Mössbauer spectra of nitrogen model compounds with double-cubane configuration (Et
4
N)
4
[Mo
2
Fe
7
S
8
(sph)
12
] have been measured. The data have been fitted successfully with a least-squares fitting computer program. The Mössbauer parameters measured at 16℃ are as follows. For Fe
I
δ=0.315±0.002mm/s
∆E
Q
=0.691±0.002mm/s and the line width is 0.304±0.002mm/s; For Fe
II
δ=0.972±0.002mm/s
ΔEQ
=1.741±0.002mm/s and the line width is 0.273±0.002mm/s. The isomer shift δ is relative to α—Fe. The ratio of quadrupole split areas for Fe
I
and Fe
II
is about 6:1. From these parameters it is found that Fe
II
is in +2 high spin state. Using an empirical formula about the isomer shift δ and the mean oxidation state s of Fe atoms in tetrahedron FeS
I
:d=1.44-0.43s
we have deduced that Fe
I
is in +2.67 high spin state.
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references
E. Münck et al . , Biochim. Biophys. Acta , 400 ( 1975 ), 32 .