Two Tb-III complexes with the same N6O3 donor atoms but different coordination geometries, "fac"- [Tb-III(HLDL-ala)(3)]center dot 7H(2)O (1) and "mer"- [Tb-III(HLDL-phe)(3 center dot)7H(2)O (2), were synthesized, where H2LDL-ala and H2L2DL-phe are N-imidazol-4-yl)methylidene-DL-alanine and -DL-phenylalanine, respectively. Each Tb-III ion is coordinated by three electronically mononegative NNO tridentate ligands to form a coordination geometry of a tricapped trigonal prism. Compound 1 consists of enantiomers "fac"-[Tb-III(HLD-ala)(3)] and "fac"-[Tb-III(HLL-ala)(3)], while 2 consists of "mer"-[Tb-III(HLD-phe)(2)(HLD-Phe)(HLL-Phe)(2)]. Magnetic data were analyzed by a spin Hamiltonian including the crystal field effect on the Tb-III ion (4f(8), J = 6, S = 3, L = 3, gi = 3/2, F-7(6)). The Stark splitting of the ground state 7F6 was evaluated from magnetic analysis, and the energy diagram pattern indicated easyplane and easy-axis (Ising type) magnetic anisotropies for 1 and 2, respectively. Highly efficient luminescences with phi = 0.50 and 0.61 for 1 and 2, respectively, were observed, and the luminescence fine structure due to the D-5(4) -> F-7(6) transition is in good accordance with the energy diagram determined from magnetic analysis. The energy diagram of 1 shows an approximate single-well potential curve, whereas that of 2 shows a double- or quadruple-well potential within the F-7(6) multiplets. Complex 2 displayed an onset of the out-of-phase signal in alternating current (ac) susceptibility at a direct current bias field of 1000 Oe on cooling down to 1.9 K. A slight frequency dependence was recorded around 2 K. On the other hand, 1 did not show any meaningful out-of-phase ac susceptibility. Pulsed-field magnetizations of 1 and 2 were measured below 1.6 K, and only 2 exhibited magnetic hysteresis. This finding agrees well with the energy diagram pattern from crystal field calculation on 1 and 2. DFT calculation allowed us to estimate the negative charge distribution around the Tb-III ion, giving a rationale to the different magnetic anisotropies of 1 and 2.