Effect of temperature on the adsorption of water in porous carbons

We report experimental and simulation studies to investigate the effect of temperature on the adsorption isotherms for water in carbons. Adsorption isotherms are measured by a gravimetric technique in carbon-fiber monoliths at 378 and 423 K and studied by molecular simulation in ideal carbon pores in the temperature range 298-600 K. Experimental adsorption isotherms show a gradual water uptake, as the pressure increases, and narrow adsorption-desorption hysteresis loops. In contrast, simulated adsorption isotherms at room temperature are characterized by negligible uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. As the temperature increases, the relative pressure at which pore filling occurs increases and the size of the hysteresis loop decreases. Experimental adsorption-desorption hysteresis loops are narrower than those from simulation. Discrepancies between simulation and experimental results are attributed to heterogeneities in chemical composition, pore connectivity, and nonuniform pore-size distribution, which are not accounted for in the simulation model. The hysteresis phase diagram for confined water is obtained by recording the pressure-density conditions that bound the simulated hysteresis loop at each temperature. We find that the hysteresis critical temperature, i.e., the lowest temperature at which no hysteresis is detected, can be hundreds of degrees lower than the vapor-liquid critical temperature for bulk model water. The properties of confined water are discussed with the aid of simulation snapshots and by analyzing the structure of the confined fluid.     

Engineering silver(I) coordination networks through hydrogen bonding

The silver(I) coordination networks [Ag2(mu-O2CCF3)2(mu-NN)2](infinity) exist as a polymer of macrocycles or a double-stranded polymer when NN = 1,2-C6H4[NHC(O)-4-C5H4N]2 or 1,2-C6H4[NHC(O)-3-C5H4N]2, respectively. Crystal engineering of the polymers is achieved through interchain hydrogen bonds.     

Ring-opening polymerization of gold macrocycles and self-assembly of a coordination polymer through hydrogen-bonding

The equilibrium between digold and tetragold rings and a ring-opened oligomer and polymer is established by NMR and ESI-MS studies in solution and by structure determinations in the solid state; the polymer containing amide-derivatized ligands undergoes self-assembly through hydrogen bonding to give an ordered network.     

Optical constants and integrated intensities of liquid hexafluorobenzene between 4000 and 250 cm at 25 °C

The optical constants (real and imaginary refractive indices) of hexafluorobenzene were determined at 25 °C via transmission measurements. Experimental absorbance spectra measured on a Nicolet Impact 410 FTIR were converted to imaginary refractive indices using methods described in the literature. The real refractive indices were obtained by Kramers–Kronig transformation of the imaginary refractive indices. From the complex refractive indices, the molar absorption coefficient (E_m) and complex molar polarizability spectra were calculated. The integrated intensities for the E_1u fundamentals were obtained from the areas under the bands in the spectrum. These integrated intensities are compared to those for benzene and benzene-d₆ in the literature.     

Synthesis and characterisation of triselenocarbonate [CSe3]2- complexes

[Pt(CSe3)(PR3)2] (PR3= PMe3, PMe2Ph, PPh3, P(p-tol)3, 1/2 dppp, 1/2 dppf) were all obtained by the reaction of the appropriate metal halide containing complex with carbon diselenide in liquid ammonia. Similar reaction with [Pt(Cl)2(dppe)] gave a mixture of triselenocarbonate and perselenocarbonate complexes. [{Pt(mu-CSe3)(PEt3)}4] was formed when the analogous procedure was carried out using [Pt(Cl)2(PEt3)2]. Further reaction of [Pt(CSe3)(PMe2Ph)2] with [M(CO)6] (M = Cr, W, Mo) yielded bimetallic species of the type [Pt(PMe2Ph)2(CSe3)M(CO)5] (M = Cr, W, Mo). The dimeric triselenocarbonate complexes [M{(CSe3)(eta5-C5Me5)}2] (M = Rh, Ir) and [{M(CSe3)(eta6-p-MeC6H4(i)Pr)}2] (M = Ru, Os) have been synthesised from the appropriate transition metal dimer starting material. The triselenocarbonate ligand is Se,Se' bidentate in the monomeric complexes. In the tetrameric structure the exocyclic selenium atoms link the four platinum centres together.