Halogen bonding in solution

Review: 89 refs.

The title compound, a new fluorinated stilbazole-based chromophore combines hydrocarbon (HC) donor and perfluorocarbon (PFC) acceptor sites in one rigid-rod-type conjugated molecule. The bifunctional stilbazole derivative combines several possibilities of weak, medium, and strong intermolecular interactions leading to an attractive crystal packing. The chromophore shows strong π−π stacking behavior in solution, while its crystal structure consists of an infinite unimolecular network involving both interchain π−π stacking and N···Br halogen bonding. The latter Lewis acid−base interactions do not play a dominant role in controlling the solution optical properties. In the solid state, the molecules are aligned in one-dimensional infinite head-to-tail chains as a result of attractive halogen bonding. Adjacent chains are oriented in opposite directions.

The study of effects of ionizing radiation (IR) on plants is important in relation to several problems: (I) the existence of zones where background radiation – either natural or technogenic – is increased; (II) the problems of space biology; (III) the use of IR in agricultural selection; (IV) general biological problems related to the fundamental patterns and specifics of the effects of IR on various living organisms. By now, researchers have accumulated and systematized a large body of data on the effects of IR on the growth and reproduction of plants, as well as on the changes induced by IR at the genetic level. At the same time, there is a large gap in understanding the mechanisms of IR influence on the biochemical and physiological processes – despite the fact that these processes form the basis determining the manifestation of IR effects at the level of the whole organism. On the one hand, the activity of physiological processes determines the growth of plants; on the other, it is determined by changes at the genetic level. Thus, it is the study of IR effects at the physiological and biochemical levels that can give the most detailed and complex picture of IR action in plants.The review focuses on the effects of radiation on the essential physiological processes, including photosynthesis, respiration, long-distance transport, the functioning of the hormonal system, and various biosynthetic processes. On the basis of a large body of experimental data, we analyze dose and time dependences of the IR-induced effects – which are qualitatively similar – on various physiological and biochemical processes. We also consider the sequence of stages in the development of those effects and discuss their mechanisms, as well as the cause-effect relationships between them. The primary IR-induced physicochemical reactions include the formation of various forms of reactive oxygen species (ROS) and are the cause of the observed changes in the functional activity of plants. The review emphasizes the role of hydrogen peroxide, a long-lived ROS, not only as a damaging agent, but also as a mediator – a universal intracellular messenger, which provides for the mechanism of long-distance signaling. A supposition is made that IR affects physiological processes mainly by violating the regulation of their activity. The violation seems to become possible due to the fact that there exists a crosstalk between different signaling systems of plants, such as ROS, calcium, hormonal and electrical systems. As a result of both acute and chronic irradiation, an increase in the level of ROS can influence the activity of a wide range of physiological processes – by regulating them both at the genetic and physiological levels. To understand the ways, by which IR affects plant growth and development, one needs detailed knowledge about the mechanisms of the processes that occur at the (i) genetic and (ii) physiological levels, as well as their interplay and (iii) knowledge about regulation of these processes at different levels.

A systematic investigation of the coordination behavior of Pn complexes towards the main group Lewis acids Tl+ and In+ is presented. While the reaction of the tetrahedral P2 complex [{CpMo(CO)2}2(μ,η2:η2-P2)] (A1) with Tl[TEF] ([TEF] = [Al{OC(CF3)3}4]-) leads to the formation of the dicationic complex [Tl2(A1)6]2+ (1) with a central six-membered Tl2P4 ring, the analogous reaction with In[TEF] leads instead to a tetranuclear [In4(A1)8]4+ complex (3) exhibiting a weak InI-InI interaction in the solid state. When the Cp*-analogous P2 complex [{Cp*Mo(CO)2}2(μ,η2:η2-P2)] (A2) is reacted with Tl[TEF] the dinuclear complex [Tl2(A2)4]2+ (2) is formed, containing only four P2 ligands but also featuring a six-membered Tl2P4 ring motif. From the reactions of the cyclo-P3 complexes [CpM'(CO)2(η3-P3)] (M' = Cr (B1), Mo (B2)) with In[TEF] and Tl[TEF], a series of four isostructural one-dimensional coordination polymers (4a-d) are obtained which exhibit a novel bridging coordination mode of the cyclo-P3 ligands in the solid state. Additionally, the mixed PmSn ligand complex [(Cp*Mo)2(μ,η3:η3-P3)(μ,η2:η2-PS)] (C) was reacted with Tl[TEF] to afford a novel one-dimensional coordination polymer (5), which shows an unprecedented bridging s-1,3-coordination mode of ligand C towards Tl+. The compounds were analyzed by single-crystal X-ray structure determination, elemental analysis, and mass spectrometry, as well as by multinuclear NMR and IR spectroscopy. All products are readily soluble in CH2Cl2, despite in many cases being polymeric in the solid state. Multinuclear NMR spectroscopy suggests a highly dynamic coordination behavior in solution, including fast equilibria between different monomeric species, which is also supported by DFT calculations. The one-dimensional polymers 4c and 4d reveal a triplet in the 31P{1H} MAS NMR spectrum at room temperature, which could be explained by fast rotation of the P3 rings in the solid state.

Studies of N-heterocyclic olefins as donors in triarylboranes and electron-poor phenylpyridyl-fused boroles

Frustrated Lewis pair (FLP) chemistry, a concept that has emerged in the last decade, presents unique systems capable of metal-free hydrogenation by using simple combinations of cooperative main group element components. This finding is particularly interesting given that hydrogenation is a chemical reaction that is performed on a huge scale worldwide with current technologies relying on metal-based catalysts. Over the last 10 years, the range of FLP catalysts has been probed and expanded. At the same time, the concept has also been exploited to employ simple combinations of main group reagents to activate a range of other small molecules. In some cases, these …

Mixed imido/oxo rhenium(VII) complexes, formal derivatives of methyltrioxorhenium(VII) (1) with (2,6-diisopropylphenyl)imido ligands of general formula CH3ReO3-x(NR)x (x = 1, and 2; compounds 2 and 3, respectively), have been synthesized. Their structures and behavior in solution have been studied by dynamic 1H and 17O NMR spectroscopy. In the solid state, compounds 2 and 3 display dimeric structures, as shown by X-ray crystallography. In solution, monomeric and dimeric forms exist in equilibria. At elevated temperatures, the monomers are dominant. In the solid state, the dimeric compounds are bridged by oxygen ligands, forming Re2O2 units, while in solution, nitrogen bridging is also evident. Formal replacement of all three oxo groups in 1 by (2,6-diisopropylphenyl)imido ligands leads to a compound of formula CH3Re(NR)3 (4). Complex 4 is monomeric both in solution, regardless of the temperature, and in the solid state. Ligand exchange processes take place via dimeric intermediates if organorhenium oxides...

An axially chiral dihydroborepine with a binaphthyl backbone and a C(6)F(5) substituent at the boron atom was prepared by transmetalation from the corresponding tin precursor. This novel motif was structurally characterized by X-ray diffraction analysis as its THF and its PhCN Lewis acid/base complex. (1)H NMR measurements at variable temperatures of the former adduct revealed a remarkable dynamic behavior in solution. Several more Lewis pairs with oxygen, nitrogen, carbon, and phosphorus σ-donors were synthesized and analyzed by multinuclear NMR spectroscopy. The determination of the borane's Lewis acidity with the Gutmann-Beckett method attests its substantial Lewis acidity [85% with Et(3) PO as well as 74% with Ph(3) PO relative to the parent B(C(6)F(5))(3)]. Representative examples of Si-H bond activation (carbonyl reduction and dehydrogenative Si-O coupling) are included, demonstrating the chemical stability and the synthetic potential of the new chiral boron-based Lewis acid.

The impact of the molecular structure on aggregation and solid state luminescence of 2,3-diarylfumaronitriles

Organic chemistry: an acid-base approach

Density Functional Theory Investigations of Zeolite and Intermetallic Alloy Active Site Structures for Kinetics of Heterogeneous Catalysis

Reaction of complex [Cp2Mo2(CO)4(micro,eta 2-P2)] (Cp=C5H5 (1)) with CuPF6, AgX (X=BF4, ClO4, PF6, SbF6, Al{OC(CF3)3}4) and [(Ph3P)Au(THF)][PF6] (THF=tetrahydrofuran), respectively, results in the facile formation of the dimers 3 b-h of the general formula [M2({Cp2Mo2 (CO)4(micro,eta 2:eta 2-P2)}2)({Cp2Mo2(CO)4 (micro,eta 2:eta 1:eta 1-P2)}2)][X]2 (M=Cu, Ag, Au; X=BF4, ClO4, PF6, SbF6, Al{OC(CF3)3}4). As revealed by X-ray crystallography, all these dimers comprise dicationic moieties that are well-separated from the weakly coordinating anions in the solid state. If 1 is allowed to react with AgNO2 and LAuCl (L=CO or tetrahydrothiophene), respectively, the dimer [Ag2{Cp2Mo2 (CO)4(micro,eta 2:eta 1:eta 1-P2)}2(eta 2-NO2)2] (5) and the complex [AuCl{Cp2Mo2(CO)4(micro,eta 2:eta 1-P2)}] (6) are formed, which have also been characterised by X-ray crystallography. In compounds 5 and 6, the anions remain coordinated to the Group 11 metal centres. Spectroscopic data suggest that the dimers 3 b-h display dynamic behaviour in solution and this is discussed by using the comprehensive results obtained for 3 g (M=Ag; X=Al{OC(CF3)3}4) as a basis. The interpretation of the experimental results is facilitated by density functional theory (DFT) calculations on 3 g (structures, energetics, NMR shielding tensors). The 31P magic angle spinning (MAS) NMR spectra recorded for the dimers 3 b (M=Cu; X=PF6) and 3c (M=Ag; X=BF4) as well as that of the previously reported one-dimensional (1 D) polymer [Ag2{Cp2Mo2(CO)4(micro,eta 2:eta 1:eta 1-P2)}3(micro,eta 1:eta 1-NO3)]n[NO3]n (4) are also discussed herein and the strong dependence of the chemical shift of the phosphorus atoms within each compound on subtle structural differences in the solid state is demonstrated. Furthermore, the X-ray crystallographic and 31P MAS NMR spectroscopic characterisation of a new polymorph of 1 is reported.

Syntheses, solid structures, and behavior in solution of [MI2(CO)3(pyrazole)2] complexes (M = Mo, W)

Synthesis, photophysical behavior in solution, aggregates, solid state and computational study of new derivatives of 2,2′-bis(indolyl)methane-triphenylamine

A pillar[6]arene-based [2]pseudorotaxane was constructed in solution and studied in the solid state, and its photo-responsive self-assembly behavior in solution was investigated.