Chiral-at-Molybdenum – A Computational Study on N-Substituted cis-MoO2(nacnac)2

Cis-MoO₂(nacnac)₂ (nacnac=β-diketiminate) can be a viable chiral-at-metal catalyst when its two β-diketiminate (nacnac) ligands are N-substituted to prevent Λ⇌Δ racemization. Even simple methyl groups raise the barriers for racemization significantly for the Bailar, Rây-Dutt, Conte-Hippler, and Dhimba-Muller-Lammertsma (DML) twists to a respectable 28.5, 37.8, 30.5, and 25.1 kcal/mol, respectively, at ωB97X-D/6-311+G(2d,p) (LANL2DZ for Mo) including acetonitrile solvation. The lowest energy DML barrier increases to ΔG^o=27.4 kcal/mol with N-substituted t-butyl groups. The nacnac ligands’ electronic and steric components to the racemization barriers are discussed.     

Intermolecular Order of Poly-(2,5-dimethyl-para-phenylene vinylene) and Poly-(para-phenylene vinylene) – A Comparison

Summary.  Poly-(para-phenylene vinylene) (2b, PPV) and poly-(2,5-dimethyl-para-phenylene vinylene) (1b) were prepared via the formation of a double bond by thermal elimination of an octylsulfinyl side group at 200°C under vacuum. X-Ray diffraction experiments revealed a certain degree of long-range order within both polymers. However, considerable differences in the diffraction pattern were observed, the packing of the polymer chains within the bulk structure being responsible for these differences. Within the crystal structure of 2b, neighbouring PPV chains pack in a zig-zag arrangement (herringbone pattern). Analysis of the diffraction pattern of 1b on the basis of the crystal structure of a model compound (2,5,2′,5′-tetramethylstilbene) revealed that the molecular planes of neighbouring polymer chains pack parallel to each other. A model for the crystal structure of 1b is given. The change of packing from a herringbone to a parallel arrangement of the molecular planes is related to the introduction of methyl groups as side chains to PPV. Received December 14, 2000. Accepted (revised) December 20, 2000     

Tectona grandis (teak) – A review on its phytochemical and therapeutic potential

Tectona grandis Linn (Teak), is locally known as Sagwan, belongs to Lamiaceae family. It is one of the most valuable timber in the world, due to its beautiful surface and its resistance to termite and fungal damage. The main active ingredient compounds that are responsible for these action are tectoquinone, lapachol and deoxylapachol. Naphthoquinones, anthraquinones and isoprenoid quinones are abundant metabolites in teak. In addition to these, teak contains several other phytochemicals such as triterpenoids, steroids, lignans, fatty esters and phenolic compounds. Pharmacologically, the plant has been investigated for antioxidant, anti-inflammatory, anti-pyretic, cytotoxic, analgesic, hypoglycemic, wound healing and antiplasmodial activities. The present review highlights the phytochemical and pharmacological aspects of teak.     

Ethylene addition to Ru(CH2)(O)3 – A theoretical study

Quantum chemical calculations using density functional theory (B3LYP) were carried out to elucidate the reaction pathways for ethylene addition to the ruthenium compound RuO₃CH₂. These investigations show that the parent compound is relatively unstable and its rearrangement gives access to very diverse isomers and addition products with comparable relative energies and reaction barriers. The results are compared to our previous study on the analogous osmium system OsO₃CH₂ and we show that reactivity of both compounds towards ethylene is quite similar. In both cases, the [3 + 2]_C,O cycloaddition pathway is preferred kinetically and thermodynamically. The exothermicity (–68.8 kcal/mol) of this reaction is higher for the ruthenium system than for the osmium homologue. While this pathway is unrivaled for the osmium system, the [3 + 2]_O,O cycloaddition pathway is able to compete kinetically for the ruthenium system.     

Stereo-controlled synthesis of erythronolides A and B from 1,6-anhydro-β-D-glucopyranose (levoglucosan). Skeleton assembly in (C9 – C13) + (C7 – C8) + (C1 – C6) sequence

Stereospecific syntheses of erythronolides A and B have been accomplished starting from 1,6-anhydro-β-D-glucopyranose (levoglucosan) in a uniform synthetic sequence.     

Malatoplatinum(II) complexes – carboplatin analogs

A series of new neutral dicarboxylatoplatinum(II) complexes, containing D(+), L(−) or DL-malate dianion and ethylenediamine, 1-ethylimidazole or 1-propylimidazole as amine ligands, have been synthesized and characterized by elemental analysis, t.l.c., conductance, i.r., n.m.r., mass spectra (m/z) and electronic spectra. The new cytotoxic malatoplatinum(II) complexes are very soluble in water and resist hydrolysis. Their reactivity against glutathione is comparable with the reactivity of carboplatin, which suggests that these new complexes may be promising candidates in the search for low toxicity platinum cytostatics. This revised version was published online in June 2006 with corrections to the Cover Date.     

Iodophthalocyaninato(2–)thallium(III) – Synthese und Kristallstruktur

Iodophthalocyaninato(2–)thallium(III) – Synthesis and Crystal Structure Oxidation of dithalliumphthalocyaninate(2–) with excess iodine yields crystalline, blue-green iodophthalocyaninato(2–)thallium(III). It crystallizes in the orthorhombic space group Pnma (no. 62) with lattice parameters: a = 13.778(3) Å, b = 14.649(2) Å, c = 14.907(1) Å, Z = 4. The Tl atom coordinates four N_iso atoms (isoindole N atoms) and one I atom in a tetragonal pyramidal arrangement. The Tl atom is located out of the centre of the (N_iso)₄ plane towards the iodine atom by 0.959(3) Å. The Tl–I distance is 2.674(1) Å, the Tl–N_iso distances range from 2.20(1) to 2.23(1) Å (average 2.22(1) Å). The phthalocyaninate(2–) is severely distorted from planarity (concave distortion).     

Thermal degradation chemistry of poly(ethylene naphthalate) – A study by thermal volatilisation analysis

Although the fundamental degradation chemistry of poly(ethylene naphthalate), PEN, is thought to be similar to that of poly(ethylene terephthalate), PET, there is very little evidence in the literature to support this. This paper presents data on the thermal degradation of PEN, in comparison to PET, with particular reference to evolved gas analysis undertaken by thermal volatilisation analysis (TVA). Our thermal degradation studies highlight strong similarities in the degradation behaviour of PET and PEN, despite some evidence of increased thermal stability of PEN in comparison to PET. Identical primary and secondary thermal degradation mechanisms are proposed for PET and PEN, with radical degradation processes thought to dominate at high temperature.     

Ligand-Induced Donor State Destabilisation – A New Route to Panchromatically Absorbing Cu(I) Complexes

The intense absorption of light to covering a large part of the visible spectrum is highly desirable for solar energy conversion schemes. To this end, we have developed novel anionic bis(4H-imidazolato)Cu(I) complexes (cuprates), which feature intense, panchromatic light absorption properties throughout the visible spectrum and into the NIR region with extinction coefficients up to 28,000 M⁻¹ cm⁻¹. Steady-state absorption, (spectro)electrochemical and theoretical investigations reveal low energy (Vis to NIR) metal-to-ligand charge-transfer absorption bands, which are a consequence of destabilized copper-based donor states. These high-lying copper-based states are induced by the σ-donation of the chelating anionic ligands, which also feature low energy acceptor states. The optical properties are reflected in very low, copper-based oxidation potentials and three ligand-based reduction events. These electronic features reveal a new route to panchromatically absorbing Cu(I) complexes.     

The Indide Er2.30(1)Ni1.84(1)In0.70(1) – A New Superstructure of the U3Si2 Family

Summary. Single crystals of the indide Er_2.30(1)Ni_1.84(1)In_0.70(1) were isolated from an arc-melted sample of the initial composition 5Er:2Ni:1In. Er_2.30Ni_1.84In_0.70 crystallizes with a new superstructure of the Mo₂FeB₂ type: P4/m, a = 738.6(2), c = 361.4(1) pm, wR2 = 0.0393, 487 F² values, 22 variables, BASF = 0.500(3) (meroedric twin matrix 010 100 00 ). The structure may be described as an intergrowth variant of slightly distorted AlB₂ and CsCl related slabs. Formation of the superstructure results in two crystallographically independent sites 1a and 1c that center the CsCl slab. These sites have different size and they are occupied by 90% In + 10% Er (1c) and 51% In + 49% Er (1a), respectively. The crystal chemical consequences are discussed on the basis of a group-subgroup scheme.     

CaNa[Cr(OH)6] – A Layered Hydroxochromate(III) with Ordered Brucite Structure and its Thermal Decomposition

Green single-crystals of the hydroxochromate(III) CaNa[Cr(OH)₆] were grown under highly alkaline hydrothermal conditions at about 200 °C. The starting materials Ca(NO₃)₂ · 6H₂O and Cr(NO₃)₃ · 9H₂O were reacted in a mixture of water and sodium hydroxide with the molar ratio of 2.8:1. CaNa[Cr(OH)₆] crystallizes in the non-centrosymmetric trigonal space group R3 with the lattice parameters a = 583.86(2) pm and c = 1428.73(6) pm [T = 100(1) K]. Characteristically, the crystals are reverse-obverse as well as inversion twins. The crystal structure is a stack of uncharged metal hydroxide layers, which can be regarded as a cation-ordered rhombohedral variant of the Mg(OH)₂ (brucite) structure type. The oxidation state of chromium(III) and its coordination by hydroxide groups was confirmed by UV/Vis and IR spectroscopy, respectively. Temperature-dependent magnetic measurements revealed paramagnetic behavior with an effective moment of 3.82 μ_B per chromium atom. The thermal decomposition of CaNa[Cr(OH)₆] takes place at about 225 °C, where the fast elimination of 1.5 equivalents of water is followed by the oxidation of chromium(III) to chromium(VI). Upon further heating to 1000 °C and 1200 °C, the intermediate decomposition products CaCrO₄ and Na₂CrO₄ transform into the oxochromates(V) Ca₅(CrO₄)₃O_0.5 and Ca₃(CrO₄)₂, respectively.     

Self-diffusion in poly(N -vinyl pyrrolidone) – poly(ethylene glycol) systems

 We have applied the PFG NMR technique to investigate the translational mobility in the PVP-PEG system as a function of composition and temperature at the stages of PVP-PEG complex formation, its swelling, and dissolution in excess of liquid PEG. It has been found that the variations of the spin-echo attenuation with PEG content, water amount, and temperature reflect the different stages. The first two stages are characterized by a distribution of the self-diffusion coefficients of PEG involved in the network. The dissolution shows two diffusion coefficients; the fast one is attributed to PEG molecules, the slow one to the associates of PEG and PVP. The temperature dependencies can be described by an Arrhenius law with an activation energy depending on the composition of the blend. The concentration dependence of the PEG self-diffusion coefficients in the blend occurred to be independent of the molecular weight of PVP. The results are discussed in terms of the Mackie-Meares model. Received: 23 August 2000 Accepted: 19 October 2000     

Impact of 1,8-diiodooctane on the morphology of organic photovoltaic (OPV) devices – A Small Angle Neutron Scattering (SANS) study

The impact of the additive 1,8-diiodooctane on the morphology of bulk-heterojunction solar cells based on the systems P3HT:PC₇₁BM, PTB7:PC₇₁BM and PTB7-Th:PC₇₁BM is studied using a combination of Small Angle Neutron Scattering (SANS) and Atomic Force Microscopy (AFM). The results clearly show that while in the P3HT:PC₇₁BM system, the additive DIO promotes a slight coarsening of the phase domains (type I additive), in the systems PTB7:PC₇₁BM and PTB7-Th:PC₇₁BM, DIO promotes a large decrease in the size of the phase domains (type II additive). SANS is demonstrated as being particularly useful at detecting the minor morphological changes observed in the P3HT:PC₇₁BM system, which can be hardly seen in AFM. This work illustrates how SANS complements AFM and both techniques when used together provide a deeper insight into the nanoscale structure in thin organic photovoltaic (OPV) device films.