Crystal chemistry of the gold (I) trimer,Au(3)(NC(5)H(4))(3): formation of hourglass figures and self-association through aurophilic attraction

X-ray crystallography reveals that individual molecules of Au(3)(NC(5)H(4))(3) self-associate through aurophilic interactions into two distinct structural motifs that involve both extended chains of molecules connected by pairwise Au.Au contacts and individual Au.Au contacts and discrete dimers linked by pairwise Au.Au contacts. The colorless or pale yellow crystals are remarkable for the formation of a distinct hourglass shape within the crystals that develops after months of standing in the atmosphere or after immersion in 4 M hydrochloric acid for a few days. The hourglass figures appear to result from the deposition of gold and are unusual in being formed by a chemical reaction within a crystal rather than as a result of dying the crystal during growth.     

Anchimerically assisted redox reactions : Comparisons of the effect of transannular - OH and -NH2 group son the rate of the aqueous I2 oxidation of thioethers. Structures of the heteroatom bridged l-thioniabicyclo[3.3.1]nonane intermediates

The rate law for the aqueous I₂ oxidation of 5-amino-1-thiacyclooctane has been determined and compared with 5-hydroxy-l-thiacyclooctane. The crystal structures of the 9-aza- and 9-oxa-l-thioniabicyclo[3.3.1]nonanes formed on oxidative cyclization are compared.     

Rhodium(II) dimers: The preparation and structureof[(p-CH3C6H4NC)8Rh2I2]-[PF6]2

Oxidation of [(p-CH₃C₆H₄NC)₄Rh][PF₆] with one half mole of iodine or bromine produces [(p-CR₃C₆R₄NC)₈Rh₂X₂][PF₆]₂. The crystal structure of the iodide complex establishes the existence of a direct RhRh bond (2.785 Å) with pseudooctahedral coordination about each rhodium completed by terminal isocyanide and iodide ligands.     

Photolabile ruthenium nitrosyls with planar dicarboxamide tetradentate N(4) ligands: effects of in-plane and axial ligand strength on NO release

Four ruthenium nitrosyls, namely [(bpb)Ru(NO)(Cl)] (1), [(Me(2)bpb)Ru(NO)(Cl)] (2), [(Me(2)bpb)Ru(NO)(py)](BF(4)) (3), and [(Me(2)bqb)Ru(NO)(Cl)] (4) (H(2)bpb = 1,2-bis(pyridine-2-carboxamido)benzene, H(2)Me(2)bpb = 1,2-bis(pyridine-2-carboxamido)-4,5-dimethylbenzene, H(2)Me(2)bqb = 1,2-bis(quinaldine-2-carboxamido)-4,5-dimethylbenzene; H is the dissociable amide proton), have been synthesized and characterized by spectroscopy and X-ray diffraction analysis. All four complexes exhibit nu(NO) in the range 1830-1870 cm(-)(1) indicating the [Ru-NO](6) configuration. Clean (1)H NMR spectra in CD(3)CN (or (CD(3))(2)SO) confirm the S = 0 ground state for all four complexes. Although the complexes are thermally stable, they release NO upon illumination. Rapid NO dissociation occurs when solutions of 1-3 in acetonitrile (MeCN) or DMF are exposed to low-intensity (7 mW) UV light (lambda(max) = 302 nm). Electron paramagnetic resonance (EPR) spectra of the photolyzed solutions display anisotropic signals at g approximately 2.00 that confirm the formation of solvated low-spin Ru(III) species upon NO release. The ligand trans to bound NO namely, anionic Cl(-) and neutral pyridine, has significant effect on the electronic and NO releasing properties of these complexes. Change in the in-plane ligand strength also has effects on the rate of NO release. The absorption maximum (lambda(max)) of 4 is significantly red shifted (455 nm in DMF) compared to the lambda(max) values of 1-3 (380-395 nm in DMF) due to the extension of conjugation on the in-plane ligand frame. As a consequence, 4 is also sensitive to visible light and release NO (albeit at a slower rate) upon illumination to low-intensity visible light (lambda > 465 nm). Collectively, the photosensitivity of the present series of ruthenium nitrosyls demonstrates that the extent of NO release and their wavelength dependence can be modulated by changes of either the in-plane or the axial ligand (trans to bound NO) field strength.     

Nuclear spin-lattice and nuclear spin-spin relaxation time measurements in EuB6 at low temperatures using the spin-echo technique

Experimental results on the nuclear spin-lattice and nuclear spin-spin relaxation times in the ferromagnetic EuB₆ at temperatures below 4·2 K are presented using the external magnetic field,H _ext, in the range of 0 ⩽H _ext ⩽ 10 kG. Nuclear spin-spin relaxation time computed on the basis of the Suhl-Nakamura process turns out to be 3·2μs, which compares well with the experimental value 11·1μs obtained with the 10 kG magnetic field at 1·7 K. It is found that in the ferromagnetic EuB₆,T ₁ is approximately 5 × 10³ times larger thanT ₂ at 1·7 K with the 10 kG magnetic field. Thus the effect ofT ₁ onT ₂ can be neglected. From the experimental value ofT ₂, the value of the homogeneous line broadening is found to be 14 kHz. The corresponding value obtained from the cw method is 175 kHz. This evidently shows the presence of the inhomogeneous line broadening in the cw NMR.