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

Abstract

The reaction of symmetrical ligands based on 3,6-di(2-pyridyl)pyridazine (L₁) with carbocyclic rings fused to the pyridazine ring; 7,10-di(2-pyridyl)-8,9-diazafluoranthene (L₂), 1,4-di(2-pyridyl)-6,7-dihydro-5H-cyclopenta[d]pyridazine (L₃), 1,4-di(2-pyridyl)-5,6,7,8-tetrahydrophthalazine (L₄), 1,4-di(2-pyridyl)-6,7,8,9-tetrahydro-5H-cyclohepta[d]pyridazine (L₅) 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 L₁ and L₃ gave saturated triple helicates (1 and 3, respectively), while [2 × 2]-grids were formed with more sterically hindered ligands (4 from L₄ and 5 from L₅), or if methanol (rather than acetonitrile) was used as the reaction solvent with L₃ (6). The most sterically-hindered ligand L₂ formed a mononuclear complex (2). The structures of these complexes in solution was determined by ¹H-NMR, and found to match their solid-state structures. The [2 × 2]-grids are effective molecular clips able to hold solvent and anions between their arms via hydrogen bonding to a Zn₄(H₂O)₂(OH)₂ core.