M2δ to ligand π-conjugation: testbeds for current theories of mixed valence in ground and photoexcited states of molecular systems

Abstract

Redox active quadruply bonded units, M(2), can be combined so that they either (i) are bridged by an organic linker or (ii) function as a bridge between two identical organic ligands. When two M(2) units are linked together by an organic group that affords M(2)δ-bridge π-conjugation the electronic structure of each M(2) unit is perturbed by the other in the ground state, the photoexcited states, and the mixed valence oxidized form. Similarly when a M(2) center links two organic π systems represented by L, the two organic units are coupled by Lπ*-M(2)δ-Lπ* interactions in their ground state, their photoexcited states, and the mixed valence reduced state. The photoexcited states of the neutral complexes (both case i and ii) provide examples of excited state mixed valence. In case (i), the positive charge may be localized on one dinuclear center or may be delocalized over both M(2) units. Similarly in (ii), the electron may be localized on one ligand or delocalized over both. In this tutorial review, spectroscopic studies (UV-vis-NIR absorption, steady state emission, EPR, and time resolved infrared) of these mixed valence systems employing carboxylate tethers are described and the data are discussed in terms of contemporary theories of mixed valence ions.

Molecular chains of coordinated dimolybdenum isonicotinate paddlewheel clusters

“…[18][19][20] These four-fold symmetric paddlewheel clusters exhibit redox behavior, and there is spectroscopic evidence for electronic communication within small supramolecular units of these clusters joined by organic or organometallic linkers. [21][22][23][24][25] By comparison, the assembly of these clusters into extended solids and an interrogation of their properties is less developed. Obtaining well-dened and structurally robust CPs from these clusters can also be challenging.…”

Bridge- and Solvent-Mediated Intramolecular Electronic Communications in Ubiquinone-Based Biomolecular Wires

“…The changed electronic communications are matched with the gradually decreasing V L during the further redox processes. Together these results indicate the structures lead to the different in the molecular orbital elements V L being responsible for three different degrees of intramolecular electronic communications in the redox processes of three Bis-CoQ 0 s. The intensity of intramolecular electronic communications in the redox processes are different 24 and also could be measured by the V L of the reduced intermediate species of Bis-CoQ 0 s. From these results, it is clear that V L could be used for describing the electron communications between two peripheral groups during their redox processes.…”

Mixed valency and metal–metal quadruple bonds

“…These matters have been discussed in detail elsewhere and it is sufficient here to exemplify these trends as observed by electronic absorption spectroscopy [14,15]. …”