SELF-ASSEMBLING NICKEL CLUSTERS FORM BINDING-SITES FOR ALKALI-METAL CATIONS - NOVEL ANALOGS OF ENOLATE AGGREGATES

Salicylaldimine ligands having 3-methoxy or 3-(2-methoxyethoxy) side arms react with NiSO4 or Ni(OAc)2 to form novel bimetallic cage structures involving ligands, nickel atoms, and one or more types of counteranions. The cluster structures exhibit complexation properties and are of general interest because of their similarity to known alkali organometallic aggregates. Mixed transition metal-alkali metal aggregates of this type are very little known. In the present case, one aggregate is a donor-acceptor array comprised of four ligands, two nickel atoms, two sodium atoms, integral picrate anions, and water. This previously unknown complexation mode was verified in the solid state by X-ray structure analysis and in the solution state by a variety of techniques. Although the two complexes reported here have different stoichiometries and arise from different nickel reagent starting materials, the overall form of the cation-coordinating cage structure in each case is nearly identical, suggesting that the structural array is of a general type. Inferences about solution structure have been drawn from cation complexation profiles. Previous structural suggestions have proved incorrect, and follow-up work has failed to provide any structural alternative to that shown here.