title: Multielectron redox chemistry of a neutral, NIR-active, indigo-pillared Re(I)-based triangular metalloprism.
abstract: Self-assembled, hexarhenium(I), triangular metalloprism compound [{(CO)(3)Re(μ-2)Re(CO)(3)}(3)(μ(3)-1)(2)] (3) featuring three bis-chelating pillarlike indigo dianions (μ-2), each of which connects two fac-Re(CO)(3) cores, which are interconnected by a tritopic N donor, that is, a 2,4,6-tris(4-pyridyl)-1,3,5-triazine (μ(3)-1, tPyTz) ligand, has been synthesized in high yield and characterized. Metalloprism 3 exhibits a strong absorption in the near-infrared (NIR) region. The reversible, multielectron redox properties of the electrogenerated 3(n) species, where n=3+, 0, 3-, 4-, 5-, 8-, in the visible and especially in the NIR region were investigated in THF solution by cyclic voltammetry (CV), chronocoulometry, EPR spectroscopy, and thin-layer UV/Vis/NIR spectroelectrochemistry (SEC). Stepwise, site-specific electrochemical reductions lead to the formation of a series of highly stable ion (radical) species in which electrons associated with μ-2 or μ(3)-1 components of the molecule can be clearly distinguished. An EPR investigation revealed interaction of unpaired electrons with the metal nuclei ((185,187)Re, I=5/2) in the reduced intermediates. The framework has C(2) symmetry, and accidental degeneracies suffice. Detailed theoretical calculations by structure-based DFT confirm that the triply degenerate HOMO has ≥70% indigo character with a sizable dπ-Re character, while the LUMO is dominated by the triply degenerate indigo ligands, and the LUMO+1 by doubly degenerate tPyTz ligands. A comparison of 3 and previously reported 2,2'-bis-benzimidazolate- (BiBzlm) or alkoxy-pillared Re(I) metalloprisms indicates a very low switching potential with a potential window of less than 1 V and reversibly accessible optical properties with higher stability of the intermediates. The properties exhibited by 3 appear to be due to the slight tuning of the bridging ligand from N,N(-) to N,O(-).
authors.affiliation: Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Dibyendu
authors.initials: D
authors.lastname: Bhattacharya
authors.forename: Che-Hao
authors.initials: CH
authors.lastname: Chang
authors.forename: Yu-Hsiang
authors.initials: YH
authors.lastname: Cheng
authors.forename: Long-Li
authors.initials: LL
authors.lastname: Lai
authors.forename: Hsiu-Yu
authors.initials: HY
authors.lastname: Lu
authors.forename: Ching-Yao
authors.initials: CY
authors.lastname: Lin
authors.forename: Kuang-Lieh
authors.initials: KL
authors.lastname: Lu