Three-Fold Coordination of Copper in Sulfides: A Blockade for Hole Carrier Delocalization but a Driving Force for Ultralow Thermal Conductivity.

Copper-rich sulfides are very promising for energy conversion applications due to their environmental compatibility, cost effectiveness, and earth abundance. Based on a comparative analysis of the structural and transport properties of Cu3BiS3 with those of tetrahedrite (Cu12Sb4S13) and other Cu-rich sulfides, we highlight the role of the cationic coordination types and networks on the electrical and thermal properties. By precession-assisted 3D electron diffraction analysis, we find very high anisotropic thermal vibration of copper attributed to its 3-fold coordination, with an anisotropic atomic displacement parameter up to 0.09 Å2. Density functional theory calculations reveal that these Cu atoms are weakly bonded and give rise to low-energy Einstein-like vibrational modes that strongly scatter heat-carrying acoustic phonons, leading to ultralow thermal conductivity. Importantly, we demonstrate that the 3-fold coordination of copper in Cu3BiS3 and in other copper-rich sulfides constituted of interconnected CuS3 networks causes a hole blockade. This phenomenon hinders the possibility of optimizing the carrier concentration and electronic properties through mixed valency Cu+/Cu2+, differently from tetrahedrite and most other copper-rich chalcogenides, where the main interconnected Cu-S network is built of CuS4 tetrahedra. The comparison with various copper-rich sulfides demonstrates that seeking for frameworks characterized by the coexistence of tetrahedral and 3-fold coordinated copper is very attractive for the discovery of efficient thermoelectric copper-rich sulfides. Considering that lattice vibrations and carrier concentration are key factors for engineering transport phenomena (electronic, phonon, ionic, etc.) in copper-rich chalcogenides for various types of applications, our findings improve the guidelines for the design of materials enabling sustainable energy solutions with wide-ranging applications.

Cs2Ln3CuS8 (Ln = La-Nd, Sm-Tb): Synthesis, Crystal Structure, and Magnetic and Optical Properties.

This work reports the preparation of new quaternary sulfides Cs2Ln3CuS8 (Ln = La-Nd, Sm-Tb), their original crystal and electronic structures, and their magnetic properties. The sulfides were prepared using a reactive flux method from mixtures of Ln2S3 (EuS), Cs2S6, Cu2S, and S. They crystallize in a new type of structure (C2/m space group) and exhibit a layer-like crystal structure, which is a hybrid of those of the ACe2CuS6 series (A = Cs, K) and that of K2CeCu2S4. The values of the optical band gap calculated by the Kubelka-Munk equation are in the range of 1.2-2.62 eV depending on the nature of the Ln ion. The Cs2Gd3CuS8 compound displays relatively great magnetic refrigerating properties at cryogenic temperature with the mass entropy change (-ΔSM) reaching 19.5 J kg-1 K-1 at 3.5 K for ΔH = 5 T.

Synthesis, Crystal and Electronic Structures, and Electrical Properties of the Fifth Member of the Rb2(Mo9S11)(Mo6nS6n+2) Series: Rb10Mo39S43, an Atypical Reduced Molybdenum Sulfide Containing Mo9 and Mo30 Clusters.

The new compound Rb10Mo39S43 has been synthesized as single crystals by a solid-state reaction in a sealed molybdenum crucible at 1500 °C. It constitutes the fifth member of the homologous series of the trigonal (space group R3̅c) compounds Rb2n(Mo9S11)(Mo6nS6n+2). Consequently, its crystal structure is based on an equal mixture of Mo9S11 and Mo30S32 cluster units interlinked through Mo-S bonds with the Rb+ cations localized in the voids between the Mo9S11 and Mo30S32 units. The coexistence of the two high-nuclearity Mo9 and Mo30 clusters in the crystal structure leads to an unusual c parameter of 163.96(1) Å, and thus, Rb10Mo39S43 is the first ternary and multinary compound in solid-state chemistry to have such a large parameter. Contrary to the first four members, Rb10Mo39S43 was not found to be superconducting down to 2 K. First-principles calculations showed that the electronic structures of this series of compounds can be determined from those of the Mo9 and Mo6n clusters and that fewer interactions between clusters in Rb2n(Mo9S11)(Mo6nS6n+2) occur when n increases.

Electronic Band Structure and Transport Properties of the Cluster Compound Ag3Tl2Mo15Se19.

Mo-based cluster compounds are a large class of materials with complex crystal structures that give rise to very low lattice thermal conductivity. Here, we report on the crystal structure and transport property measurements (5-800 K) of the novel Tl-filled compound Ag3Tl2Mo15Se19. This compound adopts a crystal structure described in the rhombohedral R3 c space group [ a = 9.9601(1) Å, c = 57.3025(8) Å, and Z = 6] built by the covalent arrangement of octahedral Mo6 and bioctahedral Mo9 clusters in a 1:1 ratio, with the Ag and Tl atoms filling the large cavities between them. Transport property measurements performed on polycrystalline samples indicate that this compound behaves as a heavily doped semiconductor with mixed electrical conduction. Electronic band structure calculations combined with a semiclassical approach using the Boltzmann transport equation are in good agreement with these measurements. This compound exhibits a lattice thermal conductivity as low as 0.4 W m-1 K-1 because of highly disordered Ag and Tl atoms. Because of the low thermopower values induced by the mixed electrical conduction, the dimensionless thermoelectric figure of merit ZT remains moderate with a peak value of 0.18 at 750 K.

Effect of the Processing Route on the Thermoelectric Performance of Nanostructured CuPb18SbTe20.

The quaternary AgPb18SbTe20 compound (abbreviated as LAST) is a prominent thermoelectric material with good performance. Endotaxially embedded nanoscale Ag-rich precipitates contribute significantly to decreased lattice thermal conductivity (κlatt) in LAST alloys. In this work, Ag in LAST alloys was completely replaced by the more economically available Cu. Herein, we conscientiously investigated the different routes of synthesizing CuPb18SbTe20 after vacuum-sealed-tube melt processing, including (i) slow cooling of the melt, (ii) quenching and annealing, and consolidation by (iii) spark plasma sintering (SPS) and also (iv) by the state-of-the-art flash SPS. Irrespective of the method of synthesis, the electrical (σ) and thermal (κtot) conductivities of the CuPb18SbTe20 samples were akin to those of LAST alloys. Both the flash-SPSed and slow-cooled CuPb18SbTe20 samples with nanoscale dislocations and Cu-rich nanoprecipitates exhibited an ultralow κlatt ∼ 0.58 W/m·K at 723 K, comparable with that of its Ag counterpart, regardless of the differences in the size of the precipitates, type of precipitate-matrix interfaces, and other nanoscopic architectures. The sample processed by flash SPS manifested higher figure of merit ( zT ∼ 0.9 at 723 K) because of better optimization and a trade-off between the transport properties by decreasing the carrier concentration and κlatt without degrading the carrier mobility. In spite of their comparable σ and κtot, zT of the Cu samples is low compared to that of the Ag samples because of their contrasting thermopower values. First-principles calculations attribute this variation in the Seebeck coefficient to dwindling of the energy gap (from 0.1 to 0.02 eV) between the valence and conduction bands in MPb18SbTe20 (M = Cu or Ag) when Cu replaces Ag.

Synthesis, Crystal Structure, and Liquid Exfoliation of Layered Lanthanide Sulfides KLn2CuS6 (Ln = La, Ce, Pr, Nd, Sm).

Among the great amount of known lanthanide nanoparticles, reports devoted to chalcogenide ones are deficient. The properties of such nanoparticles remain almost unknown due to the lack of simple and proper synthetic methods avoiding hydrolysis and allowing preparation of oxygen-free lanthanide nanoparticles. A liquid exfoliation method was used to select the optimum strategy for the preparation of quaternary lanthanide sulfide nanoparticles. Bulk KLn2CuS6 (Ln = La-Sm) materials were obtained via a reactive flux method. The crystal structures of three new members of the KLn2CuS6 series were determined for Pr, Nd, and Sm as well as for known KLa2CuS6. KLn2CuS6 (Ln = La, Pr, Nd) compounds crystallize in the monoclinic C2 /c space group, whereas KSm2CuS6 crystallizes in the orthorhombic Fddd space group. The analysis of their electronic structures confirms that the main bonding interactions occur within the anionic {Ln2CuS6}- layers. Due to their layered structure, exfoliation of these compounds is possible using ultrasonic treatment in appropriate solvents with the formation of colloidal solutions. Colloidal particles show a plate-like morphology with a lateral size of 100-200 nm and a thickness of 2-10 nm. Highly negative or positive charges found in isopropanol and acetonitrile dispersions, respectively, are associated with high stability and concentration of the dispersions.

Enhancement of the Thermoelectric Properties of FeGa3-type Structures with Group 6 Transition Metals: A Computational Exploration.

The possible existence of group 6 TM3 compounds with T = Cr, Mo, W and M = Ga, In is investigated with the aid of density functional theory calculations. Their most probable crystal structure is expected to be of the FeGa3 type tetragonal space group P42/mnm. All compounds are computed to be semiconductors with a band gap ranging from 0.08 to 0.43 eV, at the modified Becke-Johnson level of theory. The thermoelectric properties are analyzed via calculations based on Boltzmann transport equation under a constant relaxation time approximation. Promising power factors are computed for both n- and p-type WGa3 because of a band degeneracy around the Fermi level similar to that of heavily doped PbTe and SnTe materials. If the optimal chemical potential can be reached, a thermoelectric figure of merit up to 0.6 at 800 K for both n- and p-type may be expected for WGa3.

Multinuclear NMR as a tool for studying local order and dynamics in CH3NH3PbX3 (X = Cl, Br, I) hybrid perovskites.

We report on 207Pb, 79Br, 14N, 1H, 13C and 2H NMR experiments for studying the local order and dynamics in hybrid perovskite lattices. 207Pb NMR experiments conducted at room temperature on a series of MAPbX3 compounds (MA = CH3NH3+; X = Cl, Br and I) showed that the isotropic 207Pb NMR shift is strongly dependent on the nature of the halogen ions. Therefore 207Pb NMR appears to be a very promising tool for the characterisation of local order in mixed halogen hybrid perovskites. 207Pb NMR on MAPbBr2I served as a proof of concept. Proton, 13C and 14N NMR experiments confirmed the results previously reported in the literature. Low temperature deuterium NMR measurements, down to 25 K, were carried out to investigate the structural phase transitions of MAPbBr3. Spectral lineshapes allow following the successive phase transitions of MAPbBr3. Finally, quadrupolar NMR lineshapes recorded in the orthorhombic phase were compared with simulated spectra, using DFT calculated electric field gradients (EFG). Computed data do not take into account any temperature effect. Thus, the discrepancy between the calculated and experimental EFG evidences the fact that MA cations are still subject to significant dynamics, even at 25 K.

Cu Insertion Into the Mo12 Cluster Compound Cs2Mo12Se14: Synthesis, Crystal and Electronic Structures, and Physical Properties.

Mo-based cluster compounds are promising materials for high-temperature thermoelectric applications due to their intrinsic, extremely low thermal conductivity values. In this study, polycrystalline cluster compounds Cs2CuxMo12Se14 were prepared for a wide range of Cu contents (0 ≤ x ≤ 2). All samples crystallize isostructurally in the trigonal space group R3̅. The position of the Cu atoms in the unit cell was determined by X-ray diffraction on a single-crystalline specimen indicating that these atoms fill the empty space between the Mo-Se clusters. Density functional theory calculations predict a metallic ground state for all compositions, in good agreement with the experimental findings. Magnetization measurements indicate a rapid suppression of the superconducting state that develops in the x = 0.0 sample upon Cu insertion. Transport properties measurements, performed in a wide temperature range (2-630 K) on the two end-member compounds x = 0 and x = 2, revealed a multiband electrical conduction as shown by sign reversal of the thermopower as a function of temperature.

Atom-Precise Organometallic Zinc Clusters.

The bottom-up synthesis of organometallic zinc clusters is described. The cation {[Zn10](Cp*)6 Me}(+) (1) is obtained by reacting [Zn2 Cp*2] with [FeCp2][BAr4 (F)] in the presence of ZnMe2. In the presence of suitable ligands, the high reactivity of 1 enables the controlled abstraction of single Zn units, providing access to the lower-nuclearity clusters {[Zn9 ](Cp*)6} (2) and {[Zn8 ](Cp*)5 ((t) BuNC)3}(+) (3). According to DFT calculations, 1 and 2 can be described as closed-shell species that are electron-deficient in terms of the Wade-Mingos rules because the apical ZnCp* units that constitute the cluster cage do not have three, but only one, frontier orbitals available for cluster bonding. Zinc behaves flexibly in building the skeletal metal-metal bonds, sometimes providing one major frontier orbital (like Group 11 metals) and sometimes providing three frontier orbitals (like Group 13 elements).

Evaluation of (95)Mo Nuclear Shielding and Chemical Shift of [Mo6X14](2-) Clusters in the Liquid Phase.

[Mo6X14](2-) octahedral molybdenum clusters are the main building blocks of a large range of materials. Although (95)Mo nuclear magnetic resonance was proposed to be a powerful tool to characterize their structural and dynamical properties in solution, these measurements have never been complemented by theoretical studies which can limit their interpretation for complex systems. In this Article, we use quantum chemical calculations to evaluate the (95)Mo chemical shift of three clusters: [Mo6Cl14](2-), [Mo6Br14](2-), and [Mo6I14](2-). In particular, we test various computational parameters influencing the quality of the results: size of the basis set, treatment of relativistic and solvent effects. Furthermore, to provide quantum chemical calculations that are directly comparable with experimental data, we evaluate for the first time the (95)Mo nuclear magnetic shielding of the experimental reference, namely, MoO4(2-) in aqueous solution. This is achieved by combining ab initio molecular dynamics simulations with a periodic approach to evaluate the (95)Mo nuclear shieldings. The results demonstrate that, despite the difficulty to obtain accurate (95)Mo chemical shifts, relative values for a cluster series can be fairly well-reproduced by DFT calculations. We also show that performing an explicit solvent treatment for the reference compound improves by ∼50 ppm the agreement between theory and experiment. Finally, the standard deviation of ∼70 ppm that we calculate for the (95)Mo nuclear shielding of the reference provides an estimation of the accuracy we can achieve for the calculation of the (95)Mo chemical shifts using a static approach. These results demonstrate the growing ability of quantum chemical calculations to complement and interpret complex experimental measurements.

On the origin of the differences in structure directing properties of polar metal oxyfluoride [MO(x)F(6-x)]2- (x = 1, 2) building units.

In oxyfluoride chemistry, the [MO(x)F(6-x)](2-) anions (M = transition metal) are interesting polar building units that may be used to design polar materials, but their polar vs antipolar orientations in the solid state, which directly depend on the interactions between O(2-)/F(-) ligands and the extended structure, remain difficult to control. To improve this control, these interactions were assessed through crystallization of five related [MO(x)F(6-x)](2-) (M = Ti(4+), V(5+), Mo(6+), W(6+)) anions with organic molecules. The hybrid organic-inorganic compounds, (4,4'-bpyH2)TiF6 (1), (enH2)MoO2F4 (2), (4-hpyH)2MoO2F4·H2O (3), (4,4'-bpyH2)WO2F4 (4), and (4,4'-bpyH2)VOF5 (5), exhibit isolated [MO(x)F(6-x)](2-) anions in a hydrogen bond network. The analysis of these crystal structures in combination with DFT calculations elucidate how differences in structure directing properties of these anions arise when π-overlap between O 2p orbitals and M d orbitals is weak and significantly affected by an increase of the energy of the d orbitals from 3d to 5d.

X-ray characterization, electronic band structure, and thermoelectric properties of the cluster compound Ag2Tl2Mo9Se11.

We report on a detailed investigation of the crystal and electronic band structures and of the transport and thermodynamic properties of the Mo-based cluster compound Ag2Tl2Mo9Se11. This novel structure type crystallizes in the trigonal space group R3̅c and is built of a three-dimensional network of interconnected Mo9Se11 units. Single-crystal X-ray diffraction indicates that the Ag and Tl atoms are distributed in the voids of the cluster framework, both of which show unusually large anisotropic thermal ellipsoids indicative of strong local disorder. First-principles calculations show a weakly dispersive band structure around the Fermi level as well as a semiconducting ground state. The former feature naturally explains the presence of both hole-like and electron-like signals observed in Hall effect. Of particular interest is the very low thermal conductivity that remains quasi-constant between 150 and 800 K at a value of approximately 0.6 W·m(-1)·K(-1). The lattice thermal conductivity is close to its minimum possible value, that is, in a regime where the phonon mean free path nears the mean interatomic distance. Such extremely low values likely originate from the disorder induced by the Ag and Tl atoms giving rise to strong anharmonicity of the lattice vibrations. The strongly limited ability of this compound to transport heat is the key feature that leads to a dimensionless thermoelectric figure of merit ZT of 0.6 at 800 K.

Thermotropic luminescent clustomesogen showing a nematic phase: a combination of experimental and molecular simulation studies.

Octahedral Mo6 nanoclusters are functionalized with two organic ligands containing cyanobiphenyl (CB) units, giving luminescent hybrid liquid crystals (LC). Although the mesogenic density around the bulky inorganic core is constant, the two hybrids show different LC properties. Interestingly, one of them shows a nematic phase, which is particularly rare for this kind of supermolecular system. This surprising result is explained by using large-scale molecular dynamic simulations.

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds.

Two hexanuclear niobium halide cluster compounds with a [Nb6X12](2+) (X=Cl, Br) diamagnetic cluster core, have been studied by a combination of experimental solid-state NMR/NQR techniques and PAW/GIPAW calculations. For niobium sites the NMR parameters were determined by using variable Bo field static broadband NMR measurements and additional NQR measurements. It was found that they possess large positive chemical shifts, contrary to majority of niobium compounds studied so far by solid-state NMR, but in accordance with chemical shifts of (95)Mo nuclei in structurally related compounds containing [Mo6Br8](4+) cluster cores. Experimentally determined δiso((93)Nb) values are in the range from 2,400 to 3,000 ppm. A detailed analysis of geometrical relations between computed electric field gradient (EFG) and chemical shift (CS) tensors with respect to structural features of cluster units was carried out. These tensors on niobium sites are almost axially symmetric with parallel orientation of the largest EFG and the smallest CS principal axes (Vzz and δ33) coinciding with the molecular four-fold axis of the [Nb6X12](2+) unit. Bridging halogen sites are characterized by large asymmetry of EFG and CS tensors, the largest EFG principal axis (Vzz) is perpendicular to the X-Nb bonds, while intermediate EFG principal axis (Vyy) and the largest CS principal axis (δ11) are oriented in the radial direction with respect to the center of the cluster unit. For more symmetrical bromide compound the PAW predictions for EFG parameters are in better correspondence with the NMR/NQR measurements than in the less symmetrical chlorine compound. Theoretically predicted NMR parameters of bridging halogen sites were checked by (79/81)Br NQR and (35)Cl solid-state NMR measurements.

Unprecedented electron-poor octahedral Ta(6) clusters in a solid-state compound: synthesis, characterisations and theoretical investigations of Cs(2)BaTa(6)Br(15)O(3).

The crystal structure of Cs2BaTa6Br15O3 has been elucidated by using synchrotron X-ray powder diffraction and absorption experiments. It is built from edge-bridged octahedral [(Ta6Bri9Oi3)Bra6]4− cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta6 clusters is similar to that of Cs2LaTa6Br15O3 exhibiting 14-MEs per [(Ta6Bri9Oi3)Bra6]5− motif. The poorer electron-count cluster presents longer metal­metal distances as foreseen according to the electronic structure of edge-bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13- and 14-ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid-state compounds is related to those of the discrete octahedral units. Oxygen­barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron-poor Ta6 cluster in the solid state.

DFT-assisted structure determination of α1- and α2-VOPO4: new insights into the understanding of the catalytic performances of vanadium phosphates.

Structural investigations on vanadium phosphates, which are extensively used as catalysts in industry, often resulted in important advances in the understanding of the mechanisms driving the catalytic oxidation of light hydrocarbons. Layer translations in the two lamellar vanadium phosphates α1- and α2-VOPO4 phases identified during the catalysis were investigated by the combination of first-principles calculations, synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and solid-state NMR. This analysis reveals an important feature: the α1-form is the only polymorph of VOPO4 to exhibit layer translations that prevent the formation of infinite VO6 chains. A detailed investigation of this structural characteristic in vanadium phosphates reveals the correlation between the presence of infinite VO6 chains and the catalytic performances of related phases.

95Mo solid-state nuclear magnetic resonance spectroscopy and quantum simulations: synergetic tools for the study of molybdenum cluster materials.

The ability of (95)Mo solid-state nuclear magnetic resonance (SSNMR) spectroscopy to probe the atomic and electronic structures of inorganic molybdenum cluster materials has been demonstrated for the first time. Six cluster compounds were studied: MoBr(2), Cs(2)Mo(6)Br(14), (Bu(4)N)(2)Mo(6)Br(14), each containing the octahedral Mo(6)Br(14)(2-) cluster unit, and MoS(2)Cl(3), Mo(3)S(7)Cl(4), and MoSCl that contain metallic dimers, trimers, and tetramers, respectively. To overcome inherent difficulties due to the low sensitivity of (95)Mo SSNMR, both high-magnetic-field spectrometers and the quadrupolar Carr-Purcell Meiboom-Gill sensitivity enhancement pulse sequence under magic-angle-spinning conditions, combined with a hyperbolic-secant pulse were used. Experimental measurements as well as characterization of the (95)Mo electric field gradient and chemical shift tensors have been performed with the help of quantum-chemical calculations under periodic boundary conditions using the projector augmented-wave and the gauge-including projector augmented-wave methods, respectively. A large (95)Mo chemical shift range is measured, ∼3150 ppm, and the isotropic chemical shift of the Mo atoms is clearly correlated to their formal oxidation degree in the various clusters. Furthermore, a direct relation is evidenced between the molybdenum quadrupolar coupling constant and the bond lengths with its surrounding ligands. Our results demonstrate the efficiency of the combined use of quantum-chemical calculations and (95)Mo SSNMR experiments to study inorganic molybdenum cluster compounds.

Sc(0.43(2))Rb2Mo15S19, a partially Sc-filled variant of Rb2Mo15S19.

The structure of scandium dirubidium pentadecamolybdenum nonadecasulfide, Sc(0.43(2))Rb(2)Mo(15)S(19), constitutes a partially Sc-filled variant of Rb(2)Mo(15)S(19) [Picard, Saillard, Gougeon, Noel & Potel (2000), J. Solid State Chem. 155, 417-426]. In the two compounds, which both crystallize in the R ̅3c space group, the structural motif is characterized by a mixture of Mo(6)S(i)(8)S(a)(6) and Mo(9)S(i)(11)S(a)(6) cluster units (`i' is inner and `a' is apical) in a 1:1 ratio. The two components are interconnected through interunit Mo-S bonds. The cluster units are centred at Wyckoff positions 6b and 6a (point-group symmetries ̅3. and 32, respectively). The Rb(+) cations occupy large voids between the different cluster units. The Rb and the two inner S atoms lie on sites with 3. symmetry (Wyckoff site 12c), and the Mo and S atoms of the median plane of the Mo(9)S(11)S(6) cluster unit lie on sites with .2 symmetry (Wyckoff site 18e). A unique feature of the structure is a partially filled octahedral Sc site with ̅1 symmetry. Extended Hückel tight-binding calculations provide an understanding of the variation in the Mo-Mo distances within the Mo clusters induced by the increase in the cationic charge transfer due to the insertion of Sc.

Synthesis, crystal and electronic structures, and magnetic properties of LiLn9Mo16O35 (Ln = La, Ce, Pr, and Nd) compounds containing the original cluster Mo16O36.

The new compounds LiLn(9)Mo(16)O(35) (Ln=La, Ce, Pr, and Nd) were synthesized from stoichiometric mixtures of Li(2)MoO(4), Ln(2)O(3), Pr(6)O(11) or CeO(2), MoO(3), and Mo heated at 1600 °C for 48 h in a molybdenum crucible sealed under a low argon pressure. The crystal structure, determined from a single crystal of the Nd member, showed that the main building block is the Mo(16)O(36) unit, the Mo(16) core of which is totally new and results from the fusion of two bioctahedral Mo(10) clusters. It can also be viewed as a fragment of an infinite twin chain of edge-sharing Mo(6) octahedra. The Mo(16)O(36) cluster units share some oxygen atoms to form infinite chains running parallel to the b axis, which are separated by the rare-earth and lithium cations. (7)Li-NMR experiments, carried out at high field on the nonmagnetic LiLa(9)Mo(16)O(35), provided insights into the local environment of the lithium ions. Magnetic susceptibility measurements confirmed the trivalent oxidation state of the magnetic rare-earth cations and indicated the absence of localized moments on the Mo(16) clusters. The electronic structure of the LiLn(9)Mo(16)O(35) compounds was analyzed using molecular and periodic quantum calculations. The study of the molecular orbital diagrams of isolated Mo(16)O(36) models allowed the understanding of this unique metallic architecture. Periodic density functional theory calculations demonstrated that few interactions occur between the Mo(16) clusters, and predicted semiconducting properties for LiLn(9)Mo(16)O(35) as a band gap of 0.57 eV was computed for the lanthanum phase.