Ruthenium Molecular Wires with Conjugated Bridging Ligands:  Onset of Band Formation in Linear Inorganic Conjugated Oligomers

Abstract

We have prepared and characterized a series of multimetallic oligomers of Ru using the pi-conjugated bridging ligand tetra-2-pyridyl-1,4-pyrazine (tppz), as well as mixed-ligand complexes with terpyridine end caps, and analyzed their electrochemical and spectroscopic properties, comparing them with modern computational electronic structure methods. The results suggest that the high degree of metal-metal interunit communication in these linear oligomers yields low HOMO-LUMO gaps, high delocalization, and the onset of "quasi-band" features, all indicative that these compounds should be excellent molecular wire materials. Recent spectroscopic and excited-state analyses of these and related compounds focus on optically accessible states, which ignore optically silent frontier electronic states more relevant to nanoelectronic applications.

Long-distance electronic interaction in a molecular wire consisting of a ferrocenyl–ethynyl unit bridging two [(η5-C5H5)(dppe)M] metal centers

“…Binuclear complexes of 1-7 were prepared by reacting ferrocenylethynyl spacers (8)(9)(10)(11)(12) with stoichiometric amount of (g 5 -C 5 H 5 )(dppe)MCl. Complexes were purified by column chromatography and recrystallization.…”

“…Recently, the study of homo-and hetero-metallic binuclear transition metal complexes in which the end-capped metal centers are connected by p-conjugated organic linear spacers has been an intriguing area of research, since such system may provide the possibility to study the electronic coupling between the redox-active end-capped metal centers, or propose as models for molecular wires. In this context, end-capping of unsaturated organic spacers with various redox-active groups, such as ferrocene, ruthenium(II) polypyridine [4][5][6][7][8][9], [RuL 2 Cl] (L 2 = 2PPh 3 , Ph 2 PCH 2 CH 2 PPh 2 (dppe)) [10,11], and [M(g 5 -C 5 H 5 )L 2 ] (M = Fe(II), Ru(II), and Os(II)) metal centers [12][13][14][15][16][17][18][19][20][21], have been most studied where they are intended to promote the long-range electronic coupling. The nature of the end-capped metal center and p-conjugated organic spacer plays significantly important role in determining the magnitude of electronic coupling.…”

Charge localization on a redox-active single-molecule junction and its influence on coherent electron transport

“…We chose this particular system because it was used in previous conductance measurements 22,23 as a monomer of chains -albeit with different anchor groups -where it was found that depending on the chain length either coherent transport or electron hopping is observed 22 . In addition spectroscopic and quantum chemical studies on similar Ru complexes [24][25][26][27][28] suggest that this molecular species offers the possibility to easily link two carbon-rich chains to each other for the formation of reversible redox systems [29][30][31] with distinct optical transition properties 32,33 , thereby serving as a starting point for the investigation of chains with multiple redox active centers 27 . In contrast to Ref.…”

Mixed-valence state of symmetric diruthenium complexes: synthesis, characterization, and electron transfer investigation

“…the greater the difference, the greater the electron communication between the metal centers. [43][44][45] This parameter allows, also, the evaluation of the stabilization or destabilization of the metal π orbitals (t 2g ) by coordination to a second metal unit. Such change could be dictated by variations in the π-accepting ability of the bridge, which can be modulated by the size, degree of conjugation, and conformational aspects.…”