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

Solvothermal reactions of 2,2′-biphenyldicarboxylate (H<sub>2</sub>dpa) and 4,4′-azobispyridine (azpy) in the presence of transition metal ions produce six new complexes, namely, [Co­(dpa)­(bphy)]<sub><i>n</i></sub> (<b>1</b>), [Co­(dpa)­(azpy)­(H<sub>2</sub>O)]<sub><i>n</i></sub>·0.5<i>n</i>H<sub>2</sub>O (<b>2</b>), [Zn­(dpa)­(bphy)]<sub><i>n</i></sub> (<b>3</b>), [Zn­(dpa)­(azpy)­(H<sub>2</sub>O)]<sub><i>n</i></sub> (<b>4</b>), [Mn­(dpa)­(azpy)­(H<sub>2</sub>O)]<sub><i>n</i></sub>·0.5<i>n</i>H<sub>2</sub>O (<b>5</b>), and [Mn­(dpa)­(azpy)]<sub><i>n</i></sub>·<i>n</i>H<sub>2</sub>O·<i>n</i>MeOH (<b>6</b>) (bphy = 1,2-bis­(4-pyridyl)­hydrazine). The crystal structure analyses reveal that complexes <b>1</b> and <b>3</b> are isostructural which features a plywood-like structure, while complex <b>4</b> exhibits a parallel chains array. Complexes <b>2</b> and <b>5</b> afford a two-dimensional chiral (4,4) network, and complex <b>6</b> shows a (4,4) network. It was noteworthy that the in situ reduction of azpy to bphy was found in complexes <b>1</b> and <b>3</b>, 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 <b>2</b>,<b> 4</b>, and <b>5</b>. The second-harmonic-generation (SHG) properties of <b>1</b> and <b>3</b> and the solid circular dichroism (CD) properties of <b>2</b> and <b>5</b> were investigated. In addition, luminescent properties of complexes <b>3</b> and <b>4</b> as well as magnetic properties of complexes <b>1</b>, <b>2</b>, <b>5</b>, and <b>6</b> were also studied.