9 research outputs found
Cupriphication of gold to sensitize d10âd10 metalâmetal bonds and near-unity phosphorescence quantum yields
Outer-shell s0/p0 orbital mixing with d10 orbitals and symmetry reductionuponcupriphicationofcyclic trinucleartrigonal-planargold(I) complexes are found to sensitize ground-state Cu(I)âAu(I) covalent bonds and near-unity phosphorescence quantum yields. Heterobimetallic Au4Cu2 {[Au4(ÎŒ-C2,N3-EtIm)4Cu2(ÎŒ-3,5-(CF3)2Pz)2], (4a)}, Au2Cu {[Au2(ÎŒ-C2,N3-BzIm)2Cu(ÎŒ-3,5-(CF3)2Pz)], (1) and [Au2(ÎŒ-C2, N3-MeIm)2Cu(ÎŒ-3,5-(CF3)2Pz)], (3a)}, AuCu2 {[Au(ÎŒ-C2,N3-MeIm)Cu2(ÎŒ3,5-(CF3)2Pz)2], (3b) and [Au(ÎŒ-C2,N3-EtIm)Cu2(ÎŒ-3,5-(CF3)2Pz)2], (4b)} and stacked Au3/Cu3 {[Au(ÎŒ-C2,N3-BzIm)]3[Cu(ÎŒ-3,5-(CF3)2Pz)]3, (2)} formuponreactingAu3 {[Au(ÎŒ-C2,N3-(N-R)Im)]3 ((N-R)Im = imidazolate; R =benzyl/methyl/ethyl =BzIm/MeIm/EtIm)} with Cu3 {[Cu(ÎŒ-3,5(CF3)2Pz)]3 (3,5-(CF3)2Pz = 3,5-bis(trifluoromethyl)pyrazolate)}. The crystal structures of 1 and 3a reveal stair-step infinite chains whereby adjacent dimer-of-trimer units are noncovalently packed via twoAu(I)âŻCu(I)metallophilicinteractions,whereas 4a exhibitsa hexanuclear cluster structure wherein two monomer-of-trimer units are linked by a genuine d10âd10 polar-covalent bond with ligandunassisted Cu(I)âAu(I) distances of 2.8750(8) Ă
eachâthe shortest such an intermolecular distance ever reported between any two d10 centers so as to deem it a âmetalâmetal bondâ vis-Ă -vis âmetallophilic interaction.â Density-functional calculations estimate 35â 43kcal/molbindingenergy,akintotypicalMâMsingle-bondenergies. Congruently, FTIR spectra of4a showmultiple far-IR bands within 65â 200 cmâ1, assignable to vCu-Au as validated by both the HarveyâGray method of crystallographic-distance-to-force-constant correlation and dispersive density functional theory computations. Notably, the heterobimetallic complexes herein exhibit photophysical properties that are favorable to those for their homometallic congeners, due to threefold-to-twofold symmetry reduction, resulting in cuprophilicsensitizationinextinctioncoefficientandsolid-state photoluminescence quantum yields approaching unity (ΊPL = 0.90â0.97 vs. 0â0.83 for Au3 and Cu3 precursors), which bodes well for potential future utilization in inorganic and/or organic LED applications
Remarkable Aurophilicity and Photoluminescence Thermochromism in a Homoleptic Cyclic Trinuclear Gold(I) Imidazolate Complex
A new aurophilically-bonded cyclic
trinuclear goldÂ(I) complex, trisÂ[ÎŒ<sub>2</sub>-(1-ethylimidazolato-N<sup>3</sup>,C<sup>2</sup>)ÂgoldÂ(I)] ([Au<sub>3</sub>(EtIm)<sub>3</sub>], <b>1</b>), has been synthesized and characterized by temperature-dependent
crystallographic and photophysical investigations. The crystal packing
of <b>1</b> reveals two independent molecules in the unit cell,
signifying two distinct pairs of dimer-of-trimer units convened by
pairwise intermolecular Au···Au interactions of 3.0662(3)
and 3.1407(3) Ă
at 100 K, representing the shortest pairwise
intermolecular aurophilic interactions among all cyclic trimetallic
goldÂ(I) complexes to date. Remarkably, crystals of <b>1</b> exhibit gigantic photoluminescence thermochromism of 10164 cm<sup>â1</sup>îžfrom violet to red!îžattributed to internal
conversion between a higher-energy (T<sub>2</sub> â S<sub>0</sub>; λ<sub>max</sub> âŒ409 nm) and lower-energy (T<sub>1</sub> â S<sub>0</sub>; λ<sub>max</sub> âŒ700 nm) phosphorescent
band below and above 200 K, respectively, likely representing an excited-state
phase change
Polymorphic, Porous, and HostâGuest Nanostructures Directed by MonolayerâSubstrate Interactions: Epitaxial Self-Assembly Study of Cyclic Trinuclear Au(I) Complexes on HOPG at the SolutionâSolid Interface
Synthesis, crystallographic characterization,
and molecular self-assembly
of two novel cyclotrimeric goldÂ(I) complexes, Au<sub>3</sub>[3,5-(COOEt)<sub>2</sub>Pz]<sub>3</sub> (Au<sub>3</sub>Pz<sub>3</sub>) and Au<sub>3</sub>[(<i>n</i>-PrâO)ÂCî»NÂ(Me)]<sub>3</sub> (Au<sub>3</sub>Cb<sub>3</sub>) was studied. Single crystal X-ray
crystallography data reveal that both goldÂ(I) complexes have one-dimensional
stacking patterns caused by intermolecular AuÂ(I)···AuÂ(I)
aurophilic interactions. The Au<sub>3</sub>Pz<sub>3</sub> trimer units
stack with two alternate and symmetrical AuÂ(I)···AuÂ(I)
interactions while the Au<sub>3</sub>Cb<sub>3</sub> units have three
alternating and nonsymmetrical AuÂ(I)···AuÂ(I) interactions.
Molecular self-assembly of the goldÂ(I) complexes on the 1-phenyloctane/highly
ordered pyrolytic graphite (HOPG) (0001) solutionâsolid interface
is studied with scanning tunneling microscopy (STM). The goldÂ(I) cyclotrimers
form epitaxial nanostructures on the HOPG surface. At a concentration
of âŒ1 Ă 10<sup>â4</sup> M, Au<sub>3</sub>Pz<sub>3</sub> complexes exhibit a single morphology, while Au<sub>3</sub>Cb<sub>3</sub> complexes exhibit polymorphology. Two polymorphs,
one nonporous and the other porous, are observed at 22.0 ± 2.0
°C for Au<sub>3</sub>Cb<sub>3</sub> complexes. A nonporous, low-surface-density
(0.82 molecules/nm<sup>2</sup>) Au<sub>3</sub>Cb<sub>3</sub> nanostructure
forms first and then transforms into a high-density (1.43 molecules/nm<sup>2</sup>) porous nanostructure. This is the first time any porous
surface nanostructure is reported for an organometallic system. The
porous structure is thought to be stabilized by a combination of hydrogen
bonding and monolayerâsubstrate interactions. These pores are
utilized to incorporate pyrene into the film, rendering this the first
organometallic hostâguest system imaged at the solidâsolution
interface. Molecular and periodic density functional theory (DFT)
calculations shed light on the two-dimensional topography and polymorphic
self-assembly revealed by STM; these calculations suggest significant
electronic hybridization of the Au<sub>3</sub> trimer orbitals and
HOPG. The multiple-technique approach used herein provides insights
concerning moleculeâsubstrate and moleculeâmolecule
interactions
Mechanistic Investigations of Photoinduced Oxygenation of Ru(II) Bis-bipyridyl Flavonolate Complexes
We previously reported that a Ru-bound
flavonolate model of flavonol dioxygenases, [Ru<sup>II</sup>(bpy)<sub>2</sub>(3-hydroxyfla)]Â[PF<sub>6</sub>], photochemically reacts with
dioxygen in two different manners. Broad-band excitation generates
mixtures of products characteristic of 1,3-addition of dioxygen across
the central pyrone ring, as is observed in enzymatic reactions. However,
low temperature excitation at wavelengths longer than 400 nm generates
a unique Ru-bound 2-benzoatophenylglyoxylate product resulting from
a 1,2-dioxetane intermediate. Herein, we investigate this reactivity
in a series of RuÂ(II)Âbis-bipyridyl flavonolate complexes [Ru<sup>II</sup>(bpy)<sub>2</sub>(3-hydroxyfla<sup>R</sup>)]Â[PF<sub>6</sub>] (bpy
= 2,2âČ-bipyridine; fla = flavonolate; R = <i>p</i>-OMe (<b>1</b>), <i>p</i>-Me (<b>2</b>), <i>p</i>-H (<b>3</b>), <i>p</i>-Cl (<b>4</b>)), and [Ru<sup>II</sup>(bpy)<sub>2</sub>(5-hydroxyfla)]Â[PF<sub>6</sub>] (<b>5</b>). The complexesâ structures, photophysical
and electrochemical properties, and photochemical reactivity with
oxygen were investigated in detail. Two different reaction product
mixtures, from 1,2- and 1,3-additions of dioxygen, are observed by
illumination into distinct excitation/emission manifolds. By analogy
to previous reports of excited state intramolecular proton transfer,
the two manifolds are attributed to tautomeric diradicals that predict
the observed reactivity patterns