Ferrocenyldithiodiphosphetane [FcPS(mu-S)](2) [Fc = Fe(eta(5)-C5H4)(eta(5)-C5H5)] reacts with the aminoethanol derivatives HOCH2CH2NHMe and HOCH2CH2NEt2 to give the first structurally characterised examples of zwitterionic (O-ethylammonium)ferrocenyldithiophosphonates, [FcP(S)S((OCH2CH2NHRR2)-R-1)] (R-1 = H, R-2 = Me (1); R-1 = R-2 = Et (2)). 1 and 2 were characterised by elemental analyses, IR, NMR spectroscopy (H-1, C-13 (for 2) and P-31) and mass spectrometry. A crystal structure determination was carried out on 1. (C) 2004 Elsevier Ltd. All rights reserved.