Three new metal coordination polymers of bifunctional imidazolate/tetrazolate bridges: the only example of a three-dimensional framework based on rare [Co4(μ3-OH)2(μ2-Cl)2]4+ mixed oxo-chloro-clusters

Three new metal coordination polymers [Ni(μ2-L)2(H2O)2] n (1, HL = 1-tetrazole-4-imidazole-benzene), [Co(μ2-L)2] n (2), and [Co4(μ3-OH)2(μ2-Cl)2(μ5-L)2(μ2-L)2] n ·7nH2O (3) were hydrothermally synthesized and structurally characterized. 1 displays a neutral [Ni(μ2-L)2(H2O)2] n chain built up from the Ni2+ ions bridged by deprotonated L- ligands, while 2 shows another rare neutral [Co(μ2-L)2] n chain based on Co2+ ions connected by two different coordination modes of the L- ligand. 3 exhibits a rare [Co4(μ3-OH)2(μ2-Cl)2]4+ mixed oxo-chloro-cluster-based three-dimensional framework with large elliptical channels, which are filled by unprecedented chilopod [(H2O)7] n chains. Both 1 and 2 show antiferromagnetic behavior, while 3 exhibits unusual spin-canting.

Phase transitions of amorphous solid acetone in confined geometry investigated by reflection absorption infrared spectroscopy

We investigated the phase transformations of amorphous solid acetone under confined geometry by preparing acetone films trapped in amorphous solid water (ASW) or CCl4. Reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) were used to monitor the phase changes of the acetone sample with increasing temperature. An acetone film trapped in ASW shows an abrupt change in the RAIRS features of the acetone vibrational bands during heating from 80 to 100 K, which indicates the transformation of amorphous solid acetone to a molecularly aligned crystalline phase. Further heating of the sample to 140 K produces an isotropic solid phase, and eventually a fluid phase near 157 K, at which the acetone sample is probably trapped in a pressurized, superheated condition inside the ASW matrix. Inside a CCl4 matrix, amorphous solid acetone crystallizes into a different, isotropic structure at ca. 90 K. We propose that the molecularly aligned crystalline phase formed in ASW is created by heterogeneous nucleation at the acetone-water interface, with resultant crystal growth, whereas the isotropic crystalline phase in CCl4 is formed by homogeneous crystal growth starting from the bulk region of the acetone sample.

Adsorption of acetaldehyde on ice as seen from computer simulation and infrared spectroscopy measurements

Detailed investigation of the adsorption of acetaldehyde on I(h) ice is performed under tropospheric conditions by means of grand canonical Monte Carlo computer simulations and compared to infrared spectroscopy measurements. The experimental and simulation results are in a clear accordance with each other. The simulations indicate that the adsorption process follows Langmuir behavior in the entire pressure range of the vapor phase of acetaldehyde. Further, it was found that the adsorption layer is strictly monomolecular, and the adsorbed acetaldehyde molecules are bound to the ice surface by only one hydrogen bond, typically formed with the dangling H atoms at the ice surface, in agreement with the experimental results. Besides this hydrogen bonding, at high surface coverages dipolar attraction between neighboring acetaldehyde molecules also contributes considerably to the energy gain of the adsorption. The acetaldehyde molecules adopt strongly tilted orientations relative to the ice surface, the tilt angle being scattered between 50° and 90° (i.e., perpendicular orientation). The range of the preferred tilt angles narrows, and the preference for perpendicular orientation becomes stronger upon saturation of the adsorption layer. The CH(3) group of the acetaldehyde molecules points as straight away from the ice surface within the constraint imposed by the tilt angle adopted by the molecule as possible. The heat of adsorption at infinitely low coverage is found to be -36 ± 2 kJ/mol from the infrared spectroscopy measurement, which is in excellent agreement with the computer simulation value of -34.1 kJ/mol.

Adsorption, diffusion, dewetting, and entrapment of acetone on Ni(111), surface-modified silicon, and amorphous solid water studied by time-of-flight secondary ion mass spectrometry and temperature programmed desorption

Interactions of acetone with the silicon surfaces terminated with hydrogen, hydroxyl, and perfluorocarbon are investigated; results are compared to those on amorphous solid water (ASW) to gain insights into the roles of hydrogen bonds in surface diffusion and hydration of acetone adspecies. The surface mobility of acetone occurs at ∼60 K irrespective of the surface functional groups. Cooperative diffusion of adspecies results in a 2D liquid phase on the H- and perfluorocarbon-terminated surfaces, whereas cooperativity tends to be quenched via hydrogen bonding on the OH-terminated surface, thereby forming residues that diffuse slowly on the surface after evaporation of the physisorbed species (i.e., 2D liquid). The interaction of acetone adspecies on the non-porous ASW surface resembles that on the OH-terminated Si surface, but the acetone molecules tend to be hydrated on the porous ASW film, as evidenced by their desorption during the glass-liquid transition and crystallization of water. The roles of micropores in hydration of acetone molecules are discussed from comparison with the results using mesoporous Si substrates.

Inverse temperature dependence of Henry's law coefficients for volatile organic compounds in supercooled water

Upon supercooling, water expels volatile organic compounds (VOC), and Henry's law coefficients are increasing concomitant with decreasing temperature. This unexpected observation was found by measuring the VOC partitioning between supercooled water and gas phase in the temperature range from -5 degrees C to -15 degrees C for benzene, toluene, ethlybenzene, m-, p-, o-xylenes (BTEX), methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE). Aqueous standard solutions were analyzed using a static headspace method in combination with gas chromatography/mass spectrometry (GC/MS). Dimensionless Henry's law coefficients (K(AW)) were calculated from measurements of the concentration of the VOCs in the headspace above the standard solutions at temperatures between -25 degrees C and 25 degrees C. The results show that the well known temperature dependence of Henry's law coefficients at temperatures above 0 degrees C is inversed upon decreasing the temperature below 0 degrees C and formation of supercooled water while decreasing the temperature to -15 degrees C. Upon further decrease of the temperature to -25 degrees C freezing of the supercooled water occurs. K(AW) values increase from 0.092 (benzene), 0.099 (toluene), 0.098 (ethylbenzene), 0.117 (m/p-xylene), 0.076 (o-xylene), 0.012 (MTBE) and 0.014 (ETBE at 5 degrees C to 0.298 (benzene), 0.498 (toluene), 0.944 (ethylbenzene), 0.327 (m/p-xylene), 0.342 (o-xylene), 0.029 (MTBE) and 0.041 (ETBE) at -25 degrees C, respectively. Inversion of Henry coefficients upon cooling the aqueous solutions to temperatures below 0 degrees C is explained by the increasing formation of ice-like clusters in the water below 0 degrees C. The VOC are expelled from these clusters resulting in enhanced VOC concentrations in the gas phase upon supercooling. Formation of ice upon further cooling to -25 degrees C results in a further increase of the VOC concentrations in the gas phase above the ice. The findings have implications for the partitioning of VOC in clouds between the gas phase, supercooled water droplets, aerosol particles and ice.