A new Fe(II)-Fe(III) alternating single chain magnet, catena-[Fe-II(ClO4)(H2O)Fe-III(bmpca)(2)}](ClO4)(2), was synthesized using methyl-substituted bpca(-) ligand, bmpca(-) (Hbpca and Hbmpca denote bis(2-pyridylcarbonyl)amine and bis(4-methyl-2-pyridylcarbonyl)amine, respectively). The one-dimensional complex shows the ferrimangetic behavior and frequency dependent out-of-phase ac susceptibility X ''(m), with the alpha parameter of 0.25 estimated by the semicircle Cole-Cole plot. The activation energy Delta was estimated to be 19(1) K from an Arrhenius plot. (c) 2006 Elsevier Ltd. All rights reserved.