  A large number of osmium complexes with osmium in different oxidation states
(II, III, IV, VI) have been reported recently to exhibit good antiproliferative
activity in cancer cell lines. Herein, we demonstrate new opportunities offered
by $^{187}$Os nuclear forward scattering (NFS) and nuclear inelastic scattering
(NIS) of synchrotron radiation for characterization of hyperfine interactions
and lattice dynamics in a benchmark Os(VI) complex K$_2$[OsO$_2$(OH)$_4$], by
accurate extraction of M\"ossbauer parameters and the determination of
Os-projected density of phonon states confirmed by first-principles phonon
calculations. The values of isomer shift ($\delta$ = 3.3(1) mm/s) relative to
[Os$^{IV}$ Cl$_{6}$]$^{2-}$ and quadrupole splitting ($\Delta E_Q$ = 12.0(2)
mm/s) were determined with NFS, while the Lamb-M\"ossbauer factor (0.55(1)),
the density of phonon states (DOS), and a full thermodynamics characterization
was carried out using the NIS data combined with first principle theoretical
calculations. In more general terms, this study provides strong evidence that
$^{187}$Os nuclear resonance scattering is a reliable technique for the
investigation of hyperfine interactions and Os specific vibrations in
osmium(VI) species, which might be potentially applicable for measuring such
interactions in osmium complexes of other oxidation states, including those
with anticancer activity such as Os(III) and Os(IV).
