Exploring New Zintl Phases in the 9-4-9 Family via Al Substitution. Synthesis, Structure, and Physical Properties of Ae9Mn4-xAlxSb9 (Ae = Ca, Yb, Eu).

Three new quaternary Zintl phases with the "9-4-9" formula, Ae9Mn4-xAlxSb9 (Ae = Ca, Yb, Eu), have been synthesized using Pb as the metal flux, and their crystal structures have been established by single-crystal X-ray diffraction. Both Ca9Mn2.91(4)Al1.09Sb9 and Yb9Mn3.59(6)Al0.41Sb9 are isostructural with Ca9Mn4Bi9, and they crystallize in the orthorhombic space group Pbam with unit cell dimensions of a = 12.4571(8), 12.2884(16) Å, b = 22.1352(16), 22.024(3) Å, and c = 4.6012(3), 4.6187(6) Å, respectively. Their anionic structures can be viewed as infinite ribbons based on corner-shared tetrahedrons. Also, Eu9Mn2.87(4)Al1.13Sb9 has the space group Cmca and a = 9.4883(7) Å, b = 23.6895(18) Å, and c = 24.4845(19) Å. The structural relationships between Ca9Mn2.91(4)Al1.09Sb9 and Eu9Mn2.87(4)Al1.13Sb9 are compared and discussed as well. The successful Al3+ substitution provides additional electrons to the compounds to achieve structural stability. Magnetic susceptibility and electrical resistivity measurements, performed on single crystals of Eu9Mn2.87(4)Al1.13Sb9, indicate complex magnetic properties and semiconductor behavior. The physical properties of Yb9Mn3.59(6)Al0.41Sb9 are similar to those observed for Yb9Mn4.18(2)Sb9.

Sr14Sn3As12 and Eu14Sn3As12: enantiomorph-like Zintl compounds.

Two new chiral Zintl compounds, Sr14Sn3As12 and Eu14Sn3As12, were synthesized from tin-flux reactions, and the structures were determined by using single-crystal X-ray diffraction. Both compounds crystallize in the trigonal space group R3 (No. 146, Z = 3) with the anion structures containing various units: dumbbell-shaped [Sn2As6](12-) dimers, [SnAs3](7-) triangular pyramids, and isolated As(3-) anions. Very interestingly, these two compounds exhibit opposite chirality in the observed crystal structures, resembling enantiomorphs. Detailed structure analyses suggest possible steric effects among the anion clusters, and on the basis of the calculated electronic structures, substantial electron lone pairs exist on the anions of both compounds, which may provide a hint to understanding the origination of chirality in these intermetallic compounds.

Ba13Si6Sn8As22: a quaternary Zintl phase containing adamantane-like [Si4As10] clusters.

A new quaternary arsenide Zintl phase, Ba13Si6Sn8As22, has been synthesized from the Sn-flux reactions, and the structure was determined by the single-crystal X-ray diffraction methods. The compound crystallizes in the tetragonal non-centrosymmetric space group I42m (No. 121) with unit cell parameters of a = b = 14.4857(3) Å, c = 13.5506(7) Å, V = 2843.40(17) Å(3). Its polyanion structure can be viewed as composed of [Si4As10] adamantane-like clusters and SiAs4 tetrahedra, which are linked via the [Sn2As4] groups built through two edge-sharing SnAs3 triangular pyramids. Differential thermal analysis and thermogravimetry measurements indicate that Ba13Si6Sn8As22 has good thermal stability, and does not melt or decompose below 1045 K under Ar atmosphere. Density functional calculations were performed on Ba13Si6Sn8As22 and the results suggest a band gap of around 1.0 eV for Ba13Si6Sn8As22, confirmed by the diffuse reflectance spectrum measurement. In addition, the extensively existing lone pairs of electrons on the p-orbitals of As and Sn may also hint interesting nonlinear optical properties considering the noncentrosymmetric structure.

Synthesis, crystal and electronic structures, and properties of the new pnictide semiconductors A2CdPn2 (A = Ca, Sr, Ba, Eu; Pn = P, As).

A series of ternary Zintl phases, Ca(2)CdP(2), Ca(2)CdAs(2), Sr(2)CdAs(2), Ba(2)CdAs(2), and Eu(2)CdAs(2), have been synthesized through high temperature metal flux reactions, and their structures have been characterized by single-crystal X-ray diffraction. They belong to the Yb(2)CdSb(2) structure type and crystallize in the orthorhombic space group Cmc2(1) (No. 36, Z = 4) with cell dimensions of a = 4.2066(5), 4.3163(5), 4.4459(7), 4.5922(5), 4.4418(9) Å; b = 16.120(2), 16.5063(19), 16.904(3), 17.4047(18), 16.847(4) Å; c = 7.0639(9), 7.1418(8), 7.5885(11), 8.0526(8), 7.4985(16) Å for Ca(2)CdP(2) (R1 = 0.0152, wR2 = 0.0278), Ca(2)CdAs(2) (R1 = 0.0165, wR2 = 0.0290), Sr(2)CdAs(2) (R1 = 0.0238, wR2 = 0.0404), Ba(2)CdAs(2) (R1 = 0.0184, wR2 = 0.0361), and Eu(2)CdAs(2) (R1 = 0.0203, wR2 = 0.0404), respectively. Among these, Ca(2)CdAs(2) was found to form with another closely related structure, depending on the experimental conditions--monoclinic space group Cm (No. 8, Z = 10) with lattice constants a = 21.5152(3) Å, b = 4.30050(10) Å, c = 14.3761(2) Å and ß = 110.0170(10)° (R1 = 0.0461, wR2 = 0.0747). UV/vis optical absorption spectra for both forms of Ca(2)CdAs(2) show band gaps on the order of 1.0 eV, suggesting semiconducting properties, which have also been confirmed through electronic band structure calculations based on the density-functional theory. Results from differential scanning calorimetry measurements probing the thermal stability and phase transitions in the two Ca(2)CdAs(2) polymorphs are discussed. Magnetic susceptibility measurements for Eu(2)CdAs(2), indicating divalent Eu(2+) cations, are presented as well.

Crystal structure of Ba5In4Sb6.

The title compound, penta-barium tetra-indium hexa-anti-mony, was synthesized by an indium-flux reaction and its structure features layers composed of edge-sharing In2Sb6 units. The voids between the In4Sb6 layers are filled by Ba(2+) cations, which are all surrounded by six Sb atoms and form bicapped octa-hedral or triangular prismatic coordination geometries. There are five barium ions in the asymmetric unit: one has no imposed crystallographic symmetry, two lie on mirror planes and two have mm2 point symmetry. The two In atoms and four Sb atoms in the asymmetric unit all lie on general crystallographic positions.

Synthesis, structure and bonding, optical properties of Ba4MTrQ6 (M=Cu, Ag; Tr=Ga, In; Q=S, Se).

Four new quaternary chalcogenides, Ba4AgGaS6 (1), Ba4AgGaSe6 (2), Ba4CuInS6 (3), and Ba4AgInS6 (4), were synthesized by solid-state reactions and their structures were characterized through single-crystal X-ray diffraction. In spite of their similar chemical compositions, the flexible arrangement between the transition metals and the triel atoms leads to subtle differences in their polyanion structures. All structures feature similar [MTrQ6](8-) 1D polyanionic chains (M=Cu, Ag; Tr=Ga, In; Q=S, Se), which are constructed from corner-sharing MQ4 or TrQ4 tetrahedra. However, the transition metals and triels are mixed in 1, 2, and 3, but they occupy independent crystallographic sites in 4. As a result, compounds 1-3 belong to the known Ba2CoS3 (Pnma No. 62) or Ba2 MnS3 (Pnma No. 62) class, whereas 4 crystallizes in its own structural type within the monoclinic P21/c (No. 14) space group. The structural relationship among these new phases was also studied with the aid of DFT calculations and related optical properties are presented as well.