A bis-calix[4]arene-supported [Cu II16] cage

Abstract

Reaction of 2,2′-bis-p-^tBu-calix[4]arene (H₈L) with Cu(NO₃)₂·3H₂O and N-methyldiethanolamine (Me-deaH₂) in a basic dmf/MeOH mixture affords [Cu^II₁₆(L)₂(Me-dea)₄(μ₄-NO₃)₂(μ-OH)₄(dmf)_3.5(MeOH)_0.5(H₂O)₂](H₆L)·16dmf·4H₂O (4), following slow evaporation of the mother liquor. The central core of the metallic skeleton describes a tetracapped square prism, [Cu₁₂], in which the four capping metal ions are the Cu^II ions housed in the calix[4]arene polyphenolic pockets. The [Cu^II₈] square prism is held together “internally” by a combination of hydroxide and nitrate anions, with the N-methyldiethanolamine co-ligands forming dimeric [Cu^II₂] 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 [Cu₁₆] 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.