Synthesis of a tube-like tetra-bipyridyl, tetra-ethylacetato-calix[4]arene in 1,3-alternate conformation and the unexpected crystal structure of its [bpy(CoCl2)]3-[bpy(CoCl2)(H2O)] complex

Abstract

Treating conic tetra-para-ethylacetato-calix[4]arene (1) with 2.2 equivalents of K₂CO₃ and 4 equivalents of 6-bromomethyl-6′-methyl-2,2′-bipyridine affords the expected fully substituted podand, mainly in its 1,3-alternate conformation (2). This tube-like bipyridyl derivative 2 was subjected to complexation studies with CoCl₂·6H₂O to give a blue tetra cobalt(II) complex species (3). This complex displays a unique group of 6 aromatic bipyridyl ¹H-NMR resonance signals demonstrating its high symmetry, while X-ray diffraction studies showed the presence of 3 expected tetrahedral bpy(CoCl₂) units and 1 original trigonal bipyramidal unit involving the adjunction of a fifth ligand assumed to be H₂O that could participate in the crystal scaffold.