L Complexes Research Articles

Syntactic complexity in L2 writing: Progress and expansion

In this commentary to the Special Issue, I first identify four themes that arise from the contributions that each study makes to the study of syntactic complexity in L2 writing. I then explore several other themes that stem from the collective findings from the five studies and which connect with the general landscape of the research domain. Two questions guide the domain. One question is substantive: What do we know about how syntactic complexity grows, and what factors affect this growth? The other question is methodological: How can one best measure syntactic complexity? Both, of course, are interrelated. An overarching conclusion is that much progress has been made in what is already known, substantively and methodologically. An emerging insight is that we can look forward to several areas of expansion that are imminent in the domain.

PLANNING AND WORKING MEMORY EFFECTS ON L2 PERFORMANCE IN CHINESE EFL LEARNERS’ ARGUMENTATIVE WRITING

With the guidance of Skehan’s cognitive model of L2 performance and Kellogg’s model of working memory in writing, the present study explored the effects of planning and working memory on L2 performance in Chinese EFL learners’ argumentative writings. The participants were required to complete one operation span task and two argumentative essays in pre-task planning and controlled conditions (no planning). Results showed that: 1) pre-task planning seemed to help a significant increase of lexical complexity in L2 writing performance; 2) working memory had a significant impact on syntactic complexity and fluency but no effect of working memory was found on lexical complexity and accuracy; 3) pre-planning could be integrated with working memory to affect L2 writing performance. In argumentative writings, working memory might be of great importance in planning while planning might enable learners to overcome limitations in working memory and enhance L2 writing performance.

A meaning-based approach to the study of complexity in L2 writing: The case of grammatical metaphor

This article argues for an alternative approach to complexity in L2 writing that foregrounds the link between aspects of linguistic complexity and its discourse-semantic function of constructing particular types of meanings in written texts. To illustrate a meaning- and form-integrating approach, the paper focuses on nominalizations as a linguistic form recently identified as a potentially significant indicator of complexity of advanced L2 writing. In line with the linguistic theory of meaning making, systemic functional linguistics (SFL), nominalizations are explored as realizations of grammatical metaphor (GM), a concept that helps capture the complexity of the semantic dimension of these linguistic forms. Furthermore, exploring nominalizations as GMs helps explain their discourse function as meeting the demands of more complex communicative tasks typical of advanced literacy contexts. Application of such conceptualization of complexity is illustrated by an analysis of an advanced L2 writing task that demonstrates precisely how nominalizations as GMs enable the L2 writer to meet the complexity of these demands through conceptual refiguration of experience and configuration or development of concepts in texts. The paper concludes with the implications of such an approach for L2 writing research, curriculum construction, and L2 writing pedagogy.

Low-melting cationic 3d-transition metal complexes of azole-based ligands

Ligands N-methylimidazole (MIm) and N-ethylimidazole (EIm) were used for the preparation of [FeII(L)6](NTf2)2·0.5EtOH·0.5H2O. With Tfus=83°C, the EIm complex was characterised as paramagnetic MeIL. Using bidentate imidazole ligands 2-(2-pyridyl)-1-ethylimidazole (L1) and 2-(2-pyridyl)-1-(2-methoxyethyl)imidazole (L2) 3:1 type complexes [MII(Li)3]X2 (M=Fe; Li=L1; X=ClO4, BF4, NTf2; M=Fe; Li=L2, X=ClO4, BF4; M=Co; X=ClO4; Li=L1, L2; M=Ni; X=ClO4; Li=L1, L2) were prepared. All complexes of L2 and complex [FeII(L1)3](NTf2)2 were low-melting with Tfus<200°C. Complexes of L2 additionally had glass transition temperatures below 75°C upon reheating.

Graph-Theoretical Modelling of Stability Constants of Copper(II) Complexes with Tripeptides Containing Glycine, Glutamic acid, and Histidine

Abstract Logarithms of stability constants, log β, of copper(II) complexes with tripeptides containing glycine, glutamic acid, and histidine were modelled with 3χv connectivity index. The model developed on complexes with tripeptides formed of Gly and Glu yielded S.E. = 0.47, 0.38, and 0.55, depending on whether CuL, CuH−1L, or CuH−2L complexes were taken as referent. The model was also applied to complexes with tripeptides containing His, S.E. = 1.47, 1.39, and 1.80. Although a somewhat worse result for G/E/H tripeptide complexes, much bigger range of their log β’s (29.648), in contrast to 16.671 for G/E tripeptide complexes, has to be borne in mind.

Expanding the family of heteroleptic oxidovanadium(IV) compounds with salicylaldehyde semicarbazones and polypyridyl ligands showing anti-Trypanosoma cruzi activity

Searching for prospective vanadium-based drugs for the treatment of Chagas disease, a new series of heteroleptic [VIVO(L-2H)(NN)] compounds was developed by including the lipophilic 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp) NN ligand and seven tridentate salicylaldehyde semicarbazone derivatives (L1–L7). The compounds were characterized in the solid state and in solution. EPR spectroscopy suggests that the NN ligand is bidentate bound through both nitrogen donor atoms in an axial–equatorial mode. The EPR and 51V-NMR spectra of aerated solutions at room temperature indicate that the compounds are stable to hydrolysis and that no significant oxidation of VIV to VV takes place at least in 24h. The complexes are more active in vitro against Trypanosoma cruzi, the parasite responsible for Chagas disease, than the reference drug Nifurtimox and most of them are more active than previously reported [VIVO(L-2H)(NN)] complexes of other NN co-ligands. Selectivity towards the parasite was analyzed using J-774 murine macrophages as mammalian cell model. Due to both, high activity and high selectivity, L2, L4, L5 and L7 complexes could be considered new hits for further drug development. Lipophilicity probably plays a relevant role in the bioactivity of the new compounds. The [VIVO(L-2H)(NN)] compounds were designed aiming DNA as potential molecular target. Therefore, the novel L1–L7 tmp complexes were screened by computational modeling, comparing their DNA-binding features with those of previously reported [VIVO(L-2H)(NN)] compounds with different NN co-ligands. Whereas all the complexes interact well with DNA, with binding modes and strength tuned in different extents by the NN and semicarbazone co-ligands, molecular docking suggests that the observed anti-T. cruzi activity cannot be explained upon DNA intercalation as the sole mechanism of action.

Reaction of primary amines with N-ethynyl pendant arms attached to macrocyclic nickel(II) and copper(II) complexes: Formation of the complexes with pendant imine group(s)

The two N-CH2CCH pendant arms of [NiL1]2+ (L1=2,13-bis(N-propargyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosane) react readily with benzyl amine or n-propylamine to produce the trans-octahedral complexes, [NiL2]2+ and [NiL4]2+, bearing two N-CH2C(NCH2C6H5)CH3 or two N-CH2C(NCH2CH2CH3)CH3 pendant arms. [CuL1]2+, however, reacts with the primary amines to form a square-pyramidal complex [CuL3]2+ or [CuL5]2+ bearing one N-CH2C(NCH2C6H5)CH3 or N-CH2C(NCH2CH2CH3)CH3 pendant arm as well as one N-CH2CCH group under similar experimental conditions. The pendant imine group of the nickel(II) or copper(II) complexes of L2–L5 is involved in coordination and is inert against hydrolysis, even in aqueous 1.0M HClO4 or 1.0M NaOH solutions.

Coordination of new disulfide ligands to CuI and CuII: Does a CuIIμ-thiolate complex form?

Interest in dinuclear CuIIμ-thiolate and CuI disulfide complexes is triggered by their similarity with the CuA site and the possibility to control this redox equilibrium. Three new disulfide ligands L1, L3 and L4 were synthesized and reacted with CuI salts to investigate whether thiolate or disulfide species would form. The nature of L1 precludes the formation of CuIIμ-thiolate species, resulting in the formation of [CuI2(L1)(CH3CN)](BF4)2 which was characterized via single crystal X-ray crystallography. Pyrazole-containing ligands L3 and L4 form CuI complexes that are stable in solution in air for hours with half-wave potentials of approximately +0.55V versus Ag/AgCl, indicating high stability of the CuI state rather than the CuII state. The half-wave potentials of the CuI complexes with L1 and L2 are less positive, indicating that in order to allow formation of both CuIIμ-thiolate and CuI disulfide species, a half-wave potential of roughly 0V versus Ag/AgCl would be ideal. Furthermore, CuII crystal structures with L1, L2, L3 and L4 and different counterions were compared and analyzed. Pyrazolyl-containing ligands L3 and L4 form complexes that are very similar to the complexes with pyridyl-containing ligands L1 and L2.

Gold nanostars co-coated with the Cu(II) complex of a tetraazamacrocyclic ligand.

The twelve-membered tetraazamacrocyclic ligand L1 bears an appended lipoic acid unit, whose disulphide ring is an efficient grafting moiety for the surface of gold nanostars (GNS). The GNS that were used featured a localized surface plasmon resonance (LSPR) absorption at ∼800 nm, i.e. in the near infrared (NIR). We investigated different approaches for coating them with the Cu(2+) complex of L1. While the direct reaction of [CuL1](2+) with as-prepared GNS led to aggregation, an initial coating step with polyethyleneglycol-thiol (PEG-SH) was found to be advantageous. Displacement reactions were carried out on pegylated GNS either with [CuL1](2+), directly generating [Cun(L1@GNS)](2n+), or with void L1, thus obtaining @GNS that coordinates Cu(2+) in a second step. In both cases, even with a large excess of the competing disulphide moiety, only partial displacement of PEG-SH is observed, obtaining ca. 500-1500 [CuL1](2+) per GNS depending on the conditions, with PEG-SH remaining in the [Cun(L1@GNS)](2n+) hybrids and imparting them with remarkable stability. Comparison of the photothermal and two-photon luminescence (TPL) properties of the GNS between the pegylated GNS and [Cun(L1@GNS)](2n+) revealed that the grafted copper complex does not change them to any extent. Finally, the stability against demetallation and transmetallation of the complexes, as well as the fast kinetics of complexation of the monodispersed macrocycle and of L1@GNS, have been examined, suggesting [Cun(L1@GNS)](2n+) as a device capable of TPL optical tracking and NIR photothermal therapy and as a possible agent for PET imaging.

Thermodynamic Parameters of Complexation Calixpyrrole Derivative with Lanthanides Cations (Lu3, Ho3, Eu3+ and Pr3+) in Nonaquoeus Media

Calix [4] pyrrole derivative was used to target lanthanide cations. Meso tetramethyl-tetrakis-[(4-N, N-diethylacetamide) phenoxymethyl] calix [4] pyrrole, L2 was synthesised. This receptor constituted of hard donor atoms at the lower rim which interact with lanthanide cations being hard cations. 1H NMR investigations showed that both, the pyrrolic N and the acetamide arm group provide sites for interaction with lanthanide metal cations. These findings are verified by conductance measurements in acetonitrile, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:2 complexes between this ligand with lanthanide metal cations. Standard thermodynamics parameters of complexation (log Ks, ΔHᵒc, ΔSᵒc, ΔGᵒc) of L2 with lanthanide cations in acetonitrile were determined using the Nano ITC (isothermal titration calorimetry). The complexation process between these metal cations and the receptor L2 was enthalpically controlled.

The effect of the spacer of bis(biurea) ligands on the structure of A2 L3 -type (A=anion) phosphate complexes.

By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2 L3 complexes (A represents anion, here orthophosphate PO4 (3-) ), namely helicate, mesocate, and mono-bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination-based structures as in transition-metal complexes.

Highly Electron-Rich Pincer-Type Iron Complexes Bearing Innocent Bis(metallylene)pyridine Ligands: Syntheses, Structures, and Catalytic Activity

The first neutral bis(metallylene)pyridine pincer-type [ENE] ligands (E = SiII, GeII) were synthesized, and their coordination chemistry and reactivity toward iron was studied. First, the unprecedented four-coordinate complexes κ2E,E′-[ENE]FeCl2 were isolated. Unexpectedly and in contrast to other related pyridine-based pincer-type Fe(II) complexes, the N atom of pyridine is reluctant to coordinate to the Fe(II) site due to the enhanced σ-donor strength of the E atoms, which disfavors this coordination mode. Subsequent reduction of κ2Si,Si′-[SiNSi]FeCl2 with KC8 in the presence of PMe3 or direct reaction of the [ENE] ligands using Fe(PMe3)4 produced the highly electron-rich iron(0) complexes [ENE]Fe(PMe3)2. The reduction of the iron center substantially changes its coordination features, as shown by the results of a single-crystal X-ray diffraction analysis of [SiNSi]Fe(PMe3)2. The iron center, in the latter, exhibits a pseudosquare pyramidal (PSQP) coordination environment, with a coordinative (pyridine)N→Fe bond, and a trimethylphosphine ligand occupying the apical position. This geometry is very unusual for Fe(0) low-spin complexes, and variable-temperature 1H and 31P NMR spectra of the [ENE]Fe(PMe3)2 complexes revealed that they represent the first examples of configurationally stable PSQP-coordinated Fe(0) complexes: even after heating at 70 °C for >7 days, no changes are observed. The substitution reaction of [ENE]Fe(PMe3)2 with CO resulted in the isolation of [ENE]Fe(CO)2 and the hitherto unknown κ2E,E′-[ENE]Fe(CO)2L (L = CO, PMe3) complexes. All complexes were fully characterized (NMR, MS, XRD, IR, and 57Fe Mössbauer spectroscopy), showing the highest electron density on the iron center for pincer-type complexes reported to date. DFT calculations and 57Fe Mössbauer spectroscopy confirmed the innocent behavior of these ligands. Moreover, preliminary results showed that these complexes can serve as active precatalysts for the hydrosilylation of ketones.

Conceptualizing and measuring short-term changes in L2 writing complexity

This study aims to ascertain the nature and extent of the development of English L2 writing proficiency of 45 adult ESL learners over the time of an intensive short-term academic English language programme by means of quantitative measures targeting different components of the lexical and syntactic complexity of the learners’ writing performance, and to compare the scores on these measures with subjective ratings of learners’ overall writing quality. Results reveal several linguistic complexity measures that can adequately and validly capture changes in L2 writing in short-term ESL courses, though these do not include “popular” measures such as subordination ratios and lexical richness/diversity measures. Results also suggest that different subcomponents of syntactic and lexical complexity in L2 writing develop at a different pace, underlining the importance of calculating a sufficiently wide range of judiciously selected complexity measures in order to get a comprehensive picture of L2 writing development. Interestingly, the set of progress-sensitive complexity measures identified in this study does not coincide with the set of complexity measures that best predict subjective perceptions of writing quality.

Study on Cupric Lactate Complexes in Electrodeposition of -Oriented Copper(I) Oxide

Copper(I) oxide (Cu2O) with cubic cuprite structure is known as an intrinsic p-type semiconductor, and it has 2.1 eV band gap and high optical-absorption coefficient (~104 cm−1). Hence, Cu2O is often used in connection with n-type ZnO to fabricate p-n junction solar cells. The Cu2O-ZnO device consisting of ubiquitous elements has attracted increasing attention because of its low fabrication cost. Additionally, <111>-oriented Cu2O is favorable considering the lattice match with {0001} plane of wurtzite ZnO, giving high permeability of light. Electrodeposition of Cu2O from aqueous solutions containing lactic acid and hydrated copper(II) salt has been reported in previous works[1-3]. It was revealed that Cu2O electrodeposited from pH 9.5 and 10.0 solution oriented <100> and those from pH 10.5, 11.5 and 12.5 solution oriented <111>, and <111>-oriented Cu2O could be electrodeposited even from pH 9.5 and 10.0 solution by lowering the cathode potential (see Fig. 1(b)). However, according to the E-pH diagram (see Fig. 1(a)) based on given thermodynamic data[4], above pH~8, it is expected that Cu2+ ion hydrolyzes and Cu(OH)2 precipitates. However, in our experiment, Cu2O was electrodeposited without any precipitation, implying that the stability regions for cupric lactate complexes are larger. In this study, we performed titration and UV-vis absorption spectroscopy of solutions containing lactic acid and hydrated copper(II) salt. It is discussed what kinds of complexes exist in the solution and the orientation of Cu2O. Aqueous solution containing lactic acid and hydrated copper(II) nitrate was examined by titration with potassium hydroxide aqueous solution. Above pH~4, deviation was observed from the calculated curve using given thermodynamic data[4]; moreover, a theoretical plateau centered at pH~7.2 was not seen. As a result, formation of Cu(OH)2 seems not to be realistic. Figure 2(b) demonstrates UV-vis absorption spectra of aqueous solutions containing lactic acid and hydrated copper(II) acetate at 2.0 < pH < 13.5. As pH increased from 6.0 to 9.0, blue shift was observed between 500 nm and 1000 nm, while red shift was seen between 300 nm and 400 nm. In addition, as pH increased from 9.0 to 10.5, the absorption edge shifted from about 420 nm to 380 nm. These results strongly suggest some kinds of cupric lactate complexes in the region of 6.0 < pH < 13.5. Here, we assumed three complexes (Cu(OH)L2−, Cu(OH)2L−, CuL4 2− ) at 9.5 < pH < 12.5 and three Nernst equations with a corresponding number of protons and electrons (see Table I). Figure 1(b) shows relationship between the orientation of Cu2O[3] and three assumed equations. For many cases, Cu2O electrodeposited from pH 9.5 and 10.0 solution oriented <100> and those from pH > 10.5 solution oriented <111>. Exceptionally, in the case of Eq.3, even at pH 9.5 and 10.0, we obtained <111>-oriented Cu2O when lowering the cathode potential because of increased current density proportional to v (CuOH) = k[Cu][OH] [2,3]. Suppose Eq.3 agrees with the experimental fact, since current density cannot be increased so large when lowering cathode poential considering deposition overpotential of Cu2O, Cu2O obtained from pH 9.5 and 10.0 solution should orient <100>. In consequence, Eq.3 may be inconsistent with the experimental fact and the unidentified cupric lactate complexes should be assumed as Cu(OH)L2− and/or Cu(OH)2L−.[1] K. Mizuno et al., J. Electrochem. Soc., 152, C179 (2005).[2] T. Shinagawa et al., Cryst. Growth Des., 13(1), 52 (2013).[3] Y. Seki et al., 58, The ECS Meet ing s, Vol. 2013-02, CA, USA, Oct 29, 2013.[4] R. M. Smith et al., Critical Stability Constants, Vol. 5, First Supplement, (Plenum Press, NewYork, 1982), p.291.

Photoinduced transformation of iron chelator deferiprone: Possible implications in drug metabolism and toxicity

Abstract Deferiprone (L1) is an effective iron chelating drug which is widely used for the treatment of iron overload diseases. Although L1 itself does not absorb visible light, the absorption spectra of its Fe(III) complexes exhibit intensive absorption bands between 300 and 800 nm. It was found that L1–Fe(III) complex is stable under irradiation with visible light but undergoes fast decomposition under UV irradiation (with quantum yield more than 0.7). Decomposition of L1 has been observed in the presence of Fe(II) in a dark process. Free, non iron bound L1 exhibits both electron accepting and electron donating abilities. Free radicals of L1 were detected by the chemically induced dynamic nuclear polarization (CIDNP) method during irradiation of its aqueous solution in the presence of quinones, amino acids and NADH. It indicates the ability of deferiprone to produce free radicals not only by direct UV irradiation, but also in photosensitized electron transfer reactions with various biomolecules. Phototransformation of L1 was elucidated by using CIDNP, UV–vis, NMR and mass-spectroscopy techniques. The structures of the products of L1 photolysis include 1,2-dihydro-2,3,4-trihydroxy-1,2-dimethylpyridine. It appears that the metabolism of drugs with iron binding properties can be affected by sunlight, as shown by the iron complexes of L1 and such changes may cause phototoxic and pharmacological effects in patients undergoing treatment.

Synthesis of Metallo-supramolecular Polymers with a Bis-ONO-tridentate Ligand by Coordination Programming

Abstract A novel ONO-type bis-tridentate ligand L1 was synthesized by a diazocoupling reaction of 3,3′-dihydroxybenzidine with 6-octyl-2-naphthol in 58% yield. Azo-hydrazo tautomerization in L1 was indicated by the NMR and IR spectra. The 1:1 complexation of L1 and Mn(III) or Co(II) ions was confirmed by titration experiments at room temperature. Mn-, Co-, and Cr-based metallo-supramolecular polymers were prepared via the 1:1 complexation of the ditopic ligand with the metal ions at 100 °C. The Mn- and Cr-based polymers exhibited reversible redox properties.

Chiral (η6-p-Cymene)ruthenium(II) Complexes Containing Monodentate Acylthiourea Ligands for Efficient Asymmetric Transfer Hydrogenation of Ketones

The new chiral ligands (R)-/(S)-N-((1-phenylethyl)carbamothioyl)benzamide (L1/L2), (R)-/(S)-N-((1-phenylethyl)carbamothioyl)thiophene-2-carboxamide (L3/L4), and (R)-/(S)-N-((1-phenylethyl)carbamothioyl)furan-2-carboxamide (L5/L6) were synthesized, characterized, and used to prepare novel chiral Ru(II) complexes. The chiral Ru(II) complexes 1–6 were obtained from reactions between the chiral ligands L1–L6 and [RuCl2(p-cymene)2]2. The complexes were characterized by analytical and spectroscopic (NMR, FT-IR, electronic) techniques. The solid-state structures of the ligands L1 and L3 and complexes 1, 4, and 6 were determined by single-crystal X-ray diffraction methods. In all of the complexes, the ligand is bound to the Ru(II) center only via the sulfur donor atom. This monodentate coordination of the acylthiourea ligands was observed for the first time with ruthenium. The Ru(II) complexes 1–6 all act as efficient catalysts for the asymmetric transfer hydrogenation of aromatic ketones in the presence of 2-propanol and KOH to produce chiral alcohols. All of the catalysts showed excellent conversions of up to 99% and enantiomeric excesses of up to 99%.

(Pyridyl)benzoazole ruthenium(ii) and ruthenium(iii) complexes: role of heteroatom and ancillary phosphine ligand in the transfer hydrogenation of ketones

The synthesis and structural characterization of ruthenium complexes supported by 2-(2-pyridyl)benzoazole ligands and their evaluation as catalysts in the transfer hydrogenation of ketones are reported. Reactions of 2-(2-pyridyl)benzoimidazole (L1), 2-(2-pyridyl)benzothiazole (L2) and 2-(2-pyridyl)benzoxazole (L3) with RuCl3·3H2O produced the corresponding complexes [RuCl3(L1)] (1), [RuCl3(L2)] (2) and [RuCl3(L3)] (3), respectively. Similarly, treatment of L1-L3 with RuCl2(PPh3)2 afforded the corresponding Ru(II) complexes [RuCl2(PPh3)2(L1)] (4), [RuCl2(PPh3)2(L2)] (5) and [RuCl2(PPh3)2(L3)] (6), respectively. Solid state structures of 1 and 2 confirmed the bidentate coordination mode of L1 and L2 to ruthenium. (31)P{(1)H} NMR spectroscopy revealed coordination of two PPh3 ligands trans to each other in an octahedral environment in 4-6 as confirmed by the solid state structure of 6. Complexes 1-6 produced active catalysts in the transfer hydrogenation of ketones in 2-propanol at 82 °C. Ruthenium(II) complexes 4-6, containing the PPh3 ligand, exhibited higher catalytic activities than the corresponding ruthenium(III) compounds 1-3. Complexes 1 and 4 of L1 were more active than the corresponding complexes of L2 and L3. Density functional theoretical calculations showed that dipole moments of 1-6 control their catalytic activities.

Synthesis, structure, photo- and electro-luminescence of an iridium(iii) complex with a novel carbazole functionalized β-diketone ligand

A new iridium complex containing coumarin derivative as a cyclometalated ligand (1L) and a carbazole-functionalized β-diketonate (2L) as the ancillary ligand, namely, Ir(III)bis(3-(pyridin-2-yl)coumarinato-N,C4)(1-(9-butyl-9H-carbazol-3-yl)-4,4,4-trifluoro-butane-1,3-dionato-O,O) (Ir(1L)2(2L)), was synthesized. The crystal structure of Ir(1L)2(2L) was determined via combined wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM), which showed π–π the interactions of Ir(1L)2(2L) molecules stacking along the crystal axes. The doped light-emitting diodes using this novel Ir(1L)2(2L) complex as the phosphorescent dopant were fabricated. At a Ir(1L)2(2L) concentration of 6.0 wt%, a green-yellow emitting OLED was achieved with a maximum external quantum efficiency (EQE) of 6.11% and a maximum luminous efficiency of 22.55 cd A−1 at the current density of 6.06 mA cm−2, and a maximum luminance of 6653 cd m−2 at 10.7 V. Furthermore, two reference complexes Ir(1L)2(acac) and Ir(1L)2(TTA) were also used as emitters to fabricate OLED devices with the same device configuration. The maximum luminous efficiency of Ir(1L)2(acac) doped device was measured to be 20.04 cd A−1 at 2.15 mA cm−2 (10.0 wt%), while the doped device of Ir(1L)2(TTA) had a maximum luminous efficiency of 16.59 cd A−1 at 1.36 mA cm−2. The better performances of Ir(1L)2(2L) doped devices could be largely attributed to an improved hole-transporting property due to the introduction of the carbazole moiety.

Structure and stability of molecular and ionic complexes of AlCl3 with pyrazine and 4,4′-bipyridyl

Structural and thermodynamic characteristics of molecular and ionic complexes of aluminum trichloride with pyrazine (pyz) and 4,4′-bipyridyl (bipy) are calculated at the RI-BP86/def2-SVP level. It is found that for molecular 2AlCl3·3L and 4AlCl3·3L complexes an energy difference between isomers does not exceed 4 kJ/mol, and the rotation barrier of the AlCl3 moiety relative to the N-Al-N bond does not exceed 24 kJ/mol. A comparison of the stability of molecular and ionic complexes of aluminum in the gas phase shows that the maximum energy difference is ∼60 kJ/mol. For L = pyz the molecular complex is more stable whereas for L = bipy it is the ionic one.