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A combined inelastic neutron scattering (INS) and theoretical study of H2 sorption in Y-FTZB, a recently reported metal-organic framework (MOF) with fcu topology, reveals that the strongest binding site in the MOF causes a high barrier to rotation on the sorbed H2. This rotational barrier for H2 is the highest yet of reported MOF materials based on physisorption.

A porous hybrid inorganic/organic material, NaNi3(OH)(SIP)2 [SIP = 5-sulfoisophthalate][1], is shown to strongly bind molecular hydrogen at coordinatively unsaturated metal sites. A combination of H2 sorption isotherms, temperature programmed desorption, and inelastic neutron scattering spectroscopy show the existence of a considerable number of such strong binding sites in [1] along with other sites where hydrogen is more weakly physisorbed. The overall capacity for hydrogen of this material as well as the much stronger binding of hydrogen than in typical porous material represent an important step toward a possible utilization of porous media for hydrogen storage.

The hindered rotor transitions of H(2) adsorbed in the chemically related and prototypical porous metal-organic frameworks IRMOF-1, IRMOF-8, IRMOF-11, and MOF-177 were studied by inelastic neutron scattering to gain information on the specifics of H(2) binding in this class of adsorbents. Remarkably sharp and complex spectra of these materials signify a diversity of well-defined binding sites. Similarities in the spectral features as a function of H(2) loading and correlations with recent crystallographic studies were used to assign transitions ranging in rotational barrier from <0.04 to 0.6 kcal/mol as corresponding to localized adsorption sites on the organic and inorganic components of these frameworks. We find that binding of H(2) at the inorganic cluster sites is affected by the nature of the organic link and is strongest in IRMOF-11 in accord with our adsorption isotherm data. The sites on the organic link have lower binding energies, but a much greater capacity for increases in H(2) loading, which demonstrates their importance for hydrogen uptake by these materials.

Progress in the hydrogen fuel field requires a clear understanding and characterization of how materials of interest interact with hydrogen. Due to the inherently quantum mechanical nature of hydrogen nuclei, any theoretical studies of these systems must be treated quantum dynamically. One class of material that has been examined in this context are dihydrogen complexes. Since their discovery by Kubas in 1984, many such complexes have been studied both experimentally and theoretically. This particular study examines the rotational dynamics of the dihydrogen ligand in the Fe(H)2(H2)(PEtPh2)3 complex, allowing for full motion in both the rotational degrees of freedom and treating the quantum dynamics (QD) explicitly. A "gas-phase" global potential energy surface is first constructed using density functional theory with the Becke, 3-parameter, Lee-Yang-Parr functional; this is followed by an exact QD calculation of the corresponding rotation/libration states. The results provide insight into the dynamical correlation of the two rotation angles as well as a comprehensive analysis of both ground- and excited-state librational tunneling splittings. The latter was computed to be 6.914 cm-1--in excellent agreement with the experimental value of 6.4 cm-1. This work represents the first full-dimensional ab initio exact QD calculation ever performed for dihydrogen ligand rotation in a coordination complex. [ABSTRACT FROM AUTHOR]

Examines the formulation of the two-dimensional parametrized model in the synthesis of molecular hydrogen complexes. Determination of the bond distances of hydrogen nuclei in H2 ligand; Functionality of dihydrogen ligand; Utilization of nuclear Schrodinger equation; Analysis on the interactions between the metal and H2 ligand.

Hydrogen molecules adsorbed in the nickel, cobalt, and magnesium analogs of the CPO-27 metal–organic framework at low loadings interact significantly more strongly than those adsorbed successively as a consequence of the strong interaction of hydrogen with the coordinatively unsaturated metal cations in the framework. [ABSTRACT FROM AUTHOR]

Part I of this series [J. Chem. Phys. 111, 7599 (1999)] describes a simulation of H[sub 2] adsorbed within zeolite Na-A in which a block Lanczos procedure is used to generate the first several (9) rotational eigenstates of H[sub 2], modeled as a rigid rotor, and equilibrated at a given temperature via Monte Carlo sampling. Here, we show that rotational states are strongly perturbed by the electrostatic fields in the solid. Wave functions and densities of rotational energy states are presented. Simulated neutron spectra are compared with inelastic neutron scattering data. Comparisons are made with IR spectra in which rotational levels may appear due to rovibrational coupling. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Simulations of H2 sorption were performed in Cu-MOF-74, a recent addition to the M-MOF-74 series. Electronic structure calculations revealed that the Cu2+ ions exhibit an unusually low partial positive charge distribution in Cu-MOF-74, which is a direct consequence of the Jahn-Teller effect. This is in contrast to the charge environment for the metal ions in some of the other M-MOF-74 variants as determined in previous work [Pham, T.; J. Phys. Chem. C 2015, 119, 1078-1090]. Because of the low magnitude of the partial charges of the Cu2+ ions in Cu-MOF-74, this MOF displays the lowest H2 uptake and Qst values of the M-MOF-74 series, which is consistent with what was observed experimentally for H2 sorption in this series of MOFs. Control simulations of H2 sorption in a nonphysical Cu-MOF-74 variant were performed in which a set of calculated partial charges, appropriate for one of the other M-MOF-74 analogues, were used. These simulations utilize a much higher partial positive charge for the metal ions and, as a result, a different shape for the simulated H2 sorption isotherms was obtained compared to that using the normal force field. This shape was not representative of the experimental isotherm for Cu-MOF-74, and thus, confirms the notion that the electrostatic parameters on the metal ions are the key to understanding the H2 sorption behavior in this MOF. Examining the distribution of the induced dipoles and the Cu2+-H2 distance via simulated annealing and executing two-dimensional quantum rotation calculations have also verified that the H2-metal interaction in Cu-MOF-74 is the weakest in the M-MOF-74 series. This study shows the power of using computational modeling to explain certain experimental observables and trends in a series of MOFs. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the occurrence of exceptional stability and high hydrogen uptake in hydrogen-bonded metal-organic cubes that have ACO and AST zeolite-like topologies. The study has synthesized and characterized two robust porous zeolite-like metal-organic frameworks (ZMOFs).

Single-crystal neutron diffraction, inelastic neutron scattering, and density functional calculations provide experimental and theoretical analyses of the nature of the osmium-bound, "elongated" dihydrogen ligands in [Cp*OsH4(L)][BF4) complexes (L = PPh3, AsPh3, or PCy3). The PPh3 and AsPh3 complexes clearly contain one dihydrogen ligand and two terminal hydrides; the H2 ligand is transoid to the Lewis base, and the H-H vector connecting the central two hydrogen atoms lies parallel to the Ct-Os-L plane (Ct = centroid of Cp* ring). In contrast, in the PCy3 complex the H-H vector is perpendicular to the Ct- Os-L plane. Not only the orientation of the central two hydrogen atoms but also the H-H bond length between them depends significantly on the nature of L: the H┅H distance determined from neutron diffraction is 1.01(1) and 1.08(1) Å for L = PPh3 and AsPh3, respectively, but 1.31(3) Å for L = PCy3. Density functional calculations show that there is a delicate balance of electronic and steric influences created by the L ligand that change the molecular geometry (steric interactions between the Cp* and L groups most importantly change the Ct-Os-L angle), changing the relative energy of the Os 5d orbitals, which in turn govern the H-H distance, preferred H-H orientation, and rotational dynamics of the elongated dihydrogen ligand. The geometry of the dihydrogen ligand is further tuned by interactions with the BF4- counterion. The rotational barrier of the bound H2 ligand in [Cp*OsH4(PPh3)]+, determined experimentally (3.1 kcal mol-1) from inelastic neutron scattering experiments, is in reasonable agreement with the B3LYP calculated H2 rotational barrier (2.5 kcal mol-1). [ABSTRACT FROM AUTHOR]

The article discusses the exceptionally strong binding of molecular hydrogen in a porous material. The author relates that the most serious outstanding problem in the potential utilization of porous material is the binding energies for physisorbed hydrogen which are too low to reduce the equilibrium pressure of adsorbed hydrogen.