Synthesis, Structure, and Luminescence of Di- and Trinuclear Palladium/Gold and Platinum/Gold Complexes with (2,7-Di-tert-butylfluoren-9-ylidene)methanedithiolate,1

Dinuclear ligand-to-ligand charge transfer complexes

The synthesis and characterization of dinuclear ligand-to-ligand charge transfer complexes are described. Each complex is comprised of square-planar platinum(II) coordinated to a 3-tert-butyl-orthocatecholate donor and a 4,4'-di-tert-butyl-2,2'-bipyridine acceptor. Both complexes exhibit donor → acceptor ligand-to-ligand charge transfer (LL'CT) bands in the visible spectrum. The platinum complexes are covalently attached at the catecholate 5-position to either a meta- or para-phenylene bridge fragment. Both cyclic voltammetry and electronic absorption spectroscopy exhibit features characteristic of intramolecular interaction between the platinum centres. The LL'CT excited state lifetimes are ∼twofold longer than the mononuclear parent complex. The properties of these complexes are discussed and compared to similar complexes in the literature.

Comprehensive Investigation of the Photophysical Properties of Alkynylcoumarin Gold(I) Complexes

Six gold(I) complexes (R₃P-Au-Coum) containing three different alkynylcoumarin chromophores (Coum) with different electron-donating and electron-withdrawing characteristics and two different water-soluble phosphanes (PR₃ = PTA (a) and DAPTA (b)) have been synthesized (1a,b, unsubstituted coumarin; 2a,b, 4-methyl substituted coumarin; 3a,b, 3-chloro and 4-methyl substituted coumarin). A comprehensive study of the photophysical properties of the R₃P-Au-Coum, together with their propynyloxycoumarin precursors 1-3, was performed in solution at room and low temperatures. Spectral and photophysical characteristics of the R₃P-Au-Coum essentially depend on the electronic characteristics of the propynyloxycoumarin ligand. The presence of the Au(I) atom was found to be responsible for an increase of the intersystem crossing, with triplet state quantum yield values, ϕ_T, ranging from ∼0.05 to 0.35 and high coumarin phosphorescence quantum yield values for derivatives 1 and 2; fluorescence dominates the deactivation in derivatives 3. Efficient singlet oxygen photosensitization was observed for the new compounds 3a,b. From TDDFT calculations, the relevant HOMO and LUMO of the compounds, i.e., those involved in the transitions, are dominated by the frontier orbitals associated with the coumarin core. The Au(I)-phosphane structure introduces a new transition assigned to an intraligand transition involving the phosphane ligand, and π(C≡C) system, to the p orbitals of phosphorus and gold atoms.

New heteroleptic [Ni(ii) 1,1-dithiolate-phosphine] complexes: synthesis, characterization and electrocatalytic oxygen evolution studies

Four new heteroleptic Ni(ii) complexes with general formula [Ni(ii)(LL')] (L = 2-(methylene-1,1'-dithiolato)-5-phenylcyclohexane-1,3-dione (L1) and 2-(methylene-1,1'-dithiolato)-5,5'-dimethylcyclohexane-1,3-dione (L2); L' = 1,2-bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)monosulphide methane (dppms) have been synthesized and characterized by elemental analysis and spectroscopy (IR, UV-Vis, 1H, 13C{1H} and 31P{1H} NMR). All complexes 1-4 have also been characterized by PXRD and single crystal X-ray crystallography. The solid state molecular structures revealed distorted square planar geometry about the four-coordinate Ni(ii) metal centre together with rare NiH-C intra/intermolecular anagostic interactions in axial positions. In these complexes supramolecular structures have been sustained by non-covalent C-HO, C-OH-O, C-Hπ, C-Hπ (NiCS2, chelate), ππ and HH interactions. Their electrocatalytic properties have been investigated for oxygen evolution reaction (OER) in which complex 2 showed the highest activity with 10 mA cm-2 at the potential of 1.58 V vs. RHE. In addition, complex 2 also exhibits an OER onset potential at 1.52 V vs. RHE.

Europium(III) Photoluminescence Governed by d8-d10 Heterometallophilic Interactions in Trimetallic Cyanido-Bridged Coordination Frameworks

We report an efficient pathway toward sensitization of red room temperature Eu^III emission by the charge-transfer (CT) states related to d⁸-d¹⁰ heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of Pt^II/Pd^II and dicyanidometallates of Au^I/Ag^I in the construction of a trimetallic d-d-f assembly. The combination of Eu³⁺, [M^II(CN)₄]^2- (M = Pt, Pd), and [M^I(CN)₂]^- (M = Au, Ag) ions along with 4,4'-bipyridine N,N'-dioxide (4,4'-bpdo) results in four novel isostructural 2D {[Eu^III(4,4'-bpdo)(H₂O)₂][M^II(CN)₄]}·[M^I(CN)₂]·H₂O (M^II/M^I = Pt/Au, 1; Pt/Ag, 2; Pd/Au, 3; Pd/Ag, 4) coordination networks. They are built of hybrid coordination layers, based on cyanido-bridged {Eu^III[M^II(CN)₄]}_n square grids coexisting with metal-organic {Eu^III(4,4'-bpdo)}_n chains, with the further attachment of [M^I(CN)₂]^- ions through metallophilic {M^II-M^I} interactions. This results in dinuclear {M^IIM^I} units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d⁸-d¹⁰ metal centers. Thanks to these CT states, 1-4 exhibit room temperature red Eu^III photoluminescence enhanced by energy transfer from {M^IIM^I} units, with the additional role of 4,4'-bpdo also transferring the energy to lanthanides. These donor CT states lying in the visible range successfully broaden the available efficient excitation range up to 500 nm. The overall emission quantum yield ranges from 8(1)% for 4 to 15(2)% for 1, with the intermediate values for 2 and 3 relatively high among the reported Eu^III-based compounds with tetracyanido- and dicyanidometallates. We found that the sensitization efficiency is equally high for all compounds because of the similar energies of the CT states, while the main differences are related to the observed emission lifetimes ranging from ca. 80 μs for 4 to 120-130 μs for 2 and 3 to ca. 180 μs for 1. This phenomenon was correlated with the energies of the vibrational states, e.g., cyanide stretching vibrations, responsible for nonradiative deactivation of Eu^III excited states, which are the highest for the Pd/Ag pair of 4 and the lowest for the Pt/Au pair in 1. Thus, the heaviest pair of Pt^II/Au^I cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature Eu^III luminescence.

Near-unity thermally activated delayed fluorescence efficiency in three- and four-coordinate Au(i) complexes with diphosphine ligands

The synthesis and photoluminescence properties of three-coordinate Au(i) complexes with rigid diphosphine ligands LMe {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, LEt {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and LiPr {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene} are investigated. The LMe and LEt ligands afford two types of complexes: dinuclear complexes [μ-LMe(AuCl)2] (1d) and [μ-LEt(AuCl)2] (2d) with an Au(i)-Au(i) bond and mononuclear three-coordinate Au(i) complexes LMeAuCl (1) and LEtAuCl (2). On the other hand, the bulkiest ligand, LiPr, affords three-coordinate Au(i) complexes, LiPrAuCl (3) and LiPrAuI (4), but no dinuclear complexes. X-ray analysis suggests that both 3 and 4 possess a highly distorted trigonal planar geometry. Moreover, luminescence data reveal that at room temperature, 3 and 4 exhibit yellow-green thermally activated delayed fluorescence in the crystalline state with maximum emission wavelengths at 558 and 549 nm, respectively. The emission yields are close to unity. Quantum chemical calculations suggest that the emission of 4 originates from the (σ + X) → π* excited state that possesses strong intraligand charge-transfer character. The luminescent properties of four-coordinate Au(i) complex (5) possessing a tetrahedral geometry are discussed on the basis of the emission spectra and decay times measured in a temperature range of 309-77 K.

Octanuclear gold(i) alkynyl-diphosphine clusters showing thermochromic luminescence

The unprecedented Au(i) alkynyl-diphosphine clusters demonstrate intense phosphorescence in solution and thermally dependent emission in the crystalline form.