Oligomeric main-chain Schiff-base compounds 4 and 5 have been synthesized by the trans-esterification of their respective doubly functionalized monomeric precursors [M((eta(5)-C5H5)Fe(eta(5)-C5H4)C(=O)CH=C(4-C6H4OH)NCH2CH2N= CH-(2-O,4-CO2H-C6H3)}] [M = Ni (2), Cu (3)] in dmf. The new compounds were characterized by elemental analysis, ETIR and multidimensional NMR spectroscopy, mass spectrometry, and cyclic voltammetry. Compounds 2, 3, and 6, the corresponding amide of 2, were characterized by X-ray structural investigation. Gel permeation chromatography estab- fished that oligomers 4 and 5 are formed of approximately six monomeric units, and differential scanning calorimetry and thermal gravimetric analysis indicated that they are thermally stal)le with decomposition temperatures exceeding 230 degrees C. Harmonic light scattering measurements showed. that compounds 2-5 exhibit.rather high second-order.noidinear responses, between 224 x 10(-30) and 399 x 10(-30) esu, with hyperpolarizability beta(1.91) values that increase significantly on passing from the monomeric to the oligomeric species.