A [4Fe-4S] cluster dimer bridged by bis(2,2 ': 6 ',2 ''-terpyridine-4 '-thiolato)iron(II)

The use of 2,2':6',2"-terpyridine-4'-thiol (tpySH) was explored as a bridging ligand for the formation of stable. assemblies containing both [4Fe-4S] clusters and single metal ions. Reaction of tpySH (2 equiv) with (NH4)(2)Fe(SO4)(2)center dot 6H(2)O generated the homoleptic complex [Fe(tpySH)(2)](2+), which was isolated as its PF6- salt. The compound could be fully deprotonated to yield neutral [Fe(tpyS)(2)], and the absorption spectrum is highly dependent on the protonation state, Reaction of [Fe(tpySH)(2)](PF6)(2) with the new 3:1 site-differentiated cluster (n-Bu4N)(2)[Fe4S4(TriS)(SEt)] yielded the first metal-bridged [4Fe-4S] cluster dimer, (n-Bu4N)(2)[{Fe4S4(TriS)(mu-Stpy)}(2)Fe]. Electrochemical, studies indicate that the [4Fe-4S] clusters in the dimer act as independent redox units, while UV-vis spectroscopy provides strong evidence for a thioquinonoid electron distribution in the bridging tpyS(-) ligand. TpySH thus acts as a directional bridging ligand between [4Fe-4S] clusters and single metal ions, thereby opening the way to the synthesis of larger, more complex assemblies.