Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains

New CoII members of the family of multifunctional materials of general formula [DAMS]4[M2Co(C2O 4)6]·2DAMBA·2H2O (MIII = 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 ZnII, MnII, 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 RhIII derivative demonstrate that high spin octacoordinated CoII centers behave very similarly to the hexacoordinated CoII ones, being dominated by a large orbital contribution. The CrIII derivative is characterized by ferromagnetic CrIII-CoII interactions. Most relevantly, the Fe III compound is characterized by a moderate antiferromagnetic interaction between FeIII and CoII, resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ0 = 8.6 × 10-11 s and ΔE = 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. © 2010 American Chemical Society.