An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
In a series of Pt(II) complexes [Pt(dba)(L)] containing the very rigid, dianionic, bis-cyclometalating, tridentate C^N^C2− heterocyclic ligand dba2− (H2dba = dibenzo[c,h]acridine), the coligand (ancillary ligand) L = dmso, PPh3, CNtBu and Me2Imd (N,N’-dimethylimidazolydene) was varied in order to improve its luminescence properties. Beginning with the previously reported dmso complex, we synthesized the PPh3, CNtBu and Me2Imd derivatives and characterized them by elemental analysis, 1H (and 31P) NMR spectroscopy and MS. Cyclic voltammetry showed partially reversible reduction waves ranging between −1.89 and −2.10 V and increasing along the series Me2Imd < dmso ≈ PPh3 < CNtBu. With irreversible oxidation waves ranging between 0.55 (L = Me2Imd) and 1.00 V (dmso), the electrochemical gaps range between 2.65 and 2.91 eV while increasing along the series Me2Imd < CNtBu < PPh3 < dmso. All four complexes show in part vibrationally structured long-wavelength absorption bands peaking at around 530 nm. TD-DFT calculated spectra agree quite well with the experimental spectra, with only a slight redshift. The photoluminescence spectra of all four compounds are very similar. In fluid solution at 298 K, they show broad, only partially structured bands, with maxima at around 590 nm, while in frozen glassy matrices at 77 K, slightly blue-shifted (~580 nm) bands with clear vibronic progressions were found. The photoluminescence quantum yields ΦL ranged between 0.04 and 0.24, at 298 K, and between 0.80 and 0.90 at 77 K. The lifetimes τ at 298 K ranged between 60 and 14040 ns in Ar-purged solutions and increased from 17 to 43 µs at 77 K. The TD-DFT calculated emission spectra are in excellent agreement with the experimental findings. In terms of high ΦL and long τ, the dmso and PPh3 complexes outperform the CNtBu and Me2Imd derivatives. This is remarkable in view of the higher ligand strength of Me2Imd, compared with all other coligands, as concluded from the electrochemical data.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Cyclometalated Pd(II) complexes generally show inferior luminescence properties compared with their Pt(II) analogues. The established approach employing tridentate cyclometalating ligands has allowed us to create a series of square planar Pd(II) complexes [Pd( )X] from their protoligands H (2‐(6‐phenylpyridin‐2‐yl)thiazoles and ‐benzothiazoles; coligands X=Cl, Br, I) with extensive variations at the C arene group (phenyl, naphthyl, fluorenyl), the central N pyridine (pyridine, 4‐phenylpyridine, 3,5‐di‐ tert ‐butyl‐4‐phenylpyridine), and the peripheral N thiazole (thiazole, benzothiazole) to probe for structural factors that might enhance efficient luminescence. Long‐wavelength bands at 400–500 nm were assigned to transitions into mixed ligand‐centred/metal‐to‐ligand charge transfer (MLCT) states based on time‐dependent (TD)DFT calculations. The MLCT contributions are rather low, in agreement with relatively long lifetimes and high photoluminescence quantum yields of up to 0.79 recorded in frozen glassy solvent matrices at 77 K along with emission bands showing pronounced vibrational progressions and peaking at about 520 nm. No photoluminescence was observed at 298 K in solution. Variation of the ligand allowed to shift the experimental absorption energies from about 2.4 to 2.7 eV, in good agreement with the electrochemical band gaps (2.58 to 2.81 eV). The theoretical absorption and emission spectra excellently reproduced the experimental trends.
Bis‐cyclometalated Pt II complexes of dianionic 2,5‐bis(aryl)‐pyridine ligands (L 1–6 ) 2– , carrying various cyclometalating or pending aryl groups, are synthesised in two steps. The reactions of H 2 L protoligands with K 2 [PtCl 4 ] in acetic acid give the mono‐cyclometalated complexes [Pt(HL)Cl] 2 . Heating these complexes in hot DMSO (dimethyl sulfoxide) yields the double‐cyclometalated DMSO complexes [Pt(L 1–6 )(DMSO)]. The reaction of [Pt(L 4 )(DMSO)] with N , N ‐dimethylimidazolium iodide in the presence of KO t Bu as the base gives the carbene complex [Pt(L 4 )(Me 2 Imd)]. Detailed photophysical studies reveal the intense orange luminescence of these complexes in CH 2 Cl 2 solution, with quantum yields up to 0.22, and increased quantum yields of up to 1.00 in glassy frozen CH 2 Cl 2 /MeOH (1:1) and up to 0.44 in PMMA matrices. Detailed electrochemistry (including spectroelectrochemistry) reveals reversible ligand‐based first reductions at –2.1 to –2.3 V, irreversible Pt‐centred oxidations at around 0.8 V and electrochemical band gaps of 2.8–3.0 eV. Further reduction waves at very negative potentials interfere with the solvent (THF with traces of water) discharge and can be traced, with UV/Vis spectroelectrochemistry, to Pt‐centred reductions for the DMSO complexes and to a second ligand‐centred reduction for the Me 2 Imd complex from. The photo/electrochemical properties can be roughly correlated with the ligand pattern and suggest their use in optoelectronic applications.
