A bis-calix[4]arene-supported [Cu^II ₁₆] cage

Reaction of 2,2'-bis-p-Bu-t-calix[4]arene (H8L) with Cu(NO3) (2)center dot 3H(2)O and N-methyldiethanolamine (MedeaH(2)) in a basic dmf/MeOH mixture affords [Cu-II (16)(L)(2)(Me-dea)(4)(mu(4)-NO3)(2)(mu-OH)(4)(dmf)(3.5)(MeOH)(0.5)(H2O)(2)] (H6L)center dot 16dmf center dot 4H(2)O (4), following slow evaporation of the mother liquor. The central core of the metallic skeleton describes a tetracapped square prism, [Cu-12], in which the four capping metal ions are the Cu-II ions housed in the calix[4]arene polyphenolic pockets. The [Cu-II (8)] square prism is held together "internally" by a combination of hydroxide and nitrate anions, with the N-methyldiethanolamine co-ligands forming dimeric [Cu-II (2)] units which edge-cap above and below the upper and lower square faces of the prism. Charge balance is maintained through the presence of one doubly deprotonated H6L2- ligand per [Cu-16] cluster. Magnetic susceptibility measurements reveal the predominance of strong antiferromagnetic exchange interactions and an S = 1 ground state, while EPR is consistent with a large zero-field splitting.