Half a grid is better than no grid: competition between 2,2′:6′,2′′-terpyridine and 3,6-di(pyrid-2-yl)pyridazine for copper(ii)

Abstract

The reaction between Cu(NO₃)₂·3H₂O, 2,2′:6′,2′′-terpyridine (tpy) and 3,6-di(pyrid-2-yl)pyridazine (1) in a 2 : 2 : 1 molar equivalent ratio in aqueous MeCN in the presence of excess NH₄PF₆ leads to competition between the assembly of the dinuclear half-grid [Cu₂(1)(tpy)₂][PF₆]₄·2H₂O and the mononuclear complex [Cu(1)₂(OH₂)][PF₆]₂. The yield of [Cu₂(1)(tpy)₂][PF₆]₄·2H₂O has been optimized using microwave conditions. [Cu(1)₂(OH₂)][PF₆]₂ can be selectively produced by treating Cu(NO₃)₂·3H₂O with 1 (1 : 2 molar equivalents) in aqueous MeCN in the presence of NH₄PF₆. The single crystal structures of [Cu₂(1)(tpy)₂][PF₆]₄·4MeNO₂ and [Cu(1)₂(OH₂)][PF₆]₂ are presented. In the [Cu₂(1)(tpy)₂]⁴⁺ cation, ligand 1 bridges the two copper(II) centres, each of which is further coordinated by a tpy ligand. The copper(II) coordination geometry is closely associated with the arrangement of the two tpy ligands which engage in efficient face-to-face π-stacking. Magnetic data for crystalline [Cu₂(1)(tpy)₂][PF₆]₄·4MeNO₂ are consistent with a weak antiferromagnetic interaction between the two copper(II) centres. EPR spectroscopic data for a powder sample of [Cu₂(1)(tpy)₂][PF₆]₄·2H₂O are consistent with the dinuclear structure, but in frozen DMF and DMSO solutions, the data indicate that the dinuclear structure of [Cu₂(1)(tpy)₂]⁴⁺ is not preserved.