Mössbauer-Effect Study of Nitrosyliron Bis(N, N-diethyldithiocarbamate)

The ⁵⁷Fe Mössbauer spectrum of nitrosyliron bis(N ,N‐diethyldithiocarbamate) has been measured at temperatures between 300° and 1.3°K and in external magnetic fields. In zero field, the spectrum at all temperatures consists of a quadrupole split pair of lines of unequal intensity. The intensity of the absorption increases markedly on cooling from 300° to 77°K. The isomer shift (0.34mm sec⁻¹ at 77°K, relative to iron) is higher than expected for a low‐spin Fe(I) complex and implies that the metal $s$ electrons are screened from the nucleus by electron donation from the ligands. The quadrupole splitting shows little dependence on temperature and the application of an external magnetic field shows the sign of the major component of the efg tensor to be positive. Magnetic hyperfine interactions are observed at low temperatures in large external magnetic fields. The variation of the effective hyperfine field at the nucleus with $\mathrm{H\hspace{0.17em}/\hspace{0.17em}T}$ follows the Brillouin function for $\mathrm{S\hspace{0.17em}=\hspace{0.17em}}\frac{1}{2}$ , and the value of the saturation hyperfine field was found to be 110 ± 5 kG. The orbital ground state of the iron atom cannot be deduced from the sign of the quadrupole splitting owing to the large contributions from the bonding electrons. From the magnetic hyperfine splitting, it is deduced to be $d_z^2$ .