A Benzaldehyde Derivative as a Chelating Ligand: Helical Manganese(II) Coordination Polymers Assembling into a Porous Solid

A molecular,
porous crystalline material constructed from neutral
helical coordination polymers incorporating manganese­(II) ions and
two types of bridging ligands, namely the deprotonated form of 2-hydroxy-5-methoxy-3-nitrobenzaldehyde
(HL) and isobutyrate (iB–), has
been obtained and structurally characterized. Structural analysis
reveals that within the coordination polymer each benzaldehyde derivative
ligates two manganese ions in 6-membered chelating rings, and the
isobutyrate ligands cooperatively chelate either two or three manganese
ions. The solid state assembly of the resulting polymeric chains of
formula [Mn4(L)2(iB)6]n (1), described in the
polar space group R3c, is associated
with tubular channels occupied by MeCN solvent molecules (1·xMeCN; x ≤ 9). TGA
profiles and PXRD measurements demonstrate that the crystallinity
of the solid remains intact in its fully desolvated form, and its
stability and crystallinity are ensured up to a temperature of 190
°C. Gas adsorption properties of desolvated crystals were probed,
but no remarkable sorption capacity of N2 and only a limited
one for CO2 could be observed. Magnetic susceptibility
data reveal an antiferromagnetic type of coupling between adjacent
manganese­(II) ions along the helical chains with energy parameters J1 = −5.9(6) cm–1 and J2 = −1.8(9) cm–1.