Characterization of the Self-Condensation Equilibrium of [Fe4S4(SH)4]2-: Spectroscopic Identification of a Unique Sulfido-Bridged Acyclic Tricubane Cluster
journal contribution
posted on 1997-09-24, 00:00 authored by H. R. Hoveyda, R. H. HolmOur interest in higher nuclearity sulfido-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 P21/n of
the monoclinic system with a = 26.201(1) Å,
b =
11.4999(5) Å, c = 28.090(1) Å, and β =
110.735(1)°. The X-ray structure reveals the conventional
cubane-type
geometry with an [Fe4S4]2+ core
symmetry more closely approaching Td
than the tetragonally distorted
D2d
symmetry reported for the
(PPh4)2[1] (Müller, A.;
Schladerbeck, N. H.; Bögge, 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 sulfido-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 treated with acidic thiol,
by electrospray mass spectrometry, and both 19F
and
1H NMR spectroscopy indicates the presence of a
sulfido-bridged acyclic trimer of
[Fe4S4]2+ clusters,
i.e.
{[Fe4S4(SH)3]2[Fe4S4(SH)2](μ-S)2}6-
(4), a hitherto unprecedented Fe−S structural pattern, as
the principal Fe−S
cluster self-condensation product.
