Official URL: <a href="http://dx.doi.org/10.1007/BF02679574">http://dx.doi.org/10.1007/BF02679574</a> Abstract We report a spin resonance study of the family of quasi-two-dimensional organic (super) conductors ?????-(BEDT-TTF)4[(H3O)M(C2O4)3]S, where M is a 3d transition metal ion and S is a host solvent molecule.