ABSTRACT
The inclusion properties of a calixarene-based porous material have been studied to investigate the adsorption and the desorption of carbon tetrachloride, chloroform, and water in the zeolite-like structure. Uptake and release processes have been studied both by time-resolved powder X-ray diffraction and by thermogravimetric analysis to obtain structural and kinetic information. The selected guests are able to enter the structure with an increase in the host cell volume and with time-dependent diffusivity coefficients. Chloroform molecules act as a permanent porosity switch promoting a phase transition to non-porous triclinic form.
ABSTRACT
Tunable single-molecule magnets: The spin-level landscape in a series of Fe(III) (4) single-molecule magnets with propeller-like structure was analyzed by means of high-frequency EPR spectroscopy. The zero-field splitting parameter D of the ground S=5 spin state correlates strongly with the pitch of the propeller gamma (see picture), and thus provides a simple link between molecular structure and magnetic behavior.We report three novel tetrairon(III) single-molecule magnets with formula [Fe(4)(L)(2)(dpm)(6)] (Hdpm=2,2,6,6-tetramethylheptane-3,5-dione), prepared by using pentaerythritol monoether ligands H(3)L=R'OCH(2)C(CH(2)OH)(3) with R'=allyl (1), (R,S)-2-methyl-1-butyl (2), and (S)-2-methyl-1-butyl (3), along with a new crystal phase of the complex containing H(3)L=11-(acetylthio)-2,2-bis(hydroxymethyl)- undecan-1-ol (4). High-frequency EPR (HF-EPR) spectra at low temperature were collected on powder samples in order to determine the zero-field splitting (zfs) parameters in the ground S=5 spin state. In 1-4 and in other eight isostructural compounds previously reported, a remarkable correlation is found between the axial zfs parameter D and the pitch gamma of the propeller-like structure. The relationship is directly demonstrated by 1, which features both structurally and magnetically inequivalent molecules in the crystal. The dynamics of magnetization has been investigated by ac susceptometry, and the results analyzed by master-matrix calculations. The large rhombicities of 2 and 3 were found to be responsible for the fast magnetic relaxation observed in the two compounds. However, complex 3 shows an additional faster relaxation mechanism which is unaccounted for by the set of spin Hamiltonian parameters determined by HF-EPR.
ABSTRACT
Amberlite IRA900N3 is an excellent organocatalyst for the azidation of alpha,beta-unsaturated ketones with trimethylsilyl azide under solvent-free conditions. By avoiding the use of metallic species and of the organic reaction medium, the procedure is a green tool for the preparation of beta-azido ketones under mild conditions with yields from good to excellent. The catalyst can be recovered and re-used with no loss of its efficiency.
Subject(s)
Azides/chemistry , Ketones/chemistry , Catalysis , Solvents/chemistryABSTRACT
[structure: see text]. The first examples of selectively functionalized calix[7]arenes have been obtained by weak-base promoted O-alkylation or O-benzoylation of p-tert-butylcalix[7]arene. Mono-, 1,3- and 1,4-disubstituted calix[7]arenes have been obtained in workable yields, while the 1,2,4,6-tetrasubstitution was achieved with surprisingly high selectivity (50-88% yield) by using K2CO3 as base. A rationale for this finding is proposed.
