Isotope Effect and Lanthanide Contraction for 3d-4f Cyanide-Bridged Complexes Exhibiting Negative Thermal Expansion

We have prepared some 3d-4f cyanide-bridged Ln(DMF)4(H2O)3Fe(CN)6•H2O complexes (Ln = Ce, Sm, Nd, and Gd; DMF = N,N-dimethylformamide) by substituting isotopes to 2 H-substituted H2O and DMF and 18 O-substituted H2O (and normal 1 H- and 16 O-H2O or 1 H-DMF). We examined their crystal structures exhibiting negative thermal expansion and compared in view of hydrogen bonds and lanthanide contraction. Magnetic properties and thermal analysis exhibited importance of intermolecular hydrogen bonds in crystal lattice for this behavior. While Fe2p3/2 and Fe2p1/2 XAS indicated constant inner shell electron states of low-spin Fe(III) ions.