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

Abstract

Six new manganese(II) complexes of formulas [Mn2(Rmal)2(H2O)2(azpy)]n (1–3), [Mn(Phmal)(H2O)(azpy)]n (4), [Mn2(Et2mal)2(H2O)4(azpy)2]n (5), and [Mn(Bzmal)(H2O)3(azpy)] (6) [azpy = 4,4′-azobispyridine (1–6), Rmal = methylmalonate (Memal) (1), dimethylmalonate (Me2mal) (2), and butylmalonate (Butmal) (3), Phmal = phenylmalonate (4), Et2mal = diethylmalonate (5), and Bzmal = benzylmalonate (6)] were synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1–3 are three-dimensional compounds whose structure consists of corrugated layers of manganese(II) linked through syn–anti carboxylate (Rmal) bridges, which are pillared through the bis-monodentate azpy molecule. Complex 4 has a layered structure of manganese(II) ions connected by carboxylate (Phmal) bridges in the syn–anti coordination mode as in 1–3, the azpy group acting here as a terminally bound monodentate ligand. The structure of 5 consists of Et2mal–Mn(II) neutral chains linked through the azpy ligand, giving rise to a complex three-dimensional network. Complex 6 is constituted by neutral [Mn(Bzmal)(H2O)3(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 (1–3), a binodal layered hcb (4), a uninodal CdS-type (5), and a (4,5)-connected tcs topology (6). The magnetic properties of 1–5 were investigated in the 2.0–300 K temperature range. Overall antiferromagnetic behavior occurs in 1–4 with susceptibility maxima in the range 2.8–5.5 K, the exchange pathway being provided by the syn–anti carboxylate (substituted malonate) bridge [manganese–manganese separation in the range 5.4365(3)–5.5274(1) Å]. Very weak antiferromagnetic interactions are observed in 5 through the trans-bis-monodentate Et2mal ligand, the intrachain manganese–manganese separation being 7.328(3) Å. The much larger manganese–manganese separation through the bis-monodentate azpy ligand in 1–5 (values greater than 13.5 Å) accounts for the lack of any significant magnetic interaction though this extended bridge.