Super reduced Fe4S4 cluster of Balch's dithiolene series

Abstract

A super reduced Fe(4)S(4) cluster with a sulfur based radical, [NBu(4)](4)[Fe(3)(III)Fe(II)(μ(3)-S)(4)(mnt)(3)(6-)(mnt)(1-)˙](4-)˙, (1) (mnt, maleonitrile dithiolate) which evolves H(2)S gas on treatment with acid under ambient conditions has been synthesized and structurally characterized. The Fe-S distances in 1 are in the range 2.246-2.383 Å, in stark contrast to that of the known n = -2 member of the series based on the [Fe(4)(μ(3)-S)(4)(S(2)C(2)R(2))(4)](n) unit (R = CF(3), Ph) with Fe-S bond lengths of 2.149-2.186 Å. The EPR of 1 displays very weak signals at g, 4.03 and 2.38 along with a strong S-based radical EPR signal at g, 2.003 associated with five structured components tentatively assigned to hyperfine interaction arising out of the naturally abundant (57)Fe with <A> = 88 G. The EPR profile resembles the reduced Fe-S cluster of CO inhibited Clostridium pasteurianum W5 hydrogenase or the Fe(4)S(4) centers of wild-type enzyme, IspH treated with HMBPP or IPP.

Fe4S4 Cubane Type Cluster Immobilized on a Graphene Support: A High Performance H2 Evolution Catalysis in Acidic Water

“…6 ). The waves at E, −0.49 V, −1.01 V and −1.22 V can be assigned to the DMET ligand based redox processes since these were observed also in other related iron(III) dithiolene complexes and a nickel(II) complex of the DMET ligand 30 – 32 . The reversible redox process occurring near zero (E 1/2 , +0.107 V) can be assigned to Fe 3+ /Fe 2+ and the one occurring at E 1/2 , +0.45 V can be assigned to Fe 2+ /Fe 3+ redox process.…”

“…The Fe–S bond lengths are similar at all iron centers, (Fe(1) and Fe(2)) and in the range 2.156 Å–2.250 Å. This is in contrast to the longer Fe-S bond distances (2.246 Å–2.383 Å) in the tetra anionic, super reduced cluster, [NBu 4 ] 4 [Fe 3 III Fe II (μ 3 -S) 4 (mnt) 3 6− (mnt) 1−· ] 4−· ( 2 ) (mnt = maleonitrile dithiolate) 32 . The Fe…Fe separations (Fe–Fe, 2.695 Å and 2.722 Å) are remarkably shorter in the cluster ( 1 ) in contrast to those observed in ( 2 ) (Fe-Fe, 2.843 Å–3.123 Å) and four of the C–S bond distances (S(2)–C(2) & S(2A)–C(2A), 1.718 Å and S(6)–C(8) & S(6A)–C(8A), 1.721 Å) are considerably shorter in ( 1 ) indicating oxidation of the dithiolene ligands to their monoanionic form containing sulfur based radicals.…”

“…Nickel(II)− and iron(III) dithiolenes have been reported which electro-catalyze H 2 evolution at potentials comparable to that of platinum disc electrode 30 – 32 . Recently the research on light driven H 2 production has gained momentum.…”