Kinetically inert cryptate systems: solid state and solution NMR studies†

Abstract

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 ¹H NMR solution spectra throughout the accessible (–40 to +70 °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 ^63,65Cu to ¹⁵N. 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 cadmium(II) complex, of a 13-line ¹¹³Cd resonance in the CP MAS NMR spectrum.