  We present Fe K$\beta$ X-ray emission (XES) and Fe K X-ray absorption spectra
(XAS) of Iron(II)sulfide (FeS) and Iron(II)disulfide (FeS$_2$). While XES and
XAS offer different discrimination capabilities for chemical speciation,
depending on the valence states of the compounds probed, XES allows for using
different excitation sources. The XES data was measured using polychromatic
X-ray radiation with a full-cylinder von Hamos spectrometer being characterized
by an energy window of up to 700 eV and a spectral resolving power of $E/
\Delta E = 800$. The large energy window at a single position of the
spectrometer components is made profit of to circumvent the instrumental
sensitivity of wavelength-dispersive spectrometers to sample positioning. This
results in a robust energy scale which is used to compare experimental data
with ab initio valence-to-core calculations, which are carried out using the
OCEAN package. To validate the reliability of the OCEAN package for the two
sample systems, near edge X-ray absorption fine structure measurements of the
Fe K absorption edge are compared to theory using the same input parameters as
in the case of the X-ray emission calculations. Based on the example of iron
sulfide compounds, the combination of XES experiments and OCEAN calculations
allows unravelling the electronic structure of different transition metal
sulfides and qualifying XES investigations for the speciation of different
compounds.
