Effect of methylation on the coordination of copper by small azacryptands; the role of geometrically constrained hydrogen bonding in stabilizing terminally coordinated oxygen species

Abstract

Treatment of N-methyl substituted aminocryptand hosts with copper(II) generates monocopper(II) cryptates where copper(II) coordinates an oxygen-centered species, formally H₃O⁺, which is also strongly hydrogen bonded to three aminocryptand N-methyl atoms via bonds which may best be viewed as NH^δ+⋯O^δ− in consequence of charge transfer. The strength of this hydrogen bonding precludes successful competition of another copper ion for the second coordination site thus suppressing formation of any Cu–Cu bonded average-valent system.