Two flexible, branched, and sterically constrained di- and tripodal side arms around a phenol backbone were utilized in ligands H(3)L1 and H(5)L2 to isolate {Mn-6} and {Mn-3} coordination aggregates. 2,6-Bis{(1-hydroxy-2-methylpropan-2-ylirnino)methyl}-4-methylphenol (H3L1) gave trinuclear complex [Mn-3(mu-H(2)L1)(2)(mu(1,3)-O2CCH3)(4)(CH3OH)(2)](ClO4)(2)center dot 4CH(3)OH (1), whereas 2,6-bis[{1-hydroxy-2-(hydroxymethyl)butan-2-ylimino}methyl]-4-methylphenol (H(5)L2) provided hexanuclear complex [Mn-6(mu(4)-H(2)L2)(2)(mu-HL3)(2)(mu(3)-OH)(2)(mu(1,3)-O2CC2H5)(4)](ClO4)(2)center dot 2H(2)O (2). Binding of acetates and coordination of {H(2)L1}(-) provided a linear mnuimnumnui arrangement in 1. A Mn-6(III) fused diadamantane-type assembly was obtained in 2 from propionate bridges, coordination of {H(2)L2}(3-), and in situ generated {HL3}(2-). The magnetic characterization of 1 and 2 revealed the properties dominated by intramolecular anti-ferromagnetic exchange interactions, and this was confirmed using density functional theory calculations. Complex 1 exhibited field-induced slow magnetic relaxation at 2 K due to the axial anisotropy of Mn-III centers. Both the complexes show effective solvent -dependent catechol oxidation toward 3,5-di-tert-butylcatechol in air. The catechol oxidation abilities are comparable from two complexes of different nuclearity and structure.