One new ionic penta-nuclear FeIII cluster, [HN(Et)3]·[Fe5(L3)4(ATZ)4(μ 3-O)2]·(H2O) (1), (H2L is 2-(((1H-tetrazol-5-yl)imino)methyl)-6-methoxyphenol; HATZ is 5-amino-1,2,3,4- tetrazole), was synthesized through a micro-vial reaction. Complex 1 was characterized by elemental analysis, FT-IR spectra, X-ray single crystal diffraction, thermogravimetric analysis. Complex 1 reveals high thermal stability, and displays intracluster antiferromagnetic coupling between the Fe(III) ions through μ 3-O bridges. In 1, HATZ was synthesized through in situ decomposition reaction of H2L. The Hirshfeld surface analysis results indicate that the N···H interaction is one of the most significant contacts for the complex.