Journal of Supramolecular Chemistry最新文献

The coordination polymeric compounds, M(2APM)₂Ni(CN)₄ (where M=Mn, Co, Ni or Cd; 2APM=2-aminopyrimidine) have been prepared for the first time and their FT-IR spectra are reported in the 400–4000 cm⁻¹ region. The spectral features suggest that the compounds are similar in structure to the Hofmann type two dimensional coordination polymeric compounds, formed with Ni(CN)₄⁻² ions bridged by M(2APM)₂⁺² cations. 2APM is coordinated to M(II) through one of the pyrimidine ring nitrogen atoms; the amino group is not involved in the complex formation. The coordination effect on the 2APM vibrational wavenumbers is analysed.

The new lattice inclusion host 6α,13α-dibromo-2,9-dichloro-5bα,6,12bα,13-tetrahydropentaleno[1,2-b:4,5-b′]diquinoline 8 was prepared, and found to include far fewer guests than its non-chlorinated analogue 2. Compounds (8)₂·(ethyl acetate) and (8)₂·(benzene) form molecular pen and staircase inclusion compounds respectively. Their X-ray structures are analysed and compared in crystal engineering terms.

A derivative of the metal dibenzoylmethanate (DBM) host type, accomplished through the chemical modification of the DBM ligand, is reported for the first time. The new ligand, (1-naphthoyl)benzoylmethanate (NBM) differs from the parent DBM by an additional phenylene ring. Three new complexes [NiA₂(NBM)₂], with pyridine (Py), 4-methylpyridine (4-MePy) and 4-phenylpyridine (4-PhPy) is A, were synthesized and studied for host properties. Complexes with Py and 4-MePy were isolated as solvent-free forms and did not show any ability to form inclusion compounds with ten solvents tested. Single-crystal XRD study revealed van der Waals type of crystal structure of the complexes. The nickel atom is octahedrally coordinated by two chelating NBMs in the equatorial plane and two terminal pyridines. Naphthyl ligands turn almost perpendicular to the equatorial plane of the complex filling the pocket space which usually accommodates guest species in metal DBM analogues. This ‘self-inclusion’ of its own fragment, that the molecule demonstrates, explains the inability of the complexes to entrap guest solvents. The complex with 4-PhPy forms inclusion compounds with chloroform, benzene, tetrahydrofuran and acetone, the compounds have 1:2 host to guest ratio and are isostructural. A possible explanation of such a difference is the larger size of the pocket which now cannot be completely filled with the naphthyl fragment.

The stretching vibrations of methane in the small and large cavity of structure I clathrate hydrate have been studied with ab initio molecular dynamics using a linear scaling pseudopotential density functional method. The vibrational density of states, obtained by Fourier transform of the atom velocity autocorrelation function, show complicated profiles caused by symmetry lowering and effects of non-vanishing electrostatic potential inside the clathrate cages. The calculated C–H stretching vibrations are lower than in the free molecule. Furthermore, the vibrational frequencies in the large cage are shifted to lower frequency with respect to the small cage. The theoretical predictions are in complete agreement with experiment. These theoretical findings, along with recent experimental measurements do not reveal local minima inside the cavities that may enhance the guest–host interactions as would have suggested by the ‘loose cage–tight cage’ Charles–Pimentel model.

Stability boundary for the nitrogen hydrate system is investigated in a temperature range from 285 to 310 K and pressure range up to 440 MPa. The present experimental results show that nitrogen hydrates form structure-II without any solid–solid phase transition in the present experimental conditions. The strong pressure dependence of intermolecular O–O vibration reveals that hydrate cage is shrunk by pressurization.