TRANSANNULAR OSCILLATION OF METAL CENTERS IN THE PENDANT ARM MACROCYCLIC COMPLEX [1,4,8,11-TETRAKIS(2-HYDROXYETHYL)-1,4,8,11-TETRAAZACYCLOTETRADECANE]MERCURY(II) AND ITS LEAD(II) ANALOG - NMR-STUDY OF THE C-13 NATURAL ABUNDANCE AND SPECIFICALLY ENRICHED COMPLEXES

A C-13 NMR study of [1,4,8,11-tetrakis(2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane]mercury(II) and its lead(II) analogue, [M(THEC)]2+ (M = Hg, Pb), in CD3OD, shows that the most probable structure of these complexes in solution incorporates the 1,4,8,11-tetraazacyclotetradecane ring in the trans III configuration with the metal center above the tetraaza plane and trigonal-prismatically coordinated by four ring nitrogens and two hydroxyethyl pendant arms attached to either end of the same 1,3-diaminopropane moiety. Dynamic C-13 NMR studies of [M(THEC)]2+ are consistent with a rapid pairwise intramolecular exchange of the hydroxyethyl arms between mono- and bidentate coordination simultaneously with the oscillation of M(II) through the macrocyclic annulus of THEC. This pairwise exchange of the hydroxyethyl arms is characterized by kappa{298.2 K) = 3130 +/- 120 and 11 220 +/- 200 s-1, DELTA-H = 38.0 +/- 0.6 and 45.4 +/- 0.3 kJ mol-1, and DELTA-S = -50.6 +/- 2.1 and -15.2 +/- 1.1 J K-1 mol-1, respectively, for M = Hg and Pb.