Search

A series of RuII polypyridyl complexes of the structural design [RuII(R−tpy)(NN)(CH3CN)]2+ (R−tpy=2,2′:6′,2′′-terpyridine (R=H) or 4,4′,4′′-tri- tert-butyl-2,2′:6′,2′′-terpyridine (R= tBu); NN=2,2′-bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes' reactivities. Whereas electron-donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [RuII(tpy)(6-mbpy)(CH3CN)]2+ ( trans-[ 3]2+; 6-mbpy=6-methyl-2,2′-bipyridine) and [RuII( tBu−tpy)(6-mbpy)(CH3CN)]2+ ( trans-[ 4]2+), in which the methyl group of the 6-mbpy ligand is trans to the CH3CN ligand, show electrocatalytic CO2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer-chemical reaction-electron transfer), and is a direct result of steric interactions that facilitate CH3CN ligand dissociation, CO2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations. [ABSTRACT FROM AUTHOR]

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru( tBu3tpy)(bpy)(NCCH3)]2+ ( tBu3tpy=4,4′,4′′-tri- tert-butyl-2,2′:6′,2′′-terpyridine; bpy=2,2′-bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO2 to CO. The methyl group enables CO2 binding already at the one-electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO2 reduction catalysts. [ABSTRACT FROM AUTHOR]

In the title compound, [Cu2(SO4)2(C20H36N8)(H2O)2]·6H2O, the dinuclear molecule lies across an inversion centre and contains square-pyramidal CuII ions separated by 7.5709 (18) Å. Symmetry-related molecules are linked together by hydrogen bonds between the coordinated water mol­ecules and the sulfate ligands. They are further linked by a framework of fused cyclic water tetra­meric and pseudo-hexa­gonal units in a three-dimensional hydrogen-bonded network involving both coordinated and uncoordinated water mol­ecules, as well as sulfate ligands. While the tetra­meric units are purely composed of water mol­ecules, the pseudo-hexa­gonal units involve O atoms from the sulfate. Further hydrogen bonding also involves the NH group from the imidazole in addition to the above-mentioned units. [ABSTRACT FROM AUTHOR]

In the title compound, C12H20N4O4·C2H4O2·H2O, the main fragment contains two l-alanine residues with a zwitterionic structure. The crystal structure is characterized by a two-dimensional network of O—H⋯O, O—H⋯N and N—H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]

Stable phospha- and arsaalkenes were used to synthesize polymers containing unsaturated P[double bond, length as m-dash]C and As[double bond, length as m-dash]C moieties. The composition, chemical environment, structure, optical, and electronic properties of the monomers and polymers were elucidated. The incorporation of the heteroatom-carbon double bonded units efficiently perturbs the optoelectronics and solid state features of both monomeric and polymeric scaffolds. Proof-of principle work supports their responsive character through post-functionalisation and electrochromic behaviour. To the best of our knowledge, this is the first example of a polymer containing arsenic-carbon double bonds.

A series of Ru II polypyridyl complexes of the structural design [Ru II (R-tpy)(NN)(CH 3 CN)] 2+ (R-tpy=2,2':6',2''-terpyridine (R=H) or 4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine (R=tBu); NN=2,2'-bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO 2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes' reactivities. Whereas electron-donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru II (tpy)(6-mbpy)(CH 3 CN)] 2+ (trans-[3] 2+ ; 6-mbpy=6-methyl-2,2'-bipyridine) and [Ru II (tBu-tpy)(6-mbpy)(CH 3 CN)] 2+ (trans-[4] 2+ ), in which the methyl group of the 6-mbpy ligand is trans to the CH 3 CN ligand, show electrocatalytic CO 2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer-chemical reaction-electron transfer), and is a direct result of steric interactions that facilitate CH 3 CN ligand dissociation, CO 2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The introduction of a simple methyl substituent on the bipyridine ligand of [Ru(tBu3 tpy)(bpy)(NCCH3 )](2+) (tBu3 tpy=4,4',4''-tri-tert-butyl-2,2':6',2''-terpyridine; bpy=2,2'-bipyridine) gives rise to a highly active electrocatalyst for the reduction of CO2 to CO. The methyl group enables CO2 binding already at the one-electron reduced state of the complex to enter a previously not accessible catalytic cycle that operates at the potential of the first reduction. The complex turns over with a Faradaic efficiency close to unity and at an overpotential that is amongst the lowest ever reported for homogenous CO2 reduction catalysts., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The electron-accepting ability of 6,6-dicyanopentafulvenes (DCFs) can be varied extensively through substitution on the five-membered ring. The reduction potentials for a set of 2,3,4,5-tetraphenyl-substituted DCFs, with varying substituents at the para-position of the phenyl rings, strongly correlate with their Hammett σp-parameters. By combining cyclic voltammetry with DFT calculations ((U)B3LYP/6-311+G(d)), using the conductor-like polarizable continuum model (CPCM) for implicit solvation, the absolute reduction potentials of a set of twenty DCFs were reproduced with a mean absolute deviation of 0.10 eV and a maximum deviation of 0.19 eV. Our experimentally investigated DCFs have reduction potentials within 3.67-4.41 eV, however, the computations reveal that DCFs with experimental reduction potentials as high as 5.3 eV could be achieved, higher than that of F4-TCNQ (5.02 eV). Thus, the DCF core is a template that allows variation in the reduction potentials by about 1.6 eV., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The dinuclear Co complex [(TPA)Co(μ-OH)(μ-O2 )Co(TPA)](ClO4 )3 (1, TPA=tris(2-pyridylmethyl)amine) catalyzes the oxidation of water. In the presence of [Ru(bpy)3 ](2+) and S2 O8 (2-) , photoinduced oxygen evolution can be observed with a turnover frequency (TOF) of 1.4±0.1 mol(O2 ) mol(1)(-1)  s(-1) and a maximal turnover number (TON) of 58±5 mol(O2 ) mol(1)(-1) . The complex is shown to act as a molecular and homogeneous catalyst and a mechanism is proposed based on the combination of EPR data and light-driven O2 evolution kinetics., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A 2e(-) /2H(+) redox platform has been implemented in the ethenyl-bridged bisphosphol-3-ol 1 to afford the first phospholes that feature chemically reversible oxidations. Oxidation of the title compounds to the corresponding bisphosphol-3-one 2 leads to a change in conjugation topology and a concomitant hypsochromic shift of the lowest-energy absorption maximum by 100 nm. Electrochemical oxidation proceeds without any detectable intermediates, whereas the deprotonated form of 1 can be observed in an aprotic medium during the reduction of 2. This dianionic intermediate 3 is characterized by end absorptions that are bathochromically shifted by circa 200 nm compared to those of 2., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)