A {sup 13}C NMR study of (1,4,8,11-tetrakis(2-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane)cadmium(II), (Cd(THEC)){sup 2+}, in CD{sub 3}OD shows that the most probable structure for (Cd(THEC)){sup 2+} incorporates the 1,4,8,11-tetraazacyclotetradecane ring in the trans III configuration. In this structure Cd(II) is above the tetraaza plane and is trigonal-prismatically coordinated by four ring nitrogens and two hydroxyethyl pendant arms attached to either end of the same 1,3-diaminopropane moiety. The {sup 13}C CPMAS NMR spectrum of solid (Cd(THEC)){sup 2+} is also consistent with this structure. Dynamic {sup 13}C NMR studies of natural abundance (Cd(THEC)){sup 2+} and of (Cd(THEC)){sup 2+} in which both carbons of each of the hydroxyethyl arms are 99 atom % enriched in {sup 13}C are consistent with a rapid oscillation of Cd(II) through the macrocyclic annulus of THEC. The {sup 13}C-enriched hydroxyethyl arms are characterized by {sup 13}C AB quartets under conditions of slow exchange but show a novel coalescence to a singlet under fast-exchange conditions consistent with the relative chemical shifts of the methylene carbons of the hydroxyethyl arm being reversed when it changes from the mono- to the bidentate coordination state. The pairwise exchange of the hydroxyethyl arm between the monodentate and bidentate environments is characterized by k(298.2 K) = 34,200 {plus minus} more » 1,800 s{sup {minus}1}, {Delta}H{double dagger} = 44.00 {plus minus} 0.56 kJ mol{sup {minus}1}, and {Delta}S{double dagger} = {minus}10.6 {plus minus} 2.2 J K{sup {minus}1} mol{sup {minus}1}. {sup 13}C and {sup 113}Cd NMR spectra show that intermolecular THEC and Cd(II) exchange on (Cd(THEC)){sup 2+} is a much slower process. 29 refs., 6 figs. « less