Poly[diaqua-penta-kis(µ(4)-benzene-1,2-dicarboxyl-ato)(µ(3)-benzene-1,2-dicarboxyl-ato)tetra-thulium(III)].

The title compound, [Tm(4)(C(8)H(4)O(4))(6)(H(2)O)(2)](n), has been synthesized hydro-thermally. The asymmetric unit has four unique Tm(III) ions that are six-, seven-, eight- and nine-coordinate. The cations are inter-connected by bridging benzene-1,2-dicarboxyl-ate (BDC) anions to form an infinite two-dimensional framework, in which the BDC ligands adopt three different coordination modes. Adjacent sheets are further packed to form a three-dimensional supra-molecular framework through O-H⋯O hydrogen bonds.