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Keywords:

  • Supramolecular chemistry;
  • Self-assembly;
  • Macrocycles;
  • Palladium;
  • S li­gands;
  • Density functional calculations

Abstract

Seven dinuclear macrocyclic palladium(II) dithiocarbamates have been prepared from a homologous series of aliphatic 1,x-diamines (x = 4–10); the objective was to vary systematically the size of the cavity. The resulting complexes were characterized by IR and NMR (1H, 13C) spectroscopy, high-resolution FAB mass spectrometry, and in one case additionally by single-crystal X-ray diffraction analysis. Geometry-optimizations using the B3LYP functional in combination with the def2-SVP basis set were performed for the complete series of 22- to 36-membered macrocycles and showed that these can be divided into two classes. Palladium(II) dithiocarbamates with an even number of methylene spacer groups yield macrocycles of rectangular shape with overall dimensions that vary from 6.0 × 14.5 × 12.7 to 6.0 × 15.7 × 19.9 Å3, whereas an odd number generates hexagon-shaped assemblies with overall dimensions in the range 5.0 × 16.3 × 13.0 to 6.0 × 21.1 × 18.7 Å3. The computational analysis ruled out the possibility that monomeric structures had formed and indicated that for the creation of strain-free mononuclear macrocyclic structures at least 14 methylene groups are required in the spacer.