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This work reports on a battery of coordination compounds featuring a versatile dianionic luminophore adopting three different coordination modes (mono, bi, and tridentate) while chelating Pd(II), Pt(II), Au(III), and Hg(II) centers. An in‐depth structural characterization of the ligand precursor (H2L) and six transition metal complexes ([HLPdCNtBu], [LPtCl], [LPtCNtBu], [LPtCNPhen], [HLHgCl], and [LAuCl]) is presented. The influence of the cations and coordination modes of the luminophore and co‐ligands on the photophysical properties (including photoluminescence quantum yields (ΦL), excited state lifetimes (τ), and average (non‐)radiative rate constants) are evaluated at various temperatures in different phases. Five complexes show interesting photophysical properties at room temperature (RT) in solution. Embedment in frozen glassy matrices at 77 K significantly boosts their luminescence by suppressing radiationless deactivation paths. Thus, the Pt(II)‐based compounds provide the highest efficiencies, with slight variations upon exchange of the ancillary ligand. In the case of [HLPdCNtBu], both ΦL and τ increase over 30‐fold as compared to RT. Furthermore, the Hg(II) complex achieves, for the first time in its class, a ΦL exceeding 60% and millisecond‐range lifetimes. This demonstrates that a judicious ligand design can pave the way toward versatile coordination compounds with tunable excited state properties. [ABSTRACT FROM AUTHOR]

We herein report on the synthesis and structural characterization, as well as on the photophysical properties, of a series of isoleptic Pt(II) and Pd(II) complexes featuring tridentate N^N^N chelators as luminophores while bearing diverse ancillary co-ligands. Six new palladium complexes were synthesized using 2,6-bis(3-(tert-butyl/trifluoromethyl)-1H-1,2,4-triazol-5-yl)pyridine (tbu or CF3, respectively) in combination with four distinct ancillary ligands, namely: 4-amylpyridine (AmPy), 2,6-dimethylphenyl isonitrile (CNR), triphenylphosphane (PPh3), and 1,3,5-triaza-7-phosphaadamantane (PTA). Thus, two novel Pt(II) complexes incorporating the co-ligands CNR and PTA were explored. The remaining platinum-based complexes, namely CF3-Pt-AmPy, tbu-Pt-AmPy, CF3-Pt-PPh3, and tbu-Pt-PPh3, were re-synthesized according to our previous work for a systematic comparison with their Pd(II) homologues. Thus, photophysical studies were performed in different solvents and conditions. The Pt(II) complexes demonstrated comparable or superior photophysical characteristics in toluene when compared with their solutions in liquid dichloromethane at room temperature. In contrast, the Pd(II) complexes exhibited no significant photoluminescence in dichloromethane, but a surprisingly clear emission was observed for tbu-Pd-AmPy, tbu-Pd-CNR, and tbu-Pd-PPh3 in liquid toluene at room temperature. The significant differences regarding excited state lifetimes and photoluminescence quantum yields underscore the impact of solvent selection on photophysical characteristics, emphasizing the need to consider metal-ligand interactions, as well as the surrounding microenvironment, for a comprehensive interpretation of their photophysical properties. In addition, it is clear that AmPy and CNR render better luminescence efficiencies, whereas PTA is only suitable in toluene. [ABSTRACT FROM AUTHOR]

In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on their excited state properties. Hence, a detailed analysis of the different synthetic pathways is presented; the photophysical properties were studied by using steady-state and time-resolved photoluminescence spectroscopy. We determined the absorption and emission spectra, the photoluminescence efficiencies, and the excited state lifetimes of the complexes in fluid solutions at room temperature and frozen glassy matrices at 77 K. Finally, a structure–property relationship was established, showing that the decoration of the bridging unit on the tridentate luminophores only marginally affects the excited state properties, whereas the double cyclometallation related to the tetradentate chelator prolongs the excited state lifetime and increases the photoluminescence quantum yield. [ABSTRACT FROM AUTHOR]

Depending on the chelate ring present, cyclometalated complexes are useful catalysts for various reactions. The reactivity of Ir III and Rh III NHC complexes bearing aliphatic or aromatic N,N'-substituents and thus featuring various metalation sites toward cyclometalation has been investigated. The Rh III complex bearing an N -mesityl- N '-benzyl-NHC does not participate in any cyclometalation, while the Ir III complex reacts under metalation of an ortho -methyl group of the Mes substituent to give complex [ 3 ] with a six-membered chelate ring. The Rh III and Ir III complexes bearing an N - o -tolyl, N -benzyl-NHC undergo sp 2 -CH activation to yield the cyclometalated complexes [ 4 ] and [ 5 ] featuring a five-membered C NHC ∧ C chelate ring. Density functional theory (DFT) studies corroborated the experimental findings., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The Ir III hydrido complexes [ 1 ] and [ 2 ] have been synthesized by the regioselective oxidative addition of the N7-H bond of 8-halogenotheophyllines to [IrCl(coe) 2 ] 2 in the presence of PPh 3 . The use of dppf in this reaction yielded the bimetallic Ir III /Fe II hydrido complexes [ 3 ] and [ 4 ]. X-ray diffraction studies confirmed that complexes [ 1 ]-[ 4 ] feature a theophyllinato ligand coordinated to the metal center in the rarely observed, chelating fashion via the N7 and O1 atoms. In addition, 8-bromoadenine reacts with [IrCl(coe) 2 ] 2 in the presence of PPh 3 to form the Ir III hydrido complex [ 5 ] which features one anionic 8-bromoadeninato and one neutral 8-bromoadenine ligand linked by an intramolecular hydrogen bond. Complex [ 5 ] was characterized by high-resolution mass spectrometry and an X-ray diffraction analysis but could not be analyzed by nuclear magnetic resonance spectroscopy because of its low solubility., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)