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Synthesis, characterization, electronic structure, and redox reactions of a mononuclear {FeNO} 7 complex with a very high N-O stretching frequency in solution are presented. Nitrosylation of [(L KP )Fe(DMF)] 2+ ( 1 ) (L KP = tris((1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methyl)amine) produced a five-coordinate {FeNO} 7 complex, [(L KP )Fe(NO)] 2+ ( 2 ). While complex 2 could accommodate an additional water molecule to generate a six-coordinate {FeNO} 7 complex, [(L KP )Fe(NO)(H 2 O)] 2+ ( 3 ), the coordinated H 2 O in 3 dissociates to generate 2 in solution. The molecular structure of 2 features a nearly linear Fe-N-O unit with an Fe-N distance of 1.744(4) Å, N-O distance of 1.162(5) Å, and - 1 in dichloromethane and readily dissociates NO when dissolved in coordinating solvents such as acetonitrile or N , N -dimethylformamide. Investigation of the reduction of 2 by FTIR-SEC and EPR spectroscopy shows the generation of a {Fe(NO) 2 } 9 species, and the results have been corroborated by electronic structure calculations. Furthermore, the reaction of 2 with bezenethiolate (PhS - ) and hydrosulfide (HS - ) allowed the unambiguous characterization of a dinitrosyl iron complex (DNIC), [Fe(SPh) 2 (NO) 2 ] 1 - , and an unprecedented complex, [{(L KP S 2 {Fe 6 S 6 (NO) 6 }] 2+ , featuring an iron-sulfur prismane dianion.

Herein, we present an unprecedented formation of a heterodinuclear complex [{(ppy) 2 Ir III }(μ-phpy){Ru II (tpy)}](ClO 4 ) 2 {[ 1 ](ClO 4 ) 2 } using terpyridyl/phenylpyridine as ancillary ligands and asymmetric phpy as a bridging ligand. The asymmetric binding mode (N ∧ N-∩-N ∧ N ∧ C - ) of the phpy ligand in {[ 1 ](ClO 4 ) 2 } is confirmed by 1 H, 13 C, 1 H- 1 H correlated spectroscopy (COSY), high-resolution mass spectrum (HRMS), single-crystal X-ray crystallography techniques, and solution conductivity measurements. Theoretical investigation suggests that the highest occupied molecular orbital (HOMO) and the least unoccupied molecular orbital (LUMO) of [ 1 ] 2+ are located on iridium/ppy and phpy, respectively. The complex displays a broad low energy charge transfer (CT) band within 450-575 nm. The time-dependent density functional theory (TDDFT) analysis suggests this as a mixture of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT), where both ruthenium, iridium, and ligands are involved. Complex {[ 1 ](ClO 4 ) 2 } exhibits Ru II Ir III /Ru III Ir III - and Ru III Ir III /Ru III Ir IV -based oxidative couples at 0.83 and 1.39 V, respectively. The complex shows anticancer activity and selectivity toward human breast cancer cells (IC 50 ; MCF-7: 9.3 ± 1.2 μM, and MDA-MB-231: 8.6 ± 1.2 μM) over normal breast cells (MCF 10A: IC 50 ≈ 21 ± 1.3 μM). The Western blot analysis and fluorescence microscopy images suggest that combined apoptosis and autophagy are responsible for cancer cell death.

Five new mononuclear lanthanide complexes, [LnL 2 ][Et 3 NH]·THF/H 2 O (Ln = Nd, Tb, Dy) (H 2 L Cl = 2-bis(2-hydroxy-3,5-dichloro benzyl)aminomethyl]pyridine), Ln = Nd ( 1 ), Tb ( 2 ), and Dy ( 3 ), and (H 2 L Br = 2-bis(2-hydroxy-3,5-dibromo benzyl)aminomethyl]pyridine), Ln = Nd ( 4 , H 2 O) and Tb ( 5 ), were synthesized and structurally characterized by single-crystal X-ray diffraction analyses. Being isostructural in all the five cases, the metal center is octa-coordinated with a triangular dodecahedron ( D 2 d symmetry) geometry, and it is independent of the halogen substitution (Cl/Br). This close similarity is due to the composite interplay of hydrogen/halogen bond interactions that control the overall crystal packing, yet notable differences in association patterns among the individual ones arise from the subtle stereo-electronic requirement of individual molecules in the three-dimensional (3D) architecture. Hirshfeld surface and density functional theory (DFT) calculations clearly vouch for the importance of the hydrogen bond and halogen bond interactions observed in the structure. Detailed magnetic measurements using direct-current and alternating-current susceptibility measurements show slow magnetic relaxation in 3 , a characteristic feature of the single-molecule magnets (SMMs), which is not shown by 1 and 2 . Steady-state and time-resolved photoluminescence of Tb(III) complexes shows a strong ligand-to-metal energy transfer that can be modulated by changing the substitution on phenolic ligands. The results from these analyses indicate that it may be advantageous to consider the subtle role of hydrogen bond (HB)/halogen bond (XB) intermolecular interactions judiciously for the design of SMMs and luminescent materials based on halogen-substituted ligands.

Efficient catalytic systems based on arene-Ru(II) complexes bearing bis-imidazole methane-based ligands were developed to achieve additive-free hydrogen generation from formaldehyde and paraformaldehyde in water. Our findings inferred the influential role of bis-imidazole methane ligands in the observed catalytic performance of the studied catalysts. Among the screened complexes, [(η 6 - p -cymene)RuCl( L )] + Cl - ( [Ru]-2 ) ( L = 4,4'-((2-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1 H -imidazole) outperformed others to generate hydrogen gas from paraformaldehyde in water with an exceptionally high turnover number (TON) of >20,000. A detailed mechanistic pathway for hydrogen gas generation from formaldehyde has been proposed on the basis of identified several crucial catalytic intermediate species involved in the hydrogen production process.

A series of half sandwich arene-ruthenium complexes [( η 6 -arene)RuCl( κ 2 -L)] + ( [Ru]-1 - [Ru]-10 ) containing bis-imidazole methane-based ligands {4,4'-(phenylmethylene)bis(2-ethyl-5-methyl-1 H -imidazole)} ( L1 ), {4,4'-((4-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1 H -imidazole)} ( L2 ), {4,4'-((2-methoxyphenyl)methylene)bis(2-ethyl-5-methyl-1 H -imidazole)} ( L3 ), {4,4'-((4-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1 H -imidazole)} ( L4 ), and {4,4'-((2-chlorophenyl)methylene)bis(2-ethyl-5-methyl-1 H -imidazole)} ( L5 ) are synthesized. The synthesized and purified complexes ( [Ru]-1 - [Ru]-10 ) are further employed for hydrogen production from formic acid in aqueous medium. Among the investigated complexes, [( η 6 - p -cymene)RuCl( κ 2 - L2 )] + [Ru]-2 , having Ru(II) coordinated 4-methoxy phenyl substituted bis-imidazole methane ligand ( L2 ), outperformed over others, displaying a higher catalytic turnover of 8830 and high efficiency (TOF = 1545 h -1 ) with appreciably high long-term stability for formic acid dehydrogenation in water.

Water-soluble ruthenium complexes [(η 6 -arene)Ru(κ 2 -L)] n + ( n = 0,1) ( [Ru]-1 - [Ru]-9 ) ligated with pyridine-based ligands are synthesized, and the molecular structure of the representative complex [Ru]-2 is confirmed by X-ray crystallography. The studied complexes are employed for the catalytic dehydrogenation of formic acid in water. Screening of these complexes inferred that [Ru]-1 [(η 6 -C 10 H 14 )Ru(κ 2 -N py OH- L1 )Cl] + ( L1 = pyridine-2-ylmethanol) outperformed others with an initial turnover frequency of 1548 h -1 . Complex [Ru]-1 also exhibited high stability in water and can be recycled up to seven times with a total turnover number of 6050. In addition to formic acid dehydrogenation, [Ru]-1 also catalyzed the conversion of formaldehyde to hydrogen gas in water under base-free conditions. The effects of temperature, pH, formic acid, and catalyst concentration on the reaction kinetics are investigated in detail. Mass and NMR based mechanistic investigations inferred the presence of several important intermediate species, such as ruthenium-formate species [Ru]-1B and ruthenium-hydride species [Ru]-1C , involved in the catalytic dehydrogenation reaction. Moreover, the molecular structure of a diruthenium species [Ru]-1A' is also authenticated by single-crystal X-ray crystallography.

Two mononuclear ruthenium complexes [(bpy) 2 Ru II L 1 /L 2 ](ClO 4 ) 2 ([1] 2+ /[2] 2+ ) (bpy-2,2' bipyridine, L 1 = 2,3-di(pyridin-2-yl)pyrazino[2,3-f][1,10]phenanthroline) and L 2 = 2,3-di(thiophen-2-yl)pyrazino[2,3-f][1,10]phenanthroline have been synthesized. The complexes have been characterized using various analytical techniques. The complex [1] 2+ has further been characterized by its single crystal X-ray structure suggesting ruthenium is coordinating through the N donors of phenanthroline end. Theoretical investigation suggests that the HOMOs of both complexes are composed of pyridine and pyrazine unit of ligands L 1 and L 2 whereas the LUMOs are formed by the contribution of bipyridine units. The low energy bands at ∼480 nm of the complexes can be assigned as MLCT with partial contribution from ligand transitions, whereas the rest are ligand centered. The complexes have shown Ru II /Ru III oxidation couples at E 1/2 at 1.26 (70 mV) V and 1.28 (62 mV) V for [1] 2+ and [2] 2+ vs Ag/AgCl, respectively, suggesting no significant role of distal thiophene or pyridine units of the ligands. The complexes are emissive and display solvent dependent emission properties. Both complexes have shown highest emission quantum yield and lifetime in DMSO (ϕ = 0.05 and τ avg = 460 ns and λ max em at 620 nm for [1] 2+ ; ϕ = 0.043 and τ avg = 425 ns and λ max em at 635 nm for [2] 2+ ). Further, the long luminescent lifetime of these complexes has been utilized to generate reactive oxygen species for efficient azo dye decomposition.

Iron-doped nanocrystalline particles of anatase TiO2 (denoted x% Fe-TiO2, with x the nominal [Fe] atom % in solution) have been successfully synthesized at room temperature by a controlled two-step process. Hydrolysis of titanium isopropoxide is first achieved to precipitate Ti(OH)4 species. A fine control of the pH allows one to maintain (i) soluble iron species and (ii) a sluggish solubility of Ti(OH)4 to promote a dissolution and condensation of titanium clusters incorporating iron, leading to the precipitation of iron-doped anatase TiO2. The pH does then influence both the nature and crystallinity of the final phase. After 2 months of aging at pH = 2, well-dispersed nanocrystalline iron-doped TiO2 particles have been achieved, leading to 5-6 nm particle size and offering a high surface area of ca. 280 m(2)/g. This dissolution/recrystallization process allows the incorporation of a dopant concentration of up to 7.7 atom %; the successful incorporation of iron in the structure is demonstrated by X-ray diffraction, high-resolution transmission electron microscopy, and Mössbauer spectroscopy. This entails optical-band-gap narrowing from 3.05 to 2.30 eV. The pros and cons effects of doping on the electrochemical properties of TiO2 versus lithium are herein discussed. We reveal that doping improves the power rate capability of the electrode but, in turn, deserves the electrolyte stability, leading to early formation of SEI. Finally, we highlight a beneficial effect of low iron introduction into the anatase lattice for photocatalytic applications under standard AM1.5G visible-light illumination.

Reaction of 3,6-diaryl-1,2,4,5-tetrazines (aryl = R = phenyl, 2-furyl or 2-thienyl) with 2 equiv of Ru(acac)2(CH3CN)2 results in reductive tetrazine ring opening to yield diruthenium complexes [(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2] bridged by the new 1,2-diiminohydrazido(2-) (dih-R(2-) = HNC(R)NNC(R)NH(2-)) ligands. rac/meso diastereoisomers could be detected and separated for the compounds with R = phenyl and 2-thienyl, all species are diamagnetic and were characterized by 1H NMR spectroscopy. Crystal structure determination of the meso isomers with R = phenyl and 2-thienyl confirmed the 1,2-diiminohydrazido formulation through long N-N (approximately 1.40 A) and short C=N(H) bonds (approximately 1.31 A), implying two bridged ruthenium(III) centers at about 4.765 A distance with strong antiferromagnetic coupling. The complexes undergo two reversible and well-separated one-electron reduction and oxidation processes, respectively. EPR Spectroscopy of the paramagnetic intermediates with comproportionation constants K(c) > 10(12) and UV-vis-NIR spectroelectrochemistry were used to identify the accessible redox states as [(acac)2Ru(II)(dih-R(2-))Ru(II)(acac)2]2-, [(acac)2Ru(II)(dih-R(*-))Ru(II)(acac)2]-, [(acac)2Ru(III)(dih-R(2-))Ru(III)(acac)2], [(acac)2Ru(III)(dih-R(*-))Ru(III)(acac)2]+, and [(acac)2Ru(III)(dih-R)Ru(III)(acac)2]2+. While the UV-vis-NIR spectroscopic response of [(acac)2Ru(dih-R)Ru(acac)2](0/-/2-) is very similar to that of [(bpy)2Ru(adc-R)Ru(bpy)2](4+/3+/2+), adc-R(2-) = 1,2-diacylhydrazido(2-), the EPR result indicating ligand-centered spin for [(acac)2Ru(II)(dih-R(*-))Ru(II)(acac)2]- despite deceptive NIR absorptions around 1400 nm reveals distinct differences in the electronic structures.

The new redox systems [(acac)2 Ru(mu-Q1)Ru(acac)2](n) (1(n)) and [(acac)2 Ru(mu-Q2)Ru(acac)2](n) (2(n)) with Q1 = 1,10-phenanthroline-5,6-dione and Q2 = 1,10-phenanthroline-5,6-diimine were studied for n = +, 0, -, and 2- using UV-Vis-NIR spectroelectrochemistry and, in part, EPR and susceptometry. The ligands can bind the first metal (left) through the phenanthroline nitrogen atoms and the second metal (right) at the o-quinonoid chelate site. The neutral compounds are already different: Compound 1 is formulated as a Ru(II)(mu-Q1)*- Ru(III) species with partially coupled semiquinone and ruthenium(III) centers. In contrast, a Ru(III)(mu-Q2)2- Ru(III) structure is assigned to 2, which shows a weak antiferromagnetic spin-spin interaction (J = -1.14 cm(-1)) and displays an intense half-field signal in the EPR spectrum. The one-electron reduced forms are also differently formulated as Ru(II)(mu-Q1)2- Ru(III) for 1(-) with a Ru(III)-typical EPR response and as Ru(II)(mu-Q2)*- Ru(II) for 2(-) with a radical-type EPR signal at g = 2.0020. In contrast, both 1(2-) and 2(2-) can only be described as Ru(II)(mu-Q)2- Ru(II) species. The monooxidized forms 1(+) and 2(+) show very similar spectroscopy, including a Ru(III)-type EPR signal. Although no unambiguous assignment was possible here for the alternatives Ru(II)(mu-Q)0Ru(III), Ru(III)(mu-Q)2- Ru(IV) or Ru(III)(mu-Q)*- Ru(III), the last description is favored. The reasons for identical or different oxidation state combinations are discussed.

The title compounds involving the structurally characterized bridging ligand bpytz were characterized, showing very strong electrochemical stabilization of the mixed-valent RuIIRuIII state (Kc = 10(13.9)) but no detectable (epsilon < 20 M(-1) cm(-1)) intervalence charge-transfer band in the infrared region. In situ reduction of the neutral precursor produces a diruthenium(II) complex of the bpytz radical anion according to EPR spectroscopy, whereas oxidation of the mixed-valent form leads to a diruthenium(III) species., (Copyright 2004 American Chemical Society)

The diamagnetic title complexes were obtained from Ru(acac)(2)(CH(3)CN)(2) and 2-aminophenol or 2-aminothiophenol. X-ray structure analysis of (L(1))Ru(acac)(2) (L(1) = o-iminoquinone) revealed C-C intra-ring, C-O, and C-N distances which suggest a Ru(III)-iminosemiquinone oxidation state distribution with antiparallel spin-spin coupling. One-electron oxidation and reduction of both title compounds to paramagnetic monocations [(L)Ru(acac)(2)](+) or monoanions [(L)Ru(acac)(2)](-) occurs reversibly at widely separated potentials (deltaE > 1.3 V) and leads to low-energy shifted charge transfer bands. In comparison with clearly established Ru(II)-semiquinone or Ru(III)-catecholate systems the g tensor components 2.23 > g(1) > 2.09, 2.16 > g(2) > 2.07, and 1.97 > g(3) > 1.88 point to considerable metal contributions to the singly occupied MO, corresponding to Ru(III) complexes with either o-quinonoid (--> cations) or catecholate-type ligands (--> anions) and only minor inclusion of Ru(IV)- or Ru(II)-iminosemiquinone formulations, respectively. The preference for the Ru(III) oxidation state for all accessible species is partially attributed to the monoanionic 2,4-pentanedionate (acac) co-ligands which favor a higher metal oxidation state than, e.g., neutral 2,2'-bipyridine (bpy).

Reaction of [Ru(acac)(2)(CH(3)CN)(2)] with 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,4-dihydro-1,2,4,5-tetrazine (H(2)L) results in formation of an unexpected dinuclear complex [(acac)(2)Ru(III)(L(1))Ru(III)(acac)(2)] (1) in which the bridging ligand [L(1)](2)(-) contains an (-)HN[bond]C[double bond]N[bond]N[double bond]C[bond]NH(-) unit arising from two-electron reduction of the 1,4-dihydro-1,2,4,5-tetrazine component of H(2)L. The crystal structure of complex 1 confirms the oxidation assignment of the metal ions as Ru(III) and clearly shows the consequent arrangement of double and single bonds in the bridging ligand, which acts as a bis-bidentate chelate having two pyrazolyl/amido chelating sites. Cyclic voltammetry of the complex shows the presence of four reversible one-electron redox couples, assigned as two Ru(III)/Ru(IV) couples (oxidations with respect to the starting material) and two Ru(II)/Ru(III) couples (reductions with respect to the starting material). The separation between the two Ru(III)/Ru(IV) couples (Delta E(1/2) = 700 mV) is much larger than that between the two Ru(II)/Ru(III) couples (Delta E(1/2) = 350 mV) across the same bridging pathway, because of the better ability of the dianionic bridging ligand to delocalize an added hole (in the oxidized mixed-valence state) than an added electron (in the reduced mixed-valence state), implying some ligand-centered character for the oxidations. UV-vis-NIR spectroelectrochemical measurements were performed in all five oxidation states; the Ru(II)-Ru(III) mixed-valence state of [1](-) has a strong IVCT transition at 2360 nm whose parameters give an electronic coupling constant of V(ab) approximately 1100 cm(-1), characteristic of a strongly interacting but localized (class II) mixed-valence state. In the Ru(III)-Ru(IV) mixed-valence state [1](+), no low-energy IVCT could be detected despite the strong electronic interaction, possibly because it is in the visible region and obscured by LMCT bands.

The reaction of mononuclear ruthenium precursor [Ru(II)(acac)(2)(CH(3)CN)(2)] (acac = acetylacetonate) with the thiouracil ligand (2-thiouracil, H(2)L(1) or 6-methyl -2-thiouracil, H(2)L(2)) in the presence of NEt(3) as base in ethanol solvent afforded a trinuclear triangular complex Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-sulfido) (1). In 1, each ruthenium center is linked to one usual O,O-bonded terminal acetylacetonate molecule whereas the other three acetylacetonate units act as bridging functions: each bridges two adjacent ruthenium ions through the terminal O,O-donor centers at one end and via the gamma-carbon center at the other end. Moreover, there is a mu(3)-sulfido bridging in the center of the complex unit, which essentially resulted via the selective cleavage of the carbon-sulfur bond of the thiouracil ligand. In diamagnetic complex 1, the ruthenium ions are in mixed valent Ru(III)Ru(III)Ru(II) state, where the paramagnetic ruthenium(III) ions are antiferromagnetically coupled. The single crystal X-ray structure of 1 showed two crystallographically independent C(3)-symmetric molecules, Ru(3)(O,O-acetylacetonate)(3)(mu-O,O,gamma-C-acetylacetonate)(3)(mu(3)-S) (1), in the asymmetric unit. Bond distances of both crystallographically independent molecules are almost identical, but there are some significant differences in bond angles (up to 6 degrees ) and interplanar angles (up to 8 degrees ). Each ruthenium atom exhibits a distorted octahedral environment formed by four oxygen atoms, two from each of the terminal and bridging acetylacetonate units, one gamma-carbon of an adjacent acetylacetonate ligand, and the sulfur atom in the center of the complex. In agreement with the expected 3-fold symmetry of the complex molecule, the (1)H and (13)C NMR spectra of 1 in CDCl(3) displayed signals corresponding to two types of ligand units. In dichloromethane solvent, 1 exhibited three metal center based successive quasireversible redox processes, Ru(III)Ru(III)Ru(III)-Ru(III)Ru(III)Ru(II) (couple I, 0.43 V vs SCE); Ru(III)Ru(III)Ru(IV)-Ru(III)Ru(III)Ru(III) (couple II, 1.12 V); and Ru(III)Ru(III)Ru(II)-Ru(III)Ru(II)Ru(II) (couple III, -1.21 V). However, in acetonitrile solvent, in addition to the three described couples [(couple I), 0.34 V; (couple II), 1.0 V; (couple III), -1.0], one irreversible oxidative response (Ru(III)Ru(III)Ru(IV) --> Ru(III)Ru(IV)Ru(IV) or oxidation of the coordinated sulfide center) appeared at E(pa), 1.50 V. The large differences in potentials between the successive couples are indicative of strong coupling between the ruthenium ions in the mixed-valent states. Compound 1 exhibited a moderately strong charge-transfer (CT) transition at 654 nm and multiple ligand based intense transitions in the UV region. In the Ru(III)Ru(III)Ru(III) (1(+)) state, the CT band was slightly blue shifted to 644 nm; however, the CT band was further blue shifted to 520 nm on two-electron oxidation to the Ru(III)Ru(III)Ru(IV) (1(2+)) state with a reduction in intensity.