Synthesis, Structural Characterization, Gas Sorption and Guest-Exchange Studies of the Lightweight, Porous Metal−Organic Framework α-[Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>]

Unsolvated magnesium formate crystallizes upon reaction of the metal nitrate with formic acid in DMF at elevated temperatures. Single-crystal XRD studies reveal the formation of [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃DMF], <b>1</b>, a metal−organic framework with DMF molecules filling the channels of an extended diamondoid lattice. The DMF molecules in <b>1</b> can be entirely removed without disruption to the framework, giving the guest-free material α-[Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>], <b>2</b>. Compound <b>2</b> has been characterized by both powder and single-crystal XRD studies. Thermogravimetric analyses of <b>1</b> show guest loss from 120 to 190 °C, with decomposition of the sample at approximately 417 °C. Gas sorption studies using both N<sub>2</sub> and H<sub>2</sub> indicate that the framework displays permanent porosity. The porosity of the framework is further demonstrated by the ability of <b>2</b> to uptake a variety of small molecules upon soaking. Single-crystal XRD studies have been completed on the six inclusion compounds [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃THF], <b>3</b>; [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃Et<sub>2</sub>O], <b>4</b>; [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃Me<sub>2</sub>CO], <b>5</b>; [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃C<sub>6</sub>H<sub>6</sub>], <b>6</b>; [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃EtOH], <b>7</b>; and [Mg<sub>3</sub>(O<sub>2</sub>CH)<sub>6</sub>⊃MeOH], <b>8</b>. Analyses of the metrical parameters of <b>1</b>−<b>8</b> indicate that the framework has the ability to contract or expand depending on the nature of the guest present.