Our interest in higher nuclearity sulfide-bridged Fe-S clusters, because of their occurrence in several proteins including nitrogenase, prompted us to investigate the solution chemistry of the functionalized cluster [Fe4S4(SH)(4)](2-) (1). (n-Pr4N)(2)[1] crystallizes in space group P2(1)/n of the monoclinic system with a = 26.201(1) Angstrom, b = 11.4999(5) Angstrom, c = 28.090(1) Angstrom, and beta = 110.735(1)degrees. The X-ray structure reveals the conventional cubane-type geometry with an [Fe4S4](2+) core symmetry more closely approaching T-d than the tetragonally distorted D-2d symmetry reported for the (PPh4)(2)[1] (Muller, A.; Schladerbeck, N. H.; Bogge, H. J. Chem. Soc., Chem. Commun. 1987, 35). In solution, 1 exists in dynamic equilibrium with self-condensation products formed through elimination of H2S and formation of sulfide-bridged cluster oligomers, one of which (4) is prevalent. The self-condensation equilibrium is shifted toward cluster 1. When acetonitrile solutions of 1 were treated with thiols more acidic than H2S, it was possible to detect hydrosulfido terminal ligand substitution products of 1 as well as those of the major self-condensation product 4. Detailed analysis of the products in acetonitrile solutions of 1, as well as those generated in solutions of 1 created with acidic thiol, by electrospray mass spectrometry, and both F-19 and H-1 NMR spectroscopy indicates the presence of a sulfide-bridged acyclic trimer of [Fe4S4](2+) clusters, i.e. ([Fe(4)s(4)(SH)(3)](2)[Fe4S4(SH)(2)](mu-S)(2))(6-) (4), a hitherto unprecedented Fe-S structural pattern, as the principal Fe-S cluster self-condensation product.