Palacios, M.A.; Nehrkorn, J.; Suturina, E.A.; Ruiz, E.; Gómez-Coca, S.; Holldack, K.; Schnegg, A.; Krzystek, J.; Moreno, J.M.; Colacio, E.: Analysis of magnetic anisotropy and the role of magnetic dilution in triggering SMM behaviour in a family of CoII-YIII dinuclear complexes with easy-plane anisotropy. Chemistry - A European Journal 23 (2017), p. 11649-11661
Three new closely related CoIIYIII complexes of general formula [Co(mu-L)(mu-X)Y(NO3)2] (X- = NO3- 1, benzoate, 2 and 9-anthracenecarboxylato, 3) have been prepared with the compartmental ligand N,N’,N”-trimethyl-N,N”-bis(2-hydroxy-3- methoxy-5-methylbenzyl)diethylenetriamine (H2L). In these complexes CoII and YIII are triply bridged by two phenoxide groups belonging to the dideprotonated ligand (L2-) and one ancillary anion X-. The change of the ancillary bridging group connecting CoII and YIII ions induces small differences in the trigonally distorted CoN3O3 coordination sphere with a concomitant tuning of the magnetic anisotropy and intermolecular interactions. Dc-magnetic, HFEPR and FD-FT THz-EPR measurements and ab initio theoretical calculations demonstrate that CoII ions in compounds 1-3 have large and positive D values (50 cm-1) which decrease with increasing the distortion of the pseudo-octahedral CoII coordination sphere. Dynamic ac magnetic susceptibility measurements indicate that compound 1 exhibits field induced SMMs behaviour, whereas compound 2 and 3 only display this behaviour when are magnetically diluted with diamagnetic ZnII (Zn/Co = 1/10). In view of this, it is always advisable to use magnetic diluted complexes, in which intermolecular interactions and QTM would be at least partly suppressed, so that "hidden SIM" could emerge. Field and temperature dependence of the relaxation times indicate the prevalence of the Raman process in all these complexes above approximately 3 K.