A novel manganese(II) coordination polymer with azide and neutral dicarboxylate ligands: Helical structure and magnetic properties

By using a neutral inner-salt-type dicarboxylate as coligand, a novel two-dimensional (2D) manganese(II) coordination polymer, [Mn(L)(N ₃)]ClO₄·1/2H₂O (L = 1,3-bis(3- carboxylatopyridinium)propane), was synthesized, and characterized by X-ray crystallography and magnetic measurements. The compound contains uniform Mn ^II chains with simultaneous azide and carboxylate bridges between adjacent Mn^II ions. The formally negative chains are interlinked by the positively-charged 1,3-bis(pyridinium)propane spacer, and the spiral conformation of the spacer imports intriguing helical features to the resulting 2D network, in which [MnL] helices are connected by sharing metal centers with alternating centro- and C₂-symmetry. The triple (azide) bis(carboxylate) bridge mediates overall antiferromagnetic coupling with J = -3.0 cm^-1, as a result of the competition between the antiferromagnetic (carboxylate) and ferromagnetic (azide) pathways.