Solvent-directed conformational variation of Co(ii)/(iii) complexes with a diiminopyridine ligand

Abstract

The reaction of CoCl₂·6H₂O or Co(NO₃)₂·6H₂O with a semi-rigid ditopic ligand 2,6-bis(1-(2,6-diisopropyl-4-(pyridin-3-yl)phenylimino)ethyl)pyridine (L) in various solvent systems led to four complexes, {[CoCl₂L₂]·CH₂Cl₂}_n (1a), {[Co(NO₃)₂L₂]·CH₂Cl₂}_n (1b), {[Co₄(μ₂-Cl)₂(μ₂-L)₂Cl₈]·xH₂O}_n (2), and [Co₄(NO₃)₈L₂(CH₃CN)₂]·xH₂O (3). Compounds 1a and 1b are isostructural 1D looped-chain coordination polymers constructed by 44-membered [Co₂L₂] macrocyclic units. Compound 2 shows an unprecedented double μ₂-Cl bridged 1D chain structure containing 36-membered [Co₄L₂] macrocycles. Interestingly, the Co(II) ions are partially oxidized to form the Co^III₂Cl₂ bridges, and the [Co^II₂L₂] metallocycles are linked by these Co^III₂Cl₂ units to generate the 1D chain. Compound 3 is a discrete 0D 36-membered metallomacrocycle comprised of four Co(II) ions and two bridging ligands. The structural variation of the complexes is related to the conformational changes of the semirigid ligand L induced by different solvent systems.