Pillaring Role of 4,4′-Azobis(pyridine) in Substituted Malonate-Containing Manganese(II) Complexes: Syntheses, Crystal Structures, and Magnetic Properties

Six new manganese­(II) complexes of formulas [Mn<sub>2</sub>(Rmal)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>(azpy)]<sub><i>n</i></sub> (<b>1</b>–<b>3</b>), [Mn­(Phmal)­(H<sub>2</sub>O)­(azpy)]<sub><i>n</i></sub> (<b>4</b>), [Mn<sub>2</sub>(Et<sub>2</sub>mal)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>(azpy)<sub>2</sub>]<sub><i>n</i></sub> (<b>5</b>), and [Mn­(Bzmal)­(H<sub>2</sub>O)<sub>3</sub>(azpy)] (<b>6</b>) [azpy = 4,4′-azobispyridine (<b>1</b>–<b>6</b>), Rmal = methylmalonate (Memal) (<b>1</b>), dimethylmalonate (Me<sub>2</sub>mal) (<b>2</b>), and butylmalonate (Butmal) (<b>3</b>), Phmal = phenylmalonate (<b>4</b>), Et<sub>2</sub>mal = diethylmalonate (<b>5</b>), and Bzmal = benzylmalonate (<b>6</b>)] were synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes <b>1</b>–<b>3</b> are three-dimensional compounds whose structure consists of corrugated layers of manganese­(II) linked through <i>syn</i>–<i>anti</i> carboxylate (Rmal) bridges, which are pillared through the bis-monodentate azpy molecule. Complex <b>4</b> has a layered structure of manganese­(II) ions connected by carboxylate (Phmal) bridges in the <i>syn</i>–<i>anti</i> coordination mode as in <b>1</b>–<b>3</b>, the azpy group acting here as a terminally bound monodentate ligand. The structure of <b>5</b> consists of Et<sub>2</sub>mal–Mn­(II) neutral chains linked through the azpy ligand, giving rise to a complex three-dimensional network. Complex <b>6</b> is constituted by neutral [Mn­(Bzmal)­(H<sub>2</sub>O)<sub>3</sub>(azpy)] mononuclear units, which are interlinked through O–H···O, O–H···N, and π–π type intermolecular interactions to afford a three-dimensional supramolecular structure. The topological analysis of these crystallographic structures shows the occurrence of four different nets: a (3,4)-connected InS-type (<b>1</b>–<b>3</b>), a binodal layered hcb (<b>4</b>), a uninodal CdS-type (<b>5</b>), and a (4,5)-connected tcs topology (<b>6</b>). The magnetic properties of <b>1</b>–<b>5</b> were investigated in the 2.0–300 K temperature range. Overall antiferromagnetic behavior occurs in <b>1</b>–<b>4</b> with susceptibility maxima in the range 2.8–5.5 K, the exchange pathway being provided by the <i>syn</i>–<i>anti</i> carboxylate (substituted malonate) bridge [manganese–manganese separation in the range 5.4365(3)–5.5274(1) Å]. Very weak antiferromagnetic interactions are observed in <b>5</b> through the <i>trans</i>-bis-monodentate Et<sub>2</sub>mal ligand, the intrachain manganese–manganese separation being 7.328(3) Å. The much larger manganese–manganese separation through the bis-monodentate azpy ligand in <b>1</b>–<b>5</b> (values greater than 13.5 Å) accounts for the lack of any significant magnetic interaction though this extended bridge.