An organic/inorganic hybrid system, (benzo[1,2-d:4,5-d']bis[1,3,2]dithiazole (= BBDTA)) (.) FeCl4 (.) CH3COCH3, is shown to exhibit a drastic change in magnetism after evaporation of the volatile crystal solvent, acetone. The solvated material, with a crystal structure consisting of ladder-like BBDTA and a honeycomb network of Fe(III)Cl-4, exhibits antiferromagnetic ordering at 6.3 K. Magnetic measurements and Mossbauer spectra suggest that the desolvated material includes a ferrimagnetic phase with T-N = 44.0 K. (C) 2002 Elsevier Science B.V. All rights reserved.