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Enclathration of X@La4 tetrahedra in channels of Zn-P frameworks in La3Zn4P6X (X = Cl, Br) Jian Wang, Derrick Kaseman, Kathleen Lee, Sabyasachi Sen, and Kirill Kovnir Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b01752 • Publication Date (Web): 07 Jun 2016 Downloaded from http://pubs.acs.org on June 22, 2016

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Chemistry of Materials

Enclathration of X@La4 tetrahedra in channels of Zn-P frameworks in La3Zn4P6X (X = Cl, Br) Jian Wang†, Derrick Kaseman‡, Kathleen Lee†, Sabyasachi Sen‡, Kirill Kovnir†* †

‡

Department of Chemistry, and Department of Materials Science, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States ABSTRACT: Two new quaternary lanthanum zinc phosphide-halides were synthesized via high-temperature solid-state reactions. Their complex crystal structures were determined by a combination of X-ray diffraction and advanced solidstate 31P NMR spectroscopy. La3Zn4P6Cl and La3Zn4P6.6Br0.8 share a common structural feature: a polyanionic Zn-P framework with large channels hosting complex one-dimensional cations. The cations are built from X@La4 tetrahedral chains with X = Cl (La3Zn4P6Cl) or Br0.8P0.2 (La3Zn4P6.6Br0.8). The X@La4 tetrahedra share two vertices forming one-dimensional chains. To accommodate larger bromine-containing cations the Zn-P framework is rearranged by breaking and forming several Zn-P and P-P bonds. This results in the formation of a unique [P3]3− cycle, which is isoelectronic to cyclopropane. Analysis of the electron localization and orbital overlaps confirmed the presence of different chemical bonding in the ZnP networks in the Cl- and Br-containing compounds. La3Zn4P6Cl was predicted to be a narrow bandgap semiconductor, while the formation of the [P3]3− units in the structure of La3Zn4P6.6Br0.8 was shown to lead to a narrowing of the bandgap. Characterization of the transport properties confirmed both La3Zn4P6Cl and La3Zn4P6.6Br0.8 to be narrow bandgap semiconductors with electrons as dominating charge carriers at low temperatures. La3Zn4P6Cl exhibits a n-p transition around 250 K. Due to the complex crystal structure and segregation of the areas of different chemical bonding, both title compounds exhibit ultralow thermal conductivities of 0.7 Wm–1K–1 and 1.5 Wm–1K–1 at 400 K for La3Zn4P6Cl and La3Zn4P6.6Br0.8, respectively.

Introduction Inorganic clathrates are fascinating inorganic compounds.[1,2] In their crystal structure, cations of alkali metals, alkaline-earth metals and divalent Eu are enclathrated inside large polyhedral cages. Introduction of a trivalent rare-earth cation (R3+) into the clathrate structure is highly desired since it was predicted to generate ‘stronglycorrelated’ compounds with significantly enhanced thermoelectric properties due to the interactions of localized 4f and conduction electrons.[1] Despite numerous attempts only one successful synthesis of such a clathrate has been reported.[3] The smaller size of the trivalent rareearth cations compared to the size of the mono- and divalent cations calls for an alternative approach to encapsulate rare-earth atoms or clusters within voids of negatively charged frameworks. Our group specializes in unconventional clathrates based on late transition metal and pnicogens, group 15 elements.[4,5] These frameworks are much more flexible than traditional Si-, Ge-, and Sn-based clathrates. Analysis of reported rare-earth intermetallic pnictides with low rare-earth content, less than 30 at.-%, shows that R3+ cations may segregate in certain parts of the crystal structure due to a preference for selected types of chemical bonding. For example in ROFeAs superconductors, all rareearth cations are situated in the ionic R-O layer.[6-8] Inspired by this idea we selected to work with a combination of a flexible covalent Zn-P framework to encapsulate

rare-earth cations. In this work we report the syntheses, crystal structures determined by a combination of X-ray diffraction and solid-state NMR spectroscopy, chemical bonding, and transport properties of two novel compounds, La3Zn4P6Cl and La3Zn4P6.6Br0.8. Experimental section Synthesis. All preparation and handling of samples were performed in an argon-filled glovebox with the O2 level below 1 ppm. All starting materials were commercial grade and used as received: La (Alfa Aesar, 99.9%), Zn shot (Alfa Aesar, 99.8%), red P (Alfa Aesar, 99 %), anhydrous ZnCl2 (Alfa Aesar, 99.9%), and anhydrous ZnBr2 (Aldrich, 99+ %). La3Zn4P6Cl was first found in the process of exploring the La-Zn-P-Cl system using ZnCl2 as a flux. The reactants were loaded in a ratio of La:P:ZnCl2 = 2.17:3:1 into carbonized silica ampoules, evacuated, and flame-sealed. The ampoules were heated in muffle furnaces to 773 K at a rate of 50 K/h, and then annealed at this temperature for 24 h. The ampoules were then heated up to 1073 K over 10 h and annealed at this temperature for 144 h. Finally, the ampoules were cooled down to 773 K over 20 h and annealed for 120 h at this temperature, and afterwards the furnace was turned off. The produced sample contained large amounts of black, needle-like crystals along with a small amount of amorphous powder. Selected crystals were determined to be La3Zn4P6Cl through single crystal X-ray diffraction (Tables S1-S3). The composition of a new

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phase was confirmed by energy dispersive X-ray (EDX) spectroscopy (Table S5). The crystals of the brominecontaining compound were synthesized via loading the starting materials in a ratio of La:Zn:P:ZnBr2=3:3.5:6:0.5 with the same temperature profile. All our attempts to synthesize the iodine-containing analogue “La3Zn4P6I” by varying the temperature profile were unsuccessful.

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Final refinements were performed using anisotropic atomic displacement parameters for all atoms. A summary of pertinent information relating to unit cell parameters, data collection, and refinements is provided in Table S1 and the atomic parameters and interatomic distances are provided in Tables S2 and S3. Further details of the crystal structure determination may be obtained from Fachinformationszentrum Karlsruhe by quoting the depository CSD numbers 431155 (La3Zn4P6Cl) and 431154 (La3Zn4P6.6Br0.8).

High purity, polycrystalline samples of La3Zn4P6Cl and La3Zn4P6.6Br0.8 were synthesized by stoichiometric solidstate reactions of starting materials in glassy carbon crucibles sealed in evacuated silica ampoules. These samples were heated over 17 hours to 1073 K and annealed at this temperature for 144 hours. Subsequently, these samples were opened in a glovebox, finely ground, resealed, and re-annealed second time using an identical heating profile. The re-annealing was repeated 3 times to obtain nearly phase-pure samples (Figures S1 and S2).

Sample densification. Polycrystalline samples (~200 mg) of La3Zn4P6Cl and La3Zn4P6.6Br0.8 were carefully ground into a fine powder and loaded into 5 mm ∅ graphite SPS dies in the glovebox and then sintered under dynamic vacuum at 873 K through spark plasma sintering (Dr. Sinter Lab Jr. SPS-211Lx, Sumitomo Coal Mining Co, Ltd.). A uniaxial pressure of 156 MPa was applied at 873 K for 10mins, than pressure was removed, and samples were cooled down at ambient pressure. The formed pellets with dimensions of ~5 mm ∅ and thickness of ~1.5 mm have geometric densities of 84% and 89% of the theoretical X-ray crystal structure densities for La3Zn4P6Cl and La3Zn4P6.6Br0.8, respectively. Graphite and any possible surface contaminations were removed by polishing the pellets in the glovebox. Attempts to obtain higher density pellets through sintering at higher temperatures and pressures failed due to sample decomposition.

X-ray powder diffraction and elemental analysis. The polycrystalline samples were characterized by powder X-ray diffraction (PXRD) using a Rigaku Miniflex 600 diffractometer employing Cu-Kα radiation with a Ni-Kβ filter. Elemental analysis of selected crystals was carried out on a Hitachi S4100T scanning electron microscope (SEM) with energy-dispersive X-ray (EDX) microanalysis (Oxford INCA Energy) (Table S5). Single crystal X-ray diffraction. Data were collected at 90 K using a Bruker AXS SMART diffractometer with an APEX-II CCD detector with Mo-Kα radiation. The data sets were recorded as ω-scans with a 0.4° step width and integrated with the Bruker SAINT software package.[9] Multi-scan absorption corrections were applied.[9] The solution and refinement of the crystal structures were carried out using the SHELX suite of programs.[10]

P solid-state NMR spectroscopy. All 31P NMR spectroscopy experiments were carried out using a Bruker AQS Spectrometer operating at a 31P Larmor frequency of 202.4 MHz (magnetic field of 11.7 T). Samples were crushed into fine powder and mixed with SiO2 (1:1 by volume) to ensure stable spinning speeds. The sample mixtures were packed into 7 mm ZrO2 rotors and spun at 7 kHz. The two-dimensional projection Magic Angle Turning Phase Adjusted Spinning Sidebands (pjMATPASS) technique was employed in order to separate the anisotropic and isotropic components of the chemical shift into correlated dimensions.[11a] For each 2D experiment, 32 t1 transients were acquired with each transient consisting of 3500 scans with a 1s delay between scans. Each t1 slice was acquired using five π/6 (1.0 µs) pulses with interpulse delays incremented in accordance with the MAT timings.[11b] The 2D spectra were processed via Fourier transformation in the indirect dimension followed by a shearing and Fourier transformation in the direct dimension. Pulse length calibration and chemical shift referencing were performed using 85% H3PO4 standard. Simulations of the isotropic and chemical shift anisotropy (CSA) dimensions were carried out using the simulation package Dmfit.[12] The Haeberlen convention, defined as: | − | ≥ | − | ≥ |

− | 31

La3Zn4P6Cl: due to similarities of the scattering factors for P and Cl, the occupancy of the Cl site was refined and appeared to be 101(1)%. When P is refined in this position and fixed to 100% occupancy, a 5-fold decrease of the ADPs was observed together with an increase in the Rvalue. The freely refined occupancy of P in that position was 114(1)%. This confirmed the presence of Cl in the position inside the La4 tetrahedra. La3Zn4P6.6Br0.8: when the position in the center of the La4 tetrahedra is set as Br the ADP’s of that Br position are too high and the refined occupancy is lower than 100%. Refinement of this position as P resulted in the opposite: the ADPs were too low and the refined occupancy was well above 100%. This position was finally refined as jointly occupied by P and Br with constraints of identical ADP’s and total occupancy of 100% which resulted in the composition of Br0.80(1)P0.20. Further analysis revealed that the ADPs for one of the framework phosphorus positions were too large. The occupancy of this position was allowed to vary and was finally refined as 41(2)%. The local coordination and bond lengths indicate that this is indeed P and not a light atom like O or C.

∆ = δ33 − δiso, =

2


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Chemistry of Materials which is also observed in BaP3 (2.19-2.23 Å),[21] SrP2 (2.192.23 Å),[22] Ba8Au16P30 (2.12-2.30 Å),[4] BaAu2P4 (2.21 and 2.23 Å),[23] SrNi2P4 (2.23 and 2.24 Å),[5] and LaCu4P3 (2.26 Å).[24]

1 +

+ 3 is used to describe the CSA tensors.

=

Physical properties. Electrical resistivity of the two compounds were measured in the 2-400 K temperature range by a standard four-point alternating-current technique to exclude the resistance of the leads using the commercial multipurpose Physical Properties Measurement System (PPMS, Quantum Design). The Seebeck thermopower and thermal conductivity were measured in the 2-400 K temperature range using the Thermal Transport Option (TTO).

The Cl atom in the center of the La4 tetrahedron can be substituted with a combination of P and larger Br atoms in a 1:4 ratio, resulting in the composition La3Zn4P6.4Br0.8P0.2. This compound crystallizes in the same space group as La3Zn4P6Cl but with a unit cell volume of 1189.0(6) Å3, which is smaller than that of the Clcontaining phase, 1191.8(2) Å3. This is due to the rearrangements in the Zn-P framework, which are necessary to accommodate the larger Br@La4 tetrahedra (V = 14.0 Å3) instead of the smaller Cl@La4 tetrahedra (V = 12.4 Å3). La-Cl and La-Br distances in the synthesized compounds, 2.95-2.98 Å and 3.08-3.11 Å, respectively, are close to those distances in La halides, LaCl3 and LaBr3.[25, 26]

Quantum-chemical calculations. The electronic structure calculations, including the band structure, density of states (DOS), electron localization function (ELF) analyses, and crystal orbital Hamilton population (COHP) calculations, were performed using the tight-binding, linear muffin-tin orbital, atomic sphere approximation (TB-LMTO-ASA) program.[13] The Barth-Hedin exchange potential was used for the local density approximation calculations, and the radial scalar-relativistic Dirac equation was solved to obtain the partial waves.[13b] ELF isosurfaces and slices were visualized using the Paraview software.[14] Calculations were performed for La3Zn4P6Cl, and two models for the Br-containing compound: La3Zn4P6Br and La3Zn4P7Br. Additional details pertaining to the calculations are given in Table S4.

While the basic motif and most of the La-P, Zn-P, and P-P interatomic distances are similar in both compounds, there are two structural features that differentiate La3Zn4P6.6Br0.8 from La3Zn4P6Cl. In the brominecontaining structure the empty tubular Zn4P4 channels have a different conformation (Figures 1 F). In the Clcontaining structure, half of the Zn atoms are indeed three-coordinated and the Zn-P distance indicated with a pink line in Figure 1E is non-bonding, 4.06 Å. In the bromine-containing structure, these Zn atoms are shifted towards the center of the channels forming additional relatively short Zn-P bonds of 2.85 Å (thin lines in Figures 1 B and 1F). This leads to an overall decrease of the volume of the tubular fragment and the unit cell in general. This conformational rearrangement resulted in a significant increase of the interlayer Zn-P distance from 2.92 Å in La3Zn4P6Cl to 3.46 Å in La3Zn4P6.6Br0.8. This distortion and rearrangement of the flexible [Zn4P6] framework is further analyzed by theoretical calculations (vide infra).

Results and Discussion Crystal structure La3Zn4P6Cl and La3Zn4P6.6Br0.8 crystallize in the orthorhombic space group Cmcm (No. 63) in two new structure types, which exhibit many intrinsic similarities (Figure 1). The crystal structure of La3Zn4P6Cl (Figure 1A) can be described as two-dimensional ∞2[Zn4P6]8– layers separated by one-dimensional ∞1[Cl@La3]8+ chains (Figure 1C). The two dimensional Zn4P6 layers are built from one-dimensional Zn4P4 tubes connected to each other via homoatomic P2 dumbbells. Within the Zn-P framework, there are two different types of Zn-P fragments, almost trigonal planar ZnP3 and tetrahedral ZnP4 units, that share P atoms forming empty, tubular Zn4P4 channels. Larger channels formed in between the Zn4P6 layers are filled with tetrahedral chains constructed from Cl-centered La4 tetrahedra. These tetrahedra share two out of four vertices forming the one-dimensional La3Cl chains running along [100]. There are two La, two Zn, one Cl, and three P positions in the La3Zn4P6Cl unit cell, which are all fully occupied. The La-P distances in La3Zn4P6Cl fall in the range of 2.968(2)3.086(2) Å, which are comparable to many binary or ternary compounds such as: LaP (3.01 Å),[15] LaP2 (2.93-3.18 Å),[16] LaP5 (2.99-3.12 Å),[17] La3Zn2-xP4 (2.94-3.06 Å),[18] and La5Zn2-xP6 (2.95-3.05 Å).[19] The Zn-P bonds distances in La3Zn4P6Cl, 2.356(2) to 2.557(2) Å, are comparable to Zn3P2 (2.33-2.76 Å),[20] La3Zn2-xP4 (2.48-2.52 Å),[18] and La5Zn2-xP6 (2.46-2.54 Å).[19] The P-P distance in La3Zn4P6Cl, 2.221(4) Å, is typical for homoatomic bond distances

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of cyclic clusters have been reported besides P4 tetrahedra in white phosphorus (Figure 2) including P42–,[27] P51–,[28,29] P64–,[30] P73–,[31] P88–,[32] P106–,[33] and P113–.[34] To the best of our knowledge this is the first report of an isolated P33– fragment, which is isoelectronic to cyclopropane. Only threeatomic linear fragments of phosphorus chain, P35– were reported.[35]

Figure 2. A schematic representation of isolated cyclic phosphorus fragments found in metal polyphosphides together with the species P33− discovered in this work. The extra P(5) atom is located between two La4 tetrahedra at a relatively short, 2.28 Å, Br-P(5)-Br distances to bromine (or phosphorus) atoms located inside the tetrahedra. Thus, the coordination number for a portion of the Br atoms increases to 5 or even 6, resulting in an average composition of (Br0.8P0.2)@La3P0.4 for the chain (Figure 1D). To the best of our knowledge, La3Zn4P6Cl and La3Zn4P6.6Br0.8 are the first reported quaternary compounds in the rare earth-transition metal-phosphorushalogen system. Ternary rare earth-transition metal phosphides and halides are extensively studied classes of materials.[36-39] Quaternary compounds reported in this work are structurally flexible since one position can be jointly occupied by P and Br atoms. Examples of joint P/Br occupancies of a single crystallographic site are scarce, probably due to large differences in atomic radii and chemical nature: Ba16P10.14Br1.59 and Zn3PBr3.[40,41] Another unusual feature of the title compounds is the formation of tetrahedral ∞1[La3Cl]8+ chains composed of Cl@La4 tetrahedra. The coordination of Cl atoms by four La atoms is also rarely observed. In the sole example of two isostructural compounds, La3Si3Cl2 or La3Ge3Cl2, Cl@La4 tetrahedra share three vertices forming twodimensional layers.[42,43]

Figure 1. General view of the crystal structures of (A) La3Zn4P6Cl and (B) La3Zn4P6.6Br0.8; (C) Cl@La3 tetrahedral chain present in La3Zn4P6Cl; (D) polyhedral chain [email protected] together with attached P2 dumbbells present in La3Zn4P6.6Br0.8. The main framework building unit, Zn4P6, present in the structures of (E) La3Zn4P6Cl and (F) La3Zn4P6.6Br0.8. La: red; Cl/Br: green; Zn: black; P: orange. La4 tetrahedra: green. Unit cells are shown as pink lines.

For the Cl-containing compound the electron-balanced composition can be written as [(La3+)3Cl1–][(Zn2+)4(P3–)4P24– ] assuming formal oxidation states of –3 and –2 for isolated and paired phosphorus atoms, respectively. The Brcontaining analog has a more complicated structure and composition. Assuming there are no bonds between the P(5) atoms and the atoms in the centers of the La4 tetrahedra, the composition may be written as [(La3+)3(Br1–)0.8(P3–)0.2][(Zn2+)4(P3–)4(P24–)0.6(P33–)0.4]. This

Another interesting aspect in La3Zn4P6.6Br0.8 is the triangular P3 unit, which is constructed from the interstitial P(5) atom and the P2 dumbbell. The P(5) atom is located at a bonding distance of 2.30 Å from the P2 dumbbell forming an isolated P3 triangle. For phosphorus a variety

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assumption is supported by chemical bonding calculations and transport properties characterization. The complex structure with several disordered or mixed occupancy positions prompted additional structural characterization, which was performed with advanced solid-state NMR spectroscopy.

line shapes for the two peaks at –147 and –136 ppm yields the chemical shift tensor asymmetry parameters as η = 0.18 and 0.57, respectively (Figure 3C). The P(3) environment has 3 nearly equidistant P-Zn bonds (2.36-2.42 Å) while the P(2) site has one very long P-Zn bond (2.92 Å) to the Zn atom in another layer in addition to three short P-Zn bonds (2.37-2.39 Å). Therefore, it is likely that the high symmetry of the P(3) site should result in a low η value, while the P(2) site, being more asymmetric, is characterized by a larger η value. Therefore, on the basis of the experimental η values, the P(3) site is assigned to the resonance at –136 ppm, while the P(2) site is assigned to the resonance at –147 ppm.

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P solid-state MAS NMR spectroscopy

Conventional solid-state magic angle spinning (MAS) NMR spectroscopy utilizes sample rotation to average the dipolar and CSA induced line broadening. However, such averaging may remain incomplete in the case where the magnitude of the line broadening interaction is significantly larger than the sample spinning rate. This condition leads to the creation of a large number of spinning sidebands, which may overlap with the isotropic peaks and complicate the spectrum. The Magic Angle Turning Phase Adjusted Spinning Sidebands (pjMATPASS) experiment can circumvent this problem by separating the isotropic and anisotropic components of the chemical shift into correlated dimensions.[44, 45] The line shape in the isotropic dimension is an “infinite spinning speed” MAS spectrum, free from CSA related broadening effects, while a slice of the pjMATPASS NMR spectrum at any isotropic chemical shift yields the corresponding CSA pattern in the anisotropic dimension that can be simulated to obtain the principal components of the chemical shift tensor. Dipolar couplings in the compounds studied here are expected to be on the order of ~1 kHz or less and should be completely averaged by spinning the sample at 7 kHz such that they would not influence the spectral line shapes in either dimension. The anisotropy and asymmetry of the chemical shift tensor provides additional structural information regarding the symmetry and conformation for the various structural sites. Recently, PASStype NMR experiments have successfully led to structural elucidation in a variety of crystalline and amorphous systems.[11a,44-49] Here we employed 31P MATPASS NMR spectroscopy to study the short-range structure of the local coordination of phosphorus in the two compounds La3Zn4P6Cl and La3Zn4P6.6Br0.8.

La3Zn4P6.6Br0.8. The P(2) and P(3) sites in the structure of La3Zn4P6Cl undergoes modification due to the rearrangement of the structural framework in the compound La3Zn4P6.6Br0.8. In the structure of La3Zn4P6.6Br0.8 one of these P sites is still three-coordinated and another one has a 3+1 coordination of three short and one long P-Zn bonds (Tables S2 and S3). Hence, the three-coordinated phosphorus atom is labeled as P(3) and the 3+1 coordinated atom is labeled P(2) in the crystal structure of La3Zn4P6.6Br0.8 to simplify the structural description. The 31P isotropic NMR spectrum of La3Zn4P6.6Br0.8 (Figure 3A) is characterized by four main peaks at –233, –108, +60, and +111 ppm with additional three low intensity peaks at –262, –22 and +28 ppm. According to the crystal structure determined from X-ray diffraction data, there are five P sites, two of which are unique to this structure: the P(4)/Br mixed anion site and the vacancy-containing site, P(5). Since those two atomic positions P(4) and P(5) are in the vicinity of each other, the six additional magnetically inequivalent environments should be considered, adding complexity to the NMR spectrum. The three fully occupied P sites, P(1), P(2), and P(3), have environments similar to the P atoms in La3Zn4P6Cl in a 1:1:1 ratio and constitute 90% of the P atoms in the structure. The P3 site in La3Zn4P6.6Br0.8 is similar to the P(3) site in La3Zn4P6Cl, consisting of three nearly equidistant Zn atoms. Therefore, the peak at –108 ppm is ascribed to this environment. The P(2) site has 3+1 coordination, resulting in an upfield shift from the P(3) resonance and is consistent with the peak observed at –233 ppm. The resonance at 111 ppm can be assigned to the P(1) environment when P1 is bonded to one Zn and one P atom, making it chemically equivalent to the P(1) environment in the Clcontaining analogue. When P(1) is additionally bonded to P(5) forming a P3 triangle, the P(1) resonance exhibits an upfield shift to 60 ppm consistent with the increase in coordination number. The structural model suggests the presence of two P(1) environments in a 1.5:1 ratio due to the ~40% occupancy of the P(5) site. Integration of the peak areas for the four main lines at –108, –233, 111, and 60 ppm assigned to the P(2), P(3), and two P(1) environments resulted in a 3:3:2:1 ratio, which is consistent with the single crystal X-ray diffraction model. The remaining low-intensity peaks should correspond to the P(4) and

La3Zn4P6Cl. This compound was studied as a reference to establish the 31P chemical shifts of the main P framework positions and to confirm the absence of phosphorus in the chlorine position. The isotropic projection of the 31P pjMATPASS NMR spectrum of the La3Zn4P6Cl sample is shown in Figure 3B. The spectrum consists of three peaks with isotropic 31P chemical shifts, δiso, at –147, –136, and +125 ppm in a 1:1:1 ratio, consistent with the crystal structure. The similar 31P δiso of the peaks at –147 and –136 ppm suggests that they most likely correspond to the P(2) and P(3) environments in which a central P atom is coordinated to 3 Zn atoms. The remaining peak with a δiso of +125 ppm can therefore be assigned to the P(1) which is coordinated to one P and one Zn atoms. This assignment is consistent with the fact that decreasing the coordination number leads to a corresponding downfield shift of the 31P δiso to higher ppm values. Simulation of the anisotropic

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P(5) environments. Two of these resonances, –22 and 28 ppm, are within the range consistent for the proposed coordinations of the P atoms. The low intensities of these peaks combined with the relatively low signal-to-noise in this regime prevent accurate integration of the peak areas making the exact assignment of these peaks impossible without ab initio calculations. Such calculations are hampered by the disordered nature of the structure. Finally, the peak assignment at –262 ppm most likely corresponds to a small impurity (< 2%) present in this sample. Thus, when taken together, the 31P isotropic NMR spectrum of La3Zn4P6.6Br0.8 is consistent with the structural model derived from single crystal X-ray diffraction data.

Figure 3. Isotropic projections of the 31P pjMATPASS spectrum for the compounds (A) La3Zn4P6.6Br0.8 and (B) La3Zn4P6Cl. The corresponding P coordination environment assigned to each peak is shown with an arrow. (C) CSA sideband patterns of the three isotropic peaks in the spectrum of La3Zn4P6Cl. These patterns were simulated using the Herzfeld-Berger method[12] to extract the CSA tensor parameters for further distinction between chemical environments. CSA sideband patterns of the isotropic peaks for La3Zn4P6.6Br0.8 are shown in Figure S4. Electronic structure

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The densities of states (DOS) were calculated for La3Zn4P6Cl and two models for the Br-containing analogue, La3Zn4P6Br, and La3Zn4P7Br (Figure 4). The Fermi levels were adjusted for La3Zn4P6Br and La3Zn4P7Br to account for the number of electrons in the experimentally determined composition: La3Zn4P6.6Br0.8.

ber of electrons in the experimentally determined composition, La3Zn4P6.6Br0.8. The electron localization function (ELF) was calculated for La3Zn4P6Cl and La3Zn4P7Br to elucidate chemical bonding in these compounds. ELF isosurfaces and slices for different fragments are shown in Figure 5. The expected polar covalent bonding interactions were found for Zn-P bonds in the [Zn4P6] framework in both La3Zn4P6Cl and La3Zn4P7Br with the attractors shifted towards the P atoms (Figure 5A and 5E). The Zn-P interactions in the [Zn4P4] fragments in both compounds were comparable. The COHP for the Zn-P bond connecting the [Zn4P4] fragment to the P24- dumbbells were calculated for the Cl- and Br-containing compounds (Figure S5). The – ICOHP values of 1.74 and 1.84 eV/bond were comparable for La3Zn4P6Cl, d(Zn-P) = 2.37 Å, and La3Zn4P7Br, d(Zn-P) = 2.43 Å, respectively. The COHP for the Zn(1)-P(2) bond of 2.85 Å (dashed line in Figure 1F) present in the distorted [Zn4P4] fragment in La3Zn4P7Br was also calculated. The –ICOHP value for this interaction, 0.66 eV/bond, indicates a covalent interaction between the two atoms, though weaker than the shorter Zn-P bonds. The corresponding –ICOHP value for the Zn(1)-P(2) (4.06 Å) interaction in La3Zn4P6Cl (dashed line in Figure 1E) was substantially smaller, 0.01 eV/bond, indicating a negligible bonding interaction between the two atoms, which is in agreement with the deep minima seen in the ELF slice for the [Zn4P4] fragment (Figure 5A). In the Cl-containing compound there is another long Zn-P distance of 2.92 Å. Calculated –ICOHP value for this interaction, 0.22 eV/bond, was still three times smaller than the one for Zn-P bond of 2.85 Å in Br-containing compound, 0.66 eV/bond. Bonding analysis confirmed substantial rearrangements of the chemical bonds in the Zn-P framework when going from the Cl- to the Br-containing compound.

La3Zn4P6Cl was determined to be a semiconductor with a bandgap of 0.45 eV, which is close to the activation energy of 0.24 eV determined from fitting the resistivity data for this compound (vide infra). The states near the top of the valence band are predominately P(3p) states while the states at the bottom of conduction band are dominated by La(5d) contributions. The DOS for the La3Zn4P6Br model, where the position inside the La4 tetrahedron is solely occupied by Br with no P(5) atoms, is very similar to the DOS of the Cl-containing compound. However, adjustment of the number of electrons to the real composition requires shifting the Fermi level to the conduction band. The bandgap closes for the La3Zn4P7Br model, where the P(5) atomic position is set to be fully occupied, indicating that the interstitial phosphorus atom has significant effects on the electronic structure of the Brcontaining compound. In the experimentally determined crystal structure, the P(5) position is only partially occupied, which may result in the narrowing but not complete closing of the bandgap as indicated by transport properties measurements.

Figure 5. Electron localization function (ELF) slices and isosurfaces for (top) La3Zn4P6Cl and (bottom) La3Zn4P7Br. Top: ELF slices and isosurfaces of the (A) [Zn4P4] fragment; (B) and (C) [La3Cl] fragment; and (D) P1 dumbbell in La3Zn4P6Cl. Bottom: ELF slices and isosurfaces of the (E) [Zn4P4] fragment; (F) and (G) [La3Br] with the [P3] fragments; and (H) [P3] fragment in La3Zn4P7Br. Scale bar

Figure 4. Density of states (DOS) diagrams for La3Zn4P6Br, La3Zn4P7Br, and La3Zn4P6Cl. The Fermi level was adjusted for La3Zn4P6Br and La3Zn4P7Br to the num-

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is shown at the top right. Isosurface ELF values are indicated in the figure.

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containing magnetic rare-earth metals, this bonding scheme may lead to long-range magnetic interactions. Physical properties

P24–

The ELF distribution for the dumbbell in La3Zn4P6Cl indicates one attractor for the covalent P-P bond and additional attractors for the electron lone pairs. The latter ones are not isolated from other and shifted on the side opposite to the La atoms (Figures 5B and D). Adding the P(5) atom resulted in a significant redistribution of the valence electrons around the P3 cycle (Figures 5F and 5H). For a regular P33– fragment, the formation of two covalent bonds and two electron lone pairs are expected for each P atom. In the crystal structure of La3Zn4P6.6Br0.8 the P(1)-P(1) bond, 2.27 Å, is slightly shorter than the P(5)-P(1) bonds, 2.30 Å. ELF analysis shows the presence of a P(1)-P(1) covalent bond which is slightly off center from the line connecting the two atoms together with two separated attractors for the electron lone pairs located at each P(1) atom. For the P(5) atom, the two attractors for the electron lone pairs overlap with the offcentered attractors for P-P covalent bonds. This is probably due to the presence of La atoms in close proximity to the P(5) atom. The shift of the attractors from the line connecting the two atoms is common for trigonal P fragments such as in the P3 trigonal base of heptaphosphanortricyclane P73– clusters.[50, 51]

The electrical and thermal transport properties of La3Zn4P6Cl and La3Zn4P6.6Br0.8 are depicted in Figure 6. The resistivities of La3Zn4P6Cl and La3Zn4P6.6Br0.8 decrease with increasing temperature over the entire measured temperature range, indicating thermally activated behavior that is typical for semiconductors (Figure 6 top right and bottom right). Fitting ln(1/ρ) vs. 1/T to the equation, ln(1/ρ) = ln(1/ρ0) – Ea/2kT (Figure 6, inset), gives activation energies of 0.24 and 0.03 eV for La3Zn4P6Cl and La3Zn4P6.6Br0.8, respectively. This is consistent with the trend in the bandgaps suggested by quantum chemical calculations. The resistivity value at 400 K for La3Zn4P6Cl of 0.39 Ω⋅m is also larger than that for La3Zn4P6.6Br0.8, 0.11 Ω⋅m. The thermopower for La3Zn4P6.6Br0.8 is negative from 2 to 400 K, indicating that electrons are the main charge carriers. The Seebeck coefficient of La3Zn4P6.6Br0.8 at 398 K is -122 μV/K. The thermopower of La3Zn4P6Cl shows more complex behavior, i.e. negative values from 2 to 250 K and positive values in the range of 250-400 K, indicating a complex mechanism behind this transition. The absolute value of the thermopower first increases from 2 to 168 K reaching a maximum value of -57 μV/K, then the Seebeck coefficient increases almost linearly up to +135 μV/K at 400 K. This type of reproducible “n-p” transformation (Figure S3) possibly suggests that both holes and electrons play important roles in governing the electronic transport properties of La3Zn4P6Cl. Such behavior has also been frequently observed in intrinsic semiconductors as well as in intermetallics,[54-57] and may have potential applications as novel multifunctional electronic devices.[58]

The ELF slice showing the Br-P(5) interaction does not have the deep minima or pronounced maxima between the two atoms. The bonding between these atoms was further investigated with COHP calculations. The COHP plot shows strong antibonding character for all states above –5 eV (Figure S5). However, the –ICOHP value for Br-P5 was calculated to be 1.87 eV/bond, indicating a bonding interaction. To resolve this contradiction a detailed investigation of the local structure is necessary to properly model the atomic coordination of the P(5) and Br atoms and to construct a realistic structural model for calculations. According to ELF analysis, the La-Cl and La-Br interactions are not fully ionic. Instead of spherical ELFs surrounding the halide and La atoms, the ELF shows significant structuring of their electronic shells (Figure 5C and 5G). The two attractors on the halide atoms are shifted towards the face of the La4 tetrahedron (Figure 5B and 5F). Weak bonding character for both La-Cl and La-Br interactions was confirmed by COHP analysis. The bonding and non-bonding interactions are below and at the Fermi level, while all antibonding interactions are above the Fermi level resulting in nonzero –ICOHP values in the range of 0.5-0.7 eV/bond (Figure S5). In compounds with high rare-earth content, ~50%, non-isotropic bonding interactions involving rare-earth elements were detected by ELF and electron density distribution analyses.[52,53] However, it is uncommon for compounds with low rareearth content, 21% for La3Zn4P6Cl, to exhibit such type of chemical bonding. For analogues of the title compounds

Figure 6. Thermoelectric properties of La3Zn4P6Cl (red circles) and La3Zn4P6.6Br0.8 (black squares): (top left) Seebeck thermopower; (bottom left) thermal conductivity; (right) electrical resistivity with insets showing ln(1/ρ) vs.

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Chemistry of Materials Supporting Information Powder X-ray diffraction, EDX, details pertaining to the calculations, NMR results, and additional thermoelectric properties of La3Zn4P6Cl (PDF) Crystallographic data (CIF)

1000/T dependences and linear fits of high-temperature data (orange dashed lines). The thermal conductivities of La3Zn4P6Cl and La3Zn4P6.6Br0.8 exhibit similar behaviors, increasing from minimum values at 2 K up to maximum values at given temperatures (67 K for La3Zn4P6Cl and 90 K for La3Zn4P6.6Br0.8), which is typical for crystalline solids. The thermal conductivity maximum value of La3Zn4P6Cl at 67 K is 1.0 Wm–1K–1, while La3Zn4P6.6Br0.8 possess a higher value, 1.8 Wm–1K–1, at 90 K. La3Zn4P6Cl has a low thermal conductivity at 400 K, 0.7 Wm–1K–1, which is comparable to many state-of-the-art thermoelectric materials,[59-62] while the thermal conductivity of La3Zn4P6.6Br0.8 is twice that of the Cl-compound, 1.5 Wm–1K–1 at 400 K. The contribution to the thermal conductivity from the charge carriers was estimated using the Wiedemann-Franz law.[63] For both studied compounds the charge carriers contributions are well below 1% of the total thermal conductivity at 400 K (Figure S6). The differences in the thermal conductivities in La3Zn4P6Cl and La3Zn4P6.6Br0.8 may originate from the densities of the pellets; La3Zn4P6Cl has a lower density, which may influence phonon transport. As stated in the experimental section we were not able to produce higher density pellets due to the decomposition of the title compounds at higher sintering pressures and temperatures. The thermoelectric figures of merit at 400 K are limited by the high resistivity and are lower than practical for thermoelectric materials, 2.7x10-5 and 3.4x10-5 for La3Zn4P6Cl and La3Zn4P6.6Br0.8, respectively. Modifications of the electrical conductivity through doping are currently underway.

AUTHOR INFORMATION Corresponding Author Dr. Kirill Kovnir, Department of Chemistry, University of California, Davis, CA 95616, e-mail: [email protected].

Present Address K.L.: Thermal Energy Conversion Technologies Group, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, US.

ACKNOWLEDGMENT The authors would like to thank Prof. S.M. Kauzlarich for access to the SPS. K.L. acknowledges the GAANN and ARCS fellowships. This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DESC0008931.

REFERENCES [1] The Physics and Chemistry of Inorganic Clathrates; Nolas, G. S., Ed.; Springer Science: Dordrecht, 2014. [2] Shevelkov, A.V.; Kovnir, K. Semiconducting clathrates: synthesis, structure and properties. Struct. Bond, 2011, 139, 97142. [3] Prokofiev, A.; Sidorenko, A.; Hradil, K.; Ikeda, M.; Svagera, R.; Waas, M.; Winkler, H.; Neumaier, K.; Paschen, S. Thermopower enhancement by encapsulating cerium in clathrate cages. Nat. Mater. 2013, 12, 1096-1101. [4] Fulmer, J.; Lebedev, O.I.; Roddatis, V.V.; Kaseman, D.C.; Sen, S.; Dolyniuk, J.-A.; Lee, K.; Olenev, A.V.; Kovnir, K. Clathrate Ba8Au16P30: The “Gold Standard” for Lattice Thermal Conductivity. J. Am. Chem. Soc. 2013, 135, 12313-12323. [5] Dolyniuk, J.; Wang, J.; Lee, K.; Kovnir, K. Twisted Kelvin Cells and Truncated Octahedral Cages in the Crystal Structures of Unconventional Clathrates, AM2P4 (A = Sr, Ba; M = Cu, Ni). Chem. Mater. 2015, 27, 4476-4484. [6]Ozawa, T. C.; Kauzlarich, S. M. Chemistry of layered dmetal pnictide oxides and their potential as candidates for new superconductors. Sci. Tech. Adv. Mater.2008, 9, 033003. [7] Stewart, G. R. Superconductivity in iron compounds. Rev. Mod. Phys. 2011, 83, 1589-1652. [8] Paglione, J.; Greene, R. L. High-temperature superconductivity in iron-based materials. Nat. Phys. 2010, 6, 645-658. [9] Bruker APEX2; Bruker AXS Inc.: Madison, WI, 2005. [10] Sheldrick, G.M. A short history of SHELX. Acta Crystallogr. Sect. A. 2008, A64, 112-122. [11] a) Kaseman, D. C.; Hung, I.; Lee, K.; Kovnir, K.; Gan, Z.; Aitken, B.; Sen, S. Tellurium Speciation, Connectivity, and Chemical Order in AsxTe100–x Glasses: Results from TwoDimensional 125Te NMR Spectroscopy. J. Phys. Chem. B. 2015, 119, 2081-2088; b) Hung, I; Gan, Z. On the magic-angle turning and phase-adjusted spinning sidebands experiments. J. Magn Reson. 2010, 204, 150-154. [12] Massiot, D.; Fayon, F.; Capron, M.; King, I.; Le Calvé, S.; Alonso, B.; Durand, J.-O.; Bujoli, B.; Gan, Z.; Hoatson, G. Model-

Conclusions Two new phosphide-halide compounds, La3Zn4P6Cl and La3Zn4P6.6Br0.8, were synthesized via high-temperature solid-state reactions and their structures were determined by single crystal X-ray diffraction and confirmed with solid-state 31P NMR spectroscopy. Structural flexibility is observed between the two compounds with many intrinsic similarities. Chemical bonding analysis confirmed the formation of new bonds upon structural rearrangements when going from the Cl- to the Br-containing compound. Variations in the crystal structures are reflected in the transport properties. The main charge carriers in La3Zn4P6.6Br0.8 were determined to be electrons from the negative values of Seebeck coefficients from 2 K to 400 K, while La3Zn4P6Cl shows an n-p transition around 250 K. The title compounds are small bandgap semiconductors with activation energies of 0.24 eV and 0.03 eV for La3Zn4P6Cl and La3Zn4P6.6Br0.8, respectively. Both title compounds show promising room temperature thermal conductivities not exceeding 2 Wm–1K–1. The structural flexibility in this system offers the possibility of introducing other rare earth f-electron elements, which may have interesting magnetic properties.

ASSOCIATED CONTENT

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Triphosphacyclobutenid-Ions, P3CH2−. Z. Anorg. Allg. Chem. 1987, 544, 87-94. [29] Dragulescu-Andrasi, A.; Miller, L. Z.; Chen, B.; McQuade, D. T.; Shatruk, M. Facile Conversion of Red Phosphorus into Soluble Polyphosphide Anions by Reaction with Potassium Ethoxide. Angew. Chem. Int. Ed. 2016, 55, 3904-3908. [30] Abicht, H.-P.; Hönle, W.; von Schnering, H.G. Tetrakaliumhexaphosphid: Darstellung, Struktur und Eigenschaften von α-K4P6 und β-K4P6. Z. Anorg. Allg. Chem. 1984, 519, 7-23. [31] Manriquez, V.; Hönle, W.; von Schnering, H.G. Trilithiumheptaphosphid Li3P7: Darstellung, Struktur und Eigenschaften. Z. Anorg. Allg. Chem. 1986, 539, 95-109. [32] Oleneva, O. S.; Shestimerova, T. A.; Dikarev, E. V.; Shevelkov, A.V. P88− Polyanion with Phosphorus Atoms in Three Different Formal Oxidation States Stabilized by a Combination of Ag+ and Hg2+ Cations. Angew. Chem. Int. Ed. 2006, 45, 77197722. [33] Hönle, W.; von Schnering, H.G. Cu4SnP10, a compound with decaphospha-adamantane anions P106- and four-center [SnCu3] clusters. Z. Krist. 1980, 153, 339-350. [34] von Schnering, H.G.; Somer, M.; Kliche, G.; Hönle, W.; Meyer, T.; Wolf, J.; Ohse, L.; Kempa, P.B. Darstellung, Eigenschaften und Schwingungsspektren der Käfiganionen P113− und As113−. Z. Anorg. Allg. Chem. 1991, 601, 13-30. [35] Shatruk, M.; Mustiakimov, M. Y.; Shevelkov, A. V.; Popovkin, B. A. Solid solutions of Hg7P6–xAsxBr4 – Structures containing angular anions (Z3)5– (Z = P, As). Russ. J. Inorg. Chem. 1998, 43, 1069-1072. [36] Olenev, A.V.; Shestimerova, T.A.; Schnelle, W.; Shevelkov, A. V. Synthesis, Structure, and Properties of [Hg6As4][YbBr6]Br, a Supramolecular Assembly Featuring a Discrete [YbBr6]3− Anion. Z. Anorg. Allg. Chem. 2005, 631, 1698-1701. [37] Qi, Y.; Guo, J.; Lei, H.; Xiao, Z.; Kamiya, T.; Hosono, H. Superconductivity in noncentrosymmetric ternary equiatomic pnictides LaMP (M=Ir and Rh; P = P and As). Phys. Rev. B.2014, 89, 024517. [38] Wang, J.; Xia, S.-Q.; Tao, X.-T.; Schäfer, M. C.; Bobev, S. New ternary phosphides and arsenides. Syntheses, crystal structures, physical properties of Eu2ZnP2, Eu2Zn2P3 and Eu2Cd2As3. J. Solid State Chem. 2013, 205, 116-121. [39] Kovnir, K.; Reiff, W. M.; Menushenkov, A. P.; Yaroslavtsev, A. A.; Chernikov, R. V.; Shatruk, M. “Chemical Metamagnetism”: From Antiferromagnetic PrCo2P2 to Ferromagnetic Pr0.8Eu0.2Co2P2 via Chemical Compression. Chem. Mater. 2011, 23, 3021-3024. [40] Hadenfeldt, C. Untersuchung der Systeme Ba3P2–BaX2 mit X=Cl, Br, J. Z. Anorg. Allg. Chem. 1977, 436, 113-121. [41] Reshetova, L.N.; Filatova, T.G.; Shpanchenko, R.V.; Shevel'kov, A.V.; Popovkin, B.A. Search for new zinc pnictide halides: synthesis and crystal structure of new phase Zn3PBr3. Russ.J. Inorg. Chem.1996, 41, 916-919. [42] Mattausch, H. J.; Oeckler, O.; Simon, A. Zintl-Anionen des Siliciums in den Halogeniden La3Cl2Si3 und La6Br3Si7. Z. Anorg. Allg. Chem. 1999, 625, 297-301. [43] Mattausch, H.J.; Zheng, C.; Ryazanov, M.; Simon, A. Reduced lanthanum halides with Ge as interstitials: La2I2Ge, La2I2Ge2, La3Cl2Ge3, La3Br2Ge3, La3I3Ge, La6I5Ge3 and La7+xI12Ge. Z. Anorg. Allg. Chem. 2005, 631, 302-308. [44] Hung, I.; Zhou, L.; Pourpoint, F.; Grey, C. P.; Gan, Z. Isotropic High Field NMR Spectra of Li-Ion Battery Materials with Anisotropy >1 MHz. J. Am. Chem. Soc. 2012, 134, 1898-1901. [45]Hung, I.; Edwards, T.; Sen, S.; Gan, Z. MATPASS/CPMG: A sensitivity enhanced magic-angle spinning sideband separation

ling one- and two-dimensional solid-state NMR spectra. Magn. Reson. Chem. 2002, 40, 70-76. [13] (a) Jepsen, O.; Burkhardt, A.; Andersen, O. K. The Program TB-LMTO-ASA , Version 4.7, Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany, 1999. (b) Barth, U. v.; Hedin, L. A local exchange-correlation potential for the spin polarized case. J. Phys. C: Solid State Phys. 1972, 5, 1629-1642. (c) Becke, A. D.; Edgecombe, K. E. A simple measure of electron localization in atomic and molecular systems. J. Chem. Phys. 1990,92, 5397-5403.; (d) Savin, A.; Jepsen, O.; Flad, J.; Andersen, O. K.; Preuss, H.; von Schnering, H. G. Electron Localization in Solid-State Structures of the Elements: the Diamond Structure. Angew. Chem., Int. Ed. Engl. 1992, 31, 187−188. ; (e) Savin, A.; Nesper, R.; Wengert, S.; Fässler, T. F. ELF: The Electron Localization Function. Angew. Chem., Int. Ed. Engl. 1997, 36, 1808−1832. ; (f) Dronskowski, R.; Blöchl, P. E. Crystal orbital Hamilton populations (COHP): energy-resolved visualization of chemical bonding in solids based on density-functional calculations. J. Phys. Chem. 1993, 97, 8617– 8624. [14] (a) Paraview: Parallel visualization application, version 4.1.0 64 bit; Sandia National Labs, Kitware Inc, Los Alamos National Labs: USA; http://paraview.org. 2014.9.1.; (b) Baranov, A. I. Visualization plugin for ParaView, Version 4.1.0, 2014. [15] Meng. J.; Ren, Y. Studies on the electrical properties of rare earth monophosphides. J. Solid State Chem. 1991, 95, 346-351. [16] von Schnering, H.G.; Wichelhaus, W.; Nahrup, M. S. Lanthandiphosphid LaP2; Darstellung, Struktur und Eigenschaften. Z. Anorg. Allg. Chem.1975, 412, 193-201. [17] Wichelhaus, W.; von Schnering, H.G. Die Pentaphosphide des Lanthans und Neodyms, LaP5 und NdP5. Z. Anorg. Allg. Chem.1976, 419, 77-86. [18] Lincke, H.; Nilges, T.; Johrendt, D.; Pöttgen, R. Crystal and electronic structure of La3Zn2-xP4-New phosphide with isolated P3-species. Solid State Sci. 2008, 10, 1006-1011. [19] Lincke, H.; Nilges, T.; Pöttgen, R. New Phosphides La5Zn2−xP6 and Ce5Zn2−xP6 –the n=4 Members of the REZn2P2·n(REP) Series. Z. Anorg. Allg. Chem. 2008, 634, 28852888. [20] Rao, D.R.; Nayak, A. Preparation and characterization of Zn3P2-Cd3P2 solid solutions. J. Mater. Sci.1992, 27, 4389-4392. [21] Dolyniuk, J.; Kaseman, D.; Sen, S.; Zhao, J.; Osterloh, F. E.; Kovnir, K. mP-BaP3: A New Phase from an Old Binary System. Chem.-Eur. J. 2014, 20, 10829 -10837. [22] Dolyniuk, J.; He, H.; Ivanov, A.; Boldyrev, A.; Bobev, S.; Kovnir, K. Ba and Sr Binary Phosphides: Synthesis, Crystal Structures, and Bonding Analysis. Inorg. Chem. 2015, 54, 8608-8616. [23] Fulmer, J.; Kaseman, D.; Dolyniuk, J.; Lee, K.; Sen, S.; Kovnir, K. BaAu2P4: Layered Zintl Polyphosphide with Infinite 1 – ∞ (P )Chains. Inorg. Chem. 2013, 52, 7061-7067. [24] Wang, J.; Lee, K.; Kovnir, K. Distorted Phosphorus and Copper Square-Planar Layers in LaCu1+xP2 and LaCu4P3: Synthesis, Crystal Structure, and Physical Properties. Inorg. Chem. 2015, 54, 890-897. [25] Morosin, B. Crystal structures of anhydrous rare-earth chlorides. J. Chem. Phys. 1968, 49, 3007-3012. [26] Kräemer, K.; Schleid, T.; Schulze, M.; Urland, W.; Meyer, G. Three bromides of lanthanum: LaBr2, La2Br5, and LaBr3. Z. Anorg. Allg. Chem. 1989, 575, 61-70. [27] Kraus, F.; Hanauer, T,; Korber, N. Nature of the Chemical Bond in Polypnictides: The Lone Pair Aromatic Anions P42- and As42- Inorg. Chem. 2006, 45, 1117-1123. [28] Baudler, M.; Düster, D.; Ouzounis, D. Existenz und Charakterisierung des Pentaphosphacyclopentadienid-Anions, P5−, des Tetraphosphacyclopentadienid-Ions, P4CH−, und des

10


Page 11 of 11

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experiment for disordered solids. J. Magn. Reson. 2012, 221, 103109. [46] Kaseman, D. C.; Hung, I.; Gan, Z.; Sen, S. Observation of a Continuous Random Network Structure in GexSe100–x Glasses: Results from High-Resolution 77Se MATPASS/CPMG NMR Spectroscopy. J. Phys. Chem. B. 2013, 117, 949-954. [47] Kaseman, D. C.; Hung, I.; Gan, Z. H.; Aitken, B.; Currie, S.; Sen, S. Structural and Topological Control on Physical Properties of Arsenic Selenide Glasses. J. Phys. Chem. B.2014, 118, 2284-2293. [48] Mao, A. W.; Kaseman, D. C.; Hung, I.; Gan, Z.; Aitken, B. G.; Sen, S. Mechanisms of structural accommodation of Se deficiency in binary Ga2Se3–GeSe2 glasses: Results from 77Se MATPASS/CPMG NMR spectroscopy. J. Non-Cryst. Solids 2015, 410, 14-19. [49] Kaseman, D. C.; Endo, T.; Sen, S. Structural disorder and the effects of aging in a phosphate glass: Results from twodimensional 31P PASS NMR spectroscopy. J. Non-Cryst. Solids.2013, 359, 33-39. [50] Dolyniuk, J.; Kovnir, K. Zintl Salts Ba2P7X (X = Cl, Br, and I): Synthesis, Crystal, and Electronic Structure. Crystals, 2013, 3, 431-442. [51] Dolyniuk, J.; Tran, N.; Lee, K.; Kovnir, K. Sr2P7X (X = Cl, Br, and I): Synthesis, Crystal, and Electronic Structures of Double Zintl Salts Containing Heptaphosphanortricyclane, P73-. Z. Anorg. Allg. Chem. 2015, 641, 1422-1427. [52] Kazem, N.; Zaikina, J. V.; Ohno, S.; Snyder, G. J.; Kauzlarich, S. M. Coinage-Metal-Stuffed Eu9Cd4Sb9: Metallic Compounds with Anomalous Low Thermal Conductivities. Chem. Mater. 2015, 27, 7508-7519. [53]You, T.-S.; Miller, G.J. Theoretical Interpretation of the Structural Variations along the Eu(Zn1−xGex)2 (0 ≤ x ≤ 1) Series. Inorg. Chem. 2009, 48, 6391-6401. [54] Brown, S. R.; Kauzlarich, S. M.; Gascoin, F.; Snyder, G. J. High-temperature thermoelectric studies of A11Sb10 (A=Yb, Ca). J. Solid State Chem. 2007, 180, 1414 -1420.

[55] Amato, A.; Jaccard, D.; Sierro, J.; Lapierre, F.; Haen, P.; Lejay,P.; Flouquet, J. Thermopower and magneto-thermopower of CeRu2Si2 single crystals. J. Magn. Magn. Mater. 1988, 76−77, 263-264. [56] Oeschler, N.; Deppe, M.; Hartmann, S.; Caroca-Canales, N.; Geibel, C.; Steglich, F. Thermopower of Ce1−xLaxTiGe with highly degenerate orbital ground state. J. Phys.: Conf. Ser. 2010, 200, 012148. [57] Wang, J.; Xia, S.Q.; Tao, X.-T. A5Sn2As6 (A = Sr, Eu). Synthesis, Crystal and Electronic Structure, and Thermoelectric Properties. Inorg. Chem. 2012, 51, 5771-5778. [58] Tang, Y.; Cui, B.; Zhou, C.; Grayson, M. p×n-Type Transverse Thermoelectrics: A Novel Type of Thermal Management Material. J. Electron. Mater. 2015, 44, 2095-2104. [59] Wang, J.; Kovnir, K. Elusive β-Zn8Sb7: A new zinc antimonide thermoelectric. J. Amer. Chem. Soc. 2015, 137, 1247412477. [60] Brown, S. R.; Kauzlarich, S. M.; Gascoin, F.; Snyder, G. J. Yb14MnSb11: New High Efficiency Thermoelectric Material for Power Generation. Chem. Mater. 2006, 18, 1873-1877. [61] Saramat, A.; Svensson, G.; Palmqvist, A. E. C.; Stiewe, C.; Mueller, E.; Platzek, D.; Williams, S. G. K.; Rowe, D. M.; Bryan, J. D.; Stucky, G. D. Large thermoelectric figure of merit at high temperature in Czochralski-grown clathrate Ba8Ga16Ge30. J. Appl. Phys. 2006, 99, 023708. [62] Snyder, G.J.; Toberer, E.S. Complex thermoelectric materials. Nat. Mat. 2008, 7, 105-114. [63] Kim, H.-S.; Gibbs, Z. M.; Tang, Y.; Wang H.; Snyder, G. J. Characterization of Lorenz number with Seebeck coefficient measurement. APL Mater. 2015, 3, 041506.

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X = Cl, Br - ACS Publications - American Chemical Society

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