A family of [Cu2], [Cu4] and [Cu5] aggregates: alteration of reaction conditions, ancillary bridges and capping anions

Abstract

The phenoxido-bridged [Cu₂] complex [Cu₂(μ-H₄L1)(μ-OH)(μ_1,3-NO₃)(NO₃)(OH₂)]·H₂O (1) and its hierarchical [Cu₄] and [Cu₅] assemblies [Cu₄(μ-H₄L1)₂(μ-OH)₂(μ_1,3-ClO₄)(OH₂)₂](ClO₄)₃·2H₂O (2) and [Cu₅(μ-H₄L1)₂(μ₃-OH)₂(μ_1,3-O₂CCF₃)₂(O₂CCF₃)₂](CF₃COO)₂ (3) were obtained from the reactions of H₅L1 (2,6-bis-{(1,3-dihydroxy-2-methylpropan-2-ylimino)methyl}-4-methylphenol) with three copper(II) salts. The available NO₃⁻, ClO₄⁻ and CF₃COO⁻ ions have been trapped for ‘spontaneous’ anion-directed ‘self-assembly’ reactions. All the synthesized complexes contain the [Cu₂(μ-H₄L1)(μ-OH)]²⁺ fragment, prone to assemble and crystallize [Cu₄] and [Cu₅] complexes under varying reaction conditions. They were characterized by UV-vis and IR spectroscopy, X-ray diffraction analysis and magnetic studies. A change from NO₃⁻ to ClO₄⁻ and CF₃COO⁻ results in different courses of reactions based on Cu₂(μ-H₄L1) fragments. Binding of NO₃⁻ provided 1 as an isolated [Cu₂] complex by trapping the reactive fragment. In 2 a perchlorate ligand, in the μ_1,3-binding mode, has been realized as a solitary support for the condensation of two Cu₂(μ-H₄L1) fragments. The {Cu₅(μ₃-OH)₂(μ_1,3-O₂CCF₃)₂}⁶⁺ constellation in 3 contains five Cu^II centers with a unique Z-in distorted octahedral one at the central position. Binding of different anions to the copper(II) centers controls the nuclearity of the reaction products and tuning of the self-aggregation process within the same ligand environment (μ-H₄L1⁻). The magnetic properties of the compounds have been studied both experimentally and using DFT calculations, revealing moderate to strong antiferromagnetic coupling in all aggregates.