Pentacyanoferrate II Complexes

Kinetic parameters k, often also and AS, occasionally AV ) for formation and dissociation of several pentacyanoferrate(II) complexes [Fe(CN)5L]" have been established. Ligands L include several S- and A-donor heterocycles,4-methyl- and 4-amino-pyridines, a series of alkylamines, 3- and 4-hydroxy- and 3- and 4-methoxy-pyridines, several amino acids, nicotinamide, " 4-pyridine aldoxime, 3-Me and 3-Ph sydnones, several bis-pyridine ligands,neutral, protonated, and methylated 4,4 -bipyridyl, 1,2-bis(4-pyridyl)ethane and traTO-l,2-bis0-pyridyl)ethene, pyrazine- 4,4 -bipyridyl- and bis(4-pyridyl)ethyne-pentaammine-cobalt(III), edta-ruthenium(III), and pentaammineruthenium-(II)and-(III) complexes of... 

Equilibrium constants for formation of complexes [Fe(CN)5L] can be derived from kinetics and independently from spectroscopic determinations. Values are given in many of the papers cited above stability constants for several pentacyanoferrate(II) complexes have been compared with those for their pentacyanoruthenate(II) analogues. " ... 

This experiment involves advanced theory and substantial reagent preparation that requires outside-lab prep time. The goal of this experiment is to determine the standard reduction potentials (E°, V) for a series of substituted pentacyanoferrate(II) complexes. By comparing the electrochemical behavior of each AA ligand system, information about electronic structure and solution properties will be obtained. An introduction to cyclic voltammetry is given in Appendix 2. 

Results Summary for the CV Analysis of Substituted Pentacyanoferrate(II) Complexes,... 

EXPERIMENT 4.5 SEMI-EMPIRICAL CALCULATIONS IN THE STUDY OF SUBSTITUTED PENTACYANOFERRATE(II) COMPLEXES... 

A great deal of early work on the acidities of the azoles was performed by Catalan, Abboud, and Elguero [348]. They found, for instance, that annelation increases the gas-phase acidity by 5.9-8.2 kcal/mol [349], and carried out early DFT (B3LYP/6-31G ) calculations of the gas-phase acidities [350]. Lopez et al. [351] found that the pK values of pyrazoles and benzazoles display two straight lines when plotted against the oxidation potentials of pentacyanoferrate(II) complexes of these compounds allowing estimates for missing pK, values. 

The formation of some pentacyanoferrate(ii) complexes of aromatic heterocycles has been followed by the stopped-flow method. In the presence of excess ligand, varied over a large range of concentrations, each reaction was found to obey the rate law d[Fe(CN)jL -]/dr = A f[Fe(CN)5(H20) ][L], and the kinetic parameters (in particular AS see Table 10) are interpreted in terms of an nI mechanism. A... 

A study of photosubstitution in six (substituted) pyridine and pyrazine pen-tacyanocobaltate(III) complexes [Co(CN)5L]" complements an earlier study of similar pentacyanoferrate(II) complexes. Irradiation in ligand field bands results in 100% replacement of L by water quantum yields range from 0.12 to 0.40. The results are similar to those for the iron(II) complexes, with such differences as are observed assignable to the large difference in importance of tt back bonding to cobalt(III) and to iron(II). ... 

Kinetic data for formation of pentacyanoferrate(II) complexes [Fe(CN)5L]" from [Fe(CN)5(OH2)f" are shown in Table 8.2. The Eigen-Wilkins mechanism applies here overall formation rate constants kf are determined by outer-sphere association constants that is, mainly by electrostatics. However, there is an unexpected inconsistency if one compares N2H4/N2H5 with en/enH, though this may well arise in part from solvation effects (en much less hydrophilic and thus less heavily solvated than N2H4) (cf. previous paragraph),There seems to be some difficulty... 

Table 8.1. Kinetic Parameters for Substitution at Pentacyanoferrate(II) Complexes [Fe(CN) L], in Aqueous Solution at 298.2 K...

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