[Fe(OH)(XDK)Fe2(OMe)(O2CCH3)2]6 (1; XDK = m-xylenediamine bis(Kemp's triacid imide)), a cyclic octadecairon(III) complex, the mol. 18-wheeler, was prepd., characterized by single crystal x-ray diffraction anal., and its magnetic behavior was studied. This complex, which the authors designate the "mol. 18-wheeler", is the largest cyclic ferric cluster reported so far, contg. 18 iron(III) atoms in a ring. The compn. of the cryst. compd., a double salt having the formula 1·6Et4N(NO3)·15MeOH·6Et2O·24H2O, was established by elemental anal. and single crystal x-ray diffraction anal. Each iron in 1 has a distorted octahedral symmetry. A plot of the magnetic susceptibility per Fe atom vs. temp. measured on a microcryst. sample at an applied field of 1 T in the range 2.2<T<260 K displays a broad max. at about 60 K. This behavior is indicative of antiferromagnetic interactions between the high spin iron(III) ions.