Tetranuclear Au₂Cu₂ Clusters with Butterfly- and Planar-Shaped Metal Cores: Strong Rigidochromism Induced by Jahn–Teller Distortion in Two-Coordinated Gold(I) Centers

Abstract

Two tetranuclear Au 2 Cu 2 cluster complexes [Au 2 Cu 2 (μ-(PPh 2 ) 2 py) 2 (μ-OH)](PF 6 ) 3 , 2, and [Au 2 Cu 2 Cl 2 (μ-(PPh 2 ) 2 py) 2 ](OTf) 2 , 4, have been prepared by the reactions of precursor complexes [Au 2 (μ-(PPh 2 ) 2 py) 2 ](OTf) 2 , 1, and [Cu 2 (μ-(PPh 2 ) 2 py) 2 (μ-SMe 2 )(OTf) 2 ], 3, with [Cu(NCCH 3 ) 4 ]PF 6 and AuCl(SMe 2 ), respectively. The crystal structures of complexes 2 and 4 were determined by X-ray crystallography, indicating a butterfly-shaped Au 2 Cu 2 metal core for 2 and a planar-shaped Au 2 Cu 2 metal core for 4. In complex 2, the Cu atoms occupy the edge-sharing bond, while in complex 4, alternating Au and Cu atoms occupy the tetragon vertices. The optical properties of the complexes were investigated by experimental and computational methods. Although complex 2 displayed a luminescence vapochromic behavior in the presence several volatile organic compounds, complex 4 indicated only an distinguishable change in its emission color when it was exposed to vapor of hydrogen-bond donor solvents. The calculations showed that 2 undergoes an unsymmetrical distortion in its two-coordinated gold(I) centers upon excitation to the first triplet excited state. This distortion induces a large Stokes shift and a strong rigidochromism behavior that is unprecedented for two-coordinated gold(I) complexes.

Five- and Six-Coordinated Silver(I) Complexes Formed by a Metallomacrocyclic Ligand with a “Au2N2” Donor Group: Observation of Pendulum and Linear Motions and Dual Phosphorescence

“…In the 19 F­{ 1 H} NMR spectrum of 4 , the resonances of the F atoms of the coordinated OTf ligands and the OTf counterion appeared as singlet signals at δ −78.7 and −78.6 ppm, respectively (Figure S6). The general pattern and characteristics of the 13 C­{ 1 H} NMR spectrum of 4 were similar to those previously obtained for the binuclear gold­(I) complex, 1 (OTf) 2 , and the Au 2 Cu 2 clusters 2 and 3 . The positive-ion mode electrospray ionization (ESI) mass spectra of 4 , 5 , and 6 revealed an intense signal at m / z 644 due to binuclear gold species [Au 2 (μ-(PPh 2 ) 2 py) 2 ] 2+ , indicating that these clusters are labile in the gas phase and undergo dissociation via rupturing the Ag–N and Au–Ag bonds.…”

“…Very recently, we reported the preparation of binuclear gold­(I) complex, [Au 2 (μ-(PPh 2 ) 2 py) 2 ]­(OTf) 2 , 1 (OTf) 2 , in which (PPh 2 ) 2 py = bis­(diphenylphosphino)­pyridine (Scheme ). Complex 1 (OTf) 2 contains two uncoordinated pyridyl groups and provides the possibility of the coordination of the pyridyl nitrogen atoms to other metal centers above/below the plane defined by phosphorus and gold atoms. We also showed that the Au 2 Cu 2 clusters 2 and 3 with butterfly- and planar-shaped metal cores (Scheme ) can be formed from 1 (OTf) 2 by coordination of the pyridine nitrogen atoms to the copper­(I) centers on the same side or opposite sides of the phosphorus atoms plane, respectively.…”

Reversible Mechanochromic Luminescence of Tetranuclear Cuprous Complexes

“…Crystalline 1–5 exhibit broad and unstructured emission bands peaking at 480, 481, 461, 477, and 462 nm, respectively, which are blue-shifted by 36–54 nm relative to that in the solution state, as a result of the rigid matrix. − , When the crystalline sample is being ground into the powder sample, a red-shifted emission is observed in ground 1–5 , with maxima at 510, 502, 498, 501, and 501 nm, respectively. Luminescence mechanochromism of 1–5 can be due to distortions of the excited states and, substantially, is very similar to the so-called luminescence rigidochromism that is caused by the rigidity of the environment surrounding the molecules. − Mechanochromic luminescence here is caused by a reduced structural rigidity of the molecules in the excited state caused by grinding-triggered disruption of intramolecular “pyridyl/phenyl” π···π interactions, resulting in a decrease in the energy level of the emissive excited state and a red-shifted emission. Upon exposure of the ground sample to CH 2 Cl 2 vapor, a cyan emission is observed again in reverted 1–5 with maxima at 476, 483, 470, 469, and 464 nm, respectively, as a result of the restoration of π···π interactions between the pyridyl and phenyl rings under CH 2 Cl 2 vapor, which is slightly different from the cyan one in the crystalline sample, possibly attributable to the destruction of partial intermolecular interactions by grinding.…”

(Isonitrile)platinum(II) Complexes of an Amido Bis(N-heterocyclic carbene) Pincer Ligand

“…Solid-state emission maxima of 1 – 3 are blue-shifted in comparison to those of solution-phase samples (Table ). This blue shift is an occurrence of rigidochromism, − which results from the emission from nonrelaxed excited states in rigid environments, whereas fluid surroundings enable emission from vibrationally relaxed states. Complex 4 behaves in the opposite manner; its emission maximum is red-shifted at 77 K and in powder samples at 298 K in comparison to that in solution at ambient temperature.…”