The present invention relates to accelerators for curing unsaturated polyester resins, vinyl ester resins, and acrylic resins in conjunction with peroxide type initiators. The accelerators are based on iron/manganese complexes of a tridentate, tetradentate, pentadentate, or hexadentate nitrogen donor ligands. Also disclosed are curable resin compositions including the forgoing accelerators and a curing process for employing these accelerators. These resin compositions show good curing properties and do not contain cobalt accelerators. The present invention further relates to gel coats and molded composites prepared from such unsaturated polyester, vinyl ester, and acrylic resins.