title: Poly[[diaqua-bis-(μ-oxalato-κ(4)O(1),O(2):O(1'),O(2'))bis-(μ(3)-5-oxidopyridin-1-ium-3-carboxyl-ato-κ(3)O(3):O(3'):O(5))diholmium(III)] dihydrate].
abstract: 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-hy-droxy-nicotinate ligands, four O atoms from two oxalate ligands, each lying on an inversion center, and one water mol-ecule in a distorted square-anti-prismatic geometry. The 5-hy-droxy-nicotinate ligand is protonated at the N atom and deprotonated at the hy-droxy group. The Ho(III) atoms are bridged by the carboxyl-ate and phenolate O atoms, forming a three-dimensional framework. N-H⋯O and O-H⋯O hydrogen bonds, as well as π-π inter-actions between the pyridine rings [centroid-centroid distance = 3.794 (2) Å], are observed.
authors.affiliation: Department of Materials Science and Engineering, Jinan University, Guangzhou 510632,  People's Republic of China.
authors.forename: Jun-Long
authors.initials: JL
authors.lastname: Mi
authors.forename: Jing
authors.initials: J
authors.lastname: Huang
authors.forename: Hong-Ji
authors.initials: HJ
authors.lastname: Chen