THE CRYSTAL AND MOLECULAR STRUCTURES OF TWO DERIVATIVES OF WERNER'S HEXOL CLUSTER CATION: [Co{(OH)2Co(NH3)4}3](NO3)5 (OH) · 4H2O(I) AND [Co{(OH)2Co(NH3)4}3](NO3)6 · 2H2O(II)

Abstract

Crystals of compound (I) and (II) are black in reflected light and brown‐ black in transmitted light. The ¹H-nmr of the cations of (I), recorded in D⁶-DMSO, show peaks, relative to the ¹H of D⁶-DMSO, at + 0.46 ppm(rel. int. = 3); + 0.85 ppm(rel. int. = 1.2); + 1.80 ppm (rel. int. = 3); and ?4.18 ppm(rel. int. = 1). The magnetic susceptibility of (I) is C′_m (293.18 K) = 588.45×10^?6 c.g.s. units, which corresponds to a m _eff = 0.295 B.M. per Co ion; however, the small shifts and sharp ¹H-nmr lines in the DMSO spectrum preclude the presence of paramagnetic clusters. Cyclic voltametry of the cation present in (I) shows highly distorted, irreversible, oxidation and reduction waves which indicate the lack of stability of any oxidized or reduced form ‐ a fact which accords with the sharp lines of the NMR spectra; e.g., no stable paramagnetic species are present in (I).

Compound (I), M.W. = 941.24, crystallizes in P2₁/n (No. 14), with cell constants a = 11.789(2), b = 13.855(2), c = 21.534(3) Å, β = 91.94(1)° V = 3515.44 Å ³, d (meas; z = 4) = 1.778 gm-cm^?3. A total of 4705 data were collected in the range 4° ≤ 2θ ≤ 50°. They were corrected for absorption (μ = 19.562 cm^?1; rel. trans. coeff. range = 0.8642 to 0.9997); of these, 2623 were unique and had l ≥ 3σ(l). The structure was solved by direct methods, none of the hydrogens of the amine ligands were found experimentally at sensible positions; thus, they were left out. Refinement of the heavy atoms (anisotropic) led to final residuals of R(F) = 0.0637 and 0.0771.

Compound (II), M.W. = 950.20, crystallizes in space group P1 (bar; No. 2), with cell constants a = 12.858(3), b = 12.475(2), c = 12.114(2) Å, α = 96.63(1), β = 91.94(1) and γ = 61.71(2)° V = 1615.68 Å ³, d(meas; z = 2) = 1.953 gm-cm^?3. A total of 5657 data were collected in the range 4° ≤ 2θ ≤ 50°. They were corrected for absorption (μ = 21.301 cm^?1; rel. trans. coeff. range = 0.7372 to 0.9998); of these, 4456 were unique and had l ≥ 3σ (l). The structure was solved by direct methods, the majority of the hydrogens of the amine ligands were found experimentally at sensible positions, the rest were calculated at idealized positions (N═H = 0.95 Å). The hydrogens of the OH ligands were located experimentally in a final difference Fourier map. Refinement of the heavy atoms (anisotropic) with fixed hydrogens (B = 5.00 A? ²) led to final residuals of R(F) = 0.0348 and 0.0440.

Precisely as visualized by Werner, the hexol cations consist of a central Co(III) cation surrounded by three {Co(NH₃)₄(OH)₂]¹⁺ ligands. IN (I), the O═Col═O angles are acute (av. value = 82.97°), as expected from the electrostatic repulsion of the Co(III) central cation and the monopositive ligands surrounding it. Consequently, the Co… Co distances the long (2.896, 2.888 and 2.889 A?) and the the av. Co═O═Co angles are 97.43°. The remaining portions of the cation and anions are as expected from standard values; i.e., Co═O═1.90–1.95 and Co═N = 1.95–2.00 A?. In (II), the Col═O═Co angles are also obtuse (av. value = 97.87°), as expected from the electrostatic repulsion of the Co(III) central cation, and the Co… Co distances are equally long (2.881, 2.876 and 2.874 A?; on average, 2.877 A?).     

The effect of NaOH on dodecyltrimethylammonium hydroxide aggregation in aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) in aqueous NaOH solutions was studied as a function of NaOH concentration. As in NaOH-free DTAOH aqueous solutions, the surfactant underwent a stepwise aggregation mechanism. Changes in the structure of aggregates produced an increase of the concentration at which premicellar aggregates could solubilize hydrophobic dyes and also in the concentration at which hydroxide inons join the aggregates.     

Temperature-Induced Coil-Globule Transition of Alkali Metal Polyacrylates in Aqueous Organic Solvent Mixtures

A counterion-specific coil-globule transition (CGT) has been observed for alkali metal poly(acrylate)s (PAAM, M; Li, Na, K, Cs) in aqueous organic solvent (ethanol, dimethyl sulfoxide, acetone, acetonitrile) mixtures. In the present study we found that the reduced viscosity of PAAM, except for PAALi, in the relevant mixed solvents, except for those containing acetonitrile, significantly increased with increasing temperature. The observed temperature-induced CGT was interpreted as being caused by disintegration of the ion-clusters, i.e., the associated state of contact ion-pairs formed between the polymer charge and the counterion. In fact, the NMR line width of ²³Na and ¹³³Cs, which were used as a measure of the counterion mobility, indicated that the counterion binding was significantly weakened with increasing temperature, while the temperature effects for the PAALi and acetonitrile systems were only marginal. All these results suggested that the temperature-induced CGT behavior occurs only for systems where the ion-cluster formation promotes the CGT in the relevant solvent systems, which is also consistent with the known similar behavior of some betaine polymers.     

Ion condensation onto self‐assembled nanofibers

Self‐assembled peptide amphiphile (PA) nanofibers are a class of supramolecular materials with promising applications in nanotechnology. Alignment of nanofibers, which is essential for biomaterials applications, is achieved at low salt concentrations in the PA nanofiber suspensions. Regardless of its importance, the effect of ion concentration on the properties of these nanostructures remains unexplored. Using atomistic molecular dynamics simulations, canonical PA nanostructures are investigated to elucidate the relationship between counterion condensation and morphological changes. Simulations reveal that nanofibers with the highest cross‐section density have expanded radii. This expansion decreases the accessible volume for sodium counterions and diminishes the counterion translational entropy, while also reducing the total electrostatic potential. Interestingly, we show that the competition between these effects leads to a fraction of condensed counterions independent of the fiber radius. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 901–906     

Hydration force due to the reduced screening of the electrostatic repulsion in few-nanometer-thick films

Experiments with foam films from solutions of 1 mM SDS + 100 mM electrolyte (LiCl, NaCl and CsCl) were carried out by a thin-film-pressure balance. The measured dependences of disjoining pressure versus film thickness exhibit a steep increase when the thickness of the film's water core becomes smaller than 3.7 nm. This behavior can be interpreted as a manifestation of the hydration force. We unsuccessfully tried to interpret the data with different available theoretical models. Eventually, we found that a relatively simple model of “reduced screening” can fit the data. Such reduced screening of the electric field could exist only in a narrow range of film thicknesses, which practically coincides with the region where the hydration repulsion is acting. This model and its experimental verification are described in the article.     

Thermodynamic properties and conductivities of some dodecylsurfactants in water

Densities, heat capacities, enthalpies of dilution, osmotic coefficients and conductivities are reported for dodecylamine hydrochloride, dodecyldimethylammonium and dodecyltrimethylammonium chloride in water over a wide range of concentration. The last two properties were also measured for dodecyltrimethylammonium bromide. From the thermodynamic data partial molar volumes, heat capacities and relative enthalpies and nonideal free energies and entropies were derived as a function of the surfactant concentration. The cmc's and degree of counterion dissociation were also calculated from the transport properties. It is shown that the trends of volumes, enthalpies, free energies and entropies are quite regular whereas heat capacities present maxima and minima at concentrations which depend on the nature of surfactants. Corresponding changes were observed in the osmotic coefficients and specific conductivities. The thermodynamic functions of micellization were evaluated on the basis of the pseudo-phase transition model. Finally, the effects of the introduction of methyl groups in the hydrophilic moiety of the surfactant and of the nature of the counterion on the thermodynamic properties of monomers and micelles are examined.     

Micellar effects of cetyltrimethylammonium dibromobromate in phosphoryl group transfer reactions

The nucleophilic reactivity of cetyltrimethylammonium dibromobromate (CTABr₃) with respect to organophosphorus compounds-4-nitrophenyl esters of diethylphosphoric (NPDEP) and diethylphosphonic acids (NPDEPN)-has been studied. Solution of CTABr₃ in aqueous alkali solutions generated the hypobromite anion, which permitted the formation of a micellar system with reactive α-nucleophilic counterion. The kinetics of this system was described in terms of a simple pseudo-phase model, the half-life for the conversion of the organophosphorus substrates into reaction products was 95 s (NPDEP) and 12 s (NPDEPN). __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 226–230, July–August, 2007.     

水分子在水化蒙脱石表面脱附行为的第一性原理研究

使用密度泛函理论计算研究了水分子在蒙脱石(MMT)表面的脱附作用.水分子在MMT表面的脱附受到配衡离子(Li~+,Na~+,或K~+),MMT表面和吸附水分子的共同作用.通过势能面扫描得到了脱附水分子在MMT表面脱附的能量路径.通过对脱附水分子能量路径的分析发现:水分子在MMT表面的脱附能垒受到配衡离子种类的影响,半径较小的配衡离子具有较大的脱附能垒.此外,吸附水的存在能降低脱附水分子的脱附能垒,使脱附过程容易触发.