Coordination numbers, solvent

Solvent coordination numbers of metal ions in solution. S. F. Lincoln, Coord. Chem. Rev., 1971, 6, 309-329 (133). 

H NMR spectra of A1C13, in either MeOH or EtOH solutions, indicate a solvent coordination number of four which may imply that the species AlCl2(ROH)4 AICI7 predominate.275 In the cases of A1(N03)3 and A1(C104)3 the solvation numbers are five and six,... 

One aspect of the last set of experiments on W(CO)6 in supercritical ethane that we have not yet discussed involves the possible role of local density enhancements in VER and other experimental observables for near-critical mixtures. The term local density enhancement refers to the anomalously high solvent coordination number around a solute in attractive (where the solute-solvent attraction is stronger than that for the solvent with itself) near-critical mixtures (24,25). Although Fayer and coworkers can fit their data with a theory that does not contain these local density enhancements (10,11) (since in their theory the solute-solvent interaction has no attraction), based on our theory, which is quite sensitive to short-range solute-solvent structure and which does properly include local density enhancements if present, we conclude that local density enhancements do play an important play in VER and other spectroscopic observables (26) in near-critical attractive mixtures. 

Solvent coordination number, 134, 403 Solvent effects, 385, 418 initial and transition state, 418 kinetic measures of, 427 Solvent ionizing power parameter, 430 Solvent isotope effects, 272, 300 Solvent nucleophilicity, 431 Solvent participation, covalent, 429 Solvent polarity, 399, 425 Solvent polarity parameter, 436 Solvent properties, 389 Solvent-separated complex, 152 Solvent sorting, 404 Solvent structure, 402 Solvophobic interaction, 395 Solvophobicity parameter, 427 Sound absorption chemical, 145 classical, 145... 

In solutions, the distances between the centers of ions and of the nearest atoms of the surrounding solvent molecules can also be measured by x-ray and neutron diffraction, but with a somewhat larger uncertainty, 2pm. In aqueous solutions, if the water molecule is assigned a constant radius r = 138 pm (one half of the experimental collision diameter), then the distances t((I -0 )/pm = 138-fr,/pm have been established by Marcus within the experimental uncertainty, with the same ionic radii as in the crystals [45, 46], These radii, as selected in Ref 6 and annotated there, are listed in Table 2.8. The distances between the centers of ions in solutions in solvents other than water and of the nearest atoms of the solvents have also been determined in some cases reported by Ohtaki and Radnai [50] and confirm the portability of the Tj values among solvents, provided the mean solvent coordination number is near that in water. 

Then the solvent-coordination number of the ion in the solution, h, is obtained by the integration according to Equation 4.32. Second hydration shells have been definitely ascribed to divalent and trivalent cations from x-ray diffraction measurements. The coordination number h for water molecules in this second shell is generally assumed to be 12, the number then being corroborated by the diffraction data. 

The orange-red titanium acetylacetone chelates are soluble in common solvents. These compounds are coordinately saturated (coordination number equals 6) and thus much more resistant to hydrolysis than the parent alkoxides (coordination number 4). The alkoxy groups are the moieties removed by hydrolysis. The initial product of hydrolysis is beheved to be the bis-hydroxy bis-acetylacetone titanate, (HO)2Ti(acac)2, which oligomerizes to a... 

By far the most important metal containing dyes are derived from OjO-dUiydroxyazo stmctures in which one of the two azo nitrogen atoms and the two hydroxyl oxygen atoms are involved in bonding with the metal ion. Thus these dyes serve as terdentate ligands. In the case of metal ions with a coordination number of four, eg, Cu(H), the fourth position is usuaUy occupied by a solvent molecule (47). 

Let us consider a simple self-avoiding walk (SAW) on a lattice. The net interaction of solvent-solvent, chain-solvent and chain-chain is summarized in the excluded volume between the monomers. The empty lattice sites then represent the solvent. In order to fulfill the excluded volume requirement each lattice site can be occupied only once. Since this is the only requirement, each available conformation of an A-step walk has the same probability. If we fix the first step, then each new step is taken with probability q— 1), where q is the coordination number of the lattice ( = 4 for a square lattice, = 6 for a simple cubic lattice, etc.). 

The coordination number is the number of solvent molecules in the primary solvation shell. This quantity can be estimated (for ions) by conductance measurements and by... 

The definition of solvent exchange rates has sometimes led to misunderstandings in the literature. In this review kjs 1 (or fc2lsolvent]), sometimes also referred to as keJ s 1, is the rate constant for the exchange of a particular coordinated solvent molecule in the first coordination sphere (for example, solvent molecule number 2, if the solvent molecules are numbered from 1 to n, where n is the coordination number for the solvated metal ion, [MS ]m+). Thus, the equation for solvent exchange may be written ... 

For halide ligands, a coordination number of four (/u4-X) is rare. Self-assembly of ds metal centers and halides around a pyramidal halide gives tetrapalladium complexes. In this unprecedented case the metallamacrocycle owes its formation to the halide acting as a template.347 The complexes (PPN)[Pd4(Fmes)4] (Fmes = 2,4,6-tris(trisfluoromethyl)phenyl) display fluxional behavior in solution in noncoordinating solvents.347... 

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