Super reduced Fe₄S₄ cluster of Balch's dithiolene series

Abstract

A super reduced Fe₄S₄ cluster with a sulfur based radical, [NBu₄]₄[Fe₃^IIIFe^II(μ₃-S)₄(mnt)₃⁶⁻(mnt)¹⁻˙]⁴⁻˙, (1) (mnt, which evolves H₂S 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 [Fe₄(μ₃-S)₄(S₂C₂R₂)₄]ⁿ unit (R = CF₃, 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 ⁵⁷Fe with <A> = 88 G. The EPR profile resembles the reduced Fe–S cluster of CO inhibited Clostridium pasteurianum W5 hydrogenase or the Fe₄S₄ centers of wild-type enzyme, IspH treated with HMBPP or IPP.