Sergey Yu. Ketkov

Near-infrared electroluminescent lanthanide [Pr(III), Nd(III), Ho(III), Er(III), Tm(III), and Yb(III)] N,O-chelated complexes for organic light-emitting devices

New near-IR electroluminescent complexes of Pr3+, Nd3+, Ho3+, Er3+, Tm3+, Yb3+ with N,O-chelated ligands, Ln2(OON)6 (OON = 2-(2-benzoxyazol-2-yl)phenolate) and Ln2(SON)6 (SON = 2-(2-benzothiazol-2-yl)phenolate), were synthesized by the reaction of Ln[N(SiMe3)2]3 and the corresponding N,O-chelating ligand. X-Ray analysis for the Pr and Nd compounds reveals centrosymmetric dimeric structures of the complexes. The solid-state electronic absorption spectra and the electroluminescent spectra show long-wavelength 4f–4f transitions which provide potential use of the compounds as NIR emitting materials in organic light-emitting devices (OLEDs). When constructing OLEDs based on Ln2(OON)6 and Ln2(SON)6, the best results were achieved with the Nd3+ and Yb3+ complexes, where the NIR wall plug efficiency of the ITO/TPD/Ln-complex/BATH/Yb system is 0.82 and 1.22 mW W−1, respectively.

Rydberg transitions inbis(η6-benzene)chromium; a study of isotopic effectsand vibronic structures

Gas-phase electronic absorption spectra of (η 6 -C 6 H 6 ) 2 Cr 1 and (η 6 -C 6 D 6 ) 2 Cr 2 have been measured with 30 cm -1 resolution. Both spectra show 3d(a 1g )→Rnp(e 1u ) (n=4–12) and 3d(a 1g )→Rnp(a 2u ) (n=5–8) series. The first ionization potentials, determined as a convergence limit of the Rnp(e 1u ) series, are 5.459±0.004 and 5.446±0.004 eV for 1 and 2, respectively. The Rydberg np 0 0 0 bands display a ca. 100 cm -1 shift on going from 1 to 2. The decreases in ionization potential and Rydberg frequencies have vibrational nature and indicate lower zero-level vibrational energy for bis(η 6 -benzene)chromium in the ground electronic state in comparison with that of the molecule in the Rydberg np states and the ground-state cation. A complete assignment of the vibronic components of the Rydberg transitions in 1 and 2 has been made on the basis of comparison of the spectra. In addition to vibrational progressions on the totally symmetric metal–ring stretching mode, the R4p(e 1u ) and R5p(e 1u ) transitions show components arising from excitation of CH vibrations. The corresponding absorption features are shifted towards the 0 0 0 bands on going from 1 to 2.

Combined photoelectron-photoabsorption study of (η-cycloheptatrienyl)(η-cyclopentadienyl)tungsten☆

Gas-phase UV photoelectron spectra of the mixed sandwich complexes W(η-C7H7)(η-C5SHS) and W(η-C7H7)(η-C5H4Me) and photoabsorption spectra of W(η-C7H7)(η-C5H5) have been measured. The first ionization band of the photoelectron (PE) spectra, assigned to the 2A1 ion state is very sharp, indicating a non-bonding orbital. The second band assigned to the 2E2 ion state shows a splitting of 0.35 eV, the low ionization energy component being 1.5 times the intensity of the higher component. The splitting is primarily due to spin-orbit coupling, but the unequal intensities indicate that the Ham effect is operative with Jahn-Teller distortion of the C7H7 ring competing to lift the degeneracy of the 2E2 ion state. The gas-phase electronic absorption spectrum shows comparatively sharp Rydberg bands which disappear in the solution spectrum. All Rydberg excitations originate from the non-bonding metal 5d(a1, σ+) orbital. A complete interpretation of the Rydberg structure has been given. In the short-wavelength pattern of the spectrum there are three Rydberg series with quantum defects of 3.26, 3.04 and 2.82 arising from the Rnp(π), Rnp(σ+) and Rnd(π) transitions respectively. The convergence limit of these series lies at 5.53 eV, being in good agreement with the value for first ionization potential of W(η-C7H7)(η-C5H5) determined by PE spectroscopy. Below 37 000 cm−1, the spectrum reveals several peaks which were assigned on the basis of their term values to the R6s(σ+) R6p(π), R6p(σ+), R6d(π) and R7p(π) transitions. The R6p(π) state shows unusual splitting arising from the spin-orbit coupling induced by an admixture of the valence-shell excited states derived from d-d transitions. The vibronic structures of low-lying Rydberg bands has been analysed.

Anhydrous mono- and dinuclear tris(quinolinolate) complexes of scandium: the missing structures of rare earth metal 8-quinolinolates

The first monomeric anhydrous scandium tris(8-quinolinolate) complex 1 with the 2-amino-8-quinolinolate ligands and the Sc(2)Q(6) dinuclear complex 2 with the unsubstituted 8-quinolinolate ligands have been synthesized and characterized by X-ray analysis and DFT calculations. The intramolecular hydrogen bonds appear to be responsible for the unique monomeric structure of complex 1. The DFT-based analysis of the electron density topology reveals the (3,-1) critical points corresponding to the O···H and N···H bonds. The two scandium atoms in compound 2 are inequivalent due to different ligand surroundings. They are coordinated by seven (5O, 2N) and eight (4O, 4N) ligand atoms. The increase in the coordination number is accompanied by a decrease in the positive charge of the metal atom as evidenced by the DFT calculations.

Vibrational frequencies and ionization energy of bis(η6-benzene)chromium as studied by density functional theory

The geometry of the bis(η6-benzene)chromium neutral molecule 1 and cation 1+ have been optimized at various DFT levels with use of LSDA, GGA and hybride functionals. An increase in the Cr–C distances and a decrease in the C–H distances on ionization is observed. The vibrational frequencies of 1, 1+ and their deuterated derivatives as well as the ionization potentials of the neutral molecules have been calculated and compared with the experimental data obtained for the gas-phase species. An excellent agreement with the experiment was achieved at the BPW91/TZVP level of theory for all the molecular parameters investigated including a negative shift of the ionization energy on deuteration.

From Stiba- and Bismaheteroboroxines to N,C,N-Chelated Diorganoantimony(III) and Bismuth(III) Cations—An Unexpected Case of Aryl Group Migration

An unprecedented transfer of an aryl group from boron to Sb and Bi is observed in the reaction of heteroboroxines of general formula ArM[(OBR)2O] [where M = Sb, Bi; Ar = C6H3-2,6-(CH2NMe2)2; R = Ph, 4-CF3C6H4, 4-BrC6H4] with corresponding boronic acid RB(OH)2. Using this procedure, ion pairs [ArMR](+)[R4B5O6](-) were obtained [where M = Sb and R = Ph (4), 4-CF3C6H4 (5), 4-BrC6H4 (6); where M = Bi and R = Ph (7), 4-CF3C6H4 (8), 4-BrC6H4 (9)]. All compounds were characterized using elemental analysis, electrospray ionization mass spectrometry, and multinuclear NMR spectroscopy, and molecular structures of 4 and 7 were determined by single-crystal X-ray diffraction analysis. The central metal atoms in 4-9 were arylated by respective boronic acids, which represents, to the best of our knowledge, unprecedented reaction path in the chemistry of heavier group 15 elements. Investigation of the mechanism of this transformation indicated that Lewis pairs consisting of monomeric oxides ArMO and boroxine rings are probably key intermediates. In this regard, molecular structures of ArSbO[(4-CF3C6H4)3B3O3]·(4-CF3C6H4)B(OH)2 (10) and {ArSbO[(3,5-(CF3)2C6H3)3B3O3]} (13) were established by single-crystal X-ray diffraction analysis, and compound 13 was also fully characterized in solution by multinuclear NMR spectroscopy. The bonding in 13 was analyzed in detail by using density functional theory and natural bond order calculations and compared with known adduct ArSbOB(C6F5)3 (14) and hypothetical ArSbO monomer.

Two-color resonance-enhanced multiphoton ionization study of the lowest Rydberg p state of bis(η6-benzene)chromium and its deuterated derivatives

Two-color resonance-enhanced multiphoton ionization (REMPI) spectra of jet-cooled (eta(6)-C(6)H(6))(2)Cr(1), (eta(6)-C(6)D(6))(2)Cr(2), and (eta(6)-C(6)D(6))(eta(6)-C(6)D(5)H)Cr(3) have been measured with use of the 3d(z)2-->R4p(x,y) Rydberg transition as the first step of the electronic excitation. The 0(0) (0) Rydberg component shifts by 59 and 54 cm(-1) to red when one goes from 1 to 2 and 3, respectively. Surprisingly, the REMPI spectra of 1-3 show very rich vibronic structures revealing both totally symmetric vibrations and degenerate vibrational modes. Presence of intense peaks corresponding to the e(2g) modes in the spectra of 1 and 2 is indicative of Jahn-Teller coupling in the R4p(x,y) Rydberg state. Additional REMPI resonances appear on going from 1 and 2 to 3 as a result of the symmetry reduction. The vibronic components in the spectra of 1-3 were assigned on the basis of the selection rules and comparison with the vibrational frequencies of the 1 and 2 ground-state molecules. The frequencies of over 10 normal vibrations have been determined for the gas-phase 1-3 Rydberg-state molecules from the REMPI experiment. The wavenumber corresponding to the lowest-energy mode (the ring torsion vibration) appears to be 40 cm(-1) in 1 and 35 cm(-1) in the deuterated complexes. The REMPI peaks are homogeneously broadened. The lower lifetime limits for the upper-state components increase on going from the vibrationless level to higher-lying vibronic states and on going from 1 to the deuterated derivatives.

Rydberg structures in the gas-phase electronic absorptionspectra of η-cycloheptatrienyl η-cyclopentadienyl complexes ofmolybdenum

The gas-phase electronic absorption spectra of (Ch)(Cp)Mo and (Ch)(Cp′)Mo (Ch=η 7 -C 7 H 7 , Cp=η 5 -C 5 H 5 , Cp′=η 5 -C 5 H 4 CH 3 ) have been measured for the first time and compared with those recorded in n-heptane solution. The gas-phase spectra reveal rich Rydberg structures which disappear on going to the solution phase. The Rydberg bands correspond to transitions from the non-bonding molybdenum 4d z2 orbital to Rns, Rnp and Rnd levels. On the basis of analysis of Rydberg frequencies, the first ionization potentials of (Ch)(Cp)Mo and (Ch)(Cp′)Mo have been determined as 45890 cm -1 (5.69 eV) and 45300 cm -1 (5.62 eV), respectively. Assignments based on term values and effective quantum numbers of the Rydberg transitions have been made. The R5s, R5p and R5d bands reveal vibronic components assigned to totally symmetric CC stretches, CH umbrella vibrations and metal–ring skeletal modes. Methylation of (Ch)(Cp)Mo results in splitting of the R5p x,y and R5d xz,yz transitions and appearance of the R5d xy and R5d x2 -y2 excitations. These changes are in agreement with a molecular symmetry reduction from C ∞v to C s . The spectrum of (Ch)(Cp′)Mo gives the first example of an interpretable structure of the lowest Rnp and Rnd transitions in a methylated sandwich complex. The differences between the Rydberg structures of the (Ch)(Cp)Mo and (Ch)(Cp′)Mo spectra in the n>5 region are due to changes in Rydberg–valence interactions and relative band intensities on methylation.

Catecholase activity of Mannich-based dinuclear CuII complexes with theoretical modeling: new insight into the solvent role in the catalytic cycle

Four new dinuclear CuII complexes were synthesised from two Mannich-base ligands namely 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL1) and 2-[bis(2-methoxyethyl)aminomethyl]-4-chlorophenol (HL2): [Cu2(L1)(OH)](ClO4)2·CH3OH (1), [Cu2(L2)2](ClO4)2·H2O (2), [Cu2(L2)2(NO3)2] (3) and [Cu2(L2)2(OAc)2]·H2O (4) and well characterised. X-ray diffraction analysis of the complexes reveals a Cu⋯Cu distance of 2.9183(13), 2.9604(6), 3.0278(4) and 3.0569(11) A, respectively. In 1 the metal coordination geometry is intermediate between trigonal bipyramidal (TBP) and square pyramidal (SP) (τ = 0.488), in 2 the geometry is TBP (0.828 and 0.639) and in 3 and 4 is SP (τ = 0.188 and 0.083, respectively). Spectrophotometric investigations to evaluate the catecholase activity of complexes against 3,5-di-tert-butylcatechol (3,5-DTBC) and tetrachlorocatechol (TCC) in three different solvents (acetonitrile, methanol and DMSO) under completely aerobic conditions reveal that complexes 1–4 are able to oxidise 3,5-DTBC in all the solvents, while TCC can be oxidised only in acetonitrile (kcat = 0.0002–0.02 s−1). Intensive DFT calculations prove an ionic pathway for 1–3 while a unique neutral catalytic cycle for 4.

Rydberg spectra of bis(η6-benzene)chromium derivatives Gas-phase photoabsorption study of bis(η6-1,2,4-trimethylbenzene)chromium and bis(η6-1,2,4,5-tetramethylbenzene)chromium

The gas-phase electronic absorption spectra of (η 6 -1,2,4-C 6 H 3 Me 3 ) 2 Cr ( 1 ) and (η 6 -1,2,4,5-C 6 H 2 Me 4 ) 2 Cr ( 2 ) have been measured for the first time and compared with those recorded in n -pentane solution. The gas-phase spectra of both compounds show transitions from the non-bonding chromium 3d z 2 orbital to molecular Rydberg s, p and d levels. The first ionisation potentials have been determined from the Rydberg frequencies as 4.994±0.009 and 4.862±0.009 eV for 1 and 2 , respectively. Detailed assignments of Rydberg bands have been made on the basis of analysis of the quantum defects and term values. The Rydberg structures agree with the C 1 , C s or C 2 conformation for 1 and the D 2 d geometry for 2 in the gas phase. In crystal, however, the molecule of 2 appears to adopt an eclipsed conformation close to D 2 h as indicated by the X-ray diffraction. The influence of ring methylation on the Rydberg term values has been analysed for the first time.