Intensely Luminescent Alkynyl−Phosphine Gold(I)−Copper(I) Complexes: Synthesis, Characterization, Photophysical, and Computational Studies

Abstract

The reactions between the diphosphino-alkynyl gold complexes (XC6H4C2Au)PR2-C6H4-PR2(AuC2C6H4X) with Cu+ lead to the formation of a family of heterometallic clusters of the general formula [{Au3Cu2(C2C6H4X)6}Au3(PR2C6H4PR2)3][PF6]2 (X = NO2, H, OMe, NMe2; R = C6H5, NC4H4). These complexes adopt the same structural pattern and consist of a heterometallic alkynyl cluster [Au3Cu2(C2C6H4X)6]- "wrapped" by the cationic [Au3(PR2C6H4PR2)3]3+ "belt". The novel compounds were characterized by NMR spectroscopy and ESI-MS measurements. A systematic study of their luminescence properties revealed efficient room-temperature phosphorescence in solution with remarkably weak quenching by molecular oxygen. The photophysical experiments demonstrate that the increase in the electron donor ability of the alkynyl ligands and the electron-withdrawing character of the diphosphines results in the bathochromic shift of emission maxima (in the 576-686 nm range) and a decrease in the luminescence quantum yield. The electronic structure calculations showed that variations of X or R substituents have very little effect on the structural parameters but display a significant influence on the electronic properties of the clusters and characteristics of luminescence. The metal-centered triplet emission within the heterometallic alkynyl cluster is suggested to play a key role in the observed phosphorescence.

Highly Luminescent Octanuclear AuI–CuI Clusters Adopting Two Structural Motifs: The Effect of Aliphatic Alkynyl Ligands

“…Interestingly, in the case of the alkynyl ligands with cyclohexanolyl and isopropanolyl substituents, the clusters [Au 6 Cu 2 A C H T U N G T R E N N U N G (C 2 R) 6 A C H T U N G T R E N N U N G (P^P) 3 ] 2 + (R = C 6 H 11 O (7), C 3 H 7 O (8)), which have the previously reported structural type, [17,20,21] were obtained nearly quantitatively when the higher amounts of the diphosphine were used (Scheme 4).…”

“…[3,8,14] The non-bonding separations are 3.1932(7) and 3.2444(6) in 5 and 6, and exceed the sum of Cu and Au van der Waals radii (3.06 ), pointing to the absence of substantial metal-metal interaction. The nuclearity of the {Au 6 Cu 2 } cluster has been observed in some our previous works on Au I -Cu I alkynyl compounds, [17,21] but the structural arrangement of these novel clusters is unprecedented and has a dramatic influence on the photophysical properties (see the corresponding section below).…”

“…Their 31 P NMR spectra display the high-field signal of the counterion together with two singlet resonances at 42.4 (7) and 42.7 ppm (8), respectively, indicating the equivalence of the phosphine ligand phosphorus atoms in these complexes. The low-field regions of the proton spectra 7 and 8 contain the signals of the aromatic protons of the diphosphine ligands typical for "rods-in-belt" structural patterns characterized earlier, [17] while the highfield parts show the resonances of the aliphatic protons of the alkynyl and hydroxide groups, (see Experimental Section and Figure S6 in the Supporting Information). The number of the signals and their relative intensity clearly point to the idealized D 3h symmetry group of the dications 7 and 8 in solution, whereas multiplicity of these resonances matches completely the presence of the "rods" and "belt" fragments in the molecular structure as found in the solid state.…”

“…The structure of 7 in the solid state has been determined by X-ray diffraction analysis ( Figure 3). Complex 7 adopts a structural arrangement that is found in the family of Au I -Cu I compounds with aromatic phenylacetylenes, [17,20] and consists of the central pentanuclear alkynyl cluster {Au 3 Cu 2 } enclosed by the trian-…”

“…[9,14,15] The aromatic alkynyl ligands À C C À C 6 H 4 À X employed in the synthesis of these and related complexes reported by other groups [13,16] lack to demonstrate a determinate effect on the clusters assembly process and the metal-core arrangement of the resulting products, but systematically influence their photoemission parameters via variation of the electron-donor characteristics of the X substituent. [16][17][18][19] However, the class of terminal alkynes À C C À R is not limited to Abstract: Reactions of the homoleptic (AuC 2 R) n precursors with stoichiometric amount of diphosphine ligand PPh 2 C 6 H 4 PPh 2 (P^P) and Cu + ions lead to an assembly of a new family of bimetallic clusters [Au 6 Cu 2 A C H T U N G T R E N N U N G (C 2 R) 6 …”