Poly[[diaqua­bis­(μ-oxalato-κ(4) O (1),O (2):O (1′),O (2′))bis­(μ(3)-5-oxidopyridin-1-ium-3-carboxyl­ato-κ(3) O (3):O (3′):O (5))diholmium(III)] dihydrate]

In the title compound, {[Ho(2)(C(6)H(4)NO(3))(2)(C(2)O(4))(2)(H(2)O)(2)]·2H(2)O}(n), the Ho(III) atom is coordinated by three O atoms from three 5-hy­droxy­nicotinate ligands, four O atoms from two oxalate ligands, each lying on an inversion center, and one water mol­ecule in a distorted square-anti­prismatic geometry. The 5-hy­droxy­nicotinate ligand is protonated at the N atom and deprotonated at the hy­droxy group. The Ho(III) atoms are bridged by the carboxyl­ate and phenolate O atoms, forming a three-dimensional framework. N—H⋯O and O—H⋯O hydrogen bonds, as well as π–π inter­actions between the pyridine rings [centroid–centroid distance = 3.794 (2) Å], are observed.