Influence of Water Ligands on Structural Diversity: From a One-Dimensional Linear Coordination Polymer to Three-Dimensional Ferrimagnetic Diamondoid Metal−Organic Frameworks

Four three-dimensional (3D) metal−organic frameworks [Mn<sub>3</sub>(3-Me-sal)<sub>4</sub>(py)<sub>4</sub>]<sub><i>n</i></sub> (<b>1</b>), [Mn<sub>3</sub>(4-Me-sal)<sub>4</sub>(py)<sub>4</sub>(MeOH)]<i><sub>n</sub></i>·<i>n</i>(H<sub>2</sub>O) (<b>2</b>), [Mn<sub>3</sub>(5-Me-sal)<sub>4</sub>(py)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]<sub><i>n</i></sub>·<i>n</i>(MeOH) (<b>3</b>), and [Mn<sub>3</sub>(3-Me-sal)<sub>4</sub>(4-Me-py)<sub>4</sub>]<sub><i>n</i></sub> (<b>4</b>) and the one-dimensional (1D) coordination polymer {[Mn<sub>2</sub>(4-Me-sal)<sub>2</sub>(4-Me-py)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>(MeOH)<sub>2</sub>][Mn(4-Me-sal)<sub>2</sub>(4-Me-py)<sub>2</sub>]}<sub><i>n</i></sub> (<b>5</b>) have been synthesized, where x-Me-salH<sub>2</sub> = x-methyl salicylic acid (x = 3, 4, 5), py = pyridine, and 4-Me-py = 4-methyl-pyridine. The 3D frameworks of compounds <b>1</b>−<b>4</b> can be described as diamondoid networks. Magnetic studies show that weak Mn<sup>II</sup>−Mn<sup>III</sup> antiferromagnetic interactions (in the range of −0.55 to −0.22 K) mediated by <i>syn-anti</i> carboxylate bridges are present in all compounds. While <b>5</b> remains paramagnetic down to 1.8 K, the 3D networks exhibit long-range ferrimagnetic ordering below 7.4 K for <b>1</b>, 4.6 K for <b>2</b>, 3.0 K for <b>3</b>, and 7.7 K for <b>4</b>. The decrease of the critical temperature reflects the increase of the coordination number around the Mn(II) site from four in <b>1</b>, five in <b>2</b>, and six in <b>3</b> that lower the bond strength and the magnetic interactions. This result also reinforces the hypothesis that the structures of <b>1</b> and <b>4</b> are similar as suggested by the X-ray analysis.