We hereby report a series of near-linear trinuclear [Zn2LnIII(HL)4(CH3COO)]·(NO3)2 (where LnIII = La (1-La), Ce (2-Ce), Nd (3-Nd), Sm (4-Sm), Tb (5-Tb), and Dy (6-Dy)) complexes with Schiff base ligand (H2L). Magnetization relaxation dynamic studies on complexes 2-Ce, 5-Tb, and 6-Dy reveal the existence of well resolved frequency dependent zero-field out-of-phase χ''M signals, which is an indicator of a typical single-ion magnet behavior observed only for complex 6-Dy with Ueff = 43.7 K (τ0 = 2.42 × 10-6 s). The presence of two Zn(II) ions near the coordination geometry of Dy(III) ion in 6-Dy is likely to keep the first excited mJ levels significantly away from the ground state mJ level and is responsible for the observation of zero field slow magnetic relaxation behavior. The data collected in the presence of a magnetic field of Hdc = 2 kOe enhances the energy barrier by two-fold (88.63 K, τ0 = 1.36 × 10-7 s) in 6-Dy, suggesting the presence of QTM at zero field along with other under barrier relaxations, such as the Raman process. On the other hand, complex 2-Ce shows field induced slow relaxation of magnetization behavior with an effective energy barrier of 12.24 K (τ0 = 1.89 × 10-4 s). The CASSCF/SO-RASSI/SINGLE_ANISO based ab initio calculations using MOLCAS 8.0 code further rationalized our experimentally observed magnetization dynamics.