Copper coordination to the aldehyde and hemiacetal form of 4-bromo-2-[(2-diethylaminoethyl)ethylaminomethyl]-6-formylphenol: Synthesis and structure of [Cu(H₂L)₂(X)₂] X₂ · nH₂O (X = NO₃^-, CIO₄^-) and [Cu(L′)]₂ · 2CH₃OH

The coordination behaviour of Cu²⁺ towards 4-bromo-2-[(2-diethylaminoethyl)ethyl-aminomethyl]-6-formylphenol (HL) having phenolate, amine and aldehyde donor sites has been studied. In aqueous, weakly acidic solution Cu²⁺ coordinates to the phenolate and aldehyde oxygen giving rise to the complexes [Cu(H₂L)₂X₂]X₂ (X = NO₃^- (1a) and CIO₄^- (1b)), while in alkaline solution a complex of composition [CuL₂] (2) is formed. In methanol, the aldehyde groups in 1 and 2 suffer nucleophilic attack from the solvent resulting in the formation of the hemiacetal form of the ligand and in the isolation of [Cu(L′)]₂ · 2CH₃OH (3). X-ray structures of 1a, 1b and 3 are reported, the latter featuring a rare example of a coordinated methyl-hemiacetal.