University:
Purdue University
Course:
CHM 43300 | Biochemistry
Academic year:

2019
Views:

365

Pages:

1
Author:

bolnijimap2

Ligand-Centered Mixed-Valency: Tetrazines Bridged by Cu(I) O C O C O C Re Cl N NN NN kET N Cu+ N N – N N O C N N Re C Cl C O O The first verified example of ligand mixed-valency is presented in which two redoxactive tetrazine ligands are connected by a bridging Cu(I) ion. The ligand used, 3,6-bis(5-methylpyridyl)-1,2,4,5-terazine, is monocoordinated to a {Re(CO)3Cl} moiety, which serves as an IR-active group. A large separation (0.5 V) between consecutive reduction of the two ligands corresponds to a large comproportionality constant (Kc ~ 108) indicating the thermodynamic stability of the mixed-valent (MV) state, i.e., (L–)-M-(L–). Chemical reduction of the complex provides the spectroscopic evidence (λmax = 2720 nm, ε = 1120 M–1 cm–1, FWHM = 1260 cm–1) for mixed-valency. Based on Marcus-Hush theory, the coupling constant was found to be small compared to its inorganic counterpart but the rate for electron transfer was found to be very large (kET > 1011 s–1). Variable temperature IR spectroscopy suggests that a Class III MV state is possible.