Nitroxide Radicals as Templating Agents in the Synthesis of Magnets Based on Three-Dimensional Oxalato-Bridged Heterodimetallic Networks This work was supported by the European Union (TMR ERB 4061 PL97-0197) and the Ministerio de Ciencia y Tecnología (MCT) (Project no. MAT98-0880). C.G. and F.M.R. wish to thank the MCT for a research contract (Contrato de Reincorporación).