The title heteroleptic bis--terpyridine complex, Ru(C(15)H(11)N(3))(C(17)H(11)N(3))(PF(6))(2)·2CH(3)CN, crystallized from an acetonitrile solution as a salt containing two hexa-fluoridophosphate ...counter-ions and two acetonitrile solvent mol-ecules. The Ru(II) atom has a distorted octa-hedral geometry due to the restricted bite angle 157.7 (3)° of the two mer-arranged N,N',N''-tridendate ligands, viz. 2,2':6',2''-terpyridine (tpy) and 4'-ethynyl-2,2':6',2''-terpyridine (tpy'), which are essentially perpendicular to each other, with a dihedral angle of 87.75 (12)° between their terpyridyl planes. The rod-like acetyl-ene group lies in the same plane as its adjacent terpyridyl moiety, with a maximum deviation of only 0.071 (11) Å from coplanarity with the pyridine rings. The mean Ru-N bond length involving the outer N atoms trans to each other is 2.069 (6) Å at tpy and 2.070 (6) Å at tpy'. The Ru-N bond length involving the central N atom is 1.964 (6) Å at tpy and 1.967 (6) Å at tpy'. Two of the three counter anions were refined as half-occupied.
The only operating mechanism in the oxidation of water to dioxygen catalyzed by the mononuclear cis‐RuII(bpy)2(H2O)22+ complex when treated with excess CeIV was unambiguously established. Theoretical ...calculations together with 18O‐labeling experiments (see plot) revealed that it is the nucleophilic attack of water on a RuO group.
Biopolymer-based optical hydrogels represent an emerging class of materials with potential applications in biocompatible integrated optoelectronic devices, bioimaging applications, and ...stretchable/flexible photonics. We have synthesized stimuli-responsive three-dimensional hydrogels from genetically engineered elastin-like polymers (ELPs) and have loaded these hydrogels with an amine-containing p-phenylenevinylene oligomer (OPPV) derivative featuring highly tunable, environmentally sensitive optical properties. The composite ELP/OPPV hydrogels exhibit both pH- and temperature-dependent fluorescence emission, from which we have characterized a unique optical behavior that emerged from OPPV within the hydrogel environment. By systematic comparison with free OPPV in solution, our results suggest that this distinct behavior is due to local electronic effects arising from interactions between the hydrophobic ELP microenvironment and the nonprotonated OPPV species at pH 7 or higher.
The first designed molecular catalyst for water oxidation is the “blue dimer”, cis,cis-(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)24+. Although there is experimental evidence for extensive electronic coupling ...across the μ-oxo bridge, results of earlier DFT and CASSCF calculations provide a model with magnetic interactions of weak to moderately coupled RuIII ions across the μ-oxo bridge. We present the results of a comprehensive experimental investigation, combined with DFT calculations. The experiments demonstrate both that there is strong electronic coupling in the blue dimer and that its effects are profound. Experimental evidence has been obtained from molecular structures and key bond distances by XRD, electrochemically measured comproportionation constants for mixed-valence equilibria, temperature-dependent magnetism, chemical properties (solvent exchange, redox potentials, and pK a values), XPS binding energies, analysis of excitation-dependent resonance Raman profiles, and DFT analysis of electronic absorption spectra. The spectrum can be assigned based on a singlet ground state with specific hydrogen-bonding interactions with solvent molecules included. The results are in good agreement with available experimental data. The DFT analysis provides assignments for characteristic absorption bands in the near-IR and visible regions. Bridge-based dπ → dπ* and interconfiguration transitions at RuIII appear in the near-IR and MLCT and LMCT transitions in the visible. Reasonable values are also provided by DFT analysis for experimentally observed bond distances and redox potentials. The observed temperature-dependent magnetism of the blue dimer is consistent with a delocalized, diamagnetic singlet state (dπ1*)2 with a low-lying, paramagnetic triplet state (dπ1*)1(dπ2*)1. Systematic structural–magnetic–IR correlations are observed between νsym(RuORu) and νasym(RuORu) vibrational energies and magnetic properties in a series of ruthenium-based, μ-oxo-bridged complexes. Consistent with the DFT electronic structure model, bending along the Ru–O–Ru axis arises from a Jahn–Teller distortion with ∠Ru–O–Ru dictated by the distortion and electron–electron repulsion.
We report the structural characterization of 6',6''-bis(pyridin-2-yl)-2,2':4',4'':2'',2''-quaterpyridine(2,2'-bipyridine)chloridoruthenium(II) hexafluoridophosphate, RuCl(C10H8N2)(C30H20N6)PF6, which ...contains the bidentate ligand 2,2'-bipyridine (bpy) and the tridendate ligand 6',6''-bis(pyridin-2-yl)-2,2':4',4'':2'',2'''-quaterpyridine (tpy–tpy). The RuCl(bpy)(tpy–tpy)+ monocation has a distorted octahedral geometry at the central RuII ion due to the restricted bite angle 159.32 (16)° of the tridendate ligand. The Ru-bound tpy and bpy moieties are nearly planar and essentially perpendicular to each other with a dihedral angle of 89.78 (11)° between the least-squares planes. The lengths of the two Ru—N bonds for bpy are 2.028 (4) and 2.075 (4) Å, with the shorter bond being opposite to Ru—Cl. For tpy–tpy, the mean Ru—N distance involving the outer N atomstransto each other is 2.053 (8) Å, whereas the length of the much shorter bond involving the central N atom is 1.936 (4) Å. The Ru—Cl distance is 2.3982 (16) Å. The free uncoordinated moiety of tpy–tpy adopts a trans,trans conformation about the interannular C—C bonds, with adjacent pyridyl rings being only approximately coplanar. The crystal packing shows significant π–π stacking interactions based on tpy–tpy. The crystal structure reported here is the first for a tpy–tpy complex of ruthenium.
The cationic complex in the title compound, RuCl(C10H8N2)(C19H20N3O3P)PF6·0.83CH3CN·0.17H2O, is a water-oxidation precatalyst functionalized for TiO2 attachment via terpyridine phosphonate. The The ...RuII atom in the complex has a distorted octahedral geometry due to the restricted bite angle 159.50 (18)° of the terpyridyl ligand. The dihedral angle between the least-squares planes of the terpyridyl and bipyridyl moieties is 86.04 (14)°. The mean Ru-N bond length for bipyridine is 2.064 (5) Å, with the bond opposite to Ru-Cl being 0.068 Å shorter. For the substituted terpyridine, the mean Ru-N distance involving the outer N atoms trans to each other is 2.057 (6) Å, whereas the bond length involving the central N atom is 1.944 (5) Å. The Ru-Cl distance is 2.4073 (15) Å. The P atom of the phosphonate group lies in the same plane as its adjacent pyridyl ring, with the ordinary character of the bond between P and Ctpy 1.801 (6) Å allowing for free rotation of the terpyridine substituent around the P-Ctpy axis. The acetonitrile solvent molecule was refined to be disordered with two water molecules; occupancies for the acetontrile and water molecules were 0.831 (9) and 0.169 (9), respectively. Also disordered was the PF6− counter-ion (over three positions) and one of the ethoxy substituents (with two positions). The crystal structure shows significant intra- and intermolecular H...X contacts, especially some involving the Cl− ligand.
Resonance Raman spectroelectrochemistry (RR-SEC) at −20 °C has been performed on the pyrazine-bridged dimer of μ-oxo-centered trinuclear ruthenium−acetate “clusters” ...(dmap)(CO)(μ-OAc)6(μ3-O)Ru3(μ-Lb)Ru3(μ3-O)(μ-OAc)6(CO)(dmap) n (where dmap = 4-(dimethylamino)pyridine and Lb = pyrazine-h 4 and pyrazine-d 4)in three oxidation states: n = 0, −1, and −2. In the one-electron reduced, “mixed-valent” state (overall −1 charge and a single odd electron; formal oxidation states II, II, III−III, III, II on the metal centers), the Raman excitation at 800 nm is resonant with a cluster-to-cluster intervalence charge-transfer (IVCT) band. Under these conditions, scattering enhancement is observed for all four totally symmetric vibrational modes of the bridging pyrazine ligand (ν8a, ν9a, ν1, and ν6a) in the investigated spectral range (100−2000 cm-1), and there is no evidence of activity in non-totally symmetric vibrations. Resonantly enhanced Raman peaks related to peripheral pyridyl (dmap) ligand modes and low-frequency features arising from the trigonal Ru3O cluster core and the clusterRu−Nligand vibrations were also observed in the spectra of the intermediate-valence (n = −1) cluster dimer. The vibrational assignments and interpretations proposed in this work were reinforced by observation of characteristic isotopic frequency shifts accompanying deuteration of the bridging pyrazine. The results reveal that the fully symmetric (A g) vibrational motions of the organic bridge are coupled to the nominally metal cluster-to-metal cluster fast intramolecular electron transfer (ET) and provide validation of the near-delocalized description according to a predicted three-site/three-state (e.g., metal−bridge−metal) vibronic coupling model, in which the important role of the bridging ligand in mediating electronic communication and delocalization between charge centers is explicitly considered. Further compelling evidence supporting an extended five-state model, which incorporates the peripheral cluster-bound pyridyl ligands, is also presented.
The novel charge-transfer ground state found in α,α‘-diimine adducts of ytterbocene (C5Me5)2Yb(L) L = 2,2‘-bipyridine (bpy) and 1,10-phenanthroline (phen) in which an electron is spontaneously ...transferred from the f14 metal center into the lowest unoccupied (π*) molecular orbital (LUMO) of the diimine ligand to give an f13−L•- ground-state electronic configuration has been characterized by cyclic voltammetry, UV−vis−near-IR electronic absorption, and resonance Raman spectroscopies. The voltammetric data demonstrate that the diimine ligand LUMO is stabilized and the metal f orbital is destabilized by ∼1.0 V each upon complexation for both bpy and phen adducts. The separation between the ligand-based oxidation wave (L0/-) and the metal-based reduction wave (Yb3+/2+) in the ytterbocene adducts is 0.79 V for both bpy and phen complexes. The UV−vis−near-IR absorption spectroscopic data for both the neutral adducts and the one-electron-oxidized complexes are consistent with those reported recently, but previously unreported bands in the near-IR have been recorded and assigned to ligand (π*)-to-metal (f orbital) charge-transfer (LMCT) transitions. These optical electronic excited states are the converse of the ground-state charge-transfer process (e.g., f13−L•- ↔ f14−L0). These new bands occur at ∼5000 cm-1 in both adducts, consistent with predictions from electrochemical data, and the spacings of the resolved vibronic bands in these transitions are consistent with the removal of an electron from the ligand π* orbital. The unusually large intensity observed in the f → f intraconfiguration transitions for the neutral phenanthroline adduct is discussed in terms of an intensity-borrowing mechanism involving the low-energy LMCT states. Raman vibrational data clearly reveal resonance enhancement for excitation into the low-lying π* → π* ligand-localized excited states, and comparison of the vibrational energies with those reported for alkali-metal-reduced diimine ligands confirms that the ligands in the adducts are reduced radical anions. Differences in the resonance enhancement pattern for the modes in the bipyridine adduct with excitation into different π* → π* levels illustrate the different nodal structures that exist in the various low-lying π* orbitals.
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