Isoreticular Curves: A Theory of Capillary Condensation To Model Water Sorption within Microporous Sorbents.

Metal-organic frameworks have gained traction as leading materials for water sorption applications due to precise chemical tunability of their well-ordered pores. These applications include atmospheric water capture, heat pumps, desiccation, desalination, humidity control, and thermal batteries. However, the relationships between the framework pore structure and the measurable water sorption properties, namely critical relative humidity for condensation, maximal capacity, and pore size or temperature for the onset of hysteresis, have not been clearly delineated.

Superior Charge Transport in Ni-Diamine Conductive MOFs.

Two-dimensional conductive metal-organic frameworks (2D cMOFs) are an emerging class of crystalline van der Waals layered materials with tunable porosity and high electrical conductivity. They have been used in a variety of applications, such as energy storage and conversion, chemiresistive sensing, and quantum information. Although designing new conductive 2D cMOFs and studying their composition/structure-property relationships have attracted significant attention, there are still very few examples of 2D cMOFs that exhibit room-temperature electrical conductivity above 1 S cm, the value exhibited by activated carbon, a well-known porous and conductive material that serves in myriad applications.

Humidity-Mediated Dual Ionic-Electronic Conductivity Enables High Sensitivity in MOF Chemiresistors.

In the presence of water, the electrically conductive metal-organic framework (MOF) CuHHTT (HHHTT = 2,3,7,8,12,13-hexahydroxy-4b1,5,10,15-tetraazanaphtho[1,2,3-gh]tetraphene) provides a conduit for proton transport, thereby becoming a dual ionic-electronic conductor. Owing to its dual conducting nature and its high density of imine and open metal sites, the MOF operates as a particularly sensitive chemiresistor, whose sensing mechanism changes with relative humidity. Thus, the interaction of NH gas with the MOF under low humidity promotes proton transport, which translates to high sensitivity for ammonia detection.

A Layered Organic Cathode for High-Energy, Fast-Charging, and Long-Lasting Li-Ion Batteries.

Eliminating the use of critical metals in cathode materials can accelerate global adoption of rechargeable lithium-ion batteries. Organic cathode materials, derived entirely from earth-abundant elements, are in principle ideal alternatives but have not yet challenged inorganic cathodes due to poor conductivity, low practical storage capacity, or poor cyclability. Here, we describe a layered organic electrode material whose high electrical conductivity, high storage capacity, and complete insolubility enable reversible intercalation of Li ions, allowing it to compete at the electrode level, in all relevant metrics, with inorganic-based lithium-ion battery cathodes.

A Solid Zn-Ion Conductor from an All-Zinc Metal-Organic Framework Replete with Mobile Zn Cations.

We describe the synthesis and properties of Zn[(ZnCl)(BTT)] (ZnZnBTT, BTT = 1,3,5-benzenetristetrazolate), a heretofore unknown member of a well-known, extensive family of metal-organic frameworks (MOFs) with the general formula M[(MCl)(BTT)], which adopts an anionic, sodalite-like structure. As with previous members in this family, ZnZnBTT presents two crystallographically distinct metal cations: a skeletal Zn site, fixed within ZnCl(tetrazole) secondary building units (SBUs), and a charge-balancing Zn site. Self-assembly of ZnZnBTT from its building blocks has remained elusive; instead, we show that ZnZnBTT is readily accessed by quantitative postsynthetic exchange of all Mn ions in MnMnBTT with zinc.

Tunable Low-Relative Humidity and High-Capacity Water Adsorption in a Bibenzotriazole Metal-Organic Framework.

Materials capable of selectively adsorbing or releasing water can enable valuable applications ranging from efficient humidity and temperature control to the direct atmospheric capture of potable water. Despite recent progress in employing metal-organic frameworks (MOFs) as privileged water sorbents, developing a readily accessible, water-stable MOF platform that can be systematically modified for high water uptake at low relative humidity remains a significant challenge. We herein report the development of a tunable MOF that efficiently captures atmospheric water (up to 0.

Ultrafast Water H-Bond Rearrangement in a Metal-Organic Framework Probed by Femtosecond Time-Resolved Infrared Spectroscopy.

We investigated the water H-bond network and its dynamics in NiClBTDD, a prototypical MOF for atmospheric water harvesting, using linear and ultrafast IR spectroscopy. Utilizing isotopic labeling and infrared spectroscopy, we found that water forms an extensive H-bonding network in NiClBTDD. Further investigation with ultrafast spectroscopy revealed that water can reorient in a confined cone up to ∼50° within 1.

Conceptual and Practical Aspects of Metal-Organic Frameworks for Solid-Gas Reactions.

The presence of site-isolated and well-defined metal sites has enabled the use of metal-organic frameworks (MOFs) as catalysts that can be rationally modulated. Because MOFs can be addressed and manipulated through molecular synthetic pathways, they are chemically similar to molecular catalysts. They are, nevertheless, solid-state materials and therefore can be thought of as privileged solid molecular catalysts that excel in applications involving gas-phase reactions.

Solid-State Investigation, Storage, and Separation of Pyrophoric PH and P H with α-Mg Formate.

Phosphane, PH -a highly pyrophoric and toxic gas-is frequently contaminated with H and P H , which makes its handling even more dangerous. The inexpensive metal-organic framework (MOF) magnesium formate, α-[Mg(O CH) ], can adsorb up to 10 wt % of PH . The PH -loaded MOF, PH @α-[Mg(O CH) ], is a non-pyrophoric, recoverable material that even allows brief handling in air, thereby minimizing the hazards associated with the handling and transport of phosphane.

Dipole-mediated exciton management strategy enabled by reticular chemistry.

Selectively blocking undesirable exciton transfer pathways is crucial for utilizing exciton conversion processes that involve participation of multiple chromophores. This is particularly challenging for solid-state systems, where the chromophores are fixed in close proximity. For instance, the low efficiency of solid-state triplet-triplet upconversion calls for inhibiting the parasitic singlet back-transfer without blocking the flow of triplet excitons.

Pyrogallate-Based Metal-Organic Framework with a Two-Dimensional Secondary Building Unit.

We report a metal-organic framework (MOF) with a rare two-dimensional (2D) secondary building unit (SBU). The SBU comprises mixed-valent Fe and Fe metal ions bridged by oxygen atoms pertaining to the polytopic ligand 3,3',4,4',5,5'-hexahydroxybiphenyl, which also define the iron-oxide 2D layers. Overall, the anionic framework exhibits rare topology and evidences strong electronic communication between the mixed-valence iron sites.

Strong magnetic exchange coupling in a radical-bridged trinuclear nickel complex.

Reaction of 2,3,6,7,10,11-hexaaminotriphenylene hexahydrochloride (HATP·6HCl) and (TpNi)Cl (Tp = tris(3,5-diphenyl-1-pyrazolyl)borate) produces the radical-bridged trinickel complex [(TpNi)(HITP)] (HITP˙ = 2,3,6,7,10,11-hexaiminotriphenylene). Magnetic measurements and broken-symmetry density functional theory calculations reveal strong exchange coupling persisting at room temperature between HITP˙ and two of the three Ni centers, a rare example of strong radical-mediated magnetic coupling in multimetallic complexes. These results demonstrate the potential of radical-bearing tritopic HITP ligands as building blocks for extended molecule-based magnetic materials.

Dimensionality Modulates Electrical Conductivity in Compositionally Constant One-, Two-, and Three-Dimensional Frameworks.

We reveal here the construction of Ni-based metal-organic frameworks (MOFs) and conjugated coordination polymers (CCPs) with different structural dimensionalities, including closely π-stacked 1D chains (), aggregated 2D layers (), and a 3D framework (), based on 2,3,5,6-tetraamino-1,4-hydroquinone (TAHQ) and its various oxidized forms. These materials have the same metal-ligand composition but exhibit distinct electronic properties caused by different dimensionalities and supramolecular interactions between SBUs, ligands, and structural motifs. The electrical conductivity of these materials spans nearly 8 orders of magnitude, approaching 0.

Isolation of a Side-On V(III)-(η-O) through the Intermediacy of a Low-Valent V(II) in a Metal-Organic Framework.

We report the isolation of vanadium(II) in a metal-organic framework (MOF) by the reaction of the chloride-capped secondary building unit in the all-vanadium(III) V-MIL-101 () with 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine. The reduced material, , has a secondary building unit with the formal composition [VV], with each metal ion presenting one open coordination site. Subsequent reaction with O yields a side-on η vanadium-superoxo species, .

Divergent Adsorption Behavior Controlled by Primary Coordination Sphere Anions in the Metal-Organic Framework NiXBTDD.

CO, ethylene, and H demonstrate divergent adsorption enthalpies upon interaction with a series of anion-exchanged NiXBTDD materials (X = OH, F, Cl, Br; HBTDD = bis(1-1,2,3-triazolo[4,5-][4',5'-])dibenzo[1,4]dioxin)). The dissimilar responses of these conventional π-acceptor gaseous ligands are in contrast with the typical behavior that may be expected for gas sorption in metal-organic frameworks (MOFs), which generally follows similar periodic trends for a given set of systematic changes to the host MOF structure. A combination of computational and spectroscopic data reveals that the divergent behavior, especially between CO and ethylene, stems from a predominantly σ-donor interaction between the former and Ni and a π-acceptor interaction for the latter.

Aperiodic metal-organic frameworks.

Metal-organic frameworks (MOFs) represent one of the most diverse structural classes among solid state materials, yet few of them exhibit aperiodicity, or the existence of long-range order in the absence of translational symmetry. From this apparent conflict, a paradox has emerged: even though aperiodicity frequently arises in materials that contain the same bonding motifs as MOFs, aperiodic structures and MOFs appear to be nearly disjoint classes. In this perspective, we highlight a subset of the known aperiodic coordination polymers, including both incommensurate and quasicrystalline structures.

Electronic Structure of Tetracyanonickelate(II).

Tetracyanonickelate(II) has been a poster child of ligand field theory for several decades. We have revisited the literature assignments of the absorption spectrum of [Ni(CN)] and the calculated ordering of orbitals with metal d character. Using low-temperature single-crystal absorption spectroscopy and accurate ab initio and density functional quantum mechanical methods (NEVPT2-CASSCF, EOM-CCSD, TD-DFT), we find an ordering of the frontier d- and p-orbitals of < , < < < - < , and assign the d-d bands in the absorption spectrum to A → B < E < A < B < E < A.

Accurate non-bonded potentials based on periodic quantum mechanics calculations for use in molecular simulations of materials and systems.

Molecular dynamics simulations require accurate force fields (FFs) to describe the physical and chemical properties of complex materials and systems. FF parameters for valence interactions can be determined from high-quality Quantum Mechanical (QM) calculations. However, it has been challenging to extract long-range nonbonded interaction potentials from QM calculations since there is no unambiguous method to separate the total QM energy into electrostatics (polarization), van der Waals (vdW), and other components.

First-principles-based reaction kinetics from reactive molecular dynamics simulations: Application to hydrogen peroxide decomposition.

This paper presents our vision of how to use in silico approaches to extract the reaction mechanisms and kinetic parameters for complex condensed-phase chemical processes that underlie important technologies ranging from combustion to chemical vapor deposition. The goal is to provide an analytic description of the detailed evolution of a complex chemical system from reactants through various intermediates to products, so that one could optimize the efficiency of the reactive processes to produce the desired products and avoid unwanted side products. We could start with quantum mechanics (QM) to ensure an accurate description; however, to obtain useful kinetics we need to average over ∼10-nm spatial scales for ∼1 ns, which is prohibitively impractical with QM.

Extension of the Polarizable Charge Equilibration Model to Higher Oxidation States with Applications to Ge, As, Se, Br, Sn, Sb, Te, I, Pb, Bi, Po, and At Elements.

We recently developed the polarizable charge equilibration (PQEq) model to predict accurate electrostatic interactions for molecules and solids and optimized parameters for H, C, N, O, F, Si, P, S, and Cl elements to fit polarization energies computed by quantum mechanics (QM). Here, we validate and optimize the PQEq parameters for other p-block elements including Ge, As, Se, Br, Sn, Sb, Te, I, Pb, Bi, Po, and At using 28 molecular structures containing these elements. For these elements, we now include molecules with higher oxidation states: III and V for the As column, IV and VI for the Se column, and I, III, and V for the Br column.