Flexible polytopic aminopolyalcohol ligands such as triethanolamine, N-butyldiethanolamine, and N-methyldiethanolamine that can bond to metals in many ways have been extensively used to develop new Fe or Fe-Ln coordination clusters with high nuclearities [1, 2]. A new dodecanuclear iron(III) carboxylate cluster [Fe12O6(OH)4(piv)10(mdea)4(mdeaH)2] (1) (where mdeaH2 = N-methyldiethanolamine; pivH = pivalic acid) has been synthesized by the slow diffusion of diethyl ether solution of pre-synthesized [Fe14O10(OH)4(piv)18] precursor into acetonitrile solution containing N-methyldiethanolamine ligand. Cluster 1 crystallizes in the triclinic P-1 space group with a = 14.179(8), b = 14.717(8), c = 15.549(8) Å, α = 84.989(9), ß = 63.426(9), γ = 71.725(9)°, Z = 1, V = 12750(3) Å3. A single-crystal X-ray analysis of 1 showed that twelve FeIII atoms are bridged by six μ3-O2- ions, four μ2-OH- groups, four doubly deprotonated mdea2-, two partly deprotonated mdeaH- ligands and ten carboxylates (Figure 1a). The core of 1 can be considered as the arrangement of six {Fe3O} non-equilateral triangles with a central μ3-oxygen as shown in Figure 1b. The Fe…Fe distances in triangles are in the range from 2.941(2) to 3.571(2) Å and the Fe-(μ3-oxo) distances vary from 1.858(4) to 1.988(4) Å. All Fe atoms are hexa-coordinated and adopt distorted octahedral O6 (Fe2, Fe3, Fe5) or O5N (Fe1, Fe4 and Fe6) coordination environments. (Fe-O, 1.858(4) - 2.256(4) Å; Fe‒N, 2.235(5) - 2.318(7) Å). The spectroscopic and thermal properties of 1 have also been studied and will be discussed in terms of known structure.