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)

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.