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 [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.