M(R-dmet)2] bis(1,2-dithiolenes): a promising new class intermediate between [M(dmit)2] and [M(R,R'-timdt)2] (M = Ni, Pd, Pt)

We report the first examples of metal dithiolenes belonging to the class [M(R-dmet)(2)] [R-dmet = formally monoreduced N-substituted thiazolidine-2,4,5-trithione; R = Et, M = Ni (1), Pd (2), Pt (3)]. A comparative spectroscopic, electrochemical, and density functional theory theoretical investigation indicates that [M(R-dmet)(2)] complexes show features intermediate between those of the dithiolenes belonging to the previously reported classes [M(R,R'-timdt)(2)] and [M(dmit)(2)] (R,R'-timdt = formally monoreduced N,N'-disubstituted imidazolidine-2,4,5-trithione; dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato). UV-vis-near-IR spectroscopy and cyclic voltammetry/differential pulsed voltammetry measurements performed on 1 and 3 proved that the new dithiolenes are stable as neutral, monoanionic, and bianionic species and feature a near-IR electrochromic absorption falling at about 1000 and 1250 nm for neutral and monoanionic species, respectively.     

Photoinduced electroreduction of chlorophyllide on alkanethiol-coated mercury

Monolayers of n-alkanethiols of chain length from C12 to C18 were self-assembled on a hanging mercury drop electrode, and a film of chlorophyllide (Chlide) was adsorbed on top of them. The reduction photocurrents following illumination of the Chlide film were measured over the potential range in which the Chlide is electroinactive in the dark, and their action spectra were determined. Plotting the derivative of the photocurrents with respect to the applied potential against potential yields bell-shaped curves that can be fitted to a Gaussian. The potential of the Gaussian maximum was used to determine the reorganization energy lambda for the Chlide electroreduction process. An increase in the thiol chain length causes lambda to decrease regularly and the photocurrent to decay exponentially with the monolayer thickness, with a decay constant beta of about 0.17 A(-1).     

Binuclear wirelike dimers based on ruthenium(II)-bipyridine units linked by ethynylene-oligothiophene-ethynylene bridges

The syntheses, structural characteristics, electrochemical behavior, ground-state spectra, photophysical properties, and transient absorption (TA) spectra in CH(3)CN solvent are reported for binuclear [(bpy)(2)Ru(bpy-E(T)(n)()E-bpy)Ru(bpy)(2)](4+) complexes, Ru(bpyT(n)bpy)Ru, where the Ru-based units are connected by alternating 3,4-dibutylthiophene (DBT')/thiophene (T') fragments linked via ethynyl groups (E) to bpy ligands at the 5-position (bpy is 2,2'-bipyridine). The ligand bpyT(3)bpy represents a module containing DBT'/T'/DBT' subunits, and bpyT(5)bpy accounts for a DBT'/T'/DBT'/T'/DBT' pattern. The syntheses and electrochemical and spectroscopic (emission and TA) properties in CH(2)Cl(2) solvent of the bpyT(n)()bpy ligands are likewise reported. The behavior of the Ru(bpyT(n)bpy)Ru dimers has been compared to that of the bpyT(n)bpy ligands and to that of a related mononuclear complex, [(bpy)(2)Ru(bpy-E-DBT')](2+), Ru(bpyDBT'). For the dimeric complexes, the electrochemical results show that the first reduction step takes place at the bpy ligand(s) bearing an ethynylene group, the first oxidation step is thiophene-centered, and further oxidation involves the metal centers, which are only weakly interacting. The photophysical and TA results for the Ru(bpyT(n)bpy)Ru dimers account for the presence of low-lying oligothiophene-centered (3)pi,pi levels, while higher-lying metal-ligand charge transfer ((3)MLCT) levels are thermally accessible only for the case of Ru(bpyT(3)bpy)Ru; the possible role of charge separation (CS) levels (from oxidation at the thiophene bridge and reduction at one of the coordinated bpy's) is also discussed.     

An infrared spectroscopic investigation on N-methyl-1,3-thiazolidine-2-thione and -2-selone

An infrared investigation cm N-methyl-1,3-thiazolidine-2-thione and -2-selone in the range 4000-200 cm^?1 is reported. The v CS and v CSe vibrations give contributions to the absorptions around 1000 cm^?1 and below 600 cm^?1. The assignments are supported by comparison of their ir spectra with those of S- and Se-methiodides. The π-bond orders of the thio- and seleno-ketonic links in these compounds are higher than those found for 1,3-imidazolidine-2-thione and -2-selone.     

Determination of calcium,strontium and barium in single crystals of alkali halides by neutron activation

The determination by neutron activation of trace quantities of calcium, strontium and barium in single crystals of alkali halides has been studied. The matrix is eliminated before the irradiation by an ion-exchange procedure. Gamma spectroscopy after radiochemical separation is used to determine strontium and barium. Calcium is determined by measuring the β-activity of ⁴⁹Sc formed by the decay of ⁴⁹Ca. Long-lived radioactive tracers are used to determine the chemical yields.     

Synthesis, Electrochemistry and Crystal Structure of the [Ni36Pt4(CO)45]6− and [Ni37Pt4(CO)46]6− Hexaanions

The [Ni₃₆Pt₄(CO)₄₅]^6- and [Ni₃₇Pt₄(CO)₄₆]^6- clusters have been obtained in mixture upon reaction in acetonitrile of [Ni₆(CO)₁₂]^2- salts with K₂PtCl₄ in a 2.5:1 molar ratio. The two hexaanions were indistinguishable by spectroscopic techniques. Crystallization of their trimethylbenzylammonium salts led to crystals of composition 0.5[NMe₃CH₂Ph]₆[Ni₃₆Pt₄(CO)₄₅]-0.5[NMe₃CH₂Ph]₆[Ni₃₇Pt₄(CO)₄₆]·C₃H₈O, hexagonal,space group P6₃ (No. 173), a=17.853(9), c=27.127(13) Å, Z=2; final R=0.057. The metal core of the [Ni₃₆Pt₄(CO)₄₅]^6- anion consists of a Pt₄ tetrahedron fully encapsulated in a shell of 36 Ni atoms belonging to a very distorted and incomplete ₅ tetrahedron. The [Ni₃₇Pt₄(CO)₄₆]^6- hexaanion derives from the former by capping the unique triangular face of the metal polyhedron with an additional Ni(CO) fragment. The [Ni₃₆Pt₄(CO)₄₅]^6--[Ni₃₇Pt₄(CO)₄₆]^6- mixture is rapidly degraded to the known [Ni₉Pt₃(CO)₂₁]^4- cluster by exposure to carbon monoxide. Its reaction with protic acids initially affords the corresponding [H_6-nNi₃₆Pt₄(CO)₄₅]^n--[H_6-nNi₃₇Pt₄(CO)₄₆]^n- (n=5, 4) derivatives, and eventually leads to rearrangement to the known [H_6-n Ni₃₈Pt₆(CO)₄₈]^n- species. Both [Ni₃₆Pt₄(CO)₄₅]^6--[Ni₃₇Pt₄(CO)₄₆]^6- and [HNi₃₆Pt₄(CO)₄₅]^5--[HNi₃₇Pt₄(CO)₄₆]^5- mixtures have been chemically and electrochemically reduced to their corresponding [Ni₃₆Pt₄(CO)₄₅]^n--[Ni₃₇Pt₄(CO)₄₆]^n- (n=7–9) and [HNi₃₆Pt₄(CO)₄₅]^n--[HNi₃₇Pt₄(CO)₄₆]^n- (n=6–8) mixtures.     

Reactivity of 2-amino-1,3,4-thiadiazoles. Nucleophilic behaviour of some 2-amino-1,3,4-thiadiazoles: Model compounds

The ambident nucleophilic behaviour of some 2-amino-5-H-1,3,4-thiadiazoles in alkylation, acylation and nitrosation reaction has been verified. The structures assigned to the 2-amino-1,3,4-thiadiazoles ( 1a-i ) and to the Δ²-1,3,4-thiadiazolines ( 2a-e ) agree with the spectral data.     

Ytterbium triflate-promoted tandem one-pot oxidation-Cannizzaro reaction of aryl methyl ketones

[reaction: see text] Ytterbium triflate was shown to be an effective catalyst in promoting the synthesis of either isopropyl esters or free alpha-hydroxy-arylacetic acids from substituted aromatic glyoxals and aryl methyl ketones, respectively. The reaction to provide acids starting from differently substituted ketones was carried out by an environmentally friendly method using an aqueous medium as a solvent and giving the adducts in 78-99% yield without any further purification after the usual workup.     

α-Hydroxyalkylation of heteroaromatic bases by alcohols and hydroxylamine-O-sulphonic acid

The homolytic decomposition of hydroxylamine-O-sulphonic acid in alcoholic solvents was investigated in the presence or absence of protonated heteroaromatic bases and Fe(II) salt. The addition of the α-hydroxyalkyl radicals to the base and their oxidation by Fe(III) salt to the corresponding alkyl cyanide were competitive processes. A redox chain process involving the amino radical cation, NH₃^t., is suggested and the factors affecting the yields of the homolytic substitution are discussed.     

On the cavitation energy of water

Free-energy-perturbation theory from molecular dynamics calculations has been used to obtain the DeltaG of adjoining cavities' formation in water. The DeltaGs for systems with three, five and seven cavities are compared with that of a single cavity of the same volume, and found to be in good agreement. The conditions under which the analytical formulation of the energy of cavity formation proposed by Pierotti holds are discussed. The data for a single cavity have been tabulated and can lend themselves to a simple numerical implementation in standard quantum chemical packages, which can be used when high accuracy for DeltaG(cav) is required.