Three new dinuclear bis-μ-azido-bridged Cu(II) compounds with di-2-pyridylamine as a ligand: Syntheses,X-ray structure and magnetic measurements

Three new dinuclear copper(II) compounds: [Cu₂(dpyam)₂(μ_1,1-N₃)₂(O₂CH)₂] (1), [Cu₂(dpyam)₂(μ_1,1-N₃)₂(O₂CCH₃)₂] (2) and [Cu₂(dpyam)₂(μ_1,1-N₃)₂(O₂CCH₂CH₃)₂] (3) have been synthesized and characterized crystallographically and spectroscopically. Compounds 1, 2 and 3 consist of a dinuclear unit in which both Cu(II) ions are connected through two end-on azido bridges providing a distorted square pyramidal geometry with a CuN₄O chromophore. The Cu?Cu separations are 3.195, 3.200 and 3.247 Å for compounds 1, 2 and 3, respectively. The magnetic properties have been measured in the range from 5 to 300 K and correlated with the molecular structures. All three compounds show a medium to weak ferromagnetic exchange interactions between the Cu(II) ions dominated by the bridging azido ligands, with a singlet-triplet splitting (J) of 63.3, 63.8 and 5.1 cm⁻¹, for compounds 1, 2 and 3, respectively. A large zero-field splitting of about 0.4 cm⁻¹ is observed in the EPR for compounds 1 and 2.     

New series of triply bridged dinuclear Cu(II) compounds: synthesis, crystal structure, magnetic properties, and theoretical study

Five new triply bridged dinuclear Cu(II) compounds have been synthesized, and their magnetic properties have been measured and characterized. The magnetic coupling constants (J) of these compounds plus a previously structurally characterized compound of the same type have been derived by appropriate fitting of the experimentally measured molar susceptibility variation with the temperature. Two of the compounds are ferromagnetically coupled, and three are antiferromagnetically coupled with J values in the [+150, -40] cm(-1) range. The validity of the structural aggregate Addison's parameter as a qualitative magneto-structural correlation is confirmed. The origin of the magnetic interactions and the magnitude of the magnetic coupling have been analyzed by means of density functional theory-based calculations using a variety of state of the art exchange-correlation potentials. It is shown that the long-range separated LC-ωPBE provides the overall best agreement with experiment for this family as well as for a set of previously reported hetero triply bridged dinuclear Cu(II) compounds, especially for ferromagnetic systems.     

A novel approach for the synthesis of lophocladines A, B and C1 analogues

A novel approach for the syntheses of lophocladines A and B has been developed. These compounds were prepared in 4-6 steps with moderate to excellent overall yields. The key step involved the nucleophilic substitution of 4-chloronicotinic acid with the carbanion generated from phenylacetonitrile. Subsequent reduction of the cyano group, lactamization and oxidation furnished lophocladine A in 50% yield over 4 steps. Further amination with various amines led to lophocladine B and its C1 analogues in good yields. In addition, the synthesized compounds were evaluated for their cytotoxicity against leukaemia cells.     

Novel C3v-symmetrical N7-Hexahomotriazacalix[3]cryptand: a highly efficient receptor for halide anions

[structure: see text] We report the synthesis of a novel C(3)(v)()-symmetrical N(7)-hexahomotriazacalix[3]cryptand (1). Compound 1 was shown to be in a fixed cone conformation by (1)H NMR spectroscopy and X-ray single-crystal structure determination. Complexation studies showed that 1 is a selective receptor for halide ions. The effects of zinc metal cation on the receptor (1-Zn(2+)) upon anion recognition are also shown.     

Crystal Structure of Curcumenol: Evidence of Asymmetric O–H...O (bridged) Hydrogen-Bonded Closed Dimer

Curcumenol, C₁₅H₂₂O₂, was isolated from Globba malaccensis Ridl. The compound was crystallized from ethylacetate/hexane solution in the monoclinic system, space group C2, with cell dimensions a = 16.8467(4) , b = 7.6799(2) , c = 11.8613(10) , = 115.9970(10)°. The molecules form a distorted centrosymmetric dimer linked by hydrogen bonds between the hydroxyl O2 atom and the bridged O1 ether atom (O2...O1(–x+2, y, –z+1), 2.8297(15) ; (O2–H2O–O1), 169(2)°). This is an interesting example of an O–H...O (bridged ether) asymmetric hydrogen-bonded dimer.     

Solvent-assisted mechanochemical synthesis of metal complexes

The application of solvent-assisted mechanochemical synthesis to the study of metal complex formation is illustrated by examples involving complexes of silver halides with ethylenethiourea.     

Conformation-selective synthesis and binding properties of N-benzylhexahomotriaza-p-chlorocalix[3]trinaphthylamide

N-benzylhexahomotriaza-p-chlorocalix[3]trinaphthylamide in partial cone conformation was selectively synthesized by appropriately controlling the steric effect during the amidation reactions of N-benzylhexahomotriaza-p-chlorocalix[3]tri(ethyl acetate) in cone or partial cone conformations with use of 1-aminomethylnaphthalene. The conformation was confirmed by (1)H, (13)C, and 2D NMR and X-ray single-crystal analysis. Analyses of the complexes revealed that recognition is strongly affected by Cd(2+), Pb(2+), and F(-) ions.     

X-ray guided H NMR analysis of pinched cone calix[4]arenes

The analysis of structural parameters of azobenzene- and stilbene-bridged calix[4]arene obtained from AM1 calculation are in good agreement with those obtained from X-ray crystallography. The bridge longer than 9.0 Å such as p,p-trans-azobenzene and p,p-trans-stilbene cannot be constructed over the narrow rim of calix[4]arene through two ethylene oxide linkers. The m,m-stilbene bridge is the most promising photo switch because its shorter cis stereoisomer (5.85 Å) allows calix[4]arene to assume the perfect cone conformation, whilst its longer trans stereoisomer (8.00 Å) forces calix[4]arene to adapt a pinched cone conformation. The pinched cone conformation has longer distances between the neighbouring phenoxyl groups causing the weaker intramolecular hydrogen bonding and the upfield shifts of the phenolic proton signals to below 7.00 ppm. This upfield shift is useful for quick identification of pinched cone conformation of new calix[4]arene compounds.