Antimony (Sb)-based materials show great promise for hydrogen evolution reaction (HER) catalysis owing to their unique electronic structures and efficient proton-electron transfer capabilities. However, despite their potential, the molecular-level development of Sb-based catalysts has been hindered by significant synthetic challenges, particularly the difficulty in constructing well-defined molecular architectures, such as Sb-porphyrins or clusters. Herein, we report a new synthetic strategy to access two novel stiboviologens-decorated Sb4O6 clusters (SbVO-Me and SbVO-Ph) via directed oxidative coupling of stiboviologens. SbVO-Me and SbVO-Ph exhibit excellent redox activity, multielectron transfer capacity, and robust electrochromic behavior. DFT calculations and electrostatic potential mapping analyses reveal a cooperative electron-proton management mechanism: the viologen moiety acts as an "electron sponge," mediating charge accumulation and delivery, while the tetraantimony hexaoxide (Sb4O6) core serves as a "proton engine" to accelerate proton transport. In homogeneous acidic HER catalysis, the system achieves an overpotential of 535 mV with a Faradaic efficiency of 74.5%. Upon immobilization, the heterogeneous system delivers enhanced activity with a reduced overpotential of 182 mV. Mechanistic investigations support a cooperative catalytic pathway involving the viologens and Sb centers. This study introduces stiboviologens as a new class of main-group molecular catalysts, expanding the design landscape for viologen-based redox systems and offering new opportunities in proton-coupled electrocatalysis.

Half-Heusler (HH) alloys are among the best high-temperature thermoelectric (TE) materials able to operate above 700 °C. Here, we report on a detailed experimental study of the oxidation behavior of commercial n- and p-type HH alloys, Hf0.6Zr0.4NiSn0.98Sb0.02 and Hf0.2Zr0.75Ti0.05CoSb0.8Sn0.2, respectively, and of their integration into high-power-density TE generators (TEGs). Oxidation behaviors were investigated from room temperature to 800 °C in air on consolidated small pieces and large pellets using thermogravimetric/differential scanning calorimetry (TG/DSC). Combined with scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDXS) and powder X-ray diffraction (PXRD), these experiments enabled the identification of the oxidation products and the determination of the oxidation pathway followed by each alloy. n-type HH initially slowly oxidizes upon heating to 350 °C before rapidly oxidizing above this temperature, giving rise to a significant mass loss in the form of gaseous Sb4O6. The inward diffusion of oxygen and outward diffusion of Sb led to the formation of an inner core separated from an outer layer by an empty space. In spite of the higher amount of Sb in the p-type alloy, its oxidation behavior differs, with no significant mass loss observed. In contrast, Sb reacts with Co to form oxides near the surface. A two-couple TEG was fabricated with leg height L = 2.0 mm. A maximum output power density pmax of 7.5 W cm[-2] was achieved under a temperature difference ΔT of 575 K. Of particular relevance, reducing L does not necessitate the insertion of mechanical buffers due to the excellent mechanical strength of these alloys. Using shortened legs allows for an increase in pmax at lower ΔT, thereby reaching a temperature range over which these alloys could remain stable against oxidation if further passivation optimization could be realized.

Inorganic molecular crystal (IMC) is a trending class of materials in which structural units comprise molecular cages or clusters bonded via van der Waal forces. The structure-property relationship in IMCs is less known due to the unusual assembly of molecular clusters in these materials. In this paper, the density functional theory-calculated electronic transport properties of the molecular clusters of antimony oxide (Sb4O6), phosphorus triselenide (P4Se3), and phosphorus trioxide (P4O6) are described in detail. The calculated values of highest occupied molecular orbital-lowest unoccupied molecular orbital gaps appeared as 5.487, 2.296, and 4.425 eV for Sb4O6, P4Se3, and P4O6, respectively. The work was carried out to explore the charge transport mechanism in IMCs in order to disclose their potential in practical applications. The calculations involved charge-transfer integral based on Marcus theory to compute the electronic coupling (V), reorganization energies (λ), and hopping rate (k) in the structures. The hopping rate for Sb4O6, P4Se3, and P4O6 is found as 8.49 × 10-12, 1.28 × 10-14, and 2.51 × 10-20 s-1, respectively. The transport properties of Sb4O6 are found better, which predicts the application of the relevant IMC for device grade applications. The findings of this study are important for future application of the IMCs in electronic and optoelectronic applications.

The cubic-phase antimony trioxide (α-Sb2O3) is a room-temperature stable molecular crystal, composed of cage-like tetraantimony hexoxide (Sb4O6) molecules. Despite its versatile functionality, the van der Waals (vdW) bond-dominated nanomechanics is still unclear. Here, the bending plate-like linear behaviors of high-quality α-Sb2O3 nanoflakes were observed using the nanoindentation method. It is found that the cage-molecular crystal owns a very low in-plane Young's modulus of 14.9 ± 0.8 GPa and a remarkable maximum tensile strain of 6.0-8.8%, corresponding to a rupture strength of 0.89-1.31 GPa. Elucidated by the atomistic simulations, the compliant elastic modulus and the unexpectedly strong rupture strain are associated with the high-symmetry vdW bonding structure. The vdW nanomechanics is of fundamental and technological relevance to nanoelectronics.

For the interlayer dielectric in microelectronics, light element compounds are preferably accepted due to less electronic polarization. Here, the nontrivial dielectric nature of the Sb4O6 cage-molecular crystal, known as α-antimony trioxide (α-Sb2O3), is reported. The gas-phase synthesized α-Sb2O3 nanoflakes are of high crystal quality, from which the abnormal local admittance responses were revealed by scanning microwave impedance microscopy (sMIM). The remarkably low dielectric constant (k), 2.0∼2.5, is corroborated by the analysis of the thickness-dependent sMIM-capacitance signal. In light of the theoretical calculations, the ultralow molecular density and the significantly suppressed ionic polarization are both crucial to the highly reduced k. Combining with the excellent optical band gap, thermal stability, and breakdown strength, α-Sb2O3 is a promising low k dielectric.

Antimony oxide nanostructures have been identified as candidates for a range of electronic and optoelectronic applications. Here we demonstrate the growth of 2-dimensional antimony oxide nanostructures on various substrates, including highly oriented pyrolytic graphite (HOPG), MoS2 and α-Bi(110) nanoislands. Using scanning tunneling microscopy (STM) we show that the nanostructures formed are exclusively highly crystalline α-Sb2O3(111) monolayers with a lattice constant of 796 pm ± 7 pm. The nanostructures are triangular with lateral dimensions of up to ∼30 nm. Even though elemental antimony nanostructures are grown simultaneously mixed phases are not observed and both materials exhibit their own distinct growth modes. Moiré patterns are also observed and simulated, allowing confirmation of the atomic unit cell and an understanding of the orientation of the Sb2O3 structures with respect to the supporting materials. As in the bulk, the Sb2O3 nanostructures are formed from Sb4O6 molecules that are weakly interacting through van der Waals forces. This allows physical modification of the nanostructures with the STM tip. Scanning tunnelling spectroscopy reveals a wide band gap of at least 3.5 eV. Finally, we show that possible alternative structures that have unit cells comparable to those observed can be excluded based on our DFT calculations. The considered structures are a 2 × 2 reconstruction of β-Sb with one vacancy per unit cell and a van der Waals solid composed of Sb4 clusters. Previous reports have predominantly demonstrated Sb2O3 structures with much larger thicknesses.

The molecular structure of a fundamental binary compound [antimony(III) oxide] has been re-determined to a far higher accuracy and precision than previously reported. The structure is compared to those determined by various ab initio methods, X-ray diffraction and to a previous gas-phase structure determined by electron diffraction prior to modern-day developments for data extraction and manipulation. The experiments utilised a new very-high-temperature (VHT) inlet nozzle system that has been designed and constructed for the gas electron diffraction (GED) apparatus now based at the University of Canterbury (formerly at the University of Edinburgh). The VHT-GED system is capable of heating samples to temperatures of up to 1100 K. The VHT system was tested by studying the gas-phase structure of antimony(III) oxide. Data were collected at 750 K and the contents of the gas flow analysed by mass spectrometry. In the gas phase at this temperature, antimony(III) oxide (Sb(2)O(3)) exists as a dimer (Sb(4)O(6)) with tetrahedral symmetry. The Sb-O bond length (r(a3,1)) was determined to be 195.66(4) pm and the O-Sb-O bond angle was 98.15(3)°. Unusually, the Sb-O bond length observed from X-ray diffraction investigation of Sb(4)O(6) was longer than the gas phase bond length [197.7(1) pm as compared to 195.66(4) pm].

High-resolution X-ray diffraction data have been collected on the cubic polymorph of antimony(III) oxide (senarmontite) to determine the charge distribution in the crystal. The results are in quantitative agreement with crystal Hartree-Fock calculations for this polymorph, and have been compared with theoretical calculations on the orthorhombic polymorph (valentinite). Information about the nature of bonding and relative bond strengths in the two polymorphs has been extracted in a straightforward manner via topological analysis of the electron density. All the close contacts in both polymorphs are found to be similar in nature based on the value of the Laplacian, the magnitude of the electron density and the local energy density at the bond critical points, and these characterise the observed interactions as substantially polar covalent, similar to molecular calculation results on Si-O and Ge-O. Electrostatic potential isosurfaces reveal the octopolar nature of this function for senarmontite, and shed light on the observed packing arrangement of Sb4O6 molecules in the crystal.

The first ab initio theoretical study of tetraantimony hexoxide (Sb4O6) is reported. The normal mode frequencies, intensities, and the corresponding vibrational assignments of Sb4O6 in T(d) symmetry were calculated using the GAUSSIAN 98 set of quantum chemistry codes at the Hartree-Fock (HF)/CEP-121G, Møller-Plesset (MP2)/CEP-121G, and density functional theory (DFT)/B3LYP/CEP-121G levels of theory. By comparison to experimental data deduced by our laboratory and others, correction factors for the calculated vibrational frequencies were determined and compared. Normal modes were decomposed into three non-redundant motions (Sb-O-Sb stretch, Sb-O-Sb bend, and Sb-O-Sb wag). Percent relative errors found for the HF, DFT, and MP2 corrected frequencies when compared to experiment are 5.8, 6.1, and 5.7 cm(-1), respectively. Electron distributions for selected molecular orbitals are also considered.

The novel dimeric compounds [Ph(2)Sb(O(2)PR(2))O](2).2CH(2)Cl(2) [R = cycl-C(6)H(11) (2) and cycl-C(8)H(15) (3)] have been synthesized by reacting diphenylantimony trichloride (1) with 3 mol equiv of silver acetate followed by 1 mol equiv of the phosphinic acid. By the same route under more stringent conditions to exclude moisture, the mixed phosphinate-acetate [Ph(2)Sb(O(2)P(C(6)H(11))(2))(O(2)CMe)](2)O (4) was isolated and characterized. Treatment of 2 with acetic acid/water affords the tetranuclear cage Ph(8)Sb(4)O(4)(OH)(2)(O(2)P(C(6)H(11))(2))(2).CH(3)COOH.CH(2)Cl(2) (5); it is possible to convert 5 to 2 by heating it with an excess of the phosphinic acid. Compounds 2, 3, and 5 have been characterized by X-ray structural analysis. All of them possess four membered Sb(2)O(2) rings with hexacoordinated antimony. In 5 the antimony atoms in the two Sb(2)O(2) rings are connected by oxo bridges on two sides to give an Sb(4)O(6) cage. These structures are correlated with those of known tin cages.