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.

Two luminescent heteroleptic Ru complexes with a 2,2'-biimidazole (biimH ) ligand form doubly hydrogen-bonded salt bridges to 4-sulfobenzoate anions in single crystals. The structure of one of these cation-anion adducts shows that the biimH ligand is deprotonated. Its MLCT luminescence band does not shift significantly under the influence of an external hydrostatic pressure, a behavior typical for these electronic transitions. In contrast, hydrostatic pressure on the other crystalline cation-anion adduct induces a shift of proton density from the peripheral N-H groups of biimH towards benzoate, leading to a pronounced redshift of the MLCT luminescence band. Such a significant and pressure-tunable influence from an interaction in the second coordination sphere is unprecedented in artificial small-molecule-based systems.

Luminescence spectra of isoelectronic square-planar d complexes with 3d, 4d, and 5d metal centers show d-d luminescence with an energetic order different from that of the spectrochemical series, indicating that additional structural effects, such as different ligand-metal-ligand angles, are important factors. Variable-pressure luminescence spectra of square-planar nickel(II), palladium(II), and platinum(II) complexes with dimethyldithiocarbamate ({CH}DTC) ligands and their deuterated analogues show unexpected variations of the shifts of their maxima. High-resolution crystal structures and crystal structures at variable pressure for [Pt{(CH)DTC}] indicate that intermolecular M···H-C interactions are at the origin of these different shifts.

We present the variable-pressure d-d luminescence spectra of crystalline bis-dimethyldithiocarbamate palladium(ii) and its deuterated analog. The energies and shifts of the band maxima provide evidence for intermolecular PdH-C interactions, with quantitative differences observed for the deuterated complex. Shifts show distinct interactions in three pressure ranges between 1 bar and 85 kbar.

We present the variable-pressure luminescence spectra of crystals of isostructural palladium(ii) and platinum(ii) complexes with bis-N-benzyl-N'-3-methylpyridyldithiocarbamate (bmpDTC) ligands. The d-d luminescence band maxima E for these complexes are compared to others with different peripheral substituents on the dithiocarbamate ligands in the solid state. The comparison reveals significant variations of E despite very similar metal coordination geometries. E varies by 3000 cm and 1300 cm among four dithiocarbamate complexes of platinum(ii) and palladium(ii), respectively. Variations of E with pressure reveal the effects of intermolecular MH-C interactions on several complexes. ΔE/ΔP values are negative for the bmpDTC complexes, unprecedented in the dithiocarbamate family. Static orientation and pressure-induced movement of the C-H bonds involved in intermolecular interactions have a significant effect on E and ΔE/ΔP, with a stronger impact on platinum(ii) complexes than on their palladium(ii) analogs.