Structural control: can [2 × 2] silver grids be formed from 4,5-disubstituted 3,6-di(2-pyridyl) pyridazines?

Abstract

The reaction of ligands based on 3,6-di(2-pyridyl)pyridazine with symmetrical carbocyclic rings fused to the pyridazine ring; 7,10-di(2-pyridyl)-8,9-diazafluoranthene (L₁), 1,4-di(2-pyridyl)-6,7,8,9-tetrahydro-5H-cyclo-hepta[d]pyridazine (L₂), 1,4-di(2-pyridyl)-5,6,7,8-tetrahydro-phthalazine (L₃), 1,4-di(2-pyridyl)-6,7-dihydro-5H-cyclo-penta[d]pyridazine (L₄) with silver salts gave a series of complexes (1–7). Characterisation of these using single crystal X-ray structure determination clearly showed that the steric bulk of the carbocycle affects the degree to which pyridine groups remain co-planar with pyridizine, and hence their ability to chelate. The more hindered ligands L₁–L₃ form a mixture of bischelating and tetrabridging, while the least hindered (L₄) was able to chelate exclusively. In the case of L₄, the nature of the anion and solvent were also able to affect the outcome of the reaction, with tetrafluoroborate giving the first example of a 4,5-substituted 3,6-di(2-pyridyl)pyridazine ring forming a [2 × 2]-grid.