Diphosphine ligand chelation and bridging and regiospecific ortho metalation in the reaction of 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) with Ir4(CO)12: X-ray diffraction structures of Ir4(CO)7(μ-CO)3(bpcd), Ir4(CO)5(μ-CO)3(bpcd)(μ-bpcd), and HIr4(CO)4(μ-CO)3(bpcd)[μ-PhP(C6H4)CC(PPh2)C(O)CH2C(O)]

Me₃NO activation of the tetrairidium cluster Ir₄(CO)₁₂ (1) in presence of the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) furnishes the bpcd-substituted clusters Ir₄(CO)₁₀(bpcd) (3) and Ir₄(CO)₈(bpcd)₂ (4) as the minor and major products, respectively. Cluster 3 has been isolated as the sole observable product from the reaction of [Ir₄(CO)₁₁Br][Et₄N] (2) with bpcd in presence of AgBF₄ at room temperature. Both 3 and 4 have been isolated and fully characterized in solution by spectroscopic methods. The solid-state structure of 3 reveals that the ancillary bpcd ligand is bound to a single iridium center, with chelating and bridging bpcd ligands found in the X-ray structure of cluster 4. Cluster 4 is unstable at room temperature and slowly loses CO to afford the hydride-bridged cluster HIr₄(CO)₄(μ-CO)₃(bpcd)[μ-PhP(C₆H₄)CC(PPh₂)C(O)CH₂C(O)] (5). Cluster 5 has been fully characterized in solution by IR and NMR spectroscopies, and the C–H bond activation attendant in the ortho metalation step is shown to occur regioselectively at one of the aryl groups associated with the bridging bpcd ligand. The redox properties of clusters 3–5 have been explored and the electrochemical behavior discussed with respect to extended Hückel MO calculations and related diphosphine-substituted cluster compounds prepared by our groups.     

The interaction of EDTA with barium sulfate

Ethylenediaminetetraacetic acid (EDTA) is a known complexing agent that interacts with a host of cations. In this paper, various techniques are used to elucidate the mechanism of interaction between EDTA and barium sulfate surfaces. It is shown that complexation with metal ions is not sufficient to explain the inhibition of barite crystallization but that other processes such as chemisorption must also occur. EDTA is shown to always adsorb as the mono-protonated species - suggesting that the molecule is able to lose a proton when it adsorbs at lower pH. Molecular modelling shows that the interaction of the surface barium ions with the carboxylate group is an important one. Finally, in situ turbidity measurements provide information about the mechanism of nucleation/growth modification. It is found that the EDTA molecule inhibits barium sulfate nucleation and that this could be its primary means of inhibiting precipitation of barium sulfate.     

Reaction of dichloromaleic anhydride with 1,8-diaminonaphthalene: Synthesis and X-ray diffraction structure of 8,9-dichloropyrrolo[1,2-a]perimidin-10-one

The reaction of dichloromaleic anhydride with 1,8-diaminonaphthalene in refluxing toluene or 1,2-dichloroethane produces the new heterocyclic compound 8,9-dichloropyrrolo[1,2-a]perimidin-10-one in low yields. 8,9-Dichloropyrrolo[1,2-a]perimidin-10-one has been isolated by column chromatography and characterized in solution by IR, ¹H NMR, and UV/vis spectroscopies. The solid-state structure was unequivocally established by single-crystal X-ray diffraction analysis. 8,9-Dichloropyrrolo[1,2-a]perimidin-10-one crystallizes in the monoclinic space group P2 ₁/c, a = 7.475(1)Å, b = 10.650(2)Å, c = 14.468(2)Å, = 94.478(2)°, V = 1148.3(3) ų, Z = 4, and d _calc = 1.672 Mg/m³; R = 0.0289, R _w = 0.0762 for 1644 reflections with I > 2(I). The nature of the HOMO and LUMO in 8,9-dichloropyrrolo[1,2-a]perimidin-10-one has been determined by extended Hückel molecular orbital calculations, and these data are discussed relative to the cyclic voltammetric data obtained at a platinum electrode.     

Synthesis and characterisation of lamellar ZnS nanosheets containing intercalated diamines

A solvothermal method has been used to prepare hybrid inorganic–organic composites with a lamellar structure in which layers of wurtzite ZnS are separated by intercalated diamine molecules. A hybrid composite prepared with diethylenetriamine has been isolated and characterised and its structure and properties compared with those of the composite prepared using ethylenediamine. Comparative structural and morphological studies of the two lamellar hybrid composites are described on the basis of powder XRD, electron and scanning probe microscopies and thermal analysis of the materials.     

Chemoselective N-acylation of indoles and oxazolidinones with carbonylazoles

Unique reactivity: In the presence of more reactive amine and alcohol functional groups and of carboxylic acids, the chemoselective N-acylation of indoles and oxazolidinones is achieved by taking advantage of the unique reactivity of carbonylazole acylating agents with catalytic amounts of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).     

All Titration Indicators are Not Created Equal—A Lecture Demonstration

This demonstration provides a simple method for emphasizing the importance of indicator selection to determine the end point of a titration involving the common weak base household ammonia. By using phenolphthalein and methyl red as the indicators in the titration of two samples of aqueous household ammonia with hydrochloric acid, students can discover that there is a difference between the two apparent termination points. There is clearly a visible difference in the sharpness of the color changes that take place, and the presence of ammonia at the apparent phenolphthalein endpoint is also detected by olfactory means. By showing the different termination ranges on a titration curve, the students can readily see that phenolphthalein does a poor job of showing the proper termination point,; whereas methyl red shows the proper titration end point.     

The three body interaction energy between optically active molecules

An account is given of a steady-state molecular dynamics method for the calculation of the shear viscosity of a dense fluid. The method is applied to the case of a system described by a Lennard-Jones potential with parameters appropriate to argon. Satisfactory agreement with experimental data is found over a range of temperature and density for which the viscosity varies by a factor of approximately 8. The results are interpreted in terms of a modified hard-sphere model and it is shown that the Lennard-Jones fluid obeys a Stokes-type relation in which the effective molecular diameter is close to that deduced from equilibrium structural properties.     

The asymptotic enumeration of rooted convex polyhedra

An asymptotic formula is obtained for the number of rooted c-nets with m vertices and n edges as m, n → ∞ with $\text{1}\text{2}\text{+ ε <}\text{n}\text{m}\text{< 2 ? ε}$ for some ε > 0.