Crystal structure of <i>catena</i> -poly[[tetraaquamanganese(II)]-μ-1,5-dihydroxynaphthalene-2,6-dicarboxylato]

The title compound, [Mn(H₂dondc)(H₂O)₄] _<i>n</i> or [Mn(C₁₂H₆O₆)(H₂O)₄] _<i>n</i> , was synthesized by the reaction of manganese(II) chloride (MnCl₂), 1,5-dihy-droxynaphthalene-2,6-di-carb-oxy-lic acid (H₄dondc) and lithium hydroxide (LiOH). The asymmetric unit comprises half of an Mn^II ion, half of a 1,5-dihy-droxynaphthalene-2,6-di-carboxyl-ate dianion (H₂dondc^2-) and two water mol-ecules. The Mn^II ion is located on a crystallographic inversion center and exhibits a six-coordinated MnO₆ octa-hedral geometry. The octa-hedron is comprised of two oxygen atoms from the two H₂dondc^2- ligands and four oxygen atoms from the water mol-ecules. The carboxyl-ate group and naphthalene moiety lie almost coplanar to each other and show a monodentate coordination to the Mn^II ion. The planar H₂dondc^2- ligands bridge Mn^II ions to form a one-dimensional chain along the diagonal direction of the <i>b</i> and <i>c</i> axes. In the crystal, there are two types of intra-chain hydrogen-bonding inter-actions. The first is between the phenolic hydroxyl groups and carboxyl-ate groups. The phenolic hydroxyl groups of the ligand are protonated and act as intra-chain hydrogen-bonding donors to coordinated oxygen atoms of the carboxyl-ate groups. The other is between coordinated water mol-ecules and non-coordinated oxygen atoms of the carboxyl-ate groups. The parallel chains are connected not only by inter-chain hydrogen-bonding inter-actions between coordinated water mol-ecules and phenolic hydroxyl groups but also by inter-chain hydrogen-bonding inter-actions between coordinated water mol-ecules to give two-dimensional networks. The chains are further connected by inter-chain π-π stacking inter-actions between the naphthalene moieties.