Conformational control of the self-assembly of triple helicates and [2 x 2]-grids from zinc(II) and 3,6-di(2-pyridyl)pyridazine based ligands

The reaction of symmetrical ligands based on 3,6-di(2-pyridyl)pyridazine (L-1) with carbocyclic rings fused to the pyridazine ring; 7,10-di(2-pyridyl)-8,9-diazafluoranthene (L-2), 1,4-di(2-pyridyl)-6,7-dihydro-5H-cyclopenta[d]pyridazine (L-3), 1,4-di(2-pyridyl)-5,6,7,8-tetrahydrophthalazine (L-4), 1,4-di(2-pyridyl)-6,7,8,9-tetrahydro-5H-cyclohepta[d]pyridazine (L-5) in reactions with zinc perchlorate gave a series of complexes (1-6). Characterisation of these using single crystal X-ray structure determination showed that less sterically hindered L-1 and L-3 gave saturated triple helicates (1 and 3, respectively), while [2 x 2]-grids were formed with more sterically hindered ligands (4 from L-4 and 5 from L-5), or if methanol (rather than acetonitrile) was used as the reaction solvent with L-3 (6). The most sterically-hindered ligand L-2 formed a mononuclear complex (2). The structures of these complexes in solution was determined by H-1-NMR, and found to match their solid-state structures. The [2 x 2]-grids are effective molecular clips able to hold solvent and anions between their arms via hydrogen bonding to a Zn-4(H2O)(2)(OH)(2) core.