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

Abstract

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.

Pressure-induced variations of MLCT and ligand-centered luminescence spectra in square-planar platinum(II) complexes

“…This diversity is in qualitative contrast to d-d luminescence from square-planar platinum(II) complexes where a shift to higher energy on the order of +10 cm -1 /kbar to +30 cm -1 /kbar is observed for many complexes [10], and, in exceptional cases, a strong shift to lower energy, on the order of -100 cm -1 /kbar. [16] The behavior reported here for luminescence transitions of a different type falls in between these two limits, as discussed in the following.…”

“…Trends of band maxima in the same direction at high pressure and low 5 temperature are expected, as both variations lead to a decrease of the sample volume. [10] The maximum shifts by +2.6 cm -1 /K. The band width increases from 1100 cm -1 to 1500 cm -1 between 80 K and room temperature, the characteristic signature of a vibronic intensity mechanism, as intensity increases mainly to the high-energy side of the electronic origin.…”

“…Shifts for d-d luminescence maxima are well documented and range from approximately +10 cm -1 /kbar to +50 cm -1 /kbar. [9,10] Shifts to lower energy, between -100 cm -1 /kbar and -400 cm -1 /kbar, occur for compounds with strong metal-metal interactions such as tetracyanoplatinates. [8,11] The results presented here fill the gap in these ranges and document the behavior of MLCT and ligand-centered transitions.…”

Variation of M···H–C Interactions in Square-Planar Complexes of Nickel(II), Palladium(II), and Platinum(II) Probed by Luminescence Spectroscopy and X-ray Diffraction at Variable Pressure

“…Surprisingly, the deuterated palladium(II) complex shows a significantly lower-energy maximum at 12200 cm - shows a corresponding broadening, which is typical for vibronic intensity gain as temperature increase. 39,40 The spectrum of [Pt{(CD 3 ) 2 DTC} 2 ] at 293 K, in Figure S1f, has a bandwidth of 5000 cm -1 , larger by 1000 cm -1 than for the non-deuterated complex at this temperature. This important difference cannot be accounted for by vibronic intensity gain.…”

[Pt(SCN)4]2–‐Based Coordination Polymers and Supramolecular Squares: Intermolecular Pt···H–C Interactions Probed by Luminescence Spectroscopy at Variable Pressure

“…The variation of temperature or pressure is a standard way to continuously vary structures, and while the determination of structure changes by crystallographic methods can be challenging, spectroscopic techniques often provide clearly established quantitative trends , . Only a few reports on pressure effects on coordination polymers or metal‐organic frameworks have been published,, , and the d–d luminescence of the square‐planar [Pt(SCN) 4 ] 2– units in the supramolecular systems described here provides an excellent opportunity to probe effects specific to the supramolecular structure of the materials. Thus, this complementary approach to established crystallographic and spectroscopic techniques for probing intermolecular interactions that impact physical properties – in this case, luminescence – is illustrated herein by analysis of a new series of structurally characterized, emissive [Pt(SCN) 4 ]‐based supramolecular systems.…”