THERMODYNAMIC AND STRUCTURAL ASPECTS OF THE INTERACTION BETWEEN MACROCYCLIC POLYAMMONIUM CATIONS AND COMPLEXED ANIONS

The interaction of polyprotonated forms of [3k]aneN(k) (k = 7-12) macrocycles with the complexed anions Fe(CN)64-, Co(CN)63-, and Pt(CN)42- has been studied by potentiometry in 0.15 mol dm-3 NaClO4 solution at 298.15 K, and the stability constants of the second-sphere complexes formed have been determined. The interaction of (H(k)[3k]aneN(k))k+ (k = 7-11) cations with PtCl62 and Pt(CN)42- has been followed by Pt-195 NMR spectroscopy in 0.1 mol dm-3 HCl solutions at 298 K. The crystal structures of(H10[30]aneN10)[Pt(CN)4]5.2H2O (1) and (H10[30]aneN10)(PtCl6)2Cl6.2H2O (2) solid compounds have been determined by X-ray analysis. In (H10[30]aneN10)[Pt(CN)4]5.2H2O (space group P1BAR, a = 12.710 (3) angstrom, b = 9.839 (6) angstrom, c = 11.630 (3) angstrom; alpha = 80.91 (4)-degrees, beta = 89.45 (2)-degrees, gamma = 77.60 (6)-degrees; V = 1402 (1) angstrom3; Z = 1; R = 0.032; R(W) = 0.028) the centrosymmetric decaprotonated macrocycle has an elliptical shape with intramolecular distances between symmetry-related nitrogens of 6.2-13.4 angstrom. Two independent Pt(CN)42- anions, located outside the macrocyclic cavity, form very short hydrogen bonds with the protonated nitrogen atoms of the ligand. Also in (H10[30]aneN10)(PtCl6)2Cl6.2H2O (space group P1BAR, a = 7.704 (9) angstrom, b = 12.896 (4) angstrom, c = 14.268 (10) A; alpha = 108.87 (3)-degrees, beta = 101.53 (7)-degrees, gamma = 97.66 (5)-degrees; V = 1284 (2) angstrom3; Z = 1; R = 0.058; R(W) = 0.048) the decacharged macrocyclic cation is centrosymmetric and presents an elliptical shape with intramolecular distances between symmetry-related nitrogen atoms of 9.6-11.4 angstrom. In the crystal packing there exists a wide network of intermolecular contacts involving the protonated nitrogen atoms of the macrocycle, PtCl62-, Cl- anions, and water molecules. Both PtCl62- and Cl- anions are located outside the macrocyclic cavity. All results have been interpreted and discussed in terms of electrostatic attraction and hydrogen-bond formation between the polycharged macrocyclic cations and the complexed anions, as well as in terms of thc mutual conformations of both species.