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We report the synthesis, structure, and magnetic properties of a new Zintl phase and structure type, Eu11Zn4Sn2As12. The structure and composition of this phase have been established by single-crystal X-ray diffraction and electron microprobe analysis. Eu11Zn4Sn2As12 crystallizes in monoclinic space group C2/c (No. 15) with the following lattice parameters: a = 7.5679(4) A, b = 13.0883(6) A, c = 31.305(2) A, and β = 94.8444(7)° [R1 = 0.0398; wR2 = 0.0633 (all data)]. The anisotropic structural features staggered ethane-like [Sn2As6]12– units and infinite ∞2[Zn2As3]5– sheets extended in the a–b plane. Eu cations fill the space between these anionic motifs. Temperature-dependent magnetic properties and magnetoresistance of this Zintl phase have been studied, and the electronic structure and chemical bonding were elucidated using first-principles quantum chemical calculations (TB-LMTO-ASA). Quantum chemical calculations show that the ethane-like units can be considered as consisting of covalent single bonds;...

The title compound with the nominal formula, Sr13Eu8Cd3Mn1Sb18, was synthesized by Sn-flux. Structure refinement was based on single-crystal X-ray diffractometer data. Employing the exact composition, the formula is Sr13.23Eu7.77Cd3.12Mn0.88Sb18 for the solid solution Sr21-xEuxCd4-yMnySb18. This phase adopts the Sr21Mn4Sb18 type structure with site preferences for both Eu and Cd. The structure crystallizes in the monoclinic system in space group C2/m and Z=4: a=18.1522(11), b=17.3096(10), c=17.7691(10) Å, β=91.9638(8)°, 6632 F2 values, 216 variables, R1=0.0254 and wR2=0.0563. Site selectivity of the elements in this new compound will be discussed in relationship with the Sr21Mn4Sb18 type structure and other related structure types. Temperature dependent magnetic susceptibility data reveal Curie–Weiss paramagnetism with an experimental moment of 19.3 μB/f.u. and a Weiss constant of 0.4 K. Magnetic ordering is seen at low temperatures, with a transition temperature of 3.5 K.

Eu11–xYbxCd6Sb12 Zintl solid solutions have been prepared by tin flux reaction by employing the elements Eu/Yb/Cd/Sb/Sn in the ratio 11 – xp:xp:6:12:30, where xp is an integer less than 11 representing the preparative amount of Eu (11 – xp) and Yb (xp). Efforts to make the Yb compositions for x exceeding ∼3 resulted in structures other than the Sr11Cd6Sb12 structure type. The crystal structures and compositions were determined by single-crystal and powder X-ray diffraction and wavelength-dispersive X-ray analysis measurements. The title solid-solution Zintl compounds crystallize in the centrosymmetric monoclinic space group C2/m (no. 12, Z = 2) as the Sr11Cd6Sb12 structure type (Pearson symbol mC58), and the lattice parameters decrease with increasing ytterbium content. Single crystal X-ray diffraction shows that Yb atoms are not randomly distributed in the Eu sites but have a site preference which can be attributed to size effects. The influence of the rare earth (RE) metal sites on thermal and electroni...

A novel Zintl phase structure type, Eu7Cd4Sb8-xAsx (x = 2, 3, 4, and 5), with the general formula Eu7Cd4Pn8 (Pn = mixed occupancy Sb and As), was synthesized by molten tin flux reaction. Its structure was determined using single-crystal X-ray diffraction methods. This structure type is only preserved for 2 ≤ x ≤ 5 under our experimental conditions, and efforts to synthesize samples with x2 or x5 resulted in other structure types. The mixed occupancy Sb and As can be thought of as a pseudoatom whose ideal size, in this range of Sb/As ratios, fits the structure. The title phase crystallizes in the I-centered monoclinic space group I2/m (No. 12, Z = 4) with unit cell parameters ranging as follows: a = 19.7116(17)-19.4546(13) Å, b = 4.6751(4)-4.6149(3) Å, c = 24.157(2)-23.871(15) Å, and β = 95.8798(1)-96.016(5)°, depending on the Sb/As ratio. The structure can be described as parallel double pentagonal tubes resulting from Cd-Pn and Pn-Pn bonding. These double pentagons are formed through corner sharing of the Cd-centered CdPn4 tetrahedra and a Pn-Pn interaction from two adjacent CdPn4 tetrahedra. This structure type is closely related to the Sr11Cd6Sb12 structure type as both share the same bonding features of Pn-Pn bonding and double pentagonal tubes. Electron microprobe analysis confirms the composition of these new Zintl solid solution phases. The As exhibits preferential substitution on specific sites, and site specificity trends are supported by lowest energy models from theoretical calculations. Theoretical calculations also predict that Sb-rich compounds should be metallic or semimetallic and that they should become more insulating as As content increases. Members of the solid-solution order ferromagnetically between 5 and 6 K and exhibit relatively low electrical resistivity between 50 and 300 K, ranging from ∼0.57 to ∼26 mΩ·cm, increasing with increasing As content.

The synthesis and transport properties of the family of coinage metal-stuffed Zintl compounds, Eu9Cd4–xCM2+x–y□ySb9 (CM = coinage metal, □ = vacancies), is presented as a function of coinage metal substitution. Eu9Cd4–xCM2+x–y□ySb9 compounds are shown to be rare examples of metallic Zintl phases with low thermal conductivities. While the lattice thermal conductivity is low, which is attributed to the complex structure and presence of interstitials, the electronic contribution to thermal conductivity is also low. In these p-type compounds, the carriers transmit less heat than expected, based on the Wiedemann–Franz law and metallic conduction, κe = L0T/ρ. Density functional theory (DFT) calculations indicate that the Fermi level resides in a pseudo-gap, which is consistent with the metallic description of the properties. While the contribution from the interstitial CM states to the Fermi level is small, the interstitial CMs are required to tune the position of the Fermi level. Analysis of the topology of el...

Solid-solution Zintl compounds with the formula Eu11Cd6–xZnxSb12 have been synthesized from the elements as single crystals using a tin flux according to the stoichiometry Eu:Cd:Zn:Sb:Sn of 11:6–xp:xp:12:30 with xp = 0, 1, 2, 3, 4, 5, and 6, where xp is the preparative amount of Zn employed in the reaction. The crystal structures and the compositions were established by single-crystal as well as powder X-ray diffraction and wavelength-dispersive X-ray analysis measurements. The title solid-solution Zintl compounds crystallize isostructurally in the centrosymmetric monoclinic space group C 2/m (No. 12, Z = 2) as the Sr11Cd6Sb12 structure type (Pearson symbol mC58). There is a miscibility gap at 3 ≤ xp ≤ 4 where the major product crystallizes in a disordered structure related to the Ca9Mn4Bi9 structure type; otherwise, for all other compositions, the Sr11Cd6Sb12 structure is the majority phase. Eu11Cd6Sb12 shows lower lattice thermal conductivity relative to Eu11Zn6Sb12 consistent with its higher mean atomi...

The synthesis, crystal structure, magnetic properties, and europium Mossbauer spectroscopy of the new members of the 9–4–9 Zintl family of Eu9Cd4–xCM2+x–y□ySb9 (CM = coinage metal: Au, Ag, and Cu) are reported. These compounds crystallize in the Ca9Mn4Bi9 structure type (9–4–9) with the 4g interstitial site almost half-occupied by coinage metals; these are the first members in the 9–4–9 family where the interstitial positions are occupied by a monovalent metal. All previously known compounds with this structure type include divalent interstitials where these interstitials are typically the same as the transition metals in the anionic framework. Single-crystal magnetic susceptibility data indicate paramagnetic behavior for all three compounds with antiferromagnetic ordering below 10 K (at 100 Oe) that shifts to lower temperature (

The compounds, Yb14−xTmxMnSb11 (0

Zintl phases are compounds that have shown promise for thermoelectric applications. The title solid–solution Zintl compounds were prepared from the elements as single crystals using a tin flux for compositions x = 0, 1, 2, and 3. Eu_(11)Cd_6Sb_(12–x)As_x (x < 3) crystallize isostructurally in the centrosymmetric monoclinic space group C2/m (no. 12, Z = 2) as the Sr_(11)Cd_6Sb_(12) structure type (Pearson symbol mC58). Efforts to make the As compositions for x exceeding ~3 resulted in structures other than the Sr_(11)Cd_6Sb_(12) structure type. Single-crystal X-ray diffraction indicates that As does not randomly substitute for Sb in the structure but is site specific for each composition. The amount of As determined by structural refinement was verified by electron microprobe analysis. Electronic structures and energies calculated for various model structures of Eu_(11)Cd_6Sb_(10)As_2 (x = 2) indicated that the preferred As substitution pattern involves a mixture of three of the six pnicogen sites in the asymmetric unit. In addition, As substitution at the Pn4 site opens an energy gap at the Fermi level, whereas substitution at the other five pnicogen sites remains semimetallic with a pseudo gap. Thermoelectric properties of these compounds were measured on hot-pressed, fully densified pellets. Samples show exceptionally low lattice thermal conductivities from room temperature to 775 K: 0.78–0.49 W/mK for x = 0; 0.72–0.53 W/mK for x = 1; and 0.70–0.56 W/mK for x = 2. Eu_(11)Cd_6Sb_(12) shows a high p-type Seebeck coefficient (from +118 to 153 μ V/K) but also high electrical resistivity (6.8 to 12.8 mΩ·cm). The value of zT reaches 0.23 at 774 K. The properties of Eu_(11)Cd_6Sb_(12–x)As_x are interpreted in discussion with the As site substitution.

Eu7Cd4Sb8-xAsx (x = 2, 3, 4, and 5) solid solutions are prepared from the elements in a molten Sn flux (alumina crucible in evacuated silica tubes, 1.

Enhancing the efficiency of thermoelectric devices is critical for their adoption in commercial large-scale applications aimed at converting heat into electricity. To compete with the present mechanical energy generators, thermoelectric materials need to be at least three times more efficient than today's commercial thermoelectrics. This high conversion efficiency corresponds to a thermoelectric figure of merit, zT , of ~ 3, which has remained elusive despite a long history of searching for new thermoelectric materials. The recent discoveries of high zT among Zintl phase compounds such as Yb 14 MnSb 11 , EuZn 2 Sb 2 , Yb 9 Mn 4.2 Sb 9 , clathrates, and the filled skutterudites show the potential of this class of compounds for more efficient thermoelectric materials. This perspective summarizes the recent progress on Zintl phases studied for thermoelectric applications with a focus on their chemistry, crystal structure, and transport properties.

Single crystals of Eu11Cd6-xZnxSb12 (0 ≤ x ≤ 6) are prepared by reaction of the elements in a Sn flux (950 °C; cooling to 650 °C with a rate of 5 °C/h).

The synthesis, crystal structure, magnetic properties, and europium Mössbauer spectroscopy of the new members of the 9-4-9 Zintl family of Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb(9) (CM = coinage metal: Au, Ag, and Cu) are reported. These compounds crystallize in the Ca(9)Mn(4)Bi(9) structure type (9-4-9) with the 4g interstitial site almost half-occupied by coinage metals; these are the first members in the 9-4-9 family where the interstitial positions are occupied by a monovalent metal. All previously known compounds with this structure type include divalent interstitials where these interstitials are typically the same as the transition metals in the anionic framework. Single-crystal magnetic susceptibility data indicate paramagnetic behavior for all three compounds with antiferromagnetic ordering below 10 K (at 100 Oe) that shifts to lower temperature (7 K) by applying a 3 T magnetic field. (151)Eu Mössbauer spectra were collected on polycrystalline powder samples of Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb(9) at 50 and 6.5 K in order to evaluate the valence of Eu cations. Although the Zintl formalism states that the five crystallographically distinct Eu sites in Eu(9)Cd(4-x)CM(2+x-y)□(y)Sb9 should bear Eu(2+), the Mössbauer spectral isomer shifts are clearly indicative of both 2+ and 3+ valence of the Eu cations with the Cu- and Au-containing compounds showing higher amounts of Eu(3+). This electronic configuration leads to an excess of negative charge in these compounds that contradicts the expected valence-precise requirement of Zintl phases. The spectra obtained at 6.5 K reveal magnetic ordering for both Eu(2+) and Eu(3+). The field dependence of Eu(2+) indicates two distinct magnetic sublattices, with higher and lower fields, and of a small field for Eu(3+). The site symmetry of the five Eu sites is not distinguishable from the Mössbauer data.

Octanol capped silicon nanoparticles crystallizing in the metastable BC8 structure are prepared by a colloidal route from mixtures of SiI4, n-butyllithium, dioctylether, and 1-octanol (280 °C, 72 h, 25—35% yield).

Single crystals of the title compounds are prepared from the elements in a Sn flux (alumina crucibles, 950 °C, 96 h) and characterized by powder and single crystal XRD, transport properties measurements, and TB-LMTO-ASA electronic structure calculations.

Electrophilic activation and subsequent reduction of substrates is in general not possible because highly Lewis acidic metals lack access to multiple redox states. Herein, we demonstrate that transition metal-like redox processes and electronic structure and magnetic properties can be imparted to aluminum(III). Bis(iminopyridine) complexes containing neutral, monoanionic, and dianionic iminopyridine ligands (IP) have been characterized structurally and electronically; yellow (IP)AlCl(3) (1), deep green (IP(-))(2)AlCl (2) and (IP(-))(2)Al(CF(3)SO(3)) (3), and deep purple [(IP(2-))Al](-) (5) are presented. The mixed-valent, monoradical complex (IP(-))(IP(2-))Al is unstable toward C-C coupling, and [(IP(2-))Al](2-)(μ-IP-IP)(2-) (4) has been isolated. Variable-temperature magnetic susceptibility and EPR spectroscopy measurements indicate that the biradical character of the ligand-based triplet in 2 is stabilized by strong antiferromagnetic exchange coupling mediated by aluminum(III): J = -230 cm(-1) for Ĥ = -2J(Ŝ(L(1))·Ŝ(L(2))). Coordination geometry-dependent (IP(-))-(IP(-)) communication through aluminum(III) is observed electrochemically. The cyclic voltammogram of trigonal bipyramidal 2 displays successive ligand-based oxidation events for the two IP(1-/0) processes, at -0.86 and -1.20 V vs SCE. The 0.34 V spacing between redox couples corresponds to a conproportionation constant of K(c) = 10(5.8) for the process (IP(-))(2)AlCl + (IP)(2)AlCl → 2(IP(-))(IP)AlCl consistent with Robin and Day Class II mixed-valent behavior. Tetrahedral 5 displays localized, Class I behavior as indicated by closely spaced redox couples. Furthermore, CV's of 2 and 5 indicate that changes in the coordination environment of the aluminum center shift the potentials for the IP(1-/0) and IP(2-/1-) redox couples by up to 0.9 V.