双立方烷固氮模拟物(Et_4N)_4[Mo_2Fe_7S_8(sph)_(12)]的穆斯堡尔研究

Mossbauer studies on nitrogen fixation model compounds with double-cubane configuration (Et_4N)_ 4[Mo_2Fe_7S_8 (sph) _(12)]

本实验测定了双立方烷固氮模拟物(Et_4N)_4[Mo_2Fe_7S_8(sph)_(12)]的穆斯堡尔谱。它是由两组对称的四极分裂双峰叠加而成。实验数据用最小二乘法计算机程序拟合。经计算机拟合后的穆斯堡尔参数(在16℃时)为;对于Fe_r,σ=0.315±0.002mm/s,△E_σ=0.691±0.002mm/s,线宽为0.304±0.002mm/s;对于Fe_(rr),σ=0.972±0.002mm/s,△E_σ=1.741±0.002mm/s,线宽为0.273±0.002mm/s。化学位移δ值是相对于α-Fe的。这两组四极分裂双峰的面积比约为6:1。由Fe_r的位移和四极裂距可确定它是高自旋态,价态在+2至+3之间。利用四面体FeS_4中铁原子的化学位移δ与价态s的经验公式δ=1.44-0.43s可得出Fe_r平均价态为高自旋+2.67价。从穆斯堡尔参数可确定Fe_(rr)属于高自旋+2价。由此可推论Mo为+3价。

Mossbauer spectra of nitrogen model compounds with double-cubane configuration (Et4N)4[Mo2Fe7S8(sph)12] have been measured. The data have been fitted successfully with a least-squares fitting computer program. The Mossbauer parameters measured at 16℃ are as follows. For FeIt σ=0.315±0.002mm/s, △EQ = 0.691±0.002mm/s and the line width is 0.304±0.002mm/s; For Fe11, δ=0.972±0.002mm/s, △EQ = 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 FeI and Fe11 is about 6:1. From these parameters it is found that Fe11 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 FeS4:δ=1.44-0.43s, we have deduced that FeI is in +2.67 high spin state.