Poly[[diaqua­bis­(μ-oxalato-κ⁴O¹,O²:O^1′,O^2′)bis­(μ₃-5-oxidopyridin-1-ium-3-carboxyl­ato-κ³O³:O^3′:O⁵)diholmium(III)] dihydrate]

In the title compound, {[Ho₂(C₆H₄NO₃)₂(C₂O₄)₂(H₂O)₂]·2H₂O}_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.