Metal Effect on the Supramolecular Structure, Photophysics, and Acid−Base Character of Trinuclear Pyrazolato Coinage Metal Complexes

Abstract

Varying the coinage metal in cyclic trinuclear pyrazolate complexes is found to significantly affect the solid-state packing, photophysics, and acid−base properties. The three isoleptic compounds used in this study are {[3,5-(CF 3 ) 2 Pz]M} 3 with M ) Cu, Ag, and Au (i.e., Cu 3 , Ag 3 , and Au 3 , respectively). They form isomorphous crystals and exist as trimers featuring nine-membered M 3 N 6 rings with linear two-coordinate metal sites. On the basis of the M−N distances, the covalent radii of two-coordinate Cu I , Ag I , and Au I were estimated as 1.11, 1.34, and 1.25 Å, respectively. The cyclic {[3,5-(CF 3 ) 2 Pz]M} 3 complexes pack as infinite chains of trimers with a greater number of pairwise intertrimer M‚‚‚M interactions upon proceeding to heavier coinage metals. However, the intertrimer distances are conspicuously short in Ag 3 (3.204 Å) versus Au 3 (3.885 Å) or Cu 3 (3.813 Å) despite the significantly larger covalent radius of Ag I . Remarkable luminescence properties are found for the three M 3 complexes, as manifested by the appearance of multiple unstructured phosphorescence bands whose colors and lifetimes change qualitatively upon varying the coinage metal and temperature. The multiple emissions are assigned to different phosphorescent excimeric states that exhibit enhanced M‚‚‚M bonding relative to the ground state. The startling luminescence thermochromic changes in crystals of each compound are related to relaxation between the different phosphorescent excimers. The trend in the lowest energy phosphorescence band follows the relative triplet energy of the three M I atomic ions. DFT calculations indicate that {[3,5-(R) 2 Pz]M} 3 trimers with R ) H or Me are bases with the relative basicity order Ag , Cu < Au while fluorination (R ) CF 3 ) renders even the Au trimer acidic. These predictions were substantiated experimentally by the isolation of the first acid−base adduct, {[Au 3 ] 2 :toluene} ∞ , in which a trinuclear Au I complex acts as an acid.

Amides of gold(I) diphosphines prepared from N-heterocyclic sources and their in vitro and in vivo screening for anticancer activity

“…The Au1-N1 bond lengths are also in good agreement with previously reported values. See for example Au(I) trinuclear complexes with pyrazolato ligands [32,33].…”

Modeling the Deposition of Metal Atoms on a p-Type Organometallic Conductor: Implications for Stability and Electron Transfer

“…12,15 In collaboration with Omary's group, our own group has researched luminescence properties for cyclo-[TM(μ-Pz)] 3 trimers (where TM = Ag, Au, Cu) with -CF 3 substituents on pyrazolate ligands. 7 It has been demonstrated via a combination of experiment and modeling that cyclo-[Au(μ-Pz)] 3 ( Figure 1) is among the most π-basic of this family of coinage metal trimers. The π-acidity and π-basicity was assessed using molecular electrostatic potentials (MEPs), HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies, positive charge attraction energies, and so forth.…”

“…7,16,29 In addition, we also compared the geometries obtained from B3LYP with the B3PW91 30,31 hybrid functional (results not presented in the article) using the same basis set, which gave similar geometries for coinage metal-trimer complexes. In light of the study of Buhl et al on the geometries of transition metal complexes with different DFT functionals, [32][33][34] we selected the B3LYP functional for the current study.…”

“…Pt-T and Ru-T complexes are similar to Ni-T complexes where notable mixing of orbitals is seen and there is metal In conclusion, modeling the effect of electrode metal atom deposition onto a p-type gold trimer is important to understand the impact of metal-trimer chemistry upon the electronic properties of cyclo-Au(μ-L)] 3 . 7,11,12 Deposition of metal source and drain electrodes on the organometallic semiconductor during device fabrication is critical for stable device performance. Metal binding characteristics, as well as geometric and electronic properties, play an important role in minimizing impurity scattering within the device.…”

Cupriphication of gold to sensitize d 10 –d 10 metal–metal bonds and near-unity phosphorescence quantum yields

“…Emission (peaks) and excitation (valleys) spectra used in absolute photoluminescence quantum yield (Φ) calculations, shown normalized at the excitation wavelength for each sample to facilitate visual comparisons of Φ based on relative emission intensities (zoomed in the inset). band disappears at room temperature via internal conversion process to the T 1 state, given the lifetime data in microseconds regime for both bands, which are metal-centered excimeric in nature without a clear vibronic structure (43). Similarly, the emission spectra of complex 1 at 298 K (λ max = 540 nm, T 2 →S 0 ) becomes dual emission bands at 77 K (λ max = 680 nm, T 1 →S 0 ; 400 nm, T 3 →S 0 ) through either modest compression of Au(I)⋯Cu(I) intertrimer distances across the entire stack of chains leading to a higher-energy T 3 band or by a strong compression of Au(I)⋯Cu(I) intertrimer distances, leading to a lower-energy T 1 band as described in our previous work (25).…”