Reactions of rare earth chlorides, N-(phosphonomethyl)iminodiacetic acid (H(4)pmida) and ferrous oxalate dihydrate under ionothermal conditions result in four new isostructural 3d-4f heterometal coordination polymers, [LnFe(III)Fe(6)(Hpmida)(6)]·2H(2)O {Ln = Eu (1), Dy (2), Ho (3) and Y (4)}. All compounds were characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and X-ray diffraction. The compounds feature a very interesting three dimensional (3-D) structure built up from a secondary building unit, [Fe(2)(Hpmida)(2)](2-) and possess a new topology type and complicated unique tilings. The catalytic properties of compounds 1-4 were investigated showing that these types of compounds are heterogeneous catalysts in the Knöevenagel condensation with high selectivity.