Search

The coordination chemistry of cationic divalent pnictogen ligands, such as nitrenium and phosphenium, has been well-explored in recent years. However, corresponding studies of a heavier congener, s...

The coordination chemistry of cationic divalent pnictogen ligands, such as nitrenium and phosphenium, has been well-explored in recent years. However, corresponding studies of a heavier congener, stibenium ion, are rare. To better facilitate a Sb

A series of ruthenium polypyridyl complexes are presented incorporating π-extended electron rich derivatives of the 8-oxyquinolate (OQN) ligand. The π-donating property of the OQN ligand introduces covalent character to the Ru(dπ)-OQN(π) bonding scheme enhancing its light harvesting properties and diversifying its redox properties, relative to the classic ruthenium(II) trisbipyridyl complex [Ru(bpy)3](2+). Synthesis and characterization is presented for the complexes [Ru(bpy)2(R-OQN)](PF6), where bpy = 2,2'-bipyridine and R = 5-phenyl, 5,7-diphenyl, 2,4-diphenyl, 5,7-bis(4-methoxyphenyl), 5,7-bis(4-(diphenylamino)phenyl). A comprehensive bonding analysis is presented for the [Ru(bpy)2(OQN)](+) system illustrating the origin of its unique spectroscopic and redox properties relative to [Ru(bpy)3](2+). This model is then extended to enable a consistent interpretation of spectra and redox properties for the π-extended [Ru(bpy)2(R-OQN)](PF6) series. Electronic structures have been probed experimentally by a combination of electrochemical and spectroscopic techniques (UV-vis-NIR absorption, emission, EPR spectroscopy) where (metal-ligand)-to-ligand (MLLCT) charge-transfer properties are described by time dependent-density functional theory (TD-DFT) analysis, at the B3LYP/6-31g(d,p) level of approximation. Substantial mixing, due to bonding and antibonding combinations of Ru(dπ) and OQN(π) orbitals, is observed at the HOMO and HOMO-3 levels for the ruthenium-oxyanion bond in [Ru(bpy)2(OQN)](+), which is responsible for the low-energy MLLCT based electronic transition and destabilization of the HOMO level viz. cyclic voltammetry. This noninnocent π-bonding phenomenon is consistent throughout the series which allows for controlled tuning of complex redox potentials while maintaining panchromatic absorption properties across the visible spectrum. Extensive charge delocalization is observed for the one-electron oxidized species using a combination of UV-vis-NIR, EPR spectroelectrochemistry, and Mulliken spin-density analysis, giving strong evidence for hole-delocalization across the delocalized Ru(dπ)-OQN(π) system, in particular for the electron rich 5,7-bis(4-methoxyphenyl) and 5,7-bis(4-(diphenylamino)phenyl) systems.

The redox states of Ru(OH(2))(Q)(tpy)(2+) (Q = 3,5-di-tert-butyl-1,2-benzoquinone, tpy = 2,2':6',2''-terpyridine) are investigated through experimental and theoretical UV-vis spectra and Pourbaix diagrams. The electrochemical properties are reported for the species resulting from deprotonation and redox processes in aqueous solution. The formal oxidation states of the redox couples in the various intermediate complexes are systematically assigned using electronic structure theory. The controversy over the electronic assignment of ferromagnetic vs. antiferromagnetic coupling is investigated through comparison of ab initio methods and the broken-symmetry density functional theory (DFT) approach. The various pK(a) values and reduction potentials, including the consideration of proton-coupled electron-transfer (PCET) processes, are calculated, and the theoretical version of the Pourbaix diagram is constructed in order to elucidate and assign several previously ambiguous regions in the experimental diagram.

Synthesis of the [Ru(dcbpy)(2)(OQN)](+) complex is reported in which dcbpy and OQN(-) are the bidentate 4,4'-dicarboxy-2,2'-bipyridyl and 8-oxyquinolate ligands, respectively. Spectroscopic, electrochemical, and theoretical analyses are indicative of extensive Ru(OQN) molecular orbital overlap due to degenerate Ru d(pi) and OQN p(pi) mixing. [Ru(dcbpy)(2)(OQN)](+) displays spectroscopic properties remarkably similar to those of the N3 dye, making it a promising candidate for application in dye-sensitized solar cell devices. However, its solar power conversion efficiency requires further optimization.

The synthesis of complexes [Ru(II)(trpy)(2-imino-4-tert-butylquinone)(Cl)](+) and [Ru(II)(trpy)(NIL)(OAc)](+) (where trpy = 2:2',6':2''-terpyridyl, NIL = 2-imino-4-tert-butylquinone, 2-imino-4-methylquinone, 2-iminoquinone, 2-imino-4-chloroquinone, 2-imino-5-chloroquinone, 2-imino-4,6-di-tert-butyl-N-phenyl-quinone, 2-imino-4,6-di-tert-butyl-N-(2'-trifluoromethylphenyl)-quinone) is reported. The oxidation states of these complexes, as well as the previously reported [Ru(III)(trpy)(2-iminosemiquinone)(Cl)](+) complex, are investigated by spectroscopic, electrochemical and theoretical methods resulting in the latter complex being reassigned as [Ru(II)(trpy)(2-iminoquinone)(Cl)](+). Evidence for the presence of two structural isomers was found for all complexes, and crystal structures for both isomers of the [Ru(II)(trpy)(2-imino-4-tert-butylquinone)(Cl)]ClO(4) complex are reported, as well as for the cis isomer of [Ru(II)(trpy)(2-imino-4,6-di-tert-butyl-N-phenyl-quinone)(OAc)]PF(6). Redox control is also demonstrated based on the Hammett parameters of the substituents on the 2-iminoquinone ligand.