The first three-dimensional Fe(III)-Sr(II) heterometallic coordination polymer: poly[[diaquatetrakis(μ3-pyridine-2,3-dicarboxylato)diiron(III)strontium(II)] dihydrate].

The title compound, poly[[diaqua-1κ(2)O-tetrakis(μ3-pyridine-2,3-dicarboxylato)-2:1:2'κ(10)N,O(2):O(2'),O(3):O(3');2:1:2'κ(8)O(3):O(3'):N,O(2)-diiron(III)strontium(II)] dihydrate], {[Fe2Sr(C7H3O4)4(H2O)2]·2H2O}n, which has triclinic (P-1) symmetry, was prepared by the reaction of pyridine-2,3-dicarboxylic acid, SrCl2·6H2O and Fe(OAc)2(OH) (OAc is acetate) in the presence of imidazole in water at 363 K. In the crystal structure, the pyridine-2,3-dicarboxylate (pydc(2-)) ligand exhibits μ3-η(1),η(1):η(1):η(1) and μ3-η(1),η(1):η(1),η(1):η(1) coordination modes, bridging two Fe(III) cations and one Sr(II) cation. The Sr(II) cation, which is located on an inversion centre, is eight-coordinated by six O atoms of four pydc(2-) ligands and two water molecules. The coordination geometry of the Sr(II) cation can be best described as distorted dodecahedral. The Fe(III) cation is six-coordinated by O and N atoms of four pydc(2-) ligands in a slightly distorted octahedral geometry. Each Fe(III) cation bridges two neighbouring Fe(III) cations to form a one-dimensional [Fe2(pydc)4]n chain. The chains are connected by Sr(II) cations to form a three-dimensional framework. The topology type of this framework is tfj. The structure displays O-H...O and C-H...O hydrogen bonding.