cis/trans-[Pt(C∧N)(C≡CR)(CNBut)] Isomers: Synthesis, Photophysical, DFT Studies, and Chemosensory Behavior

cis/trans Isomerism can be a crucial factor for photophysical properties. Here, we report the synthesis and optical properties of a series of trans- and cis-alkynyl/isocyanide cycloplatinated compounds [Pt(C^∧N)(C≡CR)(CNBu^t)] [R = C₆H₄-4-OMe 1, 3-C₄H₃S 2; C^∧N = 2-(2,4-difluorophenyl)pyridine (dfppy) (a), 4-(2-pyridyl)benzaldehyde (ppy-CHO) (b)]. The trans-forms do not isomerize thermally in MeCN solution to the cis forms, but upon photochemical irradiation in this medium at 298 K, a variable isomerization to the cis forms was observed. This behavior is in good agreement with the theoretically calculated energy values. The trans/cis configuration, the identity of the cyclometalated, and the alkynyl ligand influence on the absorption and emission properties of the complexes in solution, polystyrene (PS) films, and solid state are reported. All complexes are efficient triplet emitters in all media (except for trans-1a and trans-2a in CH₂Cl₂ solution at 298 K), with emission wavelengths depending mainly on the cyclometalated ligand in the region 473-490 nm (dfppy), 510-550 (ppy-CHO), and quantum yields (ϕ) ranging from 18.5 to 40.7% in PS films. The combined photophysical data and time-dependent density functional theory calculations (TD-DFT) at the excited-state T₁ geometry reveal triplet excited states of ³L'LCT (C≡CR → C^∧N)/³IL (C^∧N) character with minor ³MLCT contribution. The dfppy (a) complexes show a greater tendency to aggregate in rigid media than the ppy-CHO (b) and the cis with respect to the trans, showing red-shifted structureless bands of ³MMLCT and/or excimer-like nature. Interestingly, trans-1a,2a and cis-1a,2a undergo significant changes in the ultraviolet (UV) and emission spectra with Hg²⁺ ions enabling their use for sensing of Hg²⁺ ions in solution. This is clearly shown by the hypsochromic shift and substantial decrease of the low-energy absorption band and an increase of the intensity of the emission in the MeCN solution upon the addition of a solution of Hg(ClO₄)₂ (1:5 molar ratio). Job's plot analysis estimated a 1:1 stoichiometry in the complexation mode of Hg²⁺ by trans-2a. The binding constant (log K) calculated for this system from absorption titration data resulted to be 2.56, and the limit of the detection (LOD) was 6.54 × 10^-7 M.

The [Ag25Cu4H8Br6(CCPh)12(PPh3)12]3+ : Ag13H8 silver hydride core protected by [CuAg3(CCPh)3(PPh3)3]+ motifs

Copper alkynyl complexes [CuAg3(C[triple bond, length as m-dash]CAr)3(PPh3)3]+ (Ar = Ph, p-C6H4Me), in which three Ag(PPh3) units are bound among three C[triple bond, length as m-dash]CAr arms of trigonal-planar [Cu(C[triple bond, length as m-dash]CAr)3]2-, were selected as a protecting unit to cover the metal core of an atomically precise core-shell-type cluster. First, the formation of the protecting unit through the reaction of Cu(NCMe)4(PF6) with Ag(C[triple bond, length as m-dash]CAr) and PPh3 in a 1 : 3 : 3 ratio was confirmed. The reaction gave dimeric [CuAg3(C[triple bond, length as m-dash]CAr)3(PPh3)3]22+, in which the two planar [CuAg3(C[triple bond, length as m-dash]CAr)3(PPh3)3]+ units were stacked. Next, core-shell-type clusters were synthesized by adding NaBH4 and Et4NX (X = Cl, Br) to a solution similar to that used to prepare the protecting unit. The trigonal-planar protecting units nicely formed core-shell-type Ag nanoclusters formulated as [Ag13H8X6{CuAg3(C[triple bond, length as m-dash]CAr)3(PPh3)3}4]3+ (X = Cl, Ar = p-C6H4Me; X = Br, Ar = p-C6H4Me; X = Br, Ar = Ph). Their crystal structures revealed that the four [CuAg3(C[triple bond, length as m-dash]CAr)3(PPh3)3]+ units are linked by six halogen ions to form a tetrahedral cage that accommodates a polyhydride-Ag cluster formulated as Ag13H85+. As a concrete proof of the existence of the polyhydride, deuterated analogs Ag13D85+ were synthesized and subsequently characterized by high-resolution electrospray-ionization mass spectrometry measurements.

Keep it tight: a crucial role of bridging phosphine ligands in the design and optical properties of multinuclear coinage metal complexes

Copper subgroup metal ions in the +1 oxidation state are classical candidates for aggregation via non-covalent metal-metal interactions, which are supported by a number of bridging ligands. The bridging phosphines, soft donors with a relatively labile coordination to coinage metals, serve as convenient and essential components of the ligand environment that allow for efficient self-assembly of discrete polynuclear aggregates. Simultaneously, accessible and rich modification of the organic spacer of such P-donors has been used to generate many fascinating structures with attractive photoluminescent behavior. In this work we consider the development of di- and polynuclear complexes of M(i) (M = Cu, Ag, Au) and their photophysical properties, focusing on the effect of phosphine bridging ligands, their flexibility and denticity.

Tripodal gold(i) polypyridyl complexes and their Cu+ and Zn2+ heterometallic derivatives. Effects on luminescence

Three gold(i) tripodal complexes containing the tris(2-pyridylmethyl)amine (TPA) ligand coordinated to Au-PR₃ moieties (PR₃ = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane, PTA (1), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, DAPTA (2) and triphenylphosphane (3)) were prepared together with a cage-like structure containing triphosphane 1,1,1-tris(diphenylphosphinomethyl)ethane (4). The luminescence of these complexes has been studied and they show a red shift upon the formation of heterometallic complexes by reaction with Zn(NO₃)₂, CuCl and [Cu(CH₃CN)₄]BF₄. The different coordination motifs of the Zn²⁺ and Cu⁺ heterometallic species and the resulting changes in the recorded absorption, emission and NMR spectra were analysed and supported by TD-DFT calculations.

A model electrode of well-defined geometry prepared by direct laser-induced decoration of nanoporous templates with Au-Ag@C nanoparticles

We present an original type of model electrode system consisting of bimetallic Au-Ag nanoparticles embedded in an amorphous carbon matrix with an extremely well-defined geometry of parallel, straight, cylindrical macropores. The samples are prepared in one step by direct laser deposition of the metal/carbon composite onto the inner walls of a porous 'anodic' alumina matrix serving as a template. The coating is homogeneous from top to bottom of the pores, and the amount of material deposited can be tuned by the duration of the deposition procedure. As a test system, we demonstrate that a bimetallic Ag-Au@C system is catalytically active for the electrochemical oxidation of glucose in alkaline solution, the anodic reaction of a direct glucose fuel cell. Furthermore, the electrocatalytic current density increases with the amount of Ag-Au@C NPs deposited, up to a point at which the pores are clogged with it. This type of model system allows for the systematic study of geometric effects in fuel cell electrodes. It can be generalized to a number of different nanoparticle compositions, and thereby, to various electrocatalytic reactions.

Novel electrochemi-/photo-luminescence of Ag3Cu5 heterometallic alkynyl clusters

Two windmill-like Ag₃Cu₅ alkynyl clusters were synthesized and characterized. They display novel PL and ECL properties, which could be modified by changing the substituent on the alkynyl ligands. According to the study of EC, ECL behaviours and ECL emission spectra of the Ag₃Cu₅ clusters, a possible ECL mechanism was proposed.

Alkynyl-functionalized gold NHC complexes and their coinage metal clusters

Phenylpropynyl-functionalized N-heterocyclic carbenes as ligands for the synthesis of heterometallic hexanuclear coinagemetal clusters which exhibit mixed metallophillic interactions and intense white photoluminescence at low temperature.

Shedding light on the photochemistry of coinage-metal phosphorescent materials: a time-resolved Laue diffraction study of an Ag(I)-Cu(I) tetranuclear complex

The triplet excited state of a new crystalline form of a tetranuclear coordination d(10)-d(10)-type complex, Ag2Cu2L4 (L = 2-diphenylphosphino-3-methylindole ligand), containing Ag(I) and Cu(I) metal centers has been explored using the Laue pump-probe technique with ≈80 ps time resolution. The relatively short lifetime of 1 μs is accompanied by significant photoinduced structural changes, as large as the Ag1···Cu2 distance shortening by 0.59(3) Å. The results show a pronounced strengthening of the argentophilic interactions and formation of new Ag···Cu bonds on excitation. Theoretical calculations indicate that the structural changes are due to a ligand-to-metal charge transfer (LMCT) strengthening the Ag···Ag interaction, mainly occurring from the methylindole ligands to the silver metal centers. QM/MM optimizations of the ground and excited states of the complex support the experimental results. Comparison with isolated molecule optimizations demonstrates the restricting effect of the crystalline matrix on photoinduced distortions. The work represents the first time-resolved Laue diffraction study of a heteronuclear coordination complex and provides new information on the nature of photoresponse of coinage metal complexes, which have been the subject of extensive studies.