C6 H5 Research Articles

Photogeneration of Microporous Amorphous Coordination Polymers from Organometallic Ionic Liquids.

Ruthenium-containing organometallic ionic liquids with the B(CN)4 anion were developed that generate microporous amorphous coordination polymers upon UV irradiation. UV light irradiation of [Ru(C5 H5 )(C6 H5 R)][B(CN)4 ] (R=butyl, ethyl, octyl) quantitatively generated a yellow powder of a coordination polymer with the formula [Ru(C5 H5 ){B(CN)4 }]n . In this reaction, the arene ligand is eliminated by UV irradiation and coordination polymer is formed by coordination of the cyano groups of the anion to the Ru ion. The photogenerated solids exhibited nitrogen absorption properties due to their microporous structure. This paper proposes a method to fabricate functional coordination polymers by photoirradiation of liquids.

Strongly Coupled Tin-Halide Perovskites to Modulate Light Emission: Tunable 550-640 nm Light Emission (FWHM 36-80 nm) with a Quantum Yield of up to 6.4.

Colloidal perovskite quantum dots represent one of the most promising materials for applications in solar cells and photoluminescences. These devices require a low density of crystal defects and a high yield of photogenerated carriers, which are difficult to realize in tin-halide perovskite because of the intrinsic instability of tin during nucleation. Here, an enhancement in the luminescent property of tin-halide perovskite nanoplates (TPNPs) that are composed of strongly coupled layered structures with the chemical formula of PEA2 SnX4 (PEA = C6 H5 (CH2 )2 NH3 , X = Br, I) is reported. TPNPs (X = I) show an emission at a wavelength of 640 nm, with high quantum yield of 6.40 ± 0.14% and full width at half maximum (FWHM) as small as 36 nm. The presence of aliphatic carboxylic acid is found to play a key role in reducing the tin perovskite defect density, which significantly improves the emission intensity and stability of TPNPs. Upon mixing iodo- and bromo- precursors, the emission wavelength is successfully tuned from 640 nm (PEA2 SnI4 ) to 550 nm (PEA2 SnBr4 ), with a corresponding emission quantum yield and FWHM of 0.16-6.40% and 36-80 nm, respectively. The results demonstrate a major advance for the emission yield and tunability of tin-halide perovskites.

Excitonic Properties of Chemically Synthesized 2D Organic-Inorganic Hybrid Perovskite Nanosheets.

2D organic-inorganic hybrid perovskites (OIHPs) represent a unique class of materials with a natural quantum-well structure and quasi-2D electronic properties. Here, a versatile direct solution-based synthesis of mono- and few-layer OIHP nanosheets and a systematic study of their electronic structure as a function of the number of monolayers by photoluminescence and absorption spectroscopy are reported. The monolayers of various OIHPs are found to exhibit high electronic quality as evidenced by high quantum yield and negligible Stokes shift. It is shown that the ground exciton peak blueshifts by ≈40 meV when the layer thickness reduces from bulk to monolayer. It is also shown that the exciton binding energy remains effectively unchanged for (C6 H5 (CH2 )2 NH3 )2 PbI4 with the number of layers. Similar trends are observed for (C4 H9 NH3 )2 PbI4 in contrast to the previous report. Further, the photoluminescence lifetime is found to decrease with the number of monolayers, indicating the dominant role of surface trap states in nonradiative recombination of the electron-hole pairs.

Bonding Insights from Structural and Spectroscopic Comparisons of {SnW5 } and {TiW5 } Alkoxido- and Aryloxido-Substituted Lindqvist Polyoxometalates.

Incorporation of {MX}n+ groups into polyoxometalates (POMs) provides the means not only to introduce reactivity and functionality but also to tune the electronic properties of the oxide framework by varying M, X and n. In order to elucidate the factors responsible for differences in reactivity between {TiW5 } and {SnW5 } Lindqvist-type hexametalates, a series of alkoxido- and aryloxido-tin substituted POMs (nBu4 N)3 [(RO)SnW5 O18 ] (R=Me, Et, iPr and tBu) and (nBu4 N)3 [(ArO)SnW5 O18 ] (Ar=C6 H5 , 4-MeC6 H5 , 4-tBuC6 H5 , 4-HOC6 H4 , 3-HOC6 H4 and 2-CHOC6 H4 ) has been structurally characterised and studied by multinuclear NMR (1 H, 13 C, 17 O, 119 Sn and 183 W) and FTIR spectroscopy. Spectroscopic and structural parameters were compared with those of titanium-substituted homologues and, when coupled with theoretical studies, indicated that Sn-OR and Sn-OAr bonds are ionic with little π-contribution, whereas Ti-OR and Ti-OAr bonds are more covalent with π-bonding that is more prevalent for Ti-OR than Ti-OAr. This experimental and theoretical analysis of bonding in a homologous series of reactive POMs is the most extensive and detailed to date, and reveals factors which account for significant differences in reactivity between tin and titanium congeners.

Intramolecular π-π Interactions in Flexibly Linked Partially Fluorinated Bisarenes in the Gas Phase.

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2 )3 and (CH2 )2 SiMe2 units were synthesized by hydrosilylation and C-C coupling reactions. Their solid-state structures are dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π-π interactions. For the silicon compounds, structures characterized by σ-π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6 H5 (CH2 )3 C6 F5 , in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations.

On the Electronic Origin of Remarkable Ligand Effects on the Reactivities of [NiL]+ Complexes (L=C6 H5 , C5 H4 N, CN) towards Methane.

The gas-phase reactions of [NiL]+ (L=C6 H5 , C5 H4 N, CN) with methane have been explored by using electrospray-ionization mass spectrometry (ESI-MS) complemented by quantum chemical calculations. Though the phenyl Ni complex [Ni(C6 H5 )]+ exclusively abstracts one hydrogen atom from methane at ambient conditions, the cyano Ni complex [Ni(CN)]+ brings about both H-atom abstraction and ligand exchange to generate [Ni(CH3 )]+ . In contrast, the complex 2-pyridinyl Ni [Ni(C5 H4 N)]+ is inert towards this substrate. The presence of the empty 4s(Ni) orbital dominates the proton-coupled electron transfer (PCET) processes for the investigated systems.

Synthesis, spectroscopic characterization, X-ray diffraction studies and in-vitro antibacterial activities of diorganotin(IV) derivatives with N-methyl-4-bromobenzohydroxamic acid

Three new diorganotin(IV) complexes (CH3)2Sn(mbbha)2 (2), (C4H9)2Sn(mbbha)2 (3), (C6 H5)2Sn(mbbha)2 (4), of N-methyl-4-bromobenzohydroxamic acid (Hmbbha) (1) have been synthesized by 2:1 condensation ratio of the parent hydroxamic acid with (CH3)2SnO, (C 4H9)2SnO and (C6H5)2SnO in toluene. Ligand has been synthesized by the reaction of 4-bromobenzoyl chloride and N-methylhydroxylamine hydrochloride. Elemental analysis, IR, multinuclear 1H, 13C, 119Sn NMR spectroscopic techniques have been utilized to investigate the bonding and coordination modes of the ligand and its derivatives. It is found on the basis of spectroscopic and structural investigations that hydroxamate ligand acts as a bidentate chelator and coordinated to tin via carbonyl oxygen and deprotonated hydroxy group. The structures of complexes (3) and (4) have been deduced by X-ray crystallography which reveals octahedral geometry around tin in (C4H9)2Sn(mbbha)2 (3) and (C6 H5)2Sn(mbbha)2 (4) derivatives. The in-vitro antibacterial activities of ligand and its derivatives have been evaluated against one Gram positive and three Gram negative bacterial strains. The derivative (2) has displayed remarkable potency against both Gram positive and Gram negative strains. Anti-pathogenic results have been verified statistically.

Control of Reversible Activation Dynamics of [Ru{η6 :κ1 -C6 H5 (C6 H4 )NH2 }(XY)]n+ and the Effect of Chelating-Ligand Variation.

The potential use of organoruthenium complexes as anticancer drugs is well known. Herein, a family of activatable tethered ruthenium(II) arene complexes of general formula [Ru{η6 :κ1 -C6 H5 (C6 H4 )NH2 }(XY)]n+ (closed tether ring) bearing different chelating XY ligands (XY=aliphatic diamine, phenylenediamine, oxalato, bis(phosphino)ethane) is reported. The activation of these complexes (closed- to open-tether conversion) occurs in methanol and DMSO at different rates and to different reaction extents at equilibrium. Most importantly, RuII -complex activation (cleavage of the Ru-Ntether bond) occurs in aqueous solution at high proton concentration (upon Ntether protonation). The activation dynamics can be modulated by rational variation of the XY chelating ligand. The electron-donating capability and steric hindrance of XY have a direct impact on the reactivity of the Ru-N bond, and XY=N,N'-dimethyl-, N,N'-diethyl-, and N,N,N',N'-tetramethylethylenediamine afford complexes that are more prone to activation. Such activation in acidic media is fully reversible, and proton concentration also governs the deactivation rate, that is, tether-ring closure slows down with decreasing pH. Interaction of a closed-tether complex and its open-tether counterpart with 5'-guanosine monophosphate revealed selectivity of the active (open) complex towards interaction with nucleobases. This work presents ruthenium tether complexes as exceptional pH-dependent switches with potential applications in cancer research.

Arylthio- and Arylseleno-Substituted s-Heptazines.

In contrast to numerous thio- and selenocyanuric acid derivatives, sulfur- or selenium-containing s-heptazines have not been reported so far. Thio- and selenocyameluric acid esters were obtained by substitution reactions of s-heptazine chloride C6 N7 Cl3 with aromatic thiols and selenophenol; the resultant white or yellow solids were stable in air. They were comprehensively characterized by elemental analysis, 1 H, 13 C NMR, and IR spectroscopy. The thiocyameluric acid phenyl ester (1, C6 N7 (S(C6 H5 ))3 ) and the corresponding selenium compound (7) formed co-crystals with mesitylene, which were analyzed by single-crystal X-ray diffraction. Both structures showed unusually large channels of ≈12 Å diameter. The thermal stability was measured by TGA (thermogravimetric analysis), and the flame retardancy of compound 1 was tested in PP by carrying out limiting oxygen index (LOI) measurements, which gave promising results. Quantum chemical calculations of the title compounds were performed to explain the observed properties and structural characteristics.

Crystalline Diuranium Phosphinidiide and μ-Phosphido Complexes with Symmetric and Asymmetric UPU Cores.

Reaction of [U(TrenTIPS)(PH2)] (1, TrenTIPS=N(CH2CH2NSiPri 3)3) with C6H5CH2K and [U(TrenTIPS)(THF)][BPh4] (2) afforded a rare diuranium parent phosphinidiide complex [{U(TrenTIPS)}2(μ‐PH)] (3). Treatment of 3 with C6H5CH2K and two equivalents of benzo‐15‐crown‐5 ether (B15C5) gave the diuranium μ‐phosphido complex [{U(TrenTIPS)}2(μ‐P)][K(B15C5)2] (4). Alternatively, reaction of [U(TrenTIPS)(PH)][Na(12C4)2] (5, 12C4=12‐crown‐4 ether) with [U{N(CH2CH2NSiMe2But)2CH2CH2NSi(Me)(CH2)(But)}] (6) produced the diuranium μ‐phosphido complex [{U(TrenTIPS)}(μ‐P){U(TrenDMBS)}][Na(12C4)2] [7, TrenDMBS=N(CH2CH2NSiMe2But)3]. Compounds 4 and 7 are unprecedented examples of uranium phosphido complexes outside of matrix isolation studies, and they rapidly decompose in solution underscoring the paucity of uranium phosphido complexes. Interestingly, 4 and 7 feature symmetric and asymmetric UPU cores, respectively, reflecting their differing steric profiles.

Coupling of Magnetic and Elastic Domains in the Organic-Inorganic Layered Perovskite-Like (C6 H5 C2 H4 NH3 )2 FeII Cl4 Crystal.

Multiferroic materials coupling ferroelasticity and ferromagnetism show strong magnetoelastic effects as magnetization is induced by mechanical stress or alternately strain induced by applying a magnetic field. These effects were reported for inorganic multiferroics such as LaCox Sr1-x O3 . (C6 H5 C2 H4 NH3 )2 FeII Cl4 is the first example of an organic-inorganic perovskite to exhibit such effects below the canted antiferromagnetism at TC =98 K and ferroelasticity at TC =433 K. This is shown by switching the magnetic hysteresis on and off by uniaxial pressure through the strong coupling of the magnetic and elastic domains. The spin-canting direction was controlled by mechanical stress in the heating and cooling cycles. This unique observation gives additional impetus in the search for coupled hysteretic effect in organic-inorganic multiferroics.

Iridium-Catalyzed Reductive Strecker Reaction for Late-Stage Amide and Lactam Cyanation.

A new iridium-catalyzed reductive Strecker reaction for the direct and efficient formation of α-amino nitrile products from a broad range of (hetero)aromatic and aliphatic tertiary amides, and N-alkyl lactams is reported. The protocol exploits the mild and highly chemoselective reduction of the amide and lactam functionalities using IrCl(CO)[P(C6 H5 )3 ]2 (Vaska's complex) in the presence of tetramethyldisiloxane, as a reductant, to directly generate hemiaminal species able to undergo substitution by cyanide upon treatment with TMSCN (TMS=trimethylsilyl). The protocol is simple to perform, broad in scope, efficient (up to 99 % yield), and has been successfully applied to the late-stage functionalization of amide- and lactam-containing drugs, and naturally occurring alkaloids, as well as for the selective cyanation of the carbonyl carbon atom linked to the N atom of proline residues within di- and tripeptides.

On the Reactivity of Silylated Ge9 Clusters: Synthesis and Characterization of [ZnCp*(Ge9 {Si(SiMe3 )3 }3 )], [CuPiPr3 (Ge9 {Si(SiMe3 )3 }3 )], and [(CuPiPr3 )4 {Ge9 (SiPh3 )2 }2

We report on the synthesis of new derivatives of silylated clusters of the type [Ge9 (SiR3 )3 ]- (R = SiMe3 , Me = CH3 ; R = Ph, Ph = C6 H5 ) as well as on their reactivity towards copper and zinc compounds. The silylated cluster compounds were synthesized by heterogeneous reactions starting from the Zintl phase K4 Ge9 . Reaction of K[Ge9 {Si(SiMe3 )3 }3 ] with ZnCl2 leads to the already known dimeric compound [Zn(Ge9 {Si(SiMe3 )3 }3 )2 ] (1), whereas upon the reaction with [ZnCp*2 ] the coordination of [ZnCp*]+ to the cluster takes place (Cp*=1,2,3,4,5-pentamethylcyclopentadienyl) under the formation of [ZnCp*(Ge9 {Si(SiMe3 )3 }3 )] (2). A similar reaction leads to [CuPiPr3 (Ge9 {Si(SiMe3 )3 }3 )] (3) from [CuPiPr3 Cl] (iPr=isopropyl). Further we investigated the novel silylated cluster units [Ge9 (SiPh3 )3 ]- (4) and [Ge9 (SiPh3 )2 ]- (5), which could be identified by mass spectroscopy. Bis- and tris-silylated species can be synthesized by the respective stoichiometric reactions, and the products were characterized by ESI-MS and NMR experiments. These clusters show rather different reactivity. The reaction of the tris-silylated anion 4 with [CuPiPr3 Cl] leads to [(CuPiPr3 )3 Ge9 (SiPh3 )2 ]+ as shown from NMR experiments and to [(CuPiPr3 )4 {Ge9 (SiPh3 )2 }2 ] (6), which was characterized by single-crystal X-ray diffraction. Compound 6 shows a new type of coordination of the Cu atoms to the silylated Zintl clusters.

A Zirconium Macrocyclic Metal-Organic Framework with Predesigned Shape-Persistent Apertures.

A microporous metal-organic framework (MOF) was synthesized from [Zr6 O4 (OH)4 (C6 H5 COO)12 ] clusters and a triacid ligand based on a shape-persistent arylene ethynylene macrocycle. This framework, dubbed Zr-MCMOF, is held together by metal-ligand coordination and multiple weak interactions: hydrogen bonding, [π⋅⋅⋅π] stacking, and [C-H⋅⋅⋅π] interactions. The rigid ligand has a 9 Å-wide central void, which serves as a predesigned aperture for the 1D channels; all of the porosity of Zr-MCMOF comes from the ligand. The resulting framework possesses high hydrolytic and thermal stability and a flexible structure unique among Zr-based MOFs.

Tetraarylethylenes from Diarylmethanones and Hexachlorodisilane: The "Sila-McMurry" Reaction.

Hexachlorodisilane reacts with diarylmethanones (aryl=C6 H5 , 4-MeC6 H4 , 4-tBuC6 H4 , 4-ClC6 H4 , 4-BrC6 H4 ) to furnish the corresponding tetraarylethylenes in good yields. The reductive conversion requires temperatures of about 160 °C and reaction times of 60-72 h. In the initial step, the Lewis-basic carbonyl groups likely generate low-valent [SiCl2 ] as an analogue of [TiCl2 ] in the classical McMurry reaction. The coupling sequence further proceeds via benzopinacolones, which have been isolated as key intermediates.

Decelerating and Trapping Large Polar Molecules

Manipulating the motion of large polyatomic molecules, such as benzonitrile (C6 H5 CN), presents significant difficulties compared to the manipulation of diatomic molecules. Although recent impressive results have demonstrated manipulation, trapping, and cooling of molecules as large as CH3 F, no general technique for trapping such molecules has been demonstrated, and cold neutral molecules larger than 5 atoms have not been trapped (M. Zeppenfeld, B. G. U. Englert, R. Glöckner, A. Prehn, M. Mielenz, C. Sommer, L. D. van Buuren, M. Motsch, G. Rempe, Nature 2012, 491, 570-573). In particular, extending Stark deceleration and electrostatic trapping to such species remains challenging. Here, we propose to combine a novel "asymmetric doublet state" Stark decelerator with recently demonstrated slow, cold, buffer-gas-cooled beams of closed-shell volatile molecules to realize a general system for decelerating and trapping samples of a broad range of volatile neutral polar prolate asymmetric top molecules. The technique is applicable to most stable volatile molecules in the 100-500 AMU range, and would be capable of producing trapped samples in a single rotational state and at a motional temperature of hundreds of mK. Such samples would immediately allow for spectroscopy of unprecedented resolution, and extensions would allow for further cooling and direct observation of slow intramolecular processes such as vibrational relaxation and Hertz-level tunneling dynamics.

Investigation on fragmentation pathways of bisphenols by using electrospray ionization Orbitrap mass spectrometry.

Bisphenols, such as bisphenol A (BPA) and bisphenol S (BPS), are widely used in industrial products, although they have been demonstrated to be environmental contaminants with toxicity. However, few studies on the mass spectrometric fragmentation pathway of these compounds have been reported using high-resolution mass spectrometry (HRMS). The MS/MS fragmentations of nine bisphenols, together with several corresponding isotope-labeled compounds, were studied by Orbitrap MS using electrospray ionization (ESI) in negative ion mode and higher energy collisional-dissociation (HCD). The [M-H](-) ions of the compounds formed by ESI were selected as the precursor ions for MS/MS. The accurate m/z values for product ions were acquired to deduce the elemental compositions and fragmentation pathways. The elemental compositions of the ions were calculated from the accurate mass data. Common MS/MS product ions and characteristic neutral losses were summarized. Six bisphenols formed the common product ion at m/z 93 (C6 H5 O). The [M-H](-) ions of five bisphenols were found to lose a phenol group (C6 H5 OH). Four bisphenols formed the [M-H-CH4 ](-) ion. The proposed fragmentation pathways of representative compounds of BPA and BPS were verified from the analysis of isotope-labeled compounds. The MS/MS fragmentation pathways of nine bisphenols were, for the first time, systematically investigated with HRMS. The obtained data could be valuable for the identification of a variety of bisphenols in environmental and biological samples.

Siloxymethylamines as Aminomethylation Reagents for Amines Leading to Labile Diaminomethanes That can be Trapped as Their [Mo(CO)4 ] Complexes.

Compound Et3 SiOCH2 NMe2 transfers Me2 NCH2 to R2 NH (R2 =Et2 , PhMe, [Cr(η(6) -C6 H5 )(CO)3 ]Me, PhH) to form previously unknown diaminomethanes, Me2 NCH2 NR2 and, in the case of R2 =PhH, the triamine Me2 NCH2 N(Ph)CH2 NMe2 . The diaminomethanes exhibit an unreported disproportionation to a mixture of (R2 N)2 CH2 , (Me2 N)2 CH2 , and Me2 NCH2 NR2 , which can be trapped as their [Mo(CO)4 (diamine)] complexes. Whereas PhMeNCH2 NMe2 is a labile material, the metal-substituted ([(η(6) -C6 H5 )Cr(CO)3 ]MeNCH2 NMe2 is a stable material. The triamine Me2 NCH2 N(Ph)CH2 NMe2 is unstable with respect to transformation to 1,3,5-triphenyltriazine, but is readily trapped as the bidentate-triamineMo(CO)4 . All metal complexes were characterized by single-crystal X-ray diffraction.

Breaking and Making of Carbon-Carbon Bonds by Lanthanides and Third-Row Transition Metals.

Carbon-atom extrusion from the ipso-position of a halobenzene ring (C6 H5 X; X=F, Cl, Br, I) and its coupling with a methylene ligand to produce acetylene is not confined to [LaCH2 ](+) ; also, the third-row transition-metal complexes [MCH2 ](+) , M=Hf, Ta, W, Re, and Os, bring about this unusual transformation. However, substrates with substituents X=CN, NO2 , OCH3 , and CF3 are either not reactive at all or give rise to different products when reacted with [LaCH2 ](+) . In the thermal gas-phase processes of atomic Ln(+) with C7 H7 Cl substrates, only those lanthanides with a promotion energy small enough to attain a 4f(n) 5d(1) 6s(1) configuration are reactive and form both [LnCl](+) and [LnC5 H5 Cl](+) . Branching ratios and the reaction efficiencies of the various processes seem to correlate with molecular properties, like the bond-dissociation energies of the C-X or M(+) -X bonds or the promotion energies of lanthanides.

Aggregation Behavior of Several Ionic Liquids in Molecular Solvents of Low Polarity--Indication of a Bimodal Distribution.

The structure and dynamics of ion pairing and aggregation is studied by concentration- and temperature-dependent measurements of (1) H and (19) F self-diffusion coefficients, viscosity, and conductivity for the following five solutions: 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([Cn mim][NTf2], n=2, 4, 6) in dichloromethane (CH2Cl2), and [C6 mim][NTf2] in tetrahydrofuran (THF) and chlorobenzene (C6 H5 Cl). The temperature dependence of these properties at constant IL concentrations follows the Arrhenius law for all five solutions. The IL-concentration dependence of the respective activation energies obtained from the Arrhenius analysis is nonlinear in the case of conductivity, but indicates linear relationships for viscosity and self-diffusion. All five solutions studied display average solute radius maxima as plotted against IL concentration. The maximum average solute radii follow an order of solvents of CHCl3 >C6 H5 Cl>CH2 Cl2 ≈THF, which corresponds to the order of increasing solvent dielectric constant. The observed trends in the physical properties of these solutions indicate the development of a bimodal distribution of solute size with increasing IL concentration. Specifically, the presence of aggregates is supported by the analysis of the conductivity data and the observation of the same self-diffusion coefficients for the cation and anion. The concurrent presence of freely dissolved ions is supported by the obtained average solute radii that do not exceed the radii of the corresponding ion pairs.