The complex GdFe(CN)6.4H2O was synthesized and characterized by elemental analysis and infrared spectrum. The crystal structure of the title complex was determined by X-ray diffraction analysis. It crystallizes in the monoclinic system, space group C2, with a=1.2759(6), b=0.7404(1), c=1.3654(5)nm and Z=4, β=90.22(3)°. The variable-temperature magnetic susceptibility of the complex was measured over 4.2-300K. The magnetic analysis was performed by using the Hamiltonian operator (H=-2JS1S2, S1=1/2, S2=7/2), giving the antiferromagnetic coupling parameter of J=-69.1 cm^-^1. This result indicates that there exists a mediate antiferromagnetic spin-exchange interaction between Gd(III) ion and Fe(III) ion that are bridged by the cyanide ion. According to our best knowledge, the magnetic interaction is the strongest interaction between Gd(III) ion and transition metal ion that was found so far.

Key words: CYANIDES, INFRARED SPECTROPHOTOMETRY, ELEMENTAL ANALYSIS, CRYSTAL STRUCTURE, X-RAY DIFFRACTION ANALYSIS, IRON COMPLEX, MAGNETISM, GADOLINIUM COMPLEX