A novel molecular-based magnet of three-dimensional (3-D) cyanide-bridged bimetallic assembly, [{Ni(tn)(2)}(5)-{Fe-III(CN)(6)}(3)](n)(ClO4)(n). 2.5nH(2)O where tn = trimethylenediamine, was synthesized and structurally characterized. The compound with an asymmetric unit of C24H52.5Cl0.5Fe1.5N19Ni2.5O3.255 crystallized in the monoclinic system of the space group P2(1)/n with a 10.173(3) Angstrom, b = 16.053(2) Angstrom, c 26.309(3) Angstrom, beta = 91.30(2)degrees,and Z = 4. The assembly has a 3-D network structure extended by three different types of Fe-III-CN-Ni-II-NC-Fe-III linkages. The iron (Fe-III) atoms are located in two different chemical environments, which were confirmed by Mossbauer experimental results. The nickel (Ni-II) atoms have three different coordination environments. Cryomagnetic properties revealed that 3-D magnetic ordering occurs over the lattice below the Curie temperature around 10 K.