Kinetically inert cryptate systems: solid state and solution NMR studies

Mononuclear cryptates of Pb2+, Cd2+ and Hg2+ with the small host 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosa-4,6,13,15,21,23-hexaene (imBT) showed satellite peaks in H-1 NMR solution spectra throughout the accessible (-40 to +70 degrees C) fluid range of solvents used indicating kinetic inertness toward decomplexation. Solid-state MAS NMR studies were made on these cryptates and on dinuclear silver(I) and copper(I) analogues, in the latter case establishing coupling of Cu-63,Cu-65 to N-15. A crystal structure determination of the mercury cryptate showed a symmetrical six-co-ordinate site for Hg2+ with all imino nitrogens co-ordinated, consistent with the observation, for the isomorphous cadium(II) complex, of a 13-line Cd-113 resonance in the CP MAS NMR spectrum.