• complexation;
  • copper;
  • host–guest systems;
  • metallacrowns;
  • supramolecular chemistry


Reaction of CuF2 with one equivalent of 3{5}-(pyrid-2-yl)-5{3}-(tertbutyl)pyrazole (HL) and excess NH4OH in MeOH affords crystalline [NH4{Cu(μ-F)(μ-L)}6(CH2Cl2)2]HF2 in moderate yield. This compound contains the 12-MC-6 metallacrown [{Cu(μ-F)(μ-L)}6] (1) with a NH4+ ion at its center, and CH2Cl2 molecules complexed in bowl-shaped cavities above and below the Cu6F6 ring. Similar reactions using the bases MeNH2, glycine, l-alanine or β-alanine afforded solvated crystals of [1(H3NMe)2]Cl2, [1(gly)2], [1(l-ala)2], and [1(β-ala)2], respectively. The metallacrown 1 in these products contains methylammonium and zwitterionic amino-acid guests in its two bowl-shaped cavities; each of the amino acids hydrogen-bonds to three F atoms. A related reaction using 1,6-diaminohexane resulted in fixation of CO2 from the air to give solvated [1(H3NC6H12NHCO2)2], again with a zwitterionic guest. NMR, ESI-MS and UV/vis measurements suggest that the metallacrown 1 retains its integrity in several organic solvents, although it is unclear to what extent guest binding takes place in solution.