Pyridazine-bridged copper(i) complexes of bis-bidentate ligands: tetranuclear [2 × 2] grid versus dinuclear side-by-side architectures as a function of ligand substituents?

Dalton Transactions Pub Date: 2007-03-06 DOI: 10.1039/B700503B

Abstract

Eight bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted amino-benzenes, have been prepared. A variety of electron donating/withdrawing and/or sterically demanding/undemanding substituents were employed. Two ligands and five of the six pure copper(I) complexes have been structurally characterised. The sterically unhindered ligand derived from 3,5-difluoroaniline, Lm,m-F, was almost completely flat whereas the very sterically hindered ligand derived from trimethylaniline, Lo,o,p-Me, was severely twisted. The only dinuclear side-by-side complex obtained, [CuI2(Lo-Ph)2](PF6)2, was of the ligand derived from 2-aminobiphenyl. All five of the other complexes are believed to be [2 × 2] tetranuclear grid complexes, and this was unequivocally shown to be the case for four of these complexes, [CuI4(Lp-Me)4](PF6)4, [CuI4(Lo,p-Me)4](PF6)4, [CuI4(Lm,m-F)4](PF6)4 and [CuI4(Lm,m-Cl)4](PF6)4. In all cases the copper(I) centres are substantially distorted from tetrahedral, with the most severe distortion present in the side-by-side complex. In the absence of any special effects, tetracopper(I) [2 × 2] grid architectures are observed to be the favored outcome for 1?:?1 reactions of these bis-bidentate ligands with copper(I) ions. Only when the aromaticity of the ligand was extended by employing a phenyl substituent on the phenyl rings, Lo-Ph, did a dicopper(I) side-by-side architecture result. Cyclic voltammetry in acetone revealed that the free ligands did not undergo reduction until potentials below ?0.8 V, whereas between three and four reversible one electron reductions were observed, between +0.16 and ?0.71 vs. AgCl/Ag, for the tetranuclear copper(I) [2 × 2] grid complexes. The redox potentials observed for these complexes are highly dependent on the nature of the ligand phenyl ring substituent(s). The side-by-side complex had one irreversible reduction process, Epcca. ?0.5 V.

Graphical abstract: Pyridazine-bridged copper(i) complexes of bis-bidentate ligands: tetranuclear [2 × 2] grid versus dinuclear side-by-side architectures as a function of ligand substituents
Recommended Literature