Two series of new organometallic salts (CpFeBz)nM(mnt)2 and (CpFeBz)nM(dmit)2 (M=Ni, Pd, Pt, Cu or Co; Cp=Cyclopentadienyl, Bz=Benzene, H2mnt=maleonitriledithiol; H2dmit=4, 5-dimercapto-1, 3-dithiole-2-thione, n=1 or 2) were synthesized by metathetical reaction. They were characterized by EA, IR and 1H NMR. The third-order optical nonlinearity of organometallic salts was studied by DFWM method for the first time. These molecules exhibit second hyperpolarizability which is in the order of 10^-^3^0 esu. The results also show that the nonlinearity mainly comes from the contribution of the planar conjugated anions.

Key words: INFRARED SPECTROPHOTOMETRY, ELEMENTAL ANALYSIS, BENZENE P, CYCLOPENTADIENE P, IRON COMPLEX, PROTON MAGNETIC RESONANCE SPECTROMETRY, NON LINEAR OPTICS