Synthesis, conformational studies and inclusion properties of N-substituted tetrahomodiazacalix[4]arenes

A series of tetrahomodiazacalix[4]arenes (1–8) with different substituents (or substituted) at the upper rim and/or N-side arm has been synthesized with acceptable yields. The compounds were characterized by elemental analysis, IR, MS and NMR methods. In particular, 5 was shown by X-ray crystallography to adopt the cone conformation in the solid state. Two-phase picrate extraction showed that 2 and 6, bearing N-2-picolyl arms, are the best extractants. Of the cations tested, Ag(I) is the best extracted by almost all ligands and the extraction efficiency follows the order 2-picolyl > 3-picolyl > 4-picolyl.