Manganese(II/III) complexes of a phenol-based tetradentate ligand L2-[H2L = N,N'-dimethyl-N,N'-bis(2-hydroxy-3,5-dimethylbenzyl)-ethylenediamine), namely, [Mn-4(L)(2)(PhCOO)(6)] (1), [Mn-3(L)(2)(CH3CH2COO)(2)(OMe)(2)]center dot H2O (2), and [Mn(L){(CH3)(3)CCOO}(CH3OH)]center dot CH3OH (3), have been synthesized. The basicity and steric congestion provided by the carboxylate moiety used as an ancillary ligand have profound influence on tuning the nuclearity of these compounds. Results of X-ray crystallography, electronic spectroscopy, and variable-temperature (1.8-300 K) magnetic measurements have been used to characterize these compounds. Complex 1 has a very interesting centrosymmetric structure that involves two crystallographically equivalent binuclear [Mn-II-Mn-III] units, connected together by a pair of syn-anti bridging benzoates to generate a "dimer of dimers" structural motif. Compound 2 with propionate as the ancillary ligand, on the other hand, has a nearly linear Mn-III-Mn-II-Mn-III core with antiferromagnetically coupled (J = -0.13 cm(-1)) metal centers. Compound 1 has an S-T = 9 spin ground state with ferromagneticlly coupled metal centers (J(wb) = 2.8(1) and J(bb) = 0.09(2) cm(-1)) that failed to function as a single molecule magnet due to the presence of low-lying excited states with smaller spin values and a weak magnetic anisotropy. The electron paramagnetic resonance spectrum of 1 in the frozen solution (12 K) displays two signals in the g = 2 and g = 4 regions, each split into six lines due to Mn-55 (l = 5/2) superhyperfine couplings. The use of bulky pivalate as a replacement for benzoate provides enough steric bulk to generate a mononuclear species [Mn(L){(CH3)(3)CCOO}(CH3OH)]center dot CH3OH (3). The lone manganese(Ill) center in this compound has an octahedral geometry, completed by the tetradentate ligand L2- together with an axially coordinated methanol molecule and a monodentate pivalate. The latter two are connected by a hydrogen bond, thus stabilizing the monodentate carboxylate moiety. Redox behaviors (CV) of 1 and 3 are grossly similar, each undergoing a quasi-reversible reduction process at E-1/2 = -0.03 and -0.11 V, respectively, versus a Ag/AgCl reference.