Solvents and ligands

Colloidal solutions of gold in different solvents have been one of the most intensively studied and well-understood systems. Polar solvents such as acetone, dimethylformamide, tetrahydrofuran... and nonpolar solvents such as toluene, hexane, cyclohexane, decane... were broadly used as reaction media or solvent-madiated media. Acetone, as a polar solvent, solvates the metal atoms and clusters during the warmup stage [23]. In this way steric stabilization is achieved and some metal colloids can be stable for months. This behavior is the main motivation for choosing polar solvent as an initial solvent or co-stabilizer. Generally, the additional stabilizing agent such as alkylamine, alkylthiol, or alkylalcohol is mostly needed for the stabilization of final metal fluid. As reported [24, 25], two types of stabilization are characteristic for these systems  

1) an increase of Sm decreases the SP band energy, resulting in the red shift of the SP band position and that 

2) a particle with a small core size and a thick shell causes a large g value, thereby decreasing the SP band shift, which is due to the solvent. 

Two parameters, 1) core size and 2) film thickness, are adopted to examine the effect of each on the spectral changes by employing 1 and 2. As an example, the UV-Vis spectral changes of the gold-thiol (the thiolate-covered gold nanoparticles) film as a function of the solvent refractive index were investigated [38]. From the 

Heat transport in suspensions of Au-core silica-shell nanoparticles was reported to depend on the composition of the solvent i.e., solvent penetration into the porous silica shell changed the thermal conductivity of the shell significantly [40]. Ge et al. have emphasized the role of the nanoparticle/surfactant/fluid interfaces on thermal transport from nanoparticles to the surrounding fluid [41]. In aqueous suspensions, these interface effects are relatively weak because the thermal conductance of the nanoparticle/water interface is large. 

---

The unstable pale blue-green bis(2,276, 2 -terpyridine)iron(3+) ion [47779-99-7], [Fe(terpy)2], has been obtained by oxidation of [Fe(terpy)2]. It is very unstable with respect to reduction by solvent and ligand dissociation. The perchlorate salt [2153642-5] has been reported. 

Ionic liquid as solvent and ligand/ligand precursor... 

Both the solvent and ligand were found to play pivotal roles in the reaction. In dioxane the byproduct formation was minimized while acceptable rates and yields were retained. In these studies it was also shown that both n-Bu3P and Ph3P are efficient ligands for the hydrogenolysis, but it is important that the ligand Pd(0) ratio be kept below 1 [158]. 

Direct kinetic studies of water exchange on [Pd(H20)4]2+ and [Pt(H20)4]2+, the parameters for which appear in Table XIV (267-274), were first reported well after the chemistry outlined in the preceding paragraph had become established. Solvent and ligand exchange on... 

Quantum chemical methods are well established, accepted and of high potential for investigation of inorganic reaction mechanisms, especially if they can be applied as a fruitful interplay between theory and experiment. In the case of solvent exchange reactions their major deficiency is the limited possibility of including solvent effects. We demonstrated that with recent DFT-and ab initio methods, reaction mechanisms can be successfully explored. To obtain an idea about solvent effects, implicit solvent models can be used in the calculations, when their limitations are kept in mind. In future, more powerful computers will be available and will allow more sophisticated calculations to be performed. This will enable scientists to treat solvent molecules explicitly by ab initio molecular dynamics (e.g., Car-Parrinello simulations). The application of such methods will in turn complement the quantum chemical toolbox for the exploration of solvent and ligand exchange reactions. 

Use of molten salts as solvent allows easy separation of organic products by distillation (376), and in this way PtCl2 with tetraalkylammonium salts of SnCl3 and GeCl3 has been used to selectively hydrogenate 1,5,9-cyclododecatriene to cyclododecene the salts in this case act as both solvent and ligand (377). A molten salt medium has been used in a homogeneously catalyzed Fischer-Tropsch synthesis (see Section VI,B). 

Aldol Condensation of 60 and 61 with Benzaldehyde (eq. [49,50]) Solvent and ligand Effects (6)... 

Hitoshi dedicated his life to Science and to the organization of Science. As a scientist, I remember the studies by X-ray of the coordination compounds in solution of metal ions with monodentate ligands which constituted milestones in the field. Eventually, he started simulating through informatic tools the interaction of solvents and ligands with metal ions. 

Fig. 20. Space-filling views of distal pockets in NP4-NO (left) and NP4—NH3 (right) structures. View is from above the distal pocket, with heme, solvent, and ligands shown in black. Waters 1-3 (right) are expelled as L130 and loop 31-37 pack against NO (left). Reproduced with permission from Ref. (47).

Fe(gmi)3] in glycol-water and a range of other binary aqueous solvent mixtures. These results, along with further results for AV for base hydrolysis of [Fe(phen)3] " and of [Fe(bipy)3] " in alcohol-water mixtures, have permitted the construction of a scheme combiniim solvent and ligand effects on AF for base hydrolysis of a range of diimine-iron(II) complexes. ... 

In 1996, an optimization of the oxidation protocol was described by De Vos and Bein who found a dependence of catalytic activity on temperature, solvent, and ligand structure . Their investigations showed that different substituents on the nitrogen atoms of the triazacyclononane ligands 168 have a great effect on the activity... 

Ghosh SK, Nath S, Kundu S, Esumi K, Pal T (2004) Solvent and ligand effects on the localized surface plasmon resonance (LSPR) of gold colloids. J Phys Chem B 108 13963-13971... 

Over the past few years, it has been shown that the electroreduction of NiLn complexes is feasible in various solvents (DMF, acetonitrile, THF,. ..) at potential values depending on the nature of both solvent and ligand. The electroformed species reacts by oxidative addition with halogenated derivatives including organic halides (iodide, bromide, chloride) (equation 27). 

---