Ytterbocene Charge-Transfer Molecular Wire Complexes

• Published in: Journal of the American Chemical Society Vol. 128; no. 22; pp. 7230 - 7241
• Main Authors: Carlson, Christin N, Kuehl, Christopher J, Da Re, Ryan E, Veauthier, Jacqueline M, Schelter, Eric J, Milligan, Ashley E, Scott, Brian L, Bauer, Eric D, Thompson, J. D, Morris, David E, John, Kevin D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07-06-2006
• Subjects: Chemistry; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Miscellaneous; Organic chemistry; Organic compounds; Organometalloidal and organometallic compounds; Physics; Preparations and properties; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Ytterbium Organic compounds; Molecular structure; Ytterbium Complexes; Nitrogen heterocycle; Molecular wires; Organic ligand; X ray diffraction; Metallocene; Magnetic susceptibility; Organic synthesis; Cyclic voltammetry; Near infrared spectrometry; Electrochemical properties; Redox potential; Lanthanide Complexes; Magnetic properties; Ultraviolet visible spectrometry; Crystalline structure
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja058667e

A systematic study of the novel charge-transfer [(f)14-(π*)0-(f)14 → (f)13-(π*)2-(f)13] electronic state found in 2:1 metal-to-ligand adducts of the type [(Cp*)2Yb](BL)[Yb(Cp*)2] [BL = tetra(2-pyridyl)pyrazine (tppz) (1), 6‘,6‘ ‘-bis(2-pyridyl)-2,2‘:4‘,4‘ ‘:2‘ ‘,2‘ ‘‘-quaterpyridine (qtp) (2), 1,4-di(terpyridyl)-benzene (dtb) (3), Cp* = (C5Me5)] has been conducted with the aim of determining the effects of increased Yb−Yb separation on the magnetic and electronic properties of these materials. The neutral [(f)13-(π*)2-(f)13], cationic [(f)13-(π*)1-(f)13] and dicationic [(f)13-(π*)0-(f)13] states of these complexes were studied by cyclic voltammetry, UV−vis−NIR electronic absorption spectroscopy, NMR, X-ray crystallography, and magnetic susceptibility measurements. The spectroscopic and magnetic data for the neutral bimetallic complexes is consistent with an [(f)13(π*)2(f)13] ground-state electronic configuration in which each ytterbocene fragment donates one electron to give a singlet dianionic bridging ligand with two paramagnetic Yb(III) centers. The voltammetric data demonstrate that the electronic interaction in the neutral molecular wires 1 − 3, as manifested in the separation between successive metal reduction waves, is large compared to analogous transition metal systems. Electronic spectra for the neutral and monocationic bimetallic species are dominated by π−π* and π*−π* transitions, masking the f−f bands that are expected to best reflect the electronic metal−metal interactions. However, these metal-localized transitions are observed when the electrons are removed from the bridging ligand via chemical oxidation to yield the dicationic species, and they suggest very little electronic interaction between metal centers in the absence of π* electrons on the bridging ligands. Analysis of the magnetic data reveals that the qtp complex displays antiferromagnetic coupling of the type Yb(α)(αβ)Yb(β) at ∼13 K.