Interpreting Effects of Structure Variations Induced by Temperature and Pressure on Luminescence Spectra of Platinum(II) Bis(dithiocarbamate) Compounds

Luminescence spectra of two square-planar
dithiocarbamate complexes of platinum­(II) with different steric bulk,
platinum­(II) bis­(dimethyldithiocarbamate) (Pt­(MeDTC)2)
and platinum­(II) bis­(di­(o-pyridyl)­dithiocarbamate)
(Pt­(dopDTC)2), are presented at variable temperature and
pressure. The spectra show broad d–d luminescence transitions
with maxima at approximately 13500 cm–1 (740 nm).
Variations of the solid-state spectra with temperature and pressure
reveal intrinsic differences due to subtle variations of molecular
and crystal structures, reported at 100 and 296 K for Pt­(dopDTC)2. Luminescence maxima of Pt­(MeDTC)2 shift to higher
energy as temperature increases by +320 cm–1 for
an increase by 200 K, mainly caused by a bandwidth increase from 3065
to 4000 cm–1 on the high-energy side of the band
over the same temperature range. Luminescence maxima of Pt­(dopDTC)2 shift in the opposite direction by −460 cm–1 for a temperature increase by 200 K. The bandwidth of approximately
2900 cm–1 does not vary with temperature. Both ground
and emitting-state properties and subtle structural differences between
the two compounds lead to this different behavior. Luminescence maxima
measured at variable pressure show shifts to higher energy by +47
± 3 and +11 ± 1 cm–1/kbar, for Pt­(MeDTC)2 and Pt­(dopDTC)2, respectively, a surprising difference
by a factor of 4. The crystal structures indicate that decreasing
intermolecular interactions with increasing pressure are likely to
contribute to the exceptionally high shift for Pt­(MeDTC)2.