PROTON-TRANSFER IN A PHENOL-BASED COMPARTMENTAL CRYPTATE - SOLUTION AND SOLID-STATE STRUCTURAL STUDIES

Under pH-neutral conditions, a potentially dinucleating azacryptand N[ (CH2)2N=CH-R-CH=N(CH2)2]3N L1(R = m-C6H2OH-2-Me-5) was found to accomm odate just one metal cation; H-1 NMR spectra showed that the second si te is occupied by three protons transferred from phenol to imino N. Un der basic conditions, the protons can be displaced by a second cation forming a dinuclear cryptate. X-Ray crystallographic structure determi nations have been made for the complexes [PbL1][BPh4]2, two forms of [ CdL1][ClO4]2, a and b and [Cd2(L1 - 3H)][ClO4]2. In the first three co mplexes one metal ion is encapsulated within the macrocycle. However i n all three cases the position is disordered over two equivalent sites ; in the lead compound in the ratio 0.87:0.13 and in the cadmium compo und a 0.66:0.34. In b the disorder is over two equivalent crystallogra phic positions so the ratio is 0.50:0.50. In the last complex two cadm ium cations occupy the macrocycle. In all four structures the metal at oms are bonded to all three oxygen atoms and three imine atoms. In add ition there is an interaction with a bridgehead nitrogen atom so that the metal co-ordination spheres can best be considered as seven-co-ord inate capped octahedra.