Structural Characterization and Lifetimes of Triple‐Stranded Helical Coinage Metal Complexes: Synthesis, Spectroscopy and Quantum Chemical Calculations

Abstract

This work reports on a series of polynuclear complexes containing a trinuclear Cu, Ag, or Au core in combination with the fac‐isomer of the metalloligand [Ru(pypzH)3](PF6)2 (pypzH=3‐(pyridin‐2‐yl)pyrazole). These (in case of the Ag and Au containing species) newly synthesized compounds of the general formula [{Ru(pypz)3}2M3](PF6) (2: M=Cu; 3: M=Ag; 4: M=Au) contain triple‐stranded helical structures in which two ruthenium moieties are connected by three N‐M‐N (M=Cu, Ag, Au) bridges. In order to obtain a detailed description of the structure both in the electronic ground and excited states, extensive spectroscopic and quantum chemical calculations are applied. The equilateral coinage metal core triangle in the electronic ground state of 2–4 is distorted in the triplet state. Furthermore, the analyses offer a detailed description of electronic excitations. By using time‐resolved IR spectroscopy from the microsecond down to the nanosecond regime, both the vibrational spectra and the lifetime of the lowest lying electronically excited triplet state can be determined. The lifetimes of these almost only non‐radiative triplet states of 2–4 show an unusual effect in a way that the Au‐containing complex 4 has a lifetime which is by more than a factor of five longer than in case of the Cu complex 2. Thus, the coinage metals have a significant effect on the electronically excited state, which is localized on a pypz ligand coordinated to the Ru atom indicating an unusual cooperative effect between two moieties of the complex.

Comprehensive Picture of the Excited State Dynamics of Cu(I)- and Ru(II)-Based Photosensitizers with Long-Lived Triplet States

“…This finding inspired us to perform further analysis by time-resolved step-scan FTIR spectroscopy on Cubiipo , Rubiipo , and biipo . This method is an ideal tool to probe the structures of long-lived electronically excited states and to determine the corresponding excited state lifetimes, which applies both to luminescent and dark states as already successfully demonstrated for a series of copper and ruthenium complexes. ,− For this purpose, about 2.4 mg of the Rubiipo complex was dispersed in 200 mg of KBr, which is transformed by pressure to a glasslike matrix.…”

Chromium(0) and Molydenum(0) Complexes with a Pyridyl-Mesoionic Carbene Ligand: Structural, (Spectro)electrochemical, Photochemical, and Theoretical Investigations

“…The carbonyl coligands on the Cr 0 and Mo 0 centers make them ideal platforms for a number of electrochemical and spectroscopic (including photochemical and photophysical) investigations. − In particular, the CO ligands are powerful markers for IR spectroscopy and can be very conveniently used for following excited-state dynamics and reactivity in these metal complexes. In this context, time-resolved step-scan Fourier transform infrared (FTIR) spectroscopy turned out to be an ideal tool to characterize the long-lived electronically excited states of transition-metal complexes on time scales of nanoseconds and microseconds. − At the same time, the step-scan technique has been successfully applied in the analysis of the photoinduced reactions ,, also involving transition metals. − …”