Tribological experiments with 1,3-diketone
fluids in contact with
iron surfaces show ultralow friction, which was suggested to be connected
to the formation of iron complexes. In order to support this assumption,
we calculate infrared and optical spectra of various substituted 1,3-diketones
and their iron complexes using gradient-corrected density functional
theory (DFT). The description of the complexes requires the application
of the DFT+U scheme for a correct prediction of the high spin state
on the central iron atom. With this approach, we obtain excellent
agreement between experiment and simulation in infrared and optical
spectra, allowing for the determination of 1,3-diketone tautomeric
forms. The match in the spectra of the complex strongly supports the
assumption of iron complex formation by these lubricants