Use of the tritopic bridging ligand 1,3,5-benzenetristetrazolate (BTT3-) enables formation of [Mn(DMF)6]3[(Mn4Cl)3(BTT)8(H2O)12]2.42DMF.11H2O.20CH3OH, featuring a porous metal-organic framework with a previously unknown cubic topology. Crystals of the compound remain intact upon desolvation and show a total H2 uptake of 6.9 wt % at 77 K and 90 bar, which at 60 g H2/L provides a storage density 85% of that of liquid hydrogen. The material exhibits a maximum isosteric heat of adsorption of 10.1 kJ/mol, the highest yet observed for a metal-organic framework. Neutron powder diffraction data demonstrate that this is directly related to H2 binding at coordinatively unsaturated Mn2+ centers within the framework.

The metal-organic framework, MIL-53, can have a structural transition from an open-pored to a closed-pored structure by adsorbing different guest molecules. The aid of guest molecules is believed to be necessary to initiate this "breathing" effect. Using both neutron powder diffraction and inelastic neutron scattering techniques, we find that MIL-53 exhibits a reversible structural transition between an open-pored and a closed-pored structure as a function of temperature without the presence of any guest molecules. Surprisingly, this structural transition shows a significant temperature hysteresis: the transition from the open-pored to closed-pored structure occurs at approximately 125 to 150 K, while the transition from the closed-pored to open-pored structure occurs around 325 to 375 K. To our knowledge, this is first observation of such a large temperature hysteresis of a structural transition in metal-organic frameworks. We also note that the transition from the open to closed structure at low temperature shows very slow kinetics. An ab initio computer simulation is employed to investigate the possible mechanism of the transition.

PTB7 semiconducting copolymer comprising thieno[3,4-b]thiophene and benzodithiophene alternating repeat units set a historic record of solar energy conversion efficiency (7.4%) in polymer/fullerene bulk heterojunction solar cells. To further improve solar cell performance, a thorough understanding of structure-property relationships associated with PTB7/fullerene and related organic photovoltaic (OPV) devices is crucial. Traditionally, OPV active layers are viewed as an interpenetrating network of pure polymers and fullerenes with discrete interfaces. Here we show that the active layer of PTB7/fullerene OPV devices in fact involves hierarchical nanomorphologies ranging from several nanometers of crystallites to tens of nanometers of nanocrystallite aggregates in PTB7-rich and fullerene-rich domains, themselves hundreds of nanometers in size. These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer, and likely most polymer/fullerene systems, in OPV devices.

Rietveld analyses of neutron powder diffraction data of D2 in Cu3(BTC)2, where BTC = 1,3,5-benzenetricarboxylate, reveals the location and progressive filling of six distinct D2 sites within the nanopore structure. Location of the primary site at the coordinatively unsaturated Cu atoms provides direct structural evidence of the potential importance of such metal sites to hydrogen storage. Competitive loading of the other D2 sites proceeds with the pores filling from smallest to largest.

Storing molecular hydrogen in porous media is one of the promising avenues for mobile hydrogen storage. In order to achieve technologically relevant levels of gravimetric density, the density of adsorbed H2 must be increased beyond levels attained for typical high surface area carbons. Here, we demonstrate a strong correlation between exposed and coordinatively unsaturated metal centers and enhanced hydrogen surface density in many framework structures. We show that the MOF-74 framework structure with open Zn(2+) sites displays the highest surface density for physisorbed hydrogen in framework structures. Isotherm and neutron scattering methods are used to elucidate the strength of the guest-host interactions and atomic-scale bonding of hydrogen in this material. As a metric with which to compare adsorption density with other materials, we define a surface packing density and model the strength of the H(2-)surface interaction required to decrease the H(2)-H(2) distance and to estimate the largest possible surface packing density based on surface physisorption methods.

We present a different and efficient method for implementing the analytical solution of Ornstein-Zernike equation for two-Yukawa fluids in the mean spherical approximation. We investigate, in particular, the conditions for the formation of an extra low-Q peak in the structure factor, which we interpret as due to cluster formation in the two-Yukawa fluid when the interparticle potential is composed of a short-range attraction and a long-range repulsion. We then apply this model to interpret the small angle neutron scattering data for protein solutions at moderate concentrations and find out that the presence of a peak centered at Q=0 (zero-Q peak) besides the regular interaction peak due to charged proteins implies an existence of long-range attractive interactions besides the charge repulsion.

The investigation of metal-organic frameworks has become one of the most active areas of chemical research, owing in part to their potential utility for hydrogen storage.[1] Unlike main-group and transition-metal hydrides, which chemically bind H 2 and usually release it only at high temperatures, metal-organic frameworks and other high-surface-area adsorbents establish weak van der Waals interactions with H 2 molecules, such that uptake and release can be achieved by a simple pressure swing. Typically, H 2 adsorption enthalpies of only 5-7 kJ mol À1 characterize these weak interactions, [2] necessitating the use of cryogenic temperatures to achieve significant H 2 uptake. It has been proposed, however, that adsorption enthalpies of approximately 15 kJ mol À1 would be optimal for H 2 storage at 25 8C and at fuel-cell operating pressures of 1.5-100 bar.[3] To address the challenge of producing adsorbents with an enhanced H 2 affinity, we have undertaken efforts to generate microporous metal-organic frameworks bearing a high concentration of coordinatively unsaturated metal centers. [2a, 4] Recently, we showed that the robust, sodalite-type metalorganic framework [Mn(dmf) To probe the generality of the framework structure, reactions analogous to those employed in forming 1 [5] were attempted using the chloride salts of a series of first-row transition-metal ions (Fe 2+ -Zn 2+). The solvents used included neat dimethylsulfoxide, N,N-diethylformamide, DMF, and various combinations of these with methanol; the reaction temperatures used ranged from room temperature to 130 8C. With the exception of those with Cu 2+ ions in formamide/ methanol mixtures, the reactions afforded insoluble, amorphous solids that were not further characterized. X-ray diffraction analysis of a crystal of 2 revealed a cubic metal-organic framework structure isotypic with that of 1 (Figure 1). [6] In 2, the Cu 2+ ions of chloride-centered squareplanar {Cu 4 Cl} 7+ units are connected through the N2 and N3 atoms of tetrazolate rings from eight surrounding btt 3À ligands (Figure 1 b). In turn, each triangular btt 3À ligand is connected to three {Cu 4 Cl} 7+ squares (Figure 1 a) to generate a rare 3,8-connected network. A fundamental building unit for the structure is the truncated octahedron outlined in blue in Figure 1 c, which consists of six {Cu 4 Cl} 7+ squares and eight btt 3À ligands. Each truncated octahedron is reminiscent of a sodalite cage, and, as in sodalite, the truncated octahedra share square faces to generate the cubic framework structure. Every Cu 2+ center in the framework is octahedrally coordinated and has a single water ligand (not shown) that can potentially be removed and replaced with an H 2 molecule. The anionic charge of the framework is balanced by [Cu-(dmf) 6 ] 2+ guest cations, which are situated within the truncated octahedra, and by protons, which could not be located by X-ray diffraction, but are probably bound to the nucleophilic N1 or N4 atoms of the tetrazolate rings. Notably, a proton-balanced carboxyl...

The formation of equilibrium clusters has been studied in both a prototypical colloidal system and protein solutions. The appearance of a low-Q correlation peak in small angle scattering patterns of lysozyme solution was attributed to the cluster-cluster correlation. Consequently, the presence of long-lived clusters has been established. By quantitatively analyzing both the SANS (small angle neutron scattering) and NSE (neutron spin echo) data of lysozyme solution using statistical mechanics models, we conclusively show in this paper that the appearance of a low-Q peak is not a signature of the formation of clusters. Rather, it is due to the formation of an intermediate range order structure governed by a short-range attraction and a long-range repulsion. We have further studied dynamic features of a sample with high enough concentration at which clusters are formed in solution. From the estimation of the mean square displacement by using short-time and long-time diffusion coefficient measured by NSE and NMR, we find that these clusters are not permanent but have a finite lifetime longer than the time required to diffuse over a distance of a monomer diameter.