Temperature-Dependent in Situ Reduction of 4,4′-Azobispyridine via Solvothermal Reaction

Solvothermal reactions of 2,2′-biphenyldicarboxylate (H2dpa) and 4,4′-azobispyridine (azpy) in the presence of transition metal ions produce six new complexes, namely, [Co­(dpa)­(bphy)]n (1), [Co­(dpa)­(azpy)­(H2O)]n·0.5nH2O (2), [Zn­(dpa)­(bphy)]n (3), [Zn­(dpa)­(azpy)­(H2O)]n (4), [Mn­(dpa)­(azpy)­(H2O)]n·0.5nH2O (5), and [Mn­(dpa)­(azpy)]n·nH2nMeOH (6) (bphy = 1,2-bis­(4-pyridyl)­hydrazine). The crystal structure analyses reveal that complexes 1 and 3 are isostructural which features a plywood-like structure, while complex 4 exhibits a parallel chains array. Complexes 2 and 5 afford a two-dimensional chiral (4,4) network, and complex 6 shows a (4,4) network. It was noteworthy that the in situ reduction of azpy to bphy was found in complexes 1 and 3, which were confirmed by single-crystal structures and LC-MS analyses. However, this in situ reduction was not found at a low reaction temperature in the syntheses of complexes 2, 4, and 5. The second-harmonic-generation (SHG) properties of 1 and 3 and the solid circular dichroism (CD) properties of 2 and 5 were investigated. In addition, luminescent properties of complexes 3 and 4 as well as magnetic properties of complexes 1, 2, 5, and 6 were also studied.