It is important to note from the above equations that each relaxation mechanism has its own characteristic temperature (T) and field (H) dependence. For all three complexes from the temperature dependence of  at 0 Oe, the presence of a clear temperature-independent regime at low temperatures indicates the contribution of a QTM process. In addition, the involvement of a Direct process is excluded in the absence of an external DC magnetic field. Adding only Raman or only Orbach processes is not sufficient. A model considering QTM, Raman and Orbach processes (equation ) is applied to describe the experimental temperature dependence of  The best-fit parameters are listed in Table . Table . Best-fit parameters to reproduce the temperature dependence of the magnetic relaxation for 1 -3 using equation 5. and). When compared with Dy-dbm complexes containing -diamine ligands bpy, phen, and their azacyclo-derivative dpq and dppz, complexes 1 and 2 shows much slower relaxation (τ0 -1 ) with significantly higher spin reversal energy barrier value (Ueff). While spin dynamic behaviour of complexes 1 and 2 are very much similar with the Dy-dbm complexes containing -diamine ligands dmbipy (4,4′-dimethyl-2,2′-bipyridine) and 4,5pinenepyridyl-2-pyrazine. 26 When compared with Dy-acac complexes containing -diamine ligands like phen, tmphen, and their azacyclo-derivative dpq and dppz, complexes 3 shows slower relaxation (τ0 -1 ) with slightly higher spin reversal energy barrier value (Ueff), while analogue complexes [Dy(acac)3(dmdophen)] and [Dy(acac)3bpm] shows lower τ0 -1 and higher Ueff. In addition, complexes 3