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Liquid porosimetry experiments reveal a peculiar trend of the intrusion pressure of water in hydrophobic Cu 2 (3,3',5,5'-tetraethyl-4,4'-bipyrazolate) MOF. At lower temperature (T) range, the intrusion pressure (P i ) increases with T. For higher T values, P i  first reaches a maximum and then decreases. This is at odds with the Young-Laplace law, which for systems showing a continuous decrease of contact angle with T predicts a corresponding reduction of the intrusion pressure. Though the Young-Laplace law is not expected to provide quantitative predictions at the subnanoscale of Cu 2 (tebpz) pores, the physical intuition suggests that to a reduction of their hydrophobicity corresponds a reduction of the P i . Molecular dynamics simulations and sychrothron experiments allowed to clarify the mechanism of the peculiar trend of P i with T. At increasing temperatures the vapor density within the MOF' pores grows significantly, bringing the corresponding partial pressure to ≈5 MPa. This pressure, which is consistent with the shift of P i observed in liquid porosimetry, represents a threshold to be overcame before intrusion takes place. Beyond some value of temperature, the phenomenon of reduction of hydrophobicity (and water surface tension) dominated over the opposite effect of increase of vapor pressure and P i inverts its trend with T., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

The surface of Titan, Saturn's icy moon, is believed to be composed of various molecular minerals with a great diversity in structure and composition. Under the surface conditions, 93 K and 1.45 atm, most small molecules solidify and form minerals, including acetylene and ammonia. These two compounds can not only form single-component solids but also a 1:1 binary cocrystal that exhibits intriguing rotor phase behavior. This cocrystal is a putative mineral on Titan and other planetary bodies such as comets. In addition, the structure of the cocrystal is relevant to fundamental science as it can help better understand the emergence of rotor phases. Here, we present a detailed vibrational neutron spectroscopic study supported by a neutron powder diffraction study on the cocrystal and the single-phase solids. The experimentally observed spectral bands were assigned based on theoretical calculations. The established spectra-properties correlations for the cocrystal corroborate the observed properties. To the best of our knowledge, this study presents the first example of the application of neutron vibrational spectroscopy in studying Titan-relevant organic minerals.

Fluids under extreme confinement show characteristics significantly different from those of their bulk counterpart. This work focuses on water confined within the complex cavities of highly hydrophobic metal-organic frameworks (MOFs) at high pressures. A combination of high-pressure intrusion-extrusion experiments with molecular dynamic simulations and synchrotron data reveals that supercritical transition for MOF-confined water takes place at a much lower temperature than in bulk water, ∼250 K below the reference values. This large shifting of the critical temperature ( T c ) is attributed to the very large density of confined water vapor in the peculiar geometry and chemistry of the cavities of Cu 2 tebpz (tebpz = 3,3',5,5'-tetraethyl-4,4'-bipyrazolate) hydrophobic MOF. This is the first time the shift of T c is investigated for water confined within highly hydrophobic nanoporous materials, which explains why such a large reduction of the critical temperature was never reported before, neither experimentally nor computationally.

Flexible nanoporous materials are of great interest for applications in many fields such as sensors, catalysis, material separation, and energy storage. Of these, metal-organic frameworks (MOFs) are the most explored thus far. However, tuning their flexibility for a particular application remains challenging. In this work, we explore the effect of the exogenous property of crystallite size on the flexibility of the ZIF-8 MOF. By subjecting hydrophobic ZIF-8 to hydrostatic compression with water, the flexibility of its empty framework and the giant negative compressibility it experiences during water intrusion were recorded via in operando synchrotron irradiation. It was observed that as the crystallite size is reduced to the nanoscale, both flexibility and the negative compressibility of the framework are reduced by ∼25% and ∼15%, respectively. These results pave the way for exogenous tuning of flexibility in MOFs without altering their chemistries.

A proposed low-energy alternative to the separation of alkanes from alkenes by energy-intensive cryogenic distillation is separation by porous adsorbents. Unfortunately, most adsorbents preferentially take up the desired, high-value major component alkene, requiring frequent regeneration. Adsorbents with inverse selectivity for the minor component alkane would enable the direct production of purified, reagent-grade alkene, greatly reducing global energy consumption. However, such materials are exceedingly rare, especially for propane/propylene separation. Here, we report that through adaptive and spontaneous pore size and shape adaptation to optimize an ensemble of weak noncovalent interactions, the structurally responsive metal-organic framework CdIF-13 ( sod -Cd(benzimidazolate) 2 ) exhibits inverse selectivity for propane over propylene with record-setting separation performance under industrially relevant temperature, pressure, and mixture conditions. Powder synchrotron X-ray diffraction measurements combined with first-principles calculations yield atomic-scale insight and reveal the induced fit mechanism of adsorbate-specific pore adaptation and ensemble interactions between ligands and adsorbates. Dynamic column breakthrough measurements confirm that CdIF-13 displays selectivity under mixed-component conditions of varying ratios, with a record measured selectivity factor of α ≈ 3 at 95:5 propylene:propane at 298 K and 1 bar. When sequenced with a low-cost rigid adsorbent, we demonstrated the direct purification of propylene under ambient conditions. This combined atomic-level structural characterization and performance testing firmly establishes how cooperatively flexible materials can be capable of unprecedented separation factors.

Thermal polymorphism in the alkali-metal salts incorporating the icosohedral monocarba-hydridoborate anion, CB 11 H 12 - , results in intriguing dynamical properties leading to superionic conductivity for the lightest alkali-metal analogues, LiCB 11 H 12 and NaCB 11 H 12 . As such, these two have been the focus of most recent CB 11 H 12 - related studies, with less attention paid to the heavier alkali-metal salts, such as CsCB 11 H 12 . Nonetheless, it is of fundamental importance to compare the nature of the structural arrangements and interactions across the entire alkali-metal series. Thermal polymorphism in CsCB 11 H 12 was investigated using a combination of techniques: X-ray powder diffraction; differential scanning calorimetry; Raman, infrared, and neutron spectroscopies; and ab initio calculations. The unexpected temperature-dependent structural behavior of anhydrous CsCB 11 H 12 can be potentially justified assuming the existence of two polymorphs with similar free energies at room temperature: ( i ) a previously reported, ordered R 3 polymorph stabilized upon drying and transforming first to R 3 c symmetry near 313 K and then to a similarly packed but disordered I 43 d polymorph near 353 K and ( ii ) a disordered Fm 3 polymorph that initially appears from the disordered I 43 d polymorph near 513 K along with another disordered high-temperature P 6 3 mc polymorph. Quasielastic neutron scattering results indicate that the CB 11 H 12 - anions in the disordered phase at 560 K are undergoing isotropic rotational diffusion, with a jump correlation frequency [1.19(9) × 10 11 s -1 ] in line with those for the lighter-metal analogues.

Coordinatively unsaturated metal sites within certain zeolites and metal-organic frameworks can strongly adsorb a wide array of substrates. While many classical examples involve electron-poor metal cations that interact with adsorbates largely through physical interactions, unsaturated electron-rich metal centers housed within porous frameworks can often chemisorb guests amenable to redox activity or covalent bond formation. Despite the promise that materials bearing such sites hold in addressing myriad challenges in gas separations and storage, very few studies have directly interrogated mechanisms of chemisorption at open metal sites within porous frameworks. Here, we show that nondissociative chemisorption of H 2 at the trigonal pyramidal Cu + sites in the metal-organic framework Cu I -MFU-4 l occurs via the intermediacy of a metastable physisorbed precursor species. In situ powder neutron diffraction experiments enable crystallographic characterization of this intermediate, the first time that this has been accomplished for any material. Evidence for a precursor intermediate is also afforded from temperature-programmed desorption and density functional theory calculations. The activation barrier separating the precursor species from the chemisorbed state is shown to correlate with a change in the Cu + coordination environment that enhances π-backbonding with H 2 . Ultimately, these findings demonstrate that adsorption at framework metal sites does not always follow a concerted pathway and underscore the importance of probing kinetics in the design of next-generation adsorbents.

Adsorption-based cooling is an energy-efficient renewable-energy technology that can be driven using low-grade industrial waste heat and/or solar heat. Here, we report the first exploration of fluorocarbon adsorption using porous covalent organic polymers (COPs) for this cooling application. High fluorocarbon R134a equilibrium capacities and unique overall linear-shaped isotherms are revealed for the materials, namely COP-2 and COP-3. The key role of mesoporous defects on this unusual adsorption behavior was demonstrated by molecular simulations based on atomistic defect-containing models built for both porous COPs. Analysis of simulated R134a adsorption isotherms for various defect-containing atomistic models of the COPs shows a direct correlation between higher fluorocarbon adsorption capacities and increasing pore volumes induced by defects. Combined with their high porosities, excellent reversibility, fast kinetics, and large operating window, these defect-containing porous COPs are promising for adsorption-based cooling applications., (© 2021 Wiley-VCH GmbH.)

The Kitaev model is a rare example of an analytically solvable and physically instantiable Hamiltonian yielding a topological quantum spin liquid ground state. Here we report signatures of Kitaev spin liquid physics in the honeycomb magnet Li 3 Co 2 SbO 6 , built of high-spin d 7 (Co 2+ ) ions, in contrast to the more typical low-spin d 5 electron configurations in the presence of large spin-orbit coupling. Neutron powder diffraction measurements, heat capacity, and magnetization studies support the development of a long-range antiferromagnetic order space group of C C 2/ m , below T N   =   11 K at μ 0 H   =   0 T . The magnetic entropy recovered between T   =   2 and 50 K is estimated to be 0.6 R ln2 , in good agreement with the value expected for systems close to a Kitaev quantum spin liquid state. The temperature-dependent magnetic order parameter demonstrates a β value of 0.19(3), consistent with XY anisotropy and in-plane ordering, with Ising-like interactions between layers. Further, we observe a spin-flop-driven crossover to ferromagnetic order with space group of C 2/ m under an applied magnetic field of μ 0 H   ≈   0.7 T at T   =   2   K . Magnetic structure analysis demonstrates these magnetic states are competing at finite applied magnetic fields even below the spin-flop transition. Both the d 7 compass model, a quantitative comparison of the specific heat of Li 3 Co 2 SbO 6 , and related honeycomb cobaltates to the anisotropic Kitaev model further support proximity to a Kitaev spin liquid state. This material demonstrates the rich playground of high-spin d 7 systems for spin liquid candidates and complements known d 5 Ir- and Ru-based materials.

Benzene and acetonitrile are two of the most commonly used solvents found in almost every chemical laboratory. Titan is one other place in the solar system that has large amounts of these compounds. On Titan, organic molecules are produced in the atmosphere and carried to the surface where they can mineralize. Here, we report the phase diagram of mixtures of acetonitrile and benzene, and provide an account of the structure and composition of the phases. To mimic the environment on Titan more accurately, we tested the stability of the structure under liquid ethane. The results provide new insights into the structure and stability of potential extraterrestrial minerals. In light of Dragonfly, NASA's upcoming mission to Titan, revisiting the fundamental chemistry of the smallest molecules with modern methods and techniques can have significant contributions to this epochal mission and can open new research directions in chemistry.

The design of stable adsorbents capable of selectively capturing dioxygen with a high reversible capacity is a crucial goal in functional materials development. Drawing inspiration from biological O 2 carriers, we demonstrate that coupling metal-based electron transfer with secondary coordination sphere effects in the metal-organic framework Co 2 (OH) 2 (bbta) (H 2 bbta = 1H,5H-benzo(1,2-d:4,5-d')bistriazole) leads to strong and reversible adsorption of O 2 . In particular, moderate-strength hydrogen bonding stabilizes a cobalt(III)-superoxo species formed upon O 2 adsorption. Notably, O 2 -binding in this material weakens as a function of loading, as a result of negative cooperativity arising from electronic effects within the extended framework lattice. This unprecedented behavior extends the tunable properties that can be used to design metal-organic frameworks for adsorption-based applications.

A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc) 2 ( 1 , bdc 2- = 1,4-benzenedicarboxylate) was synthesized and its H 2 and CH 4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D 2 loadings revealed a rare example of cooperative framework contraction (Δ V = -7.8%), triggered by D 2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen ( Q st = -8.6 kJ mol -1 ) per pore, in agreement with H 2 adsorption data. Analogous experiments with CD 4 ( Q st = -24.8 kJ mol -1 ) and N , N -dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal-organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity., (This journal is © The Royal Society of Chemistry 2020.)

Metal-organic frameworks featuring open metal coordination sites have been widely studied for the separation of gas mixtures. For CO 2 /N 2 separations, these materials have shown considerable promise. Herein, we report the characterization of a subset of the well-known PCN-250 class of frameworks upon CO 2 adsorption via powder neutron diffraction methods. Noteably, in contrast to previously reported data, they display only moderate CO 2 adsorption enthalpies, based on metal cation-CO 2 interactions. Further, we show charge balance in these materials is likely achieved via ligand vacancies rather than the presence of μ 3 -OH groups in the trimetallic cluster that comprises them.

The rapid growth in the global energy demand for space cooling requires the development of more efficient environmental chillers for which adsorption-based cooling systems can be utilized. Here, in this contribution, we explore sorbents for chiller use via a pore-engineering concept to construct analogs of the 1-dimensional pore metal-organic framework MOF-74 by using elongated organic linkers and stereochemistry control. The prepared pore-engineered MOFs show remarkable equilibrium adsorption of the selected fluorocarbon refrigerant that is translated to a modeled adsorption-based refrigeration cycle. To probe molecular level interactions at the origin of these unique adsorption properties for this series of Ni-MOFs, we combined in situ synchrotron X-ray powder diffraction, neutron powder diffraction, X-ray absorption spectroscopy, calorimetry, Fourier transform infrared techniques, and molecular simulations. Our results reveal the coordination of fluorine (of CH 2 F in R134a) to the nickel(II) open metal centers at low pressures for each Ni-MOF analog and provide insight into the pore filling mechanism for the full range of the adsorption isotherms. The newly designed Ni-TPM demonstrates exceptional R134a adsorption uptake compared to its parent microporous Ni-MOF-74 due to larger engineered pore size/volume. The application of this adsorption performance toward established chiller conditions yields a working capacity increase for Ni-TPM of about 400% from that of Ni-MOF-74, which combined with kinetics directly correlates to both a higher coefficient of performance and a higher average cooling capacity generated in a modeled chiller.

The emergence of electrically conductive metal-organic frameworks (MOFs) has led to applications in chemical sensing and electrical energy storage, among others. The most conductive MOFs are made from organic ligands and square-planar transition metal ions connected into two-dimensional (2D) sheets stacked on top of each other. Their electrical properties are thought to depend critically on the covalency of the metal-ligand bond, and less importance is given to out-of-plane charge transport. Here, we report a series of lanthanide-based MOFs that allow fine tuning of the sheet stacking. In these materials, the Ln 3+ ions lie between the planes of the ligands, thus connecting organic layers into a 3D framework through lanthanide-oxygen chains. Here, efficient charge transport is found to occur primarily perpendicular to the 2D sheets. These results demonstrate that high conductivity in layered MOFs does not necessarily require a metal-ligand bond with highly covalent character, and that interactions between organic ligands alone can produce efficient charge transport pathways.

Ru-HKUST-1 ( Ru 3 ( btc ) 2 X 1.5 ; btc 3 - = 1 , 3 , 5 -benzenetricarboxylate ; X - = chloride , acetate , trimesate , hydroxide ) has received considerable attention as a result of its structure type, tunability, and the redox-active nature of its constituent metal paddlewheel building units. As compared to some of the other members of the HKUST-1 family, its surface area is typically reported as ~25% lower than expected. In contrast to this, a related ruthenium-based porous coordination cage, Ru 24 ( t Bu-bdc ) 24 Cl 12 , displays the expected surface area when compared to Cr 2 + and Mo 2 + analogs. Here, we examine the factors that result in this decreased surface area for the MOF. We show that with appropriate solvent exchange and activation conditions, Ru-HKUST-1 can display a B.E.T. surface areas as high as 1439 m 2 /g. We utilize a combination of spectroscopic and diffraction techniques to accurately determine the structure of the MOF, which is most accurately described here as Ru 3 ( btc ) 2 ( OAc ) 1.07 Cl 0.43 , as prepared under our conditions. Further, by simply treating the sample as air-sensitive upon isolation, adsorption selectivities toward unsaturated molecu les greatly improve.

MCB 11 H 12 (M: Li, Na) dodecahydro-monocarba- closo -dodecaborate salt compounds are known to have stellar superionic Li + and Na + conductivities in their high-temperature disordered phases, making them potentially appealing electrolytes in all-solid-state batteries. Nonetheless, it is of keen interest to search for other related materials with similar conductivities while at the same time exhibiting even lower (more device-relevant) disordering temperatures, a key challenge for this class of materials. With this in mind, the unknown structural and dynamical properties of the heavier KCB 11 H 12 congener were investigated in detail by x-ray powder diffraction, differential scanning calorimetry, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and AC impedance measurements. This salt indeed undergoes an entropy-driven, reversible, order-disorder transformation and with a lower onset temperature (348 K upon heating) in comparison to the lighter LiCB 11 H 12 and NaCB 11 H 12 analogues. The K + cations in both the low- T ordered monoclinic ( P 2 1 / c ) and high- T disordered cubic ( Fm-3m ) structures occupy octahedral interstices formed by the CB 11 H 12 - anions. In the low- T structure, the anions orient themselves so as to avoid close proximity between their highly electropositive C-H vertices and the neighboring K + cations. In the high- T structure, the anions are orientationally disordered, although to best avoid the K + cations, the anions likely orient themselves so that their C-H axes are aligned in one of eight possible directions along the body diagonals of the cubic unit cell. Across the transition, anion reorientational jump rates change from 6.2×10 6 s -1 in the low- T phase (332 K) to 2.6×10 10 s -1 in the high- T phase (341 K). In tandem, K + conductivity increases by about thirty-fold across the transition, yielding a high- T phase value of 3.2×10 -4 S cm -1 at 361 K. Yet, this is still about one to two orders of magnitude lower than that observed for LiCB 11 H 12 and NaCB 11 H 12 , suggesting that the relatively larger K + cation is much more sterically hindered than Li + and Na + from diffusing through the anion lattice via the network of smaller interstitial sites.

We report a comprehensive neutron scattering study of low energy magnetic excitations in the breathing pyrochlore helimagnetic Cu 2 OSeO 3 . Fully documenting the four lowest energy magnetic modes that leave the ferrimagnetic configuration of the "strong tetrahedra" intact ( | ℏ ω | < 13 meV), we find gapless quadratic dispersion at the point for energies above 0.2 meV, two doublets separated by 1.6(2) meV at the R point, and a bounded continuum at the X point. Our constrained rigid spin cluster model relates these features to Dzyaloshinskii-Moriya (DM) interactions and the incommensurate helical ground state. Combining conventional spin wave theory with a spin cluster form factor accurately reproduces the measured equal time structure factor through multiple Brillouin zones. An effective spin Hamiltonian describing complex anisotropic intercluster interactions is obtained.

Porous molecular solids are promising materials for gas storage and gas separation applications. However, given the relative dearth of structural information concerning these materials, additional studies are vital for further understanding their properties and developing design parameters for their optimization. Here, we examine a series of isostructural cuboctahedral, paddlewheel-based coordination cages, M 24 ( t Bu-bdc) 24 (M = Cr, Mo, Ru; t Bu-bdc 2- = 5- tert -butylisophthalate), for high-pressure methane storage. As the decrease in crystallinity upon activation of these porous molecular materials precludes diffraction studies, we turn to a related class of pillared coordination cage-based metal-organic frameworks, M 24 (Me-bdc) 24 (dabco) 6 (M = Fe, Co; Me-bdc 2- = 5-methylisophthalate; dabco = 1,4-diazabicyclo[2.2.2]octane) for neutron diffraction studies. The five porous materials display BET surface areas from 1057-1937 m 2 /g and total methane uptake capacities of up to 143 cm 3 (STP)/cm 3 . Both the porous cages and cage-based frameworks display methane adsorption enthalpies of -15 to -22 kJ/mol. Also supported by molecular modeling, neutron diffraction studies indicate that the triangular windows of the cage are favorable methane adsorption sites with CD 4 -arene interactions between 3.7 and 4.1 Å. At both low and high loadings, two additional methane adsorption sites on the exterior surface of the cage are apparent for a total of 56 adsorption sites per cage. These results show that M 24 L 24 cages are competent gas storage materials and further adsorption sites may be optimized by judicious ligand functionalization to control extracage pore space.

Although gas adsorption properties of extended three-dimensional metal-organic materials have been widely studied, they remain relatively unexplored in porous molecular systems. This is particularly the case for porous coordination cages for which surface areas are typically not reported. Herein, we report the synthesis, characterization, activation, and gas adsorption properties of a family of carbazole-based cages. The chromium analog displays a coordination cage record BET (Brunauer-Emmett-Teller) surface area of 1235 m 2 /g. With precise synthesis and activation procedures, two previously reported cages similarly display high surface areas. The materials exhibit high methane adsorption capacities at 65 bar with the chromium(II) cage displaying CH 4 capacities of 194 cm 3 /g and 148 cm 3 /cm 3 . This high uptake is a result of optimal pore design, which was confirmed via powder neutron diffraction experiments.

Materials with the pyrochlore/fluorite structure have diverse technological applications, from magnetism to nuclear waste disposal. Here we report the observation of structural instability present in the pyrochlores A 2 Zr 2 O 6 O' (A = Pr, La) and Yb 2 Ti 2 O 6 O', that exists despite ideal stoichiometry, ideal cation-ordering, the absence of lone pair effects, and a lack of magnetic order. Though these materials appear to have good long-range order, local structure probes find displacements, of the order of 0.01 nm, within the pyrochlore framework. The pattern of displacements of the A 2 O' sublattice mimics the entropically-driven fluxional motions characteristic of and well-known in the silica mineral β-cristobalite. The universality of such displacements within the pyrochlore structure adds to the known structural diversity and explains the extreme sensitivity to composition found in quantum spin ices and the lack of ferroelectric behavior in pyrochlores.

The synthesis and characterization of two novel pillared coordination cages is reported. By utilizing 1,4-diazabicyclo[2.2.2]octane (dabco) as a pillar with increased basicity as compared to pyrazine or 4,4'-bipyridine, a stable copper-based material was prepared. Extending this strategy to iron(ii) afforded an isostructural material that similarly retains high porosity and crystallinity upon solvent evacuation. Importantly, the iron solid represents a rare example of porous iron paddlewheel-based metal-organic material that is stable to solvent evacuation. Neutron powder diffraction studies on these materials indicate the triangular and square windows of the cage are prime ethane and ethylene adsorption sites.

Inelastic neutron scattering reveals a broad continuum of excitations in Pr&#95;{2}Zr&#95;{2}O&#95;{7}, the temperature and magnetic field dependence of which indicate a continuous distribution of quenched transverse fields (Δ) acting on the non-Kramers Pr^{3+} crystal field ground state doublets. Spin-ice correlations are apparent within 0.2 meV of the Zeeman energy. A random phase approximation provides an excellent account of the data with a transverse field distribution ρ(Δ)∝(Δ^{2}+Γ^{2})^{-1}, where Γ=0.27(1)  meV. Established during high temperature synthesis due to an underlying structural instability, it appears disorder in Pr&#95;{2}Zr&#95;{2}O&#95;{7} actually induces a quantum spin liquid.

The synthesis and physical properties of two new and one known Ir-Sn-Se compound are reported. Their crystal structures are elucidated with transmission electron microscopy and powder X-ray diffraction. IrSn0.45Se1.55 is a pyrite phase which consists of tilted corner-sharing IrX6 octahedra with randomly distributed (Sn-Se)(4-) and (Se-Se)(2-) dimers. Ir2Sn3Se3 is a known trigonally distorted skutterudite that consists of cooperatively tilted corner-sharing IrSn3Se3 octahedra with ordered (Sn-Se)2(4-) tetramers. Ir2SnSe5 is a layered, distorted β-MnO2 (pyrolusite) structure consisting of a double IrSe6 octrahedral row, corner sharing in the a direction and edge sharing in the b direction. This distorted pyrolusite contains (Se-Se)(2-) dimers and Se(2-) anions, and each double row is "capped" with a (Sn-Se)n polymeric chain. Resistivity, specific heat, and magnetization measurements show that all three have insulating and diamagnetic behavior, indicative of low-spin 5d(6) Ir(3+). Electronic structure calculations on Ir2Sn3Se3 show a single, spherical, nonspin-orbit split valence band and suggest that Ir2Sn3Se3 is topologically nontrivial under tensile strain due to inversion of Ir-d and Se-p states.