI22, a=807.88(7), wR2=0.0236, 165 F2 values and ten parameters for Sr3Ir4Sn4 (Na3Pt4Ge4-type). Common to both compounds is the formation of transition metal indium(tin) polyanions, [Rh2In3] and [Ir4Sn4], which extend two-dimensionally for Sr2Rh2In3 but three-dimensionally for Sr3Ir4Sn4. According to semi-empirical band structure calculations the strongest bonding interactions are found for the Rh–In and Ir–Sn contacts. All Rh–Rh and Ir–Ir bonding and antibonding states were found to be filled, which is not surprising for a formal d10–d10 interaction. According to magnetic susceptibility measurements Sr2Rh2In3 is a Pauli paramagnet and a metallic conductor with room temperature values of −1.8×10−9 m3/mol and 415±20 μΩ cm, respectively.

The stannide Eu2Au2Sn5 was prepared by high-frequency melting of the elements in a sealed tantalum tube. The structure of Eu2Au2Sn5 was refined from single crystal X-ray data: P21/m, a = 928.6(2), b = 465.8(2), c = 1042.9(3) pm, ß = 92.28(2)°, wR2 = 0.0653, 1220 F2 values and 56 variables. The structure of Eu2Au2Sn5 is of a new type, it can be considered as an ordered defect variant of the BaAl4 type. Due to the ordered defects, the coordination number (CN) of the two crystallographically different europium sites is reduced from CN 16 to CN 14. The gold and tin atoms in Eu2Au2Sn5 form a complex three-dimensional [Au2Sn5] polyanion in which the europium atoms are embedded. Within the polyanion short Au-Sn and Sn-Sn distances are indicative of strongly bonding Au-Sn and Sn-Sn interactions. A detailed group-subgroup scheme for various ordered and defect variants of the BaAl4 family is presented. Eu2Au2Sn5 shows Curie-Weiss behavior above 50 K with an experimental magnetic moment of 7.90(5) μB/Eu, indicating divalent europium. Antiferromagnetic ordering is detected at 5.8(5) K at low fields and a metamagnetic transition occurs at a critical field of 1.4(2) T. Eu2Au2Sn5 is a metal with a specific resistivity of 150±20 μfΩcm at room temperature. The results of 151Eu and 119Sn Mössbauer spectroscopic experiments are compatible with divalent europium and show complex hyperfine field splitting with a transferred magnetic hyperfine field at the tin nuclei at low temperature.

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New stannides CaTSn2 (T = Rh, Pd, Ir) and Ca2PhSn5 were prepared as single phase materials by a reaction o f the elements in glassy carbon crucibles under flowing purified argon. The four compounds were investigated by X-ray diffraction both on powders and single crystals and their structures were refined from single crystal data. The stannides CaTSn2 (T = Rh, Pd, Ir) adopt the MgCuAl, structure with space group Cmcm: a = 434.1(1), b = 1081.7(3), c = 748.8(2) pm, wR2 = 0.040Ö, 451 F2 values for CaRhSn2, a = 442.7(2), b = 1113.8(4), c = 745.6(2) pm, wR2 = 0.0318, 471 F ; values for CaPdSn2, and a = 429.5(1), b = 1079.5(3), c = 758.6(2) pm, wR2 = 0.0465, 455 F2 values for CaIrSn2 with 16 variables for each refinement. Chemical bonding analysis leads to the description o f a distorted filled CaSni substructure in which the tin-tin bonding is modified by the insertion o f transition metal atoms into the planar calcium layers, favoring strong tin-transition metal bonding. 119Sn Mössbauer spectra show single signals for CaTSn2 (T = Rh, Pd, Ir) which are subjected to quadrupole splitting. The electron count o f the CaTSn2 compounds correlates with the ll9Sn isomer shift. Ca2Pt3Sn3 crystallizes with the Yb2Pt3Sn5 type structure: Pnma, a = 734.8(1), b = 445.50(7), c = 2634.8(5) pm, wR2 = 0.0636, 1406 F2 values and 62 variables. The platinum and tin atoms in Ca2Pt3 Sns build a complex three-dimensional [Pt3Sn5] polyanion in which the calcium cations fill distorted pentagonal and hexagonal channels. According to semi-empirical band structure calculations the strongest bonding interactions are found for the Pt-Sn contacts, follow ed by Sn-Sn bonding. The 119Sn Mössbauer spectrum of Ca2Pt3Sn5 shows two superimposed signals at δ = 2.10(3) and δ= 2.18(6) mm/s

YbZnSn, YbAgSn, and Yb2Pt2Pb were synthesized by reacting the elements in sealed tantalum tubes in a high-frequency furnace. The structures of YbAgSn and Yb2Pt2Pb were refined from single crystal X-ray data: YbAgPb type, P6m2, a=479.2(2) pm, c=1087.3(3) pm, wR2=0.050, BASF=0.34(8), 509 F2 values, 18 variables for YbAgSn and Er2Au2Sn type, a=776.0(1) pm, c=701.8(2) pm, wR2=0.072, 426 F2 values, 18 variables for Yb2Pt2Pb. The lattice constants of YbZnSn are confirmed: NdPtSb type, P63mc, a=464.7(1) pm, c=747.7(2) pm. The stannides YbZnSn and YbAgSn crystallize with superstructures of the AlB2 type. The zinc (silver) and tin atoms form ordered Zn3Sn3 and Ag3Sn3 hexagons, respectively. The stacking sequences for the differently oriented hexagons are AB, AB for YbZnSn and ABC, ABC for YbAgSn. While exclusively Zn–Sn intralayer interactions were observed in YbZnSn, intralayer Ag–Sn and significant Sn–Sn interlayer interactions at 318 pm occur in YbAgSn. The [ZnSn] and [AgSn] polyanions in YbZnSn and YbAgSn, respectively, have a pronounced two-dimensional character. This picture of chemical bonding in YbAgSn is confirmed by TB–LMTO–ASA band structure calculations. The partial densities-of-states and the valence charge densities are discussed. The magnetic (no long-range ordering, Yb2+) and the resistivity measurements (metallic behavior) are in excellent agreement with the electronic structure calculations. Yb2Pt2Pb crystallizes with the Er2Au2Sn structure, a ternary derivative of the Zr3Al2 type. This structure is composed of distorted AlB2 and CsCl related slabs of compositions YbPt2 and YbPb. Yb2Pt2Pb shows paramagnetic behavior (4.3±0.4 μB/Yb) indicating trivalent ytterbium. Magnetic susceptibility measurements on YbZnSn and YbAgSn show Pauli paramagnetism with room temperature susceptibilities of 2.5(1)×10−9 and 4.6(1)×10−9 m3/mol. Electrical resistivity measurements indicate metallic conductivity with specific resistivities of 440±40 μΩcm (YbZnSn) and 490±40 μΩcm (YbAgSn) at 300 K. 119Sn Mössbauer spectra of YbZnSn show a single signal at room temperature with an isomer shift of δ=1.85(1) mm/s. YbAgSn shows two superimposed signals at 78 K: a singlet at δ=1.94(1) mm/s and a second signal at δ=1.99(1) mm/s subjected to quadrupole splitting of ΔEQ=1.35(1) mm/s, in agreement with the two crystallographically different tin sites.

Two modifications of YbPdSn were prepared from the elements in sealed tantalum tubes at 870 K (alpha-YbPdSn) and 1400 K (beta-YbPdSn). Both structures were refined from single crystal X-ray data: alpha-YbPdSn (ZrNiAl type structure), space group2m, a = 759.0(2) pm, c = 376.98(9) pm, wR2 = 0.0541, 344 F-2 values, 14 variables; beta-YbPdSn (TiNiSi type structure), space group Pnma, a = 718.7(1) pm, b = 458.3(1) pm, c = 796.1(1) pm, wR2 = 0.0455, 391 F-2 values, 20 variables. Structural features of both modifications are palladium-centered trigonal prisms formed by the ytterbium and tin atoms. The structural similarities between alpha- and beta-YbPdSn and the relationship with the aristotype AlB2 is discussed in the framework of a group-subgroup scheme. Magnetic susceptibility data show Curie-Weiss behaviour for alpha-YbPdSn with mu(exp) = 4.2(1) mu(B) and theta = -75(2) K, indicating trivalent ytterbium. The susceptibility of beta-YbPdSn can be fitted to a modified Curie-Weiss law with mu(exp) = 1.6(1) mu(B), theta = -5(1) K and chi(0) = 3.0 x 10(-9) m(3)/mol, suggesting a tendency towards divalent ytterbium. Temperature dependent resistivity measurements indicate metallic behaviour with room temperature values of 50 +/- 20 mu Omega cm for alpha-YbPdSn and 1300 +/- 100 mu Omega cm for beta-YbPdSn. Sn-119 Mossbauer spectroscopic data show only one signal at delta = 1.84(2)mm/s (alpha-YbPdSn) and delta = 1.96(4)mm/s (beta-YbPdSn) subjected to quadrupole splitting of Delta Eq = 0.73(4) mm/s and Delta Eq = 0.97(5) mm/s, respectively.

The intermetallic compounds CaCuGe, CaAuIn, and CaAuSn can be prepared from the elements in sealed tantalum tubes or in glassy carbon crucibles in a high-frequency furnace. Their crystal structures were determined from single crystal X-ray data. The three compounds crystallize with the same subcell structure (KHg2), however, they form three clearly perceptible superstructures with different unit. cells, but all in space groups Pnma: a = 2124.9(6) pm, b = 436.0(2) pm, c=749.4(5)pm, Z=12, wR2=0.0789, 1303 F-2 values, 56 variables for CaCuGe town structure type), a = 738.2(1) pm, b = 459.4(1) pm, c = 839.4(2) pm, Z = 4, wR2 = 0.0651, 656 F-2 values, 20 variables for CaAuIn (TiNiSi type), a=3690.3(3)pm, b=470.5(1)pm, c=813.6(2)pm, Z=20, wR2=0.1294, 1730 F-2 values, 92 variables for CaAuSn (new structure type). The three structures may be considered as superstructures of the KHg2 type with an ordered arrangement of the transition metal and germanium (indium, tin) atoms on the mercury position. Each calcium atom in the structures of CaCuGe, CaAuIn, and CaAuSn has an distinctly ordered near-neighbor environment of six transition metal (T) and six p element (X) atoms in the form of two counter-tilted T3X3 hexagons. All known superstructures of the KHg2 type are described in terms of a group-sub-group scheme.

The binary silicides Eu5Si3 and Yb3Si5 were prepared from the elements in sealed tantalum tubes and their crystal structures were determined from single crystal X-ray data: I4/mcm, a = 791.88(7)pm, c = 1532.2(2)pm, Z = 4, wR2 = 0.0545, 600 F-2 values, 16 variables for EU5Si3 (Cr5B3-type ) and P (6) over bar 2m, a = 650.8(2)pm, c = 409.2(1)pm, Z = 1, wR2 = 0.0427, 375 F-2 values, 12 variables for Yb3Si5 (Th3Pd5 type). The new silicide Eu5Si3 contains isolated silicon atoms and silicon pairs with a Si-Si distance of 242.4 pm. This silicide may be described as a Zintl phase with the formula [5EU(2+)](10+)[Si](4-)[Si-2](6-). The silicon atoms in Yb3Si5 form a two-dimensional planar network with two-connected and three-connected silicon atoms. According to the Zintl-Klemm concept the formula of homogeneous mixed-valent Yb3Si5 may to a first approximation be written as [3Yb](8+)[2Si(-)](2-)[3Si(2-)](6-). Magnetic susceptibility investigations of Eu5Si3 show Curie-Weiss behaviour above 100K with a magnetic moment of 7.85(5) mu(B) which is close to the free ion value of 7.94 mu(B) for EU2+. Chemical bonding in Eu5Si3 and Yb3Si5 was investigated by semi-empirical band structure calculations using an extended Huckel hamiltonian. The strongest bonding interactions are found for the Si-Si contacts followed by Eu-Si and Yb-Si, respectively. The main bonding characteristics in EU5Si3 are antibonding Si1(2)-pi* and bonding Eu-Si1 states at the Fermi level. The same holds true for the silicon polyanion in Yb3Si5.