New applications of ruthenium solar cell sensitizers N3 and N719 as luminescence turn-on anion sensors

Optical sensing of F⁻, Cl⁻, Br⁻, I⁻, OAc⁻, , , and by cis-dithiocyanatobis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium(II) (N3) and bis(tetrabutylammonium) cis-dithiocyanatobis(2,2′-bipyridine-4-COOH,4′-COO⁻)ruthenium(II) (N719) have been investigated in dimethyl sulfoxide (DMSO), by means of UV-Vis absorption and emission spectrophotometric titrations. Additions of F⁻, OAc⁻, and in DMSO solution caused obvious UV-Vis spectral changes with appearance of several isosbestic points, and remarkable emission enhancements along with large blue shifts in emission bands. The values of F⁻-induced emission intensity enhancement factor (emission quantum yield enhancement factor), I/I₀ (φ/φ₀), were found to be 40 (86) and 38 (58) for N3 and N719, respectively. No obvious spectral changes were observed upon addition of Cl⁻, Br⁻, I⁻, and in DMSO solutions. Luminescent F⁻ sensing in DMSO/H₂O (4:1, v/v) has also been demonstrated to be operative with a luminescence enhancement factor of 12, indicating that N3 is very potential for practical application as fluorescent anion sensor in aqueous solution. An interaction mechanism of anion-induced deprotonation of N3 and N719 was confirmed, and the deprotonation reaction equilibrium constants of N3 and N719 were derived as well.     

Synthesis, structure and magnetic characterization of decamethylmetallocenium ethyl tricyanoethylenecarboxylate charge-transfer salts

Ethyl tricyanoethylenecarboxylate (ETCE) is a one-electron acceptor related to tetracyanoethylene that can serve as a building block for the construction of molecule-based magnets. The reactions of ETCE with decamethylmetallocenes, (M = Cr, Mn, Fe) give three new charge-transfer salt magnets, [ETCE] 1, [ETCE] 2 and [ETCE] 3. The expected mixed pi stacking of anions and cations is obtained, with the ETCE radical anion exhibiting typical disorder over two nearly equivalent footprints. Powder diffraction supports the belief that all three compounds are isomorphous. Magnetic measurements indicate that 1 is a soft ferromagnet, ordering below a critical temperature, T_c, of 3.8 K. Compound 2 exhibits complex magnetic behavior consisting of two frequency-dependent peaks in the ac susceptibility, the first at about 11.2 K and the second at about 7 K. At 1.8 K, the compound is hysteretic and exhibits a coercive field of 10 kG. Compound 3 is a glassy, apparently canted, ferromagnet displaying an out-of-phase ac susceptibility signal below about 3 K.     

Oxomolybdenum(III, IV and V) complexes of thiofunctional ligands

Reaction of [MoO₂(acac)₂] with (S is a thioether, S′ a thiophenolate function) yielded the compound Li₇(thf)₁₇{MoO}₈ · 10thf · hexane, where {MoO}₈ represents one 1, three (2, linked, via the oxo group, to [Li(thf)₃]⁺) and two (3a, linked by two [Li(thf)₂]⁺).A mixed-valent variant of 3, (3b, with an additional[Li(thf)₃]⁺ attached to S′), was also identified. The compounds model features pertinent to oxo-transferases containing the molybdopterin cofactor.     

Crystal structures and magnetic properties of Ni-bisdithiolene complexes with decamethylmetallocenium cations

Three new compounds of formula (1), (2), and (3) have been synthesised, and structurally and magnetically characterised (dmit²⁻ = 1,3-dithiol-2-thione-4,5-dithiolato; dmid²⁻ = 1,3-dithiol-2-one-4,5-dithiolato). Their structural features and magnetic behaviours are compared with those of and . The result of this is that the interactions between the Ni(dmit)₂ units in 1 are of ferromagnetic-type, as suggested previously for . The change from acetonitrile to acetone when going from to 2 results in stronger ferromagnetic intermolecular interactions. This better cooperativity is due to a significant increase of the number of contacts between the various moieties within the . On the contrary, the inclusion of larger solvents such as benzonitrile in this type of complexes results in a totally different structural arrangement, which leads to an antiferromagnetic behaviour for 3.     

Layered iron(II) spin crossover complex constructed by NH?Br hydrogen bonds with 2 K wide thermal hysteresis, [FeH3L]Br·CF3SO3 (H3L = tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine)

A series of compounds [Fe^IIH₃L^Me]Br·Y·nMeOH ( (1), (2), (3), (4); n = 0 or 1) were synthesized, where H₃L^Me is a hexadentate N₆ tripodal ligand of the neutral form, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine, and their structures and magnetic properties were investigated. The compounds 1−3 with counter anions , , and contain methanol as a crystal solvent, and show no SCO behaviors, while the corresponding Cl⁻ compounds have no crystal solvent and show a variety of SCO behaviors. The compound [Fe^IIH₃L^Me]Br·CF₃SO₃ (4) has no crystal solvent and has isomorphous structure to the Cl⁻ compounds, and shows an abrupt spin transition between the HS (S = 2) and LS (S = 0) states with a hysteresis about 2 K and large frozen-in effect below 72 K. The T_1/2↑ and T_1/2↓ values are 98 and 96 K, whose values are higher than those of corresponding Cl⁻ compound about 15 K and the width of hysteresis is narrower than that of corresponding Cl⁻ compound about 2 K. The crystal structures of 4 were determined at 296 and 93 K, where the crystal system and space group showed no change between these temperatures. The structures at both temperatures have a same 2D layered structure, which is composed of NH?Br⁻ hydrogen bonds between the Br⁻ ion and the imidazole NH groups of three neighboring cations [Fe^IIH₃L^Me]²⁺. This network structure is the same as that of corresponding Cl⁻ compound. The 600 nm light irradiation at 5 K induced the LIESST effect.     

Photocatalysis of chloroform degradation by μ-dichlorotetrachlorodipalladate(II)

Unlike other chlorometallate complexes that catalyze the photodecomposition of haloalkanes through photodissociation of a chlorine atom, both and catalyze chloroform decomposition through a process that appears to involve C-H bond breakage from an excited state association complex with chloroform. This would account for the greatly retarded rate of decomposition in CDCl₃ and for the generation of CCl₄ as a side product. In chloroform, and are in slow equilibrium with each other. The rate for the conversion of - in chloroform at 23 °C obeys the expression (0.03 M⁻¹ s⁻¹) [][Cl⁻]. The equilibrium constant, K = [][Cl⁻]²/[]², was estimated to be 3 × 10⁻³ M in CHCl₃.     

Conductometric and voltammetric studies on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2], where L: 2-(2′-pyridyl)quinoxaline

Conductometric investigation on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl₂(L)(PPh₃)₂] (A) (where PPh₃: triphenyl phosphine and L: 2-(2′-pyridyl)quinoxaline, C₁₃N₃H₉), in dimethylsulfoxide (DMSO) was performed at temperatures ranging from 25 to 50 °C. In addition, cyclic voltammograms of A were recorded on platinum working electrode in dichloromethane (DCM) and dimethylsulfoxide (DMSO) using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte at 25 °C. The molar conductivities (Λ) demonstrate that A behaves as uni-univalent electrolyte in DMSO over the whole temperature range. This behavior can be explained in terms of the replacement upon dissolution of chlorine and PPh₃ ligands by DMSO molecules, and consequently, the formation of the ion-pair [RuCl(L)(PPh₃)(DMSO)₂]Cl [B⁺Cl⁻] which is dissociated in some extent. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ^o) and the ion-pair association constants (K_A) of [B⁺Cl⁻]. The limiting ion conductivities for the B⁺ ion were evaluated using n-tetrabutylammonium chloride (NBu₄Cl) as “reference electrolyte”. The thermodynamic functions related with the ion association, such as Gibbs free energy , enthalpy , and entropy , were evaluated as well. The mobility of B⁺ was found to increase linearly with rising temperature and the consequent decrease of the viscosity (η) of DMSO. The K_A and values indicate that the association of [B⁺Cl⁻] increases to some extent with the rise of the temperature followed by the decrease of the dielectric constant (ε) of DMSO. The voltammetric experiments indicated that the couple Ru^3+/2+ is reversible and diffusion controlled in DCM and completely irreversible in DMSO.     

Investigation into the reaction of (t-BuC5H4)2Nb(η-Te2)H with CH3Li: Hydride abstraction versus telluride methylation

The reaction of (Cp′ = t-BuC₅H₄) with CH₃Li in THF was examined by variable temperature ¹H NMR, ESR and mass spectroscopic means. From these methods it is evident that the diamagnetic compounds and as well as the paramagnetic compound form simultaneously. In the subsequent reaction of the intermediate solution with [Co₂(CO)₈] compound 4 was consumed and the compound (5) formed in good yield. Complex 5 was characterized by IR and variable temperature ¹H NMR spectroscopies. Electrochemical two-electron reduction of 1 leads, in a quasi-reversible process, to products that are not stable in solution.     

Argentophilic interaction and anionic control of supramolecular structures in simple silver pyridine complexes

The synthesis and characterization of three simple 1:2 silver(I) pyridine adducts of different counter-anions, [Ag(py)₂]⁺ · X⁻ (X = ClO₄, 1; BF₄, 2; PF₆, 3), are reported. The structural studies for 1-3 reveal the presence of strong ligand-unsupported argentophilic interactions between [Ag(py)₂]⁺ ions, forming pairs of . The Ag?Ag contact distances are 2.96-3.00 Å. In 1 and 2, pairs of are further linked into 1-D infinite chains by a combined set of multiple Ag?Ag close contacts (3.34-3.37 Å), offset ‘head to head’ π-π stacking, and anion bridging interactions. Such combined set of interactions is anion-dependant with 1 and 2 containing anions of tetrahedral geometry and , affording essentially the same supramolecular architecture. Metal-anion interactions are crucial in organizing the 1-D chains into 3-D networks. The ES-MS studies of 1 and 2 provide positive evidence for the aggregation of silver(I) ions in solution. In contrast, for 3 with the counter-anion of octahedral , pairs of are organized into a 3-D network via a combined set of Ag?F contacts, C(H)?F hydrogen bonds, and ‘head to tail’ π-π stacking interactions. No extended 1-D polymeric chains of silver ions are present in 3.     

Density-functional analysis of the electronic structure of tris-bipyridyl Ru(II) sensitisers

Excited state transitions and energies of a series of [Ru(bpy)₃]²⁺ type complexes incorporating the ligand, 4,4′-bis-phosphonato(methyl)-2,2′-bipyridine (dmpbpy) was investigated, and the influence of this organometallic ligand on the electronic structure of the complexes was examined using Time-Dependent Density Functional Theory (TD-DFT). Experimental data and the theoretical TD-DFT calculations were presented to support the effect of non-equivalent ligand substitution on spectral and molecular orbital (MO) energy properties on this class of tris-chelate surface sensitisers. For the series of complexes studied, it was identified that the lowest lying LUMO states were consistently found to reside on the ligand 2,2′-bipyridine (bpy) for gas phase calculations. As an implication of this, it was suggested that this could impact the effectiveness of these complexes as surface sensitisers in PEC cell applications such as the dye-sensitised solar cell (DSC) due to the lower probability of the excited state electron residing on a ligand anchored to the semiconductor substrate. However, further calculations in a solvation medium showed that the electron withdrawing nature of PO₃H₂ on dmpbpy saw the lowest lying LUMO states are populated on dmpbpy. This inhomogeneous distribution of electron density across non-equivalent ligands may have implications for further ‘spectral tuning’ of surface sensitisers. Despite the TD-DFT gas phase calculations not being corrected for solvent/media effects, the three longest wavelength bands associated with known charge transfer phenomena were identified. The symmetry allowed _MLCT in the visible region was assigned as a  ← dπ transition, the mid-UV spectrum _LC was assigned  ← π in origin. Whilst the near-UV shoulder on the blue side of _MLCT showed dσ ← dπ and π∗ ← dπ transitional character and was tentatively described as _MC/MLCT. UV-Vis absorption spectra calculated for solvated analogues containing dmpbpy indicated that the low energy transitions associated with the MLCT are subject to bathochromic shift due to solvent polarity by 0.062 eV (500 cm⁻¹) compared with the gas phase calculations, which is more highly correlated to the observed experimental transitions.     

Mononuclear cobalt(II) carboxylate complexes: Synthesis, molecular structure and selective oxygenation study

Some cobalt carboxylate (both mononuclear as well as binuclear) complexes have been prepared by using hindered hydrotris(3,5-diisopropyl-1-pyrazolyl)borate (Tp^iPr2) as supporting ligand. The reaction of [Tp^iPr2Co(NO₃)] (2) with sodium benzoate resulted in the formation of acetonitrile coordinated complex [Tp^iPr2Co(OBz)(CH₃CN)] (3) whereas the reaction of 2 with sodium fluorobenzoate gave coordinately unsaturated five coordinate complex of the type [Tp^iPr2Co(F-OBz)] (4). The oxidation of compound 4 in the presence of 3,5-diisopropylpyrazole resulted in the formation of a unique compound (5) where only one methine carbon of isopropyl group on pyrazole ring of hydrotris(3,5-diisopropyl-1-pyrazolyl)borate oxidized and coordinated with cobalt center. In compound 5, the binding behavior of fluorobenzoate also changes from bidentate to monodentate and the nonbonded oxygen atom formed intramolecular hydrogen bond with the hydrogen atom of the NH fragment of the coordinated . X-ray crystallography and IR studies confirmed the existence of hydrogen bonding in complex 5. The pyrazolato bridged binuclear cobalt(II) complex (6) was prepared by the reaction of hydrated cobalt(II) nitrate, 3,5-diisopropylpyrazole and sodium nitrobenzoate where, each cobalt is four coordinate. The X-ray structure of 6 showed that the NH fragment of terminally coordinated formed intramolecular hydrogen bonding with nonbonded oxygen atom of monodentately coordinated nitrobenzoate.     

A new Cu(4,5-diazafluoren-9-one)-capped Keggin derivative: Hydrothermal synthesis and crystal characterization

A new α-Keggin POM derivative (1) (DF = 4,5-diazafluoren-9-one) has been prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR, XPS spectra, thermogravimetric analysis and cyclic voltammetry. In compound 1, the polyoxoanion cluster is decorated by a single capping {Cu(DF)}²⁺ subunit via four bridging oxygen atoms on a {Mo₄O₄} pit. The isolated copper dimer unit acts as counter cation, in which the organic ligand DF exhibits a rare coordination mode. Furthermore, the capped Keggin polyoxoanions are fused together via the copper dimers through the weak Cu ? O interactions to form chains. Hybrid 1 was used as a solid bulk modifier to fabricate a carbon paste electrode (1-CPE) by direct mixing. The electrochemical and electrocatalytic behaviors of the 1-CPE have been studied in detail.     

Synthesis and single crystal structural investigations on quaternary salts of tellurated alkylamine derivatives

Tellurated alkylamine derivatives , , and have been synthesized by reacting appropriate organic halides with the nucleophile 4-CH₃OC₆H₄Te⁻ or Te²⁻ generated in situ by borohydride reduction of (4-CH₃OC₆H₄Te)₂ or Te powder followed by reaction with HCl of appropriate concentration. The zwitterionic species was generated when single crystals of 2 were grown in methanol at 0 °C. Complexes 1-4 exhibit characteristic ¹H NMR spectra. The single crystal structures of 1-4 and 2a have been determined. In the crystals of 1, C-H?π distances have been found to be 3.31(7)-3.59(5) Å. In both 2 and 2a, weak Te?Cl interactions (3.54(2) -3.62(2) Å) are observed. The C-H?π distance in the crystal of 2 is 3.19(0) Å. In 2a and 3, water hydrogen bonds connect the water molecules with the end groups from different molecules. In the case of 3, Te?Cl weak interactions involving the Cl⁻ ions connect together two such chains. The geometry of Te in 1 is V shaped. In 2 and 3 it is pseudo trigonal bipyramidal, and in 2a, it is square pyramidal. However, in the latter case it becomes distorted octahedral due to weak Te?Cl secondary interactions. The geometry about Te in 4 is distorted octahedral due to weak Te?Cl interactions involving Cl⁻ ions. However, there are no intermolecular Te?Cl interactions.     

Coordination and derivatization of 3, 4, and 6-membered nitrogen heterocycles at a chiral tungsten(II) center

Reaction of [Tp′W(CO)₂(PhCCPh)][OTf] (1b) (Tp′ = hydridotris(3,5-dimethylpyrazolyl)borate) with excess aziridine or 2-methylaziridine followed by protonation with produces chiral tungsten(II) amine complexes (3, 4; R = Me, Ph). An azetidine amido complex, Tp′W(CO)(PhCCMe)(H₂) (5) is synthesized by reaction of [Tp′W(CO)₂(PhCCMe)][OTf] (1a) with excess azetidine. Oxidation of amido complex 5 with I₂ in the presence of a weak base provides the corresponding 1-azetine complex, (6). Addition of methylmagnesium bromide to complex 6 results in formation of predominantly one diastereomer (S_WR_C/R_WS_C) (96:4 dr) of the 2-methylazetidine complex, Tp′W(CO)(PhCCMe)(H₂) (7). Reaction of complex 5 with results in formation of a cationic azetidine complex, (8). Reaction of 1b with excess piperidine followed by oxidation affords 2,3,4,5-tetrahydropyridine complex 9b, . Formation of an enamido complex, Tp′W(CO)(PhCCPh)(H₂) (10), is observed upon addition of base to 9b. Subsequent addition of [D⁺] to the enamido β-carbon results in the formation of the deuterated product, 9b-d₁, as determined by ²H NMR. Seven X-ray crystal structures have been determined, and these encompass complexes with 3, 4, and 6-membered heterocyclic ligands. Crystal structures are reported for two aziridine adducts (2, 4) two neutral amido complexes (5, 7), one cationic imine complex (6), and one cationic amine (8) complex derived from azetidine, and the imine complex formed from piperidine (9).     

Unusual kinetic and thermodynamic control in the formation of Pt(II)-complexes of a new C1-symmetric phosphine-phosphite

Versatile synthetic routes have been applied to prepare the new asymmetric phosphine-phosphite ligands 8 and 12. The chiral ligands have been designed so that the corresponding ligating groups have similar electronic properties and steric bulk, but 8 forms 6-, while 12 forms 7-membered chelate rings in their coordination compounds. The chelate size variation results in a markedly different coordination behavior towards Pt(II). In their reactions with Pt(PhCN)₂Cl₂ at 1:1 stoichiometry 12 forms the expected Pt(12)Cl₂ complex, while 8 gives the cation quantitatively. In the kinetically controlled reaction is the major product even at a 8:Pt(PhCN)₂Cl₂ = 1:2 ratio. Most interestingly, at 1:1 ligand to precursor ratio, cation rearranges to Pt(8)Cl₂ within one day, indicating that the neutral complex is thermodynamically more favorable.     

Target syntheses of saturated Keggin polyoxometalate-based extended solids

By the approach of target synthesis, three infinitely extended hybrid compounds based on the saturated Keggin polyoxoanions have been synthesized under hydrothermal conditions: , and (phen = 1,10-phenanthroline, trea = triethylamine). The isostructural compounds 1 and 2 belong to the monoclinic space group P2₁/c and both contain neutral 2D layers and discrete polyoxometalate clusters decorated by transitional metal complexes. They represent an important example of the family of intercalated solids, in which both the 2D layers and the intercalated molecules are polyoxometalates with covalently linked transitional metal complex fragments. Compound 3, crystallizing in the monoclinic space group C2/c, consists of 1D zigzag chains constructed from alternating polyoxoanions and [Ni(phen)₂]²⁺ fragments. More interestingly, these three compounds are constructed directly from saturated polyoxometalates, in which the intact skeletons of Keggin clusters are maintained under hydrothermal conditions. Variable-temperature magnetic susceptibility measurements of compounds 1 and 2 reveal the feature of antiferromagnetic exchange interaction in these compounds.     

A trade-off relationship between energetic cost and entropic cost for in vitro evolution

In this paper, we consider two complementary cost functions for the landscape exploring processes to obtain the global optimum sequence through in vitro evolution protocol: one is the entropic cost C_etp, which is based on the deviation from the uniformity of a mutant distribution in sequence space, and the other is the energetic cost C_eng, which is based on the total number of sequences to be generated and evaluated. Based on a prior knowledge about the structure of a given fitness landscapes, the conductor of the experiment can think up the efficient search algorithm (ESA), which requires the minimum number of points (=sequences) to be searched up to the global optimum. For five typical fitness landscapes, we considered their respective (putative) ESA, and based on the ESA. As a result, we found a trade-off relationship between and for every case, that is, is approximately equal to the logarithm of the volume of the sequence space. and are interpreted in terms of the information-theoretic concepts.     

Applicability of new spin trap agent, 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide, in biological system

Electron spin resonance using spin-trapping is a useful technique for detecting direct reactive oxygen species, such as superoxide (). However, the widely used spin trap 2,2-dimethyl-3,4-dihydro-2H-pyrrole N-oxide (DMPO) has several fundamental limitations in terms of half-life and stability. Recently, the new spin trap 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (DPhPMPO) was developed by us. We evaluated the biological applicability of DPhPMPO to analyze in both cell-free and cellular systems. DPhPMPO had a larger rate constant for and formed more stable spin adducts for than DMPO in the xanthine/xanthine oxidase (X/XO) system. In the phorbol myristate acetate-activated neutrophil system, the detection potential of DPhPMPO for was significantly higher than that of DMPO (k_DMPO = 13.95 M⁻¹ s⁻¹, k_DPhPMPO = 42.4 M⁻¹ s⁻¹). These results indicated that DPhPMPO is a potentially good candidate for trapping in a biological system.     

Anionic effects on the formation of tridentate 4′-chloro-2,2′:6′,2″-terpyridine copper(II) complexes having 1:1 or 1:2 ratio of metal and ligand and their crystal symmetry

A facile synthetic procedure has been used to prepare one five-coordinate and four six-coordinate copper(II) complexes of 4′-chloro-2,2′:6′,2″-terpyridine (tpyCl) ligand with different counterions (, , , , and ) in high yields. They are formulated as [Cu(tpyCl-κ³N,N′,N′′)(SO₄-κO)(H₂O-κO)] · 2H₂O (1), trans-[Cu(tpyCl-κ³N,N′,N″)(NO₃-κO)₂(H₂O-κO)] (2), [Cu(tpyCl-κ³N,N′,N″)₂](BF₄)₂ (3), [Cu(tpyCl-κ³N,N′,N″)₂](PF₆)₂ (4) and [Cu(tpyCl-κ³N,N′,N″)₂](ClO₄)₂ (5) and versatile interactions in supramolecular level including coordinative bonding, O-H?O, O-H?Cl, C-H?F, and C-H?Cl hydrogen bonding, π-π stacking play essential roles in forming different frameworks of 1-5. It is concluded that the difference of coordination abilities of the counterions used and the experimental conditions codominate the resulting complexes with 1:1 or 1:2 ratio of metal and ligand.