Carbon capture can mitigate point-source carbon dioxide (CO ₂ ) emissions, but hurdles remain that impede the widespread adoption of amine-based technologies. Capturing CO ₂ at temperatures closer to those of many industrial exhaust streams (>200°C) is of interest, although metal oxide absorbents that operate at these temperatures typically exhibit sluggish CO ₂ absorption kinetics and instability to cycling. Here, we report a porous metal–organic framework featuring terminal zinc hydride sites that reversibly bind CO ₂ at temperatures above 200°C—conditions that are unprecedented for intrinsically porous materials. Gas adsorption, structural, spectroscopic, and computational analyses elucidate the rapid, reversible nature of this transformation. Extended cycling and breakthrough analyses reveal that the material is capable of deep carbon capture at low CO ₂ concentrations and high temperatures relevant to postcombustion capture.

A novel approach to chemical bond analysis for excited states has been developed. Using an extended adaptive natural density partitioning method (AdNDP) as implemented in AdNDP 2.0 code, we obtained chemically intuitive bonding patterns for the excited states of H₂O, B₅ ⁺, and C₂H₄ ⁺ molecules. The deformation pathway in the excited states could be easily predicted based on the analysis of the chemical bond pattern. We expect that this new method of chemical bonding analysis would be very helpful for photochemistry, photoelectron spectroscopy, electron spectroscopy and other chemical applications that involved excited states.

The variational quantum eigensolver (VQE) is a method of choice to solve the electronic structure problem for molecules on near-term gate-based quantum computers. However, the circuit depth is expected to grow significantly with the problem size. Increased depth can both degrade the accuracy of the results and reduce trainability. In this work, we propose an approach to reduce ansatz circuit depth. Our approach, called “PermVQE,” adds an additional optimization loop to the VQE that permutes qubits in order to solve for the qubit Hamiltonian that maximally localizes correlations in the ground state. The choice of permutations is based on mutual information, which is a measure of interaction between electrons and/or holes in spin-orbitals. Encoding strongly entangled spin-orbitals into proximal qubits on a quantum chip naturally reduces the circuit depth needed to prepare the ground state. For representative molecular systems, $\mathrm{LiH}$, ${\mathrm{H}}_2$, $({\mathrm{H}}_2{)}_2$, ${\mathrm{H}}_4^{\ne }$, ${\mathrm{H}}_3^{+}$, and ${\mathrm{N}}_2$, we demonstrate that placing entangled qubits in close proximity leads to shallower depth circuits required to reach a given eigenvalue-eigenvector accuracy. The approach is designed for hardware-efficient ansatz of any qubit connectivity, and examples are demonstrated for linear and two-dimensional grid architectures. The main ideas can also be applied to simulate molecules with other ansatz as well as variational quantum algorithms beyond the VQE. In particular, we demonstrate the beneficial effect of qubit permutations to build fermionic–adaptive derivative assembled pseudo-Trotter ansatz on a linear qubit connectivity architecture with nearly a twofold reduction of the number of controlled not gates.

Porous solids can accommodate and release molecular hydrogen readily, making them attractive for minimizing the energy requirements for hydrogen storage relative to physical storage systems. However, H₂ adsorption enthalpies in such materials are generally weak (-3 to -7 kJ/mol), lowering capacities at ambient temperature. Metal-organic frameworks with well-defined structures and synthetic modularity could allow for tuning adsorbent-H₂ interactions for ambient-temperature storage. Recently, Cu_2.2Zn_2.8Cl_1.8(btdd)₃ (H₂btdd = bis(1H-1,2,3-triazolo-[4,5-b],[4',5'-i])dibenzo[1,4]dioxin; Cu^I-MFU-4l) was reported to show a large H₂ adsorption enthalpy of -32 kJ/mol owing to π-backbonding from Cu^I to H₂, exceeding the optimal binding strength for ambient-temperature storage (-15 to -25 kJ/mol). Toward realizing optimal H₂ binding, we sought to modulate the π-backbonding interactions by tuning the pyramidal geometry of the trigonal Cu^I sites. A series of isostructural frameworks, Cu_2.7M_2.3X_1.3(btdd)₃ (M = Mn, Cd; X = Cl, I; Cu^IM-MFU-4l), was synthesized through postsynthetic modification of the corresponding materials M₅X₄(btdd)₃ (M = Mn, Cd; X = CH₃CO₂, I). This strategy adjusts the H₂ adsorption enthalpy at the Cu^I sites according to the ionic radius of the central metal ion of the pentanuclear cluster node, leading to -33 kJ/mol for M = Zn^II (0.74 Å), -27 kJ/mol for M = Mn^II (0.83 Å), and -23 kJ/mol for M = Cd^II (0.95 Å). Thus, Cu^ICd-MFU-4l provides a second, more stable example of optimal H₂ binding energy for ambient-temperature storage among reported metal-organic frameworks. Structural, computational, and spectroscopic studies indicate that a larger central metal planarizes trigonal Cu^I sites, weakening the π-backbonding to H₂.