The role of temperature in the synthesis of hybrid inorganic-organic materials: the example of cobalt succinates

Five different cobalt succinate materials synthesized from an identical starting mixture using temperature as the only independent variable show increasing condensation and density at higher synthesis temperatures.     

Nuclear quantum effects in calculated NMR shieldings of benzene; a Feynman path integral study

The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window.     

Single-crystal characterization of Co7(OH)6(H2O)3(C4H4O4)47H2O; A new cobalt succinate identified through high-throughput synthesis

A new form of cobalt succinate has been discovered using high-throughput methods and its structure was solved by single crystal X-ray diffraction. Co₇(C₄H₄O₄)₄(OH)₆(H₂O)₃7H₂O crystallizes in the monoclinic space group P2₁/c with cell parameters: a=7.888(2) Å, b=19.082(6) Å, c=23.630(7) Å, β=91.700(5)°, V=3555(2) Å³, R₁=0.0469. This complex structure, containing 55 crystallographically distinct non-hydrogen atoms, is compared to the previously reported nickel phase, characterized using ab initio structure solution from synchrotron powder diffraction data.     

Solid state proton spin–lattice relaxation in four structurally related organic molecules

We report and interpret the temperature dependence of the proton spin–lattice relaxation rate at 8.50 and 22.5 MHz in four polycrystalline solids composed of structurally related molecules: 2-ethylanthracene, 2-t-butylanthracene, 2-ethylanthraquinone, and 2-t-butylanthraquinone. We have been unable to grow single crystals and therefore do not know the crystal structures. Hence, we use the NMR relaxometry data to make predictions about the solid state structures. As expected, we are able to conclude that the ethyl groups do not reorient in the solid state but that the t-butyl groups do. The anthraquinones have a “simpler” structure than the anthracenes. The best dynamical models suggest that there is a unique crystallographic site for the t-butyl groups in 2-t-butylanthraquinone and two sites, each with half the molecules, for the ethyl groups in 2-ethylanthraquinone. There are also two sites in 2-ethylanthracene, but with unequal weights, suggesting four sites in the unit cell with lower symmetry than the two anthraquinones. Finally, the observed relaxation rate data in 2-t-butylanthracene is very complex and its interpretation demonstrates the uniqueness problem that arises in interpreting relaxometry data without the knowledge of the crystal structure.     

Volatile sulfur compounds in Cheddar cheese determined by headspace solid-phase microextraction and gas chromatograph-pulsed flame photometric detection

The aim of this study was to develop a methodology for the analysis of volatile sulfur compounds (VSCs) in Cheddar cheese. Solid-phase microextraction (SPME) was employed to extract VSCs from the cheese matrix using a CAR-PDMS fiber. This extraction method was combined with gas chromatography-pulsed flame photometric detection (GC-PFPD) to achieve high sensitivity for sulfur compounds. The impact of extraction parameters, including time, temperature and sample size, was evaluated to determine the best conditions to analyze sulfur compounds in Cheddar cheese. Hydrogen sulfide, methanethiol, and dimethyl sulfide were found to constitute the majority of the overall sulfur profile while dimethyl disulfide and dimethyl trisulfide were present in lesser amounts. Artifact formation of volatile sulfur compounds was found to be minimal. Two commercial cheese samples were analyzed and differences in sulfur content were observed. Overall, SPME-GC-PFPD was found to be a highly sensitive technique for the analysis of sulfur compounds in Cheddar cheese.