Valentin N. Sapunov

A new table of the thermodynamic quantities of ionic hydration: values and some applications (enthalpy–entropy compensation and Born radii)

Absolute single-ion thermodynamic quantities of hydration at 298.15 K are derivable from the conventional enthalpies and entropies if the values of S°(Haq+) and ΔhydH°(H+) are known. Here we suggest S°(Haq+) = −5.5 J K−1 mol-1 based on the thermodynamics of the dissociation of water. This assignment, in turn, corresponds to ΔhydH°(H+) = −1078 kJ mol-1 according to a self-consistent analysis of Krestov. Using these values, as a main result, the anions are more strongly hydrated than usually thought, in line with recent calculations. Only the group 1, 2, and 15 nobel gas ions are dealt with. For each series, the conventional enthalpies and entropies are linearly related to one another. From these linear free energy relationships (LFERs) a relationship between S°(Haq+) and ΔhydH°(H+) is derived. Further, a connection is detected between the Born radii rB, calculated from the free energies of hydration, and the distances d, corresponding to the upper limits of the experimental first peak position of the ionoxygen radial distribution curves, upon implication, in the case of a cation, the covalent radius rcov of oxygen, and in the case of an anion, the water radius rwater, Finally, from the differences between the enthalpies and free energies of hydration the temperature derivatives of the Born radii are determined.

The importance of interligand interactions to structure and reactivity of coordinatively unsaturated ruthenium and iron half-sandwich complexes—application of the TSC concept II

Abstract The interaction between any fragments bonded to some central atom are increasingly recognized as an important factor in determining, e.g. the geometry and properties of metal complexes. Here we analyze the class of the two-legged piano stool complexes Cp′ML 2 (Cp′=cyclopentadienyl or a derivative, M=Fe(II) and Ru(II), L=phosphorus and nitrogen co-ligands) with the aid of the through-space coupling (TSC) concept. This is the molecular orbital representation of van der Waals-like repulsive–attractive forces between the ligands in addition to the interactions with the metal center. The combination of both, i.e. the interaction between the new collective ligands orbitals and the metal AOs is shown to be the main determinant for deciding whether a planar or pyramidal structure is adopted and further, whether the complex is diamagnetic or paramagnetic. In addition the TSC concepts aids in understanding the effect of intercomplex interactions on the nucleophilic and electrophilic behavior of the 16e-complexes towards an incoming ligand. In fact, interpretations hitherto solely in terms of electronic ligand effects appear to be inadequate. The present paper is a continuation of our former work in which we successfully applied the TSC concept to rationalize the diverse array of structural arrangements as well as reactivities of the main-group Cp metal complexes (Sapunov et al. Coord. Chem. Reviews 214 (2001) 143).

Kinetik und Mechanismus des Ligandentausches zwischen Thallium(III)oxinat und Eisen(III) in Propylencarbonat

The transfer of oxinate ions from thallium (III)oxinate to trivalent Fe(DMF)63+ in propylenecarbonate takes place via rearrangements within a rapidly formed binuclear thallium(III)—iron(III) complex. In a last rapid step this rearranged complex reacts with excess reactants to the final products whose composition accordingly depends on the ratio of the reactant concentrations.

Redoxkinetik von Metallkomplexen in nichtwäßrigen Lösungen, XI. Die Reduktion von Thallium(III)oxinat mit Eisen(II) in schwach koordinierenden Lösungsmitteln

The kinetics of the iron(II) reduction of thallium(III) oxinate does not differ essentially from that of the oxinate-transfer from thallium(III)-oxinate to iron(III), described before: formation of a binuclear intermediate, rearrangements within, and subsequent reaction with the excess reactant to the final products. As for the redox process, these intermediates are binuclear Tl(II)-Fe(III) complexes which, with initial reactants, form further complexes in which the second electron is transferred. In the cases of excess Tl(ox)3 and of equimolar reactants, disproportionations are likely involved.

Ruthenium tris(pyrazolyl)borate complexes. Formation and characterization of acetone, dimethylformamide and vinylidene complexes containing N,N-donor co-ligands

Chloride abstraction from [Ru{HB(pz)3}(tmen)Cl](pz = pyrazolyl, tmen = Me2NCH2CH2NMe2) with NaBPh4 in the solvents acetone and dimethylformamide led to the formation of the respective cationic [Ru{HB(pz)3}(tmen)(solv)]+ complexes. In the presence of phenylacetylene, these are easily transformed into the first example of a ruthenium HB(pz)3 vinylidene complex. Extended-Huckel molecular-orbital calculations have been performed to establish the nature of the bonding involved. From [Ru{HB(pz)3}(py)2Cl](py = pyridine) the corresponding vinylidene complex could be prepared in the same way, although the intermediate solvent complexes could not be isolated. Selected crystal structures were determined.