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

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 CoIII2Cl2 bridges, and the [CoII2L2] metallocycles are linked by these CoIII2Cl2 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.