The syntheses, crystal structures and magnetochemical characterization are reported for two new Fe^III complexes [Fe₁₈O₆(OH)₈(pdm)₁₀(pdmH)₄(H₂O)₄](ClO₄)₁₀ (3) and [Fe₉O₄(OH)₂(O₂CMe)₁₀(pdm)(pdmH)₄](NO₃) (4). They were synthesized from the use of the potentially O,N,O tridentate chelate, 2,6-pyridinedimethanol (pdmH₂), in the presence or absence of carboxylate groups. Octadecanuclear complex 3 was obtained during reactivity studies on previously-reported [Fe₈O₃(OEt)(pdm)₄(pdmH)₄(EtOH)₂](ClO₄)₅ (2), the latter undergoing hydrolysis to 3 on recrystallization from undried MeCN. The reaction of pdmH₂ with preformed [Fe₃O(O₂CMe)₆(py)₃](NO₃) in CH₂Cl₂ gave enneanuclear complex 4. Both complexes 3 and 4 are unprecedented structural types. The core of 3 comprises a central [Fe₄O₆] defective-dicubane attached on either side to a [Fe₇O₁₁] unit, which can be described as two [Fe₄(μ₄-O)] tetrahedra fused at a common Fe atom. The core of 4 can be considered as four vertex-fused triangular [Fe₃(μ₃-O)] units. Variable-temperature (T) and -field (H) solid-state dc and ac magnetization (M) studies were carried out on complexes 3 and 4 in the 1.8–300 K range. Analysis of the obtained data revealed that complexes 3 and 4 possess an S = 4 and S = 5/2 ground state spin, respectively.