Infrared spectroelectrochemistry has been utilized to explore the vibrational properties of the high-nuclearity platinum carbonyl clusters [PtM(CO)3o]", [Pt26(CO)32]", and [Pt38(CO)44]" as a function of the charge n in dichloromethane, acetonitrile, acetone, tetrahydrofuran, and methanol. The clusters exhibit unusually reversible voltammetric and spectroelectrochemical behavior, with a sequence of redox steps spanning = 0 to (in one case) -10, having formal potentials, E¡, between ca. 0.5 and -2.5 V vs ferrocenium-ferrocene. Largely two-electron steps are observed for [Pt26(CO)32]", involving even-charge states ( = -2, -4, -6, -8, -10). Sequential one-electron steps are found for [Pt24(CO)30]" and [Pt38(CO)44]", although the regions of electrode potential over which odd-charge states (n = -1, -3, -5, -7) are stable (i.e., the spacings between E( values) are markedly smaller than those for the even-charge states. The C-O stretching frequencies for the bridging (veo) and especially the terminal (v'co) coordinated CO ligands decrease systematically as n becomes more negative; for example, t>c0 for [Pt24(CO)30]" diminishes by 15-20 cm-1 per added electron. The observation of such remarkable charge-dependent spectral properties for these large and structurally well-defined platinum clusters invites comparisons with the potential (and consequent charge)-dependent properties of CO adlayers at corresponding platinum electrode-solution interfaces. The latter systems also display decreases in veo and veo as the electrode potential, E, and hence the surface charge is made more negative, as usually ascribed either to increased dir(Pt) -* ir*(CO) backbonding or to a Stark effect. The vlco-E slopes for saturated CO adlayers at both single-crystal and polycrystalline Pt-nonaqueous interfaces are noticeably smaller than for the corresponding solvated Pt carbonyl clusters, the latter being adjudged from the vco~£f behavior. These differences are due chiefly to larger "effective surface" capacitances (i.e., charge-£f dependencies) for the clusters than those measured for the electrode-solution interfaces. Such differing capacitances can largely be accounted for by a simple geometric electrostatic model. When the ylco values are plotted versus the electronic charge per surface Pt atom ("surface charge density"), however, an essentially uniform y'co-charge dependence is observed for the different Pt clusters, with similar behavior being obtained for the Pt electrodes. These comparisons provide an intriguing link between the electronic and bonding properties of such large ionizable metal clusters with those of chargeable metal surfaces.

Europe PMC Funders Group Europe PMC Funders Author Manuscripts Europe PMC Funders Author ManuscriptsBackground & Aims-Identifying shared and disease-specific susceptibility loci for Crohn's disease (CD) and ulcerative colitis (UC) would help define the biologic relationship between the inflammatory bowel diseases. More than 30 CD susceptibility loci have been identified. These represent important candidate susceptibility loci for UC. Loci discovered by the index genome scans in CD have previously been tested for association with UC, but those identified in the recent meta-analysis await such investigation. Furthermore, the recently identified UC locus at ECM1

A solid understanding of the molecular-level mechanisms responsible for zeolite crystallization remains one of the most challenging issues in modern zeolite science. Here we investigated the formation pathway for high-silica LTA zeolite crystals in the simultaneous presence of tetraethylammonium (TEA(+)), tetramethylammonium (TMA(+)), and Na(+) ions as structure-directing agents (SDAs) with the goal of better understanding the charge density mismatch synthesis approach, which was designed to foster cooperation between two or more different SDAs. Nucleation was found to begin with the formation of lta-cages rather than the notably smaller sod and d4r-cages, with concomitant incorporation of TMA(+) and Na(+) into a very small amount of the solid phase with a low Si/Al ratio (ca. 2.5). The overall characterization results of our work demonstrate that sod-cages are first built around the preorganized lta-cages and that d4r-cages are in turn constructed by the progressive addition of low-molecular-weight (alumino)silicate species, which promotes the formation and growth of embryonic LTA zeolite crystals. We also show that the crystal growth may take place by a similar process in which TEA(+) is also incorporated, forming a single LTA zeolite phase with a higher Si/Al ratio (ca. 3.3).

Conventional (e.g. MgH 2 ) and complex hydrides (e.g. alanates, borohydrides, and amides) are the two primary classes of solid-state hydrogen-storage materials. [1][2][3] Many of these "high-density" hydrides have the potential to store large amounts of hydrogen by weight (up to 18.5 wt % for LiBH 4 ) and/or volume (up to 112 g L À1 for MgH 2 ), values that are comparable to the hydrogen content of gasoline (15.8 wt %, 112 g L À1 ). However, all known hydrides are inadequate for mobile storage applications due to one or more of the following limitations: a) unfavorable thermodynamics (they require high temperatures to release hydrogen [4] ), b) poor kinetics (low rates of hydrogen release and uptake), c) decomposition pathways involving the release of undesirable by-products (e.g. ammonia), and/or d) an inability to reabsorb hydrogen at modest temperatures and pressures (i.e. "irreversibility").In spite of these drawbacks, renewed interest in complex hydrides has been stimulated recently by substantial improvements in their kinetics and reversibility [5,6] provided by catalytic doping (e.g. TiCl 3 -doped NaAlH 4 ), [7,8] and by thermodynamic enhancements achieved through reactive binary mixtures [9] such as LiNH 2 /MgH 2 , [10,11] LiBH 4 /MgH 2 , [12] and LiNH 2 /LiBH 4 . [13,14] These compositions, previously termed "reactive hydride composites", [15] represent the state-of-the-art in hydrogen-storage materials; compared to their constituent compounds, they exhibit improved thermodynamic properties, higher hydrogen purity, and, in some cases, reversibility. The desorption behavior of these previously studied composites is illustrated in Figure 1 a. It is evident from the hydrogen desorption profile (top panel) that the composites generally desorb hydrogen at significantly lower temperatures than their individual components. For example, the lowest temperature reaction, which involves a Figure 1. a) Hydrogen (top) and ammonia (bottom) kinetic desorption data as a function of temperature (5 8C min À1 to 550 8C) for the ternary composition (blue trace) and its unary and binary constituents. Hydrogen desorption is measured in weight percent (wt %) to 1 bar whereas relative ammonia release is measured as partial pressure (torr) in a flow-through set-up (100 sccm Ar). b) Ternary phase space defined by unary compounds (nodes), LiBH 4 (pink), MgH 2 (purple), and LiNH 2 (orange) and the binary mixtures (edges), LiBH 4 /MgH 2 (gray), MgH 2 / LiNH 2 (green), and LiNH 2 /LiBH 4 (red). The present ternary composition, which is a 2:1:1 mixture of LiNH 2 , LiBH 4 , and MgH 2 , and previously investigated binaries, are identified.