Selective Extraction and Transport of the [PtCl6]2− Anion through Outer‐Sphere Coordination Chemistry

Platinum recovery : Tripodal receptors incorporating urea, amido or sulfonamido hydrogen‐bond donors show high loading and selectivity for extraction of [PtCl₆]^2? over chloride (present in 60‐fold excess) from a low pH aqueous phase to organic media (see figure). The formation of neutral 2:1 [LH]⁺/[PtCl₆]^2? packages in organic solvents is supported by single‐crystal X‐ray structure determinations.

     

Synthesis of two dibenzo-3, 2, 3-tetramines and their Ni(II), Zn(II) and Cd(II) complexes. The X-ray structure of diiodo-[2, 3:10, 11-dibenzo-1, 5, 8, 12-tetraazadodecane]cadmium(II)

Convenient syntheses of the tetramines 2, 3:10, 11-dibenzo-1, 5, 8, 12-tetraazadodecane, (L1, and 3, 4:9, 10-dibenzo-1, 5, 8, 12-tetraazadodecane (L2), are described. Both ligands form complexes with Ni(II), Zn(II) and Cd(II). The X-ray structure of [Cd(L1)I₂), confirms a five coordinate geometry for the Cd atom, where the two iodines are bonded to the metal and (L1) acts as a tridentate ligand. The complex crystallises in the monoclinic space group P2₁/c with a = 19.741(4) Å, b = 8.726(3) Å, c = 12.221(4) Å, and β = 104.55(3)°. The structure was refined to R = 0.062 for 1051 reflections.     

Enthalpy of dilution of aqueous systems containing S-trioxane and some amides. Analysis of the interaction of saccharides with amides in aqueous media

Enthalpies of dilution of aqueous systems of trioxane+formamide and trioxane+dimethylformamide have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle, and a first estimate of the pairwise group interaction enthalpy for-O-/CONH is presented. Systems of saccharides and amides are not amenable to the Savage-Wood treatment used in recent works. However, when treated in conjunction with all available data to yield a different set of group interaction parameters, saccharides behave more predictably. Implications of this state of affairs are considered.     

Metal-free macrocycles via template method: A starting point for selective complexation studies

A new range of structurally-related macrocyclic ligands have been prepared and their potential as metal-ion discriminating agents examined.     

Laboratory,Field and Modeling Studies of Radon‐222 as a Natural Tracer for Monitoring NAPL Contamination

The recently developed natural radon tracer method has potential as a rapid, lowcost, nondestructive, and noninvasive method for quantifying NAPL contamination. In the subsurface, radon222 (radon) is produced by the decay of naturally occurring radium226 contained in the mineral fraction of aquifer solids. In groundwater radon occurs as a dissolved gas, with a halflife of 3.83 days. In the absence of NAPL, the radon concentration in groundwater quickly reaches a maximum value that is determined by the mineral composition of the aquifer solids, which controls the rate of radon emanation. In the presence of NAPL, however, the radon concentration in the groundwater is substantially reduced due to the preferential partitioning of radon into the organic NAPL phase. A simple equilibrium model and supporting laboratory studies show the reduction in radon concentration can be quantitatively correlated with residual NAPL saturation. Thus, by measuring the spatial distribution in radon it may be possible to identify locations where residual NAPL is present and to quantify the NAPL saturation. When the basic processes of partitioning, radon emanation from the aquifer solids, and firstorder decay are incorporated into an advective/dispersive transport model, good agreement is obtained with the results of laboratory and field experiments. Model sensitivity analyses shows many factors can contribute to the radon concentration response, including the length of the NAPL zone, NAPL saturation, groundwater velocity, porosity, and radon emanation. Thus, care must be taken when applying the radon method to locate and quantify NAPL contamination in the subsurface.     

Acetone‐4‐methyl­thio­semicarbazone at 220 K

In the title compound, C₅H₁₁N₃S, the trans conformation is stabilized by a weak intramolecular N—H?N hydrogen bond. Unusually, one N—H bond is not involved in any hydrogen‐bond interactions and instead the mol­ecules form a one‐dimensional polymer via N—H?S intermolecular hydrogen bonds.     

Using the outer coordination sphere to tune the strength of metal extractants

A series of 3-substituted salicylaldoximes has been used to demonstrate the importance of outer-sphere interactions on the efficacy of solvent extractants that are used to produce approximately one-quarter of the world's copper. The distribution coefficient for extraction of copper by 5-tert-butyl-3-X-salicylaldoximes (X = H, Me, (t)Bu, NO(2), Cl, Br, OMe) varies by more than two orders of magnitude. X-ray structure determinations of preorganized free ligand dimers (10 new structures are reported) indicate that substituents with a hydrogen-bond acceptor atom attached to the 3-carbon atom, ortho to the phenolic oxygen, buttress the intermolecular hydrogen bond from the oximic proton. Density functional theory calculations demonstrate that this hydrogen-bond buttressing is maintained in copper(II) complexes and contributes significantly to their relative stabilities in energy-minimized gas-phase structures. A remarkable correlation between the order of the calculated enthalpies of formation of the copper complexes in the gas phase and the observed strength of the ligands as copper solvent extractants is ascribed to the low solvation energies of species in the water-immiscible phase and/or the similarities of the solvation enthalpies of the preorganized ligand dimers and their copper(II) complexes.