A new iron(III) phosphite templated by ethylenediamine has been synthesized using solvothermal conditions under autogenous pressure. The (C2N2H10)[Fe(HPO3)F-3] compound has been characterized by single-crystal X-ray diffraction data and spectroscopic and magnetic techniques. The crystal structure is formed by chains extended along the c axis and surrounded by ethylenediammonium cations. A study by diffuse-reflectance spectroscopy has been performed, and the calculated Dq, B, and C parameters for the Fe-III cations are 1030, 720, and 3080 cm(-1), respectively. The Mossbauer spectrum at room temperature is characteristic of Fe-III ions. The electron spin resonance (ESR) spectra carried out at different temperatures show isotropic signals with a g value of 2.00(l). The thermal evolution of the intensity of the ESR signals indicates the existence of antiferromagnetic interactions for the Fe-III phase. The magnetic susceptibility data of the Cr-III and V-III compounds show antiferromagnetic couplings. The J-exchange parameters of the Fe-III and Cr-III compounds have been calculated by using a model for a triangular spin ladder chain. The values are J(1) = -1.63(1) K and J(2) = -0.87(2) K with g = 2.02 for the Fe-III phase and J(1) = -0,56(2) K and J(2) = -0.40(2) K with g = 1.99 for the Cr-III compound. In the case of the V-III phase, the fit has been performed considering a linear chain with the magnetic parameters D = 2.5 cm(-1) and J = -1.15(1) K.