Self-assembly of [2+2] Co(II) metallomacrocycles and Ni(II) metallogels with novel bis(pyridylimine) ligands

Two novel 46-membered Co(II) metallomacrocycles, [Co2Cl4(L1)2]·CH2Cl2 and [Co2(NO3)2(L1)2(H2O)2⊂(NO3)](NO3)·4H2O, with 1,4-bis[4-(2-pyridylmethylideneamino)phenyloxy]benzene (L1) have been synthesized and characterized. Both Co(II) centers in these dinuclear complexes possess an octahedral coordination environment formed by a N4 donor set of two L1 ligands and two chloride or one monodentate nitrate and one water molecule, respectively. Whereas in the first case disordered solvent molecules are present in the macrocycle's cavity in the second one a nitrate anion is embedded. Furthermore, the molecular structures of L1, L3 and L4 were determined and solution studies of the complex formation of these ligands with Co(II), Ni(II) and Cu(II) in dichloromethane/methanol (v/v = 1:1) using UV/Vis and ESI-MS spectroscopic measurements were performed. In contrast to the self-assembling behavior of the bis(2-pyridylimine) ligand L1 the bis(3-pyridylimine) ligand L4 was also demonstrated to form metallogels when reacted with NiCl2·6H2O in tetrahydrofuran under defined conditions.