Coordination chemistry of the solvated AgI and AuI ions in liquid and aqueous ammonia, trialkyl and triphenyl phosphite, and tri-n-butylphosphine solutions

The coordination chemistry of solvated Ag(I) and Au(I) ions has been studied in some of the most strong electron-pair donor solvents, liquid and aqueous ammonia, and the P donor solvents triethyl, tri-n-butyl, and triphenyl phosphite and tri-n-butylphosphine. The solvated Ag(I) ions have been characterized in solution by means of extended X-ray absorption fine structure (EXAFS), Raman, and (107)Ag NMR spectroscopy and the solid solvates by means of thermogravimetry and EXAFS and Raman spectroscopy. The Ag(I) ion is two- and three-coordinated in aqueous and liquid ammonia solutions with mean Ag-N bond distances of 2.15(1) and 2.26(1) A, respectively. The crystal structure of [Ag(NH3)3]ClO4.0.47 NH3 (1) reveals a regular trigonal-coplanar coordination around the Ag(I) ion with Ag-N bond distances of 2.263(6) A and a Ag...Ag distance of 3.278(2) A separating the complexes. The decomposition products of 1 have been analyzed, and one of them, [Ag(NH3)2]ClO4, has been structurally characterized by means of EXAFS, showing [Ag(NH3)2] units connected into chains by double O bridges from perchlorate ions; the Ag...Ag distance is 3.01(1) A. The linear bisamminegold(I) complex, [Au(NH3)2]+, is predominant in both liquid and aqueous ammonia solutions, as well as in solid [Au(NH3)2]BF4, with Au-N bond distances of 2.022(5), 2.025(5), and 2.026(7) A, respectively. The solvated Ag(I) ions are three-coordinated, most probably in triangular fashion, in the P donor solvents with mean Ag-P bond distances of 2.48-2.53 A. The Au(I) ions are three-coordinated in triethyl phosphite and tri-n-butylphosphine solutions with mean Au-P bond distances of 2.37(1) and 2.40(1) A, respectively.     

Distorted five-fold coordination of Cu2+(aq) from a Car-Parrinello molecular dynamics simulation

The solvation shell structure and dynamics of a single Cu2+ ion in a periodic box with 32 water molecules under ambient conditions has been investigated using Car-Parrinello molecular dynamics simulations in a time-window of 18 ps. Five-fold coordination with four equidistant equatorial water molecules at 2.00 A and one axial water molecule at 2.45 A from the Cu2+ ion is found. A "hole" without water molecules is found on the opposite side of the axial water. The ion-water bonding character for the equatorial water molecules is different from that of the axial water molecules, as shown by a localized orbital analysis of the electronic structure. Moreover, the calculated OD stretching vibrational band for the equatorial water molecules lies ca. 175 cm-1 below the axial-water band, in good agreement with experimental data. The equatorial-water band lies below, and the axial-water band above, the pure liquid D2O band, also in agreement with experimental data.     

The solvation of Li and Na in acetonitrile from ab initio-derived many-body ion–solvent potentials

Several Li⁺- and Na⁺-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/TZV++(d,p) level for distorted ion-(MeCN)_n clusters with n=1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Böhm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li⁺(MeCN) and Na⁺(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li⁺ ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na⁺ is close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common.     

The coordination chemistry of copper(I) in liquid ammonia, trialkyl and triphenyl phosphite, and tri-n-butylphosphine solution

The coordination chemistry of the solvate complexes of the relatively soft electron-pair acceptor copper(I) has been studied in solution and solid state in seven solvents with strong electron-pair donor properties, liquid ammonia, trimethyl, triethyl, triisopropyl, tri-n-butyl and triphenyl phosphite, and tri-n-butylphosphine. The solvate complexes have been characterised by means of EXAFS and 63Cu NMR spectroscopy, and in some cases also by 65Cu NMR spectroscopy. The copper(I) ion is three-coordinated, most probably in a coplanar trigonal fashion, in liquid ammonia with a mean Cu-N bond distance of 2.00(1) Angstroms. No 63Cu NMR signal has been detected from the ammonia solvated copper(I) ion in liquid ammonia, which supports a three-coordination. The phosphite and phosphine solvated copper(I) ions are tetrahedral with Cu-P bond distances in the range 2.24-2.28 Angstrom in both solution and solid state as determined by EXAFS spectroscopy. The tetrahedral configuration of these complexes has been confirmed by 63Cu and 65Cu NMR spectroscopy through the J(63Cu-31P) and J(65Cu-31P) couplings. The fact that two of the investigated complexes, [Cu(P(OC6H5)3)4]+ and [Cu(P(C4H9)3)4]+, are 63Cu and 65Cu NMR silent is probably caused by a significantly angular distorted tetrahedral configuration.     

Electron density of H2O in a crystalline environment

The influence of the surroundings on the water molecule m LiOH·H₂O has been studied by ab initio MO LCAO SCF techniques. The main features are an enhancement of the polarity of the molecule and a decrease in the lone-pair density.     

Shaping of gelling biopolymer drops in an elongation flow

Shaping, defined as deformation in combination with gel formation of gelatine and kappa-carrageenan drops in an elongation flow, was studied. The focus was to investigate the possibility of shaping and fixating small drops in the diameter range 20 to 229 mum. In the shaping progress and the influence of experimental properties, the viscosity, temperature, and flow of the deforming fluid were examined on the final drop shape. In the experiments a hot emulsion of an aqueous biopolymer solution in silicone oil was injected into cold silicone oil where a deforming elongation flow field existed. After injection, a temperature decrease in the drops resulted in a gel formation of the biopolymer and a fixation of the deformed drop in the flow. The shape was measured and the effect on the drop aspect ratio was determined by image analysis. Over the total drop diameter range, kappa-carrageenan was more ellipsoid-shaped than gelatine, with a maximum aspect ratio of 6 compared to 4 for gelatine. For small drops, around 22 mum, it is possible to shape kappa-carrageenan, but for gelatine small drops tend to be unaffected. An increase in viscosity, temperature, and flow resulted in an increase in the final fixated shape of the drops. The differences in drop deformation between the biopolymers were explained by drop-viscosity/oil differences and differences in the kinetics of gel formation. The different gel formation kinetics resulted in a short, well-defined, shaping process for kappa-carrageenan, while for gelatine the process was more complex, with both deformation and relaxation present at different stages.     

Redshifts and blueshifts of OH vibrations

Ab initio calculations of potential energy, dipole moment, equilibrium OH distance, force constants, and anharmonic frequencies, and correlation between these quantities, are presented for a water molecule and an OH^? ion in a uniform electric field of varying field strength. It is explained why a bound H₂O molecule in nature always experiences a frequency downshift with respect to the free molecule, and a bound OH^?1 ion, either a downshift or an upshift. The frequency-field variation is well accounted for by the expression Δν_OH α ?E‖ · (d μ/dr_OH + 1/2 · ?μ/?r_OH). A frequency maximum occurs at the field strength where ?μ‖^tot/?r_OH ～ 0. Two cases can be discerned: (1) the frequency maximum falls at a positive field strength when dμ/dr_OH is positive (this is the situation for OH^?), and (2) the maximum frequency falls at a negative field when dμ/dr_OH is negative (this occurs for water). In general, for an OH bond in a bonding situation where the intermolecular interactions are dominated by electrostatic forces, the nonlinearity of the frequency shift with respect to an applied field is governed by how close to the frequency maximum one is, i.e., by both dμ/dr_OH and ?μ/?r_OH. Correlation curves between the external linear force constant, k^ext, and r_OH,e are closely linear over the whole field range studied here, whereas the frequency vs. r_OH,e and force constants vs. r_OH,e correlation curves form two approximately linear, parallel branches, corresponding to “before” and “after” the maximum in the frequency vs. field curves. Each branch of the ν vs. r_OH,e curves has a slope of ～ ? 16,000 cm^?1/Å. © 1993 John Wiley & Sons, Inc.     

Optimisation of chiral separation of omeprazole and one of its metabolites on immobilized α1-acid glycoprotein using chemometricsglycoprotein using chemometrics

Summary A strategy for the optimisation of direct chiral separation of omeprazole and a metabolite, hydroxi-omeprazole, in reversed phase liquid chromatography is described. A factorial design was used, where mobile phase pH, concentration of a mobile phase modifier, ionic strength and column temperature were tested as the variables and enantioselective retention, column efficiency and asymmetry factor as the responses. The experimental results were evaluated with multivariate analyses, which demonstrated that the column temperature and content of mobile phase acetonitrile were by far the most important variables. The enantiomers of omeprazole and one of its metabolites were baseline resolved within 15 minutes. The optimised chromatographic system was used for a separation of the enantiomers of omeprazole and its main metabolite in a patient plasma sample.