Solvent donor strengths

Well-defined coordination compounds of Pb(CH3)4 are not known. However, from the increase of the NMR coupling constants J( ° Pb, H) In various solvents, solvation of Pb(CH3)4 by one solvent molecule and formation of complexes with trigonal bipyramidal geometry were inferred. The ability of the solvent to solvate Pb(CH3)4 increased along the series CeHi2 < 1,2-dimethoxyethane dioxane hexamethylphosphortriamide < pyridine < tetrahydro-thiophene < triethylamine < THF < triethylphosphine < N,N,N, N -tetramethylethylenedi-amine acetone < dimethylformamide < dimethyl sulfoxide [2]. In another paper 2j(207pb iH) was considered to be independent of solvent donor strength and this is consistent... 

Donor strengths, taken from ref. 207b, based upon the solvent effect on the symmetric stretching frequency of the soft Lewis acid HgBr2. Gutmann s donor number taken from ref 207b, based upon AHr for the process of coordination of an isolated solvent molecule to the moderately hard SbCL molecule in dichioroethane. ° Bulk donor number calculated as described in ref 209 from the solvent effect on the adsorption spectrum of VO(acac)2. Taken from ref 58, based on the NMR chemical shift of triethylphosphine oxide in the respective pure solvent. Taken from ref 61, based on the solvatochromic shift of a pyridinium-A-phenoxide betaine dye. 

By fitting equation 19 with the experimental data, the values of Ad were obtained for the following systems CDNB-benzene = 0.76 0.02, CNTFB-benzene = 0.26 0.02, CDNB-mesitylene = 0.96 0.02 and CNTFB-mesitylene = 0.48 0.02 mol-1. It can be observed that Ad increases with increasing donor strength of the aromatic solvents115. For the reactions with piperidine, on the contrary, an increase in rate was observed with increased molar fractions of the donor solvent. This result was interpreted as a conventional solvent effect since, in this case, As = Ad-... 

On the other hand, Table 9 contains several data which cannot be interpreted by the relative donicities of donor solvent and competitive ligand the donor strength of the iodide ion is comparable to that of acetonitrile and the formation of tetraiodocobaltate in solvents of high donicity, such as DMA, DMSO and HMPA may not be anticipated. The formation of this species is however, complete with excess iodide ions and is due to the small values of the free enthalpies of the gas phase reactions ... 

The hypothetical [C0CI3 ] —ion is a stronger acceptor than VO(acac)2 and hence the thermodynamic solvation effect with a given anion and in a given solvent is smaller. The decrease of the donor strength of an anion due to solvation is less apparent in the last step required for the formation of tetrahalocobaltate. 

The Hg(II) assisted aquation of Co(III)-chloro complexes has been throughly studied to gain insight into the effects of solvent, ionic strength and polyelectrolytes on reaction rates and equilibria. For the two reactions in 1.0 M HCIO4 (4.39) and (4.40), (N)j representing five nitrogen donors in unidentates or multidentates or mixtures thereof. 

The dissociation constants of MX2 (M = Zn, Cd or Hg X = Cl, Br, I or C104) in DMF, acetone and ROH solvents have been measured.972 The order of anion donor strength is found to be 01O4Br>Cl a small-angle neutron scattering study of D20 solutions of zinc chloride has been reported.973... 

This interpretation is also supported by the results of a study correlating the observed diastereomeric excess with the Kamlet-Taft (3 parameter [29], a measure of the hydrogen-bond acceptor strength. A linear free energy relationship was found to exist between P and the diastereomeric excess for those solvents having a (hydrogen bond donor strength) = 0 [28],... 

The energy difference AGET° between the vibronically equilibrated reactant and product states can be considered as the difference between the IP of the donor and the EA of the acceptor (in the gas phase) or between the corresponding electrochemical potentials (in solution). For a set of structurally related arene donors in the same solvent, a linear (Mulliken) correlation is usually observed experimentally between the donor strength and the CT energy (due to the relatively small changes in A), i.e. ... 

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