Mechanisms for biological and bioinspired dihydrogen activation and production often invoke the intermediacy of diiron dithiolato dihydrides. The first example of such a Fe-2(SR)(2)H-2 species is provided by the complex [(term-H) (mu-H)Fe-2(pdt)(CO)(dppv)(2)] ([H1H](0)). Spectroscopic and computational studies indicate that [H1H](0) contains both a bridging hydride and a terminal hydride, which, notably, occupies a basal site. The synthesis begins with [(mu-H)Fe-2(pdt)(CO)(2)(dppv)(2)](+) ([H1(CO)](+)), which undergoes substitution to afford [(mu-H)Fe-2(pdt)(CO)(NCMe)-(dppv)(2)](+) ([H 1(NCMe)](+)). Upon treatment of [H1(NCMe)](+) with borohydride salts, the MeCN ligand is displaced to afford [H1H](0). DNMR (EXSY, SST) experiments on this complex show that the terminal and bridging hydride ligands interchange intramolecularly at a rate of 1 s(-1) at -40 degrees C. The compound reacts with D-2 to afford [D1D](0), but not mixed isotopomers such as (H1D](0). The dihydride undergoes oxidation with Fc(+) under CO to give [1(CO)](+) and H-2. Protonation in MeCN solution gives [H1(NCMe)] and H-2. Carbonylation converts [H1H](0) into [1(CO)](0).