New Co-II members of the family of multifunctional materials of general formula [DAMS]4[M2Co(C2O4)(6)]center dot 2DAMBA center dot 2H(2)O (M-III = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+) = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn-II, Mn-II, and Ni-II. This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the Rh-III derivative demonstrate that high spin octacoordinated Co-II centers behave very similarly to the hexacoordinated Co-II ones, being dominated by a large orbital contribution. The Cr-III derivative is characterized by ferromagnetic Cr-III-Co-II interactions. Most relevantly, the Fe-III compound is characterized by a moderate antiferromagnetic interaction between Fe-III and Co-II, resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (tau(0) = 8.6 x 10(-11) s and Delta E = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.