Two unusual mixed-valent trinuclear Cu^II₂Cu^I complexes containing copper(I) tribromide dianion as bridging ligand: identification of an unprecedented doubly hydrogen-bonded water dimer

Abstract

Two very rare mixed-valent Cu^II₂Cu^I trinuclear complexes, [Cu₂ (Br–L¹)₂CuBr₃]•2H₂O (1) and [Cu₂ (L²)₂CuBr₃]•2CH₃OH (2) have been synthesized using CuBr₂ and the tridentate reduced Schiff-base ligands HL¹ (2-[(2-dimethylamino-ethylamino)-methyl]-phenol) and HL² (2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol), respectively. The complexes have been characterized by X-ray structural analyses. In both complexes, the deprotonated tridentate reduced Schiff base forms a di-μ-phenoxo bridge between the two Cu^II centers and the CuBr₃²⁻ anion acts as an additional bridge between them to result in the trinuclear structures. During complex formation, ligand HL¹ has been brominated at the five position of the aromatic ring but HL² did not undergo any such reaction. In complex 1 an unprecedented doubly hydrogen-bonded water dimer, which is considered as an important transition state for the interchange of hydrogen atoms within the water dimer, has been identified. The dimensions of this water dimer agree quite well to those obtained from theoretical calculations.