Search

International audience; Reaction of [(XA2)U(CH2SiMe3)2] (1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9- dimethylxanthene) with 1 equivalent of [Ph3C][B(C6F5)4] in arene solvents afforded the arene-coordinated uranium alkyl cations, [(XA2)U(CH2SiMe3)(hn-arene)][B(C6F5)4] {arene = benzene (2), toluene (3), bromobenzene (4) and fluorobenzene (5)}. Compounds 2, 3, and 5 were crystallographically characterized, and in all cases the arene is π-coordinated. Solution NMR studies of 2-5 suggest that the binding preferences of the [(XA2)U(CH2SiMe3)]+ cation follow the order: toluene ≈ benzene > bromobenzene > fluorobenzene. Compounds 2-4 generated in C6H5R (R = H, Me or Br, respectively) showed no polymerization activity under 1 atm of ethylene. By contrast, 5 and 5-Th (the thorium analogue of 5) in fluorobenzene at 20 and 70 °C achieved ethylene polymerization activities between 16 800 and 139 200 g mol-1 h-1 atm-1, highlighting the extent to which common arene solvents such as toluene can suppress ethylene polymerization activity in sterically open f-element complexes. However, activation of [(XA2) An(CH2SiMe3)2] {M = U (1) or Th (1-Th)} with [Ph3C][B(C6F5)4] in n-alkane solvents did not afford an active polymerization catalyst due to catalyst decomposition, illustrating the critical role of PhX (X = H, Me, Br or F) coordination for alkyl cation stabilization. Gas phase DFT calculations, including fragment interaction calculations with energy decomposition and ETS-NOCV analysis, were carried out on the cationic portion of 2'-Th, 2', 3' and 5' (analogues of 2-Th, 2, 3 and 5 with hydrogen atoms in place of ligand backbone methyl and tert-butyl groups), providing insight into the nature of actinide–arene bonding, which decreases in strength in the order 2'-Th > 2' ≈ 3' > 5'.

Reactions between (Me2PCH2AlMe2)2 and late transition metal complexes led to five distinct outcomes, ranging from Me2PCH2AlMe2 coordination to in situ generation of a tris(phosphino)aluminate ligand.

Formal substitution of the oxygen atom of an iso-tellurazole N-oxide with deprotonated (ortho, meta, and para)-hydroxyphenyl groups generated molecules that readily aggregate through Te···O chalcogen bonding (ChB) interactions. The molecules undergo autoassociation in solution, as shown by variable temperature (VT) 1H NMR experiments and paralleling the behavior of iso-tellurazole N-oxides. Judicious adjustment of crystallization conditions enabled the isolation of either polymeric or macrocyclic aggregates. Among the latter, the ortho compound assembled a calixarene-like trimer, while the para isomer built a macrocyclic tetramer akin to a molecular square. The Te···O ChB distances in these structures range from 2.13 to 2.17 A, comparable to those in the structures of iso-tellurazole N-oxides. DFT calculations estimate that the corresponding Te···O ChB energies are between -122 and -195 kJ mol-1 in model dimers and suggest that macrocyclic aggregation enhances these interactions.

The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr]- , Ar=2,6-iPr2 C6 H3 , 1) shows diverse and substrate-controlled reactivity in reactions with N-heterocycles. 4-Dimethylaminopyridine (DMAP), a basic substrate in which the 4-position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C-H activation of the methyl group of 4-picoline takes place to produce a species with a reactive terminal methylene. Reaction of 1 with 3,5-lutidine results in the first example of an uncatalyzed, room-temperature cleavage of an sp2 C-H bond (in the 4-position) by an AlI species. Another reactivity mode was observed for quinoline, which undergoes 2,2'-coupling. Finally, the reaction of 1 with phthalazine produces the product of N-N bond cleavage.

Formal substitution of the oxygen atom of an iso-tellurazole

Reactions of trans-[(dmpe)2MnH(C2H4)] (1) with BH3(NMe3), 9-BBN, and HBMes2 yielded the manganese(i) borohydride complexes [(dmpe)2Mn(μ-H)2BR2] (3: R = H, 4: R2 = C8H14, 5: R = Mes). The reaction of 1 with BH3(NMe3) proceeds via ethylene substitution. By contrast, a detuerium labelling study indicates that the reaction of 1 with HBMes2 involves initial isomerization of 1 to an unobserved 5-coordinate ethyl intermediate, [(dmpe)2MnEt], which reacts with the hydroborane to afford EtBR2 and [(dmpe)2MnH], followed by reaction with a second equivalent of hydroborane to generate 5 (an analogous pathway is likely followed for other base-free hydroboranes such as 9-BBN). Identification of 3-5 as κ2-borohydride complexes, as opposed to boryl dihydride or hydroborane hydride isomers, is supported by 11B NMR spectroscopy, X-ray diffraction, and Atoms in Molecules calculations. Two byproducts were observed in the syntheses of 3-5: [{(dmpe)2MnH}2(μ-dmpe)] (6) and [(dmpe)2MnH(κ1-dmpe)] (7). These complexes were independently prepared by exposure of 1 to free dmpe under an atmosphere of Ar or H2, and the generality of this synthetic route was demonstrated by the reaction of 1 with PMe3 (under H2) to form [(dmpe)2MnH(PMe3)] (8). Complexes 6-8 can exist as isomers with either a trans or a cis relationship between the hydride and κ1-coordinated phosphine ligands on manganese. trans to cis isomerization of 6-8 is photochemically induced, whereas the reverse reaction occurs under thermal conditions. X-ray crystal structures were obtained for 3-5, trans,trans-6, cis,cis-6, trans-7, and trans-8.

The moisture instability of organic-inorganic hybrid perovskite solar cells has been a major obstacle to the commercialization, calling for mechanistic understanding of the degradation process, which has been under debate. Here we present a surprising discovery that the degradation is actually reversible, via in situ observation of X-ray diffraction, supported by FTIR and SEM. To isolate the hydrogen bond effect, water was replaced by methanol during the in situ experiment, revealing the decomposition to be initiated by the breakdown of N-H-I hydrogen bonds. This is followed by the step of organic iodide hydrolyzing, which can be inhibited in the neutral environment, making the whole process reversible under variable pH.

The reactivity of the gallium(I) compound NacNacGa (4) to a variety of unsaturated compounds has been studied. Whereas 4 proved surprisingly unreactive toward olefins, ketones, guanidines, and thioureas, it reacts with isocyanates and carbodiimides to furnish the products of coupling of two heterocumulenes. With isothiocyanate, the C═S cleavage occurs, leading to the dimer (NacNacGa)

Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ4 Te dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te⋅⋅⋅O ChB distances are 2.062 A, the shortest observed to date in aggregates of this type. DFT-D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating λ4 Te and λ2 Te centers, which calculations identified as the thermodynamically preferred arrangement.

7 pags., 6 figs., The phase transition from graphite to diamond is an appealing object of study because of many fundamental and also, practical reasons. The out-of-plane distortions required for the transition are a good tool to understand the collective behaviour of layered materials (graphene, graphite) and the van der Waals forces. As today, two basic processes have been successfully tested to drive this transition: strong shocks and high energy femtolaser excitation. They induce it by increasing either pressure or temperature on graphite. In this work, we report a third method consisting in the irradiation of graphite with ultraviolet photons of energies above 4.4 eV. We show high resolution electron microscopy images of pyrolytic carbon evidencing the dislocation of the superfcial graphitic layers after irradiation and the formation of crystallite islands within them. Electron energy loss spectroscopy of the islands show that the sp2 to sp3 hybridation transition is a surface efect. High sensitivity X-ray difraction experiments and Raman spectroscopy confrm the formation of diamond within the islands., This work is based upon research conducted at the Spanish National Centre for Electron Microscopy and at the Cornell High Energy Synchrotron Source (CHESS) which is supported by the National Science Foundation under award DMR-1332208. Additional support was provided by the Ministry of Science and Education of Spain and the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canada Foundation for Innovation (CFI) and the Ontario Ministry of Research, Science and Innovation.

The synthesis, and spectroscopic and structural characterization of bridged dicationic derivatives of benzo-2,1,3-selenadiazoles are reported. The chloride salt of [H4C6NSeN–CH2–CH2–NSeNC6H4]2+ crystallizes forming a macrocyclic structure in which two cations are bridged by Se⋯Cl chalcogen bonds (ChBs), with a third chloride at the centre of the macrocycle. The structure of [1,2-(H4C6NSeN)2-C6H10]Cl2 consists of two selenadiazolium cations linked by a chiral cyclohexane and capped by Se⋯Cl ChBs. Tetrafluoroborate salts of a xylene bridge crystallize in two pseudopolymorphs in which the cations form Se⋯F ChBs in an anti- or syn-conformation. The triflate salt of ethylene-bridged cations dimerizes through the formation of the [Se–N]2 supramolecular synthon with Se⋯O ChBs capping the second selenium atom. In contrast, [H4C6NSeN–CH2–CH2–CH2–NSeNC6H4](CF3SO3)2 only forms Se⋯O ChBs.

Pt(ii) and Rh(iii) readily form complexes with 3-methyl-5-aryl-1,2-tellurazole 2-oxides (L = (3-Me-5-Ar-1,2-C3HTe(NO)). The aryl group is either phenyl or 3,5-di-tert-butylphenyl, the latter case being a new derivative with enhanced solubility. The compound [Pt(3-Me-5-(3,5-tBu2C6H3)-1,2-C3HTe(NO))4](BF4)2 crystallizes in the P21/C space group featuring a square planar complex in the lattice. The crystal of [RhCl2(3-Me-5-(C6H5)-1,2-C3HTe(NO))4](BF4) belongs to the I4[combining macron] space group and contains an octahedral complex. In both instances, the iso-tellurazole N-oxide molecules are linked by TeO chalcogen bonding interactions confirming an annular tetramer that binds the metal ion as a κ4Te macrocycle in a boat conformation. Low-frequency shifts of the 125Te magnetic resonance upon coordination and the observation of 125Te-195Pt and 125Te-103Rh 1J coupling constants indicate that the complexes are stable species in solution. The complex ions were also observed in the electrospray mass spectra.

Wilkinson’s manganese(I) ethylene hydride complex trans-[(dmpe)2MnH(C2H4)] (1) reacts as a source of a low-coordinate manganese(I) ethyl complex. This is illustrated in the reactivity of 1 toward a variety of reagents. Reactions of 1 with primary silanes RSiH3 (R = Ph, nBu) at 60 °C afforded ethane and the disilyl hydride manganese complexes [(dmpe)2MnH(SiH2R)2] (4a, R = Ph; 4b, R = nBu). Additionally, reaction with H2 at 60 °C afforded ethane and the dihydrogen hydride complex [(dmpe)2MnH(H2)] (5), which has previously been prepared by an alternate route. The proposed low-coordinate intermediate, [(dmpe)2MnEt], was not observed spectroscopically but could be trapped using isonitrile ligands; reaction of 1 with CNR (R = tBu, o-xylyl) afforded the manganese(I) ethyl complexes [(dmpe)2MnEt(CNR)] (6a, R = tBu; 6b, R = o-xylyl). Ethyl complex 6a did not react further with CNtBu at 80 °C. In contrast, complex 6b reacted with excess o-xylyl isonitrile to form 1,1-insertion products, including the iminoacyl comp...

Development of a chiral pool-based synthesis of 10b-aza-analogues of biologically active Amaryllidaceae alkaloids is described, involving a concise reductive amination and condensation sequence, leading to ring-B/C-modified, fully functionalized ring-C derivatives. Differentiated anticancer and antiviral activities of these analogues are presented. Despite complete conformational and functional group overlap, the 10b-aza-analogues have diminished anticancer activity and no antiviral activity. These unprecedented electronic effects suggest a possible role for π-type secondary orbital interactions with the biological target.

Addition of 3.05 equiv of dme (1,2-dimethoxyethane) to an n-pentane solution of [(XA2)U(CH2SiMe3)2] (1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) and LiCH2SiMe3 (∼1:1) precipitated the tris(alkyl) 'ate' complex, [Li(dme)3][(XA2)U(CH2SiMe3)3] (2-dme). Sterically encumbered 2-dme is thermally unstable in solution, eliminating SiMe4 to form [Li(dme)3][(XA2*)U(CH2SiMe3)2] (3-dme; XA2* = XA2 cyclometallated at the methine carbon of an isopropyl group) as the major product. Compound 1 did not react with PMe3, 2,2ʹ-bipyridine (bipy), or quinuclidine in benzene at 40 °C. However, 1 reacted with 2.1 equiv of 4-(dimethylamino)pyridine (DMAP) or 9-azajulolidine (AJ; a DMAP derivative featuring a fused tricyclic structure) at 22 °C to afford [(XA2)U(CH2SiMe3)(η2CN-DMAP*)(DMAP)] (4) and [(XA2)U(CH2SiMe3)(η2CN-AJ*)(AJ)] (5), respectively, where DMAP* and AJ* are DMAP and AJ ligands cyclometallated at the 2-position. Reaction of 1 with DMAP-d2 (deuterated in the ortho positions) confirmed that 4 is formed via a direct σ-bond metathesis mechanism. All newly-isolated uranium complexes (2–5) were crystallographically characterized.

N-Bonded adducts of benzo-2,1,3-selenadiazole with BX3 (X = Ph, F, Cl, Br) were prepared and crystallographically characterized. The structures of the 1 : 1 adducts of BF3 and BCl3 demonstrate dimerization through the [Se–N]2 supramolecular synthon and enhancement of the corresponding Se⋯N chalcogen bonding interactions. However, the structures of the BPh3 and BBr3 compounds indicate that other supramolecular interactions can efficiently compete and inhibit [Se–N]2 dimerization. In the case of the BPh3 adduct, dispersion favors a dimer featuring Se⋯C interactions. In the crystal of the BBr3 derivative, the cooperative effect of Se⋯N chalcogen bonding and Br⋯Br halogen bonding interactions lead to a network structure. A 1 : 2 adduct could be isolated only in the case of BCl3; its structure features short intramolecular Se⋯Cl interactions resulting from the enhanced electrophilic character of the chalcogen atom.

Reaction of 4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H2XN2) with [Zr(NMe2)4], followed by crystallization from O(SiMe3)2, yielded [(XN2)Zr(NMe2)2]·{O(SiMe3)2}0.5 (1·{O(SiMe3)2}0.5). The zirconium dimethyl complex [(XN2)ZrMe2] (2) was subsequently accessed (a) by treatment of 1·(O(SiMe3)2)0.5 with excess AlMe3 or (b) via reaction of 1·(O(SiMe3)2)0.5 with excess Me3SiCl, affording [(XN2)ZrCl2] (3) followed by reaction of 3 with 2 equiv of MeLi. Reaction of [(XN2)ZrMe2] (2) with one equiv of B(C6F5)3 or [CPh3][B(C6F5)4] yielded cationic [(XN2)ZrMe][MeB(C6F5)3] (4) and [(XN2)ZrMe(arene)][B(C6F5)4] {arene = η6-benzene (5a), η6-toluene (5b), or bromobenzene (5c)}, respectively. Both 4 and 5b are active for ethylene polymerization under 1 atm of ethylene at 24 and 80 °C in toluene with activities ranging from 23.5–883 kg mol–1 atm–1 h–1, yielding polymers with weight-average molecular weights (Mw) of 70,800–88,100 g mol–1 and polydispersities (Mw/Mn) of 3.94–4.67.

Dilithiation of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethyl-xanthene (XBr2) followed by addition of 2 equiv. of (2,4,6-triisopropylphenyl)dichlorophosphine (TrippPCl2) afforded 4,5-bis[(2,4,6-triisopropylphenyl)chlorophosphino]-2,7-di-tert-butyl-9,9-dimethylxanthene (XP2Cl2), which was reduced to 4,5-bis[(2,4,6-triisopropylphenyl)phosphino]-2,7-di-tert-butyl-9,9-dimethylxanthene (H2XP2) using excess LiAlH4. Deprotonation of H2XP2 with excess KH in DME provided the dipotassium salt, [K2(XP2)(dme)n] (1; n = 2.5–4), and stirring 1 in THF followed by recrystallization from hexanes yielded tetrametallic [K4(XP2)2(THF)4] (2) which features a central K4P4 cage. Reaction of [YI3(THF)3.5] with [K2XP2(dme)2.5] afforded a mixture of products including [(XP2)YI(THF)2] (3) and (PTripp)3; pure 3 could be isolated in low yield by extraction with a minimum volume of hexanes or O(SiMe3)2. In the solid state, 3 adopts a face-capped trigonal bipyramidal coordination geometry with a planar xanthene backbone and an angle of 85° between the P(1)/C(4)/C(5)/P(2) and P(1)/Y/P(2) planes.

The protonation of 2,3,4,5-tetraphenylcyclopentadienone (tetracyclone) yields 6,11-diphenyl-5H-benzo[a]fluoren-5-one (17) and 2,3,4,5-tetraphenylcyclopent-2-en-1-one (18) as the major products. This contrasts with the pyrolysis of tetracyclone that yields 5,6-diphenyl-11H-benzo[a]fluoren-11-one (22) a structural isomer of 17. Mechanisms are presented that rationalize these observations. The protonation of 4-hydroxy-2,3,4-triphenylcyclopentadienone, the precursor to 2,3,4-triphenylcyclo¬pentadienone, generates 2-(2′-oxo-3′,4′,5′-triphenylcyclopent-3′-enyl)-3,4,5-triphenyl-cyclopenta-2,4-dienone, (30) which has been unequivocally characterized by X-ray crystallography. The establishment of the conformation of molecule 30 in the solid state, which correlates with its structure in solution, provides a rationale for the subsequent formation of the tetrahydro-pentaphenyl-as-indacene-3,4-dione, 32, upon further protonation.

The crystal structure of itraconazole (ITZ) Form II has been determined by single-crystal X-ray diffraction, and the effects of crystal structure and two polymer excipients, Kollidone VA64 (PVPVA64) and hydroxypropylmethyl cellulose acetate succinate (HPMCAS), on the melt crystallization kinetics of ITZ Forms I and II have been investigated. Form II structure is characterized by a unit cell similar to that of Form I, but with a different orientation of the dichlorophenyl groups. Form II displays a considerably higher crystal growth rate than Form I, which cannot be explicated by their difference in crystal density alone. Both polymers at 20% (w/w) significantly retard the crystallization of Forms I and II without altering the crystal structure of either polymorph. Crystallization kinetic analysis by the two-dimensional surface nucleation model suggests that the polymers inhibit the crystallization of ITZ from amorphous dispersions by reducing the molecular mobility in the molten state as well as augmentin...

Reaction of the ethylene hydride complex trans-[(dmpe)2MnH(C2H4)] (1) with Et2SiH2 at 20 °C afforded the silylene hydride [(dmpe)2MnH(=SiEt2)] (2 a) as the trans-isomer. By contrast, reaction of 1 with Ph2SiH2 at 60 °C afforded [(dmpe)2MnH(=SiPh2)] (2 b) as a mixture of the cis (major) and trans (minor) isomers, featuring a Mn-H-Si interaction in the former. The reaction to form 2 b also yielded [(dmpe)2MnH2(SiHPh2)] (3 b); [(dmpe)2MnH2(SiHR2)] (R=Et (3 a) and Ph (3 b)) were accessed cleanly by reaction of 2 a and 2 b with H2, and the analogous reactions with D2 afforded [(dmpe)2MnD2(SiHR2)] exclusively. Both 2 a and 2 b engaged in unique reactivity with ethylene, generating the silene hydride complexes cis-[(dmpe)2MnH(R2Si=CHMe)] (R=Et (4 a), Ph (4 b)). Compounds trans-2 a, cis-2 b, 3 b, and 4 b were crystallographically characterized, and bonding in 2 a, 2 b, 4 a, and 4 b was probed computationally.

The crystal structure of a new perovskite material, (C4H8NH2)PbI3 was determined and illustrated by single crystal X-ray diffraction. UV spectra, photoluminescence and XRD results show it is a promising alternative to hybrid organic-inorganic perovskites due to it's good water resistance and suitable bandgap.

Reaction of NacNacAl (NacNac=[DippNC(Me)CHC(Me)NDipp]- ) with one equivalent of benzophenone affords a ketylate species NacNacAl(η2 (C,O)-OCPh2 ) that undergoes easy cyclization reactions with unsaturated substrates. The scope of substrates included benzophenone, aldimine (PhNC(Ph)H), quinoline, phenyl nitrile, trimethylsilyl azide, and a saturated cyclic thiourea. The latter substrate reacted by an unusual C-N cleavage that left the C=S functionality intact. The new products were characterized by NMR spectroscopy and X-ray diffraction analysis.

Treatment of β-naphthil dihydrazone, 1, with silver oxide yields di(β-naphthyl)acetylene, 2, which undergoes Diels-Alder cycloaddition with tetra(β-naphthyl)cyclopentadienone, 4, to give hexa(β-naphthyl)benzene, 5, upon decarbonylation. Molecules 1, 2 and 4 have been characterised by X-ray crystallography, but hexa(β-naphthyl)benzene exhibits rotational disorder of the peripheral substituents. Nevertheless, calculations at the density functional level reveal the favoured structure of 5 to be a molecular propeller, in which the eight possible rotamers are essentially iso-energetic. Variable-temperature NMR spectroscopy studies yield a naphthyl rotational barrier of approximately 17 kcal mol-1 , similar to that previously found for meta-substituted phenyl groups. Enantiomerisation of hexa(β-naphthyl)benzene engendered by rotation of a single naphthyl ring has been studied by DFT calculations, and the process has been represented pictorially.

Reaction of H2XN2 {4,5-bis(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene} with [Lu(CH2SiMe3)3(THF)2], and crystallization from O(SiMe3)2, yielded [(XN2)Lu(CH2SiMe3)(THF)]·(O(SiMe3)2)1.5 (1·(O(SiMe3)2)1.5). Lanthanum complexes of the XN2 dianion were also prepared by salt metathesis; treatment of H2XN2 with excess KH in DME produced the dipotassium salt, [K2(XN2)(DME)x] (x = 2–2.5), and subsequent reaction with [LaCl3(THF)3] afforded [{(XN2)LaCl(THF)}x]·(O(SiMe3)2)0.25x (2·(O(SiMe3)2)0.25x; x = 1 or 2) after crystallization from O(SiMe3)2. Compound 2 reacted with two equivalents of LiCH2SiMe3, to form the dialkyl-‘ate’ complex, [Li(THF)x][(XN2)La(CH2SiMe3)2]·Toluene·LiCl (3·toluene·LiCl; x = 3). Both 1 and 3 (x = 4) were structurally characterized, and were evaluated as catalysts for intramolecular hydroamination; while 3 showed poor activity, 1 is highly active for both intramolecular hydroamination and more challenging intermolecular hydroamination. Reactions with unsymmetrical alkenes yielded Markovnikov products, and the activity of 1 surpassed that of the previously reported yttrium analogue in the reaction of diphenylacetylene with 4-tert-butylbenzylamine.

Iso-tellurazole N-oxides are promising supramolecular building blocks. While in neutral solutions, they form tetra- and hexameric macrocyclic aggregates linked by Te···O secondary bonding (σ hole interactions or chalcogen bonds), protonation of the oxygen atom in acidic media disrupts such supramolecular association. The process is reversible and, consequently, can be used to switch on and off the self-assembly process. Hammett acidity measurements gave pKa values of –3.2 for the protonated molecules. Adducts with HCl and HBr were isolated and structurally characterized. Protonation in solution led to the crystallization of a new polymorph of 3-methyl-5-phenyl-1,2-tellurazole N-oxide, which features a unique polymeric arrangement.

A previously unidentified polymorph of nickel niobate, NiNb2O6, was grown and stabilized in single crystalline form using an optical floating zone furnace. Key parameters of the growth procedure involved use of a slight excess of NiO (1.2% by mol), an O2 atmosphere and a growth rate of 25 mm/h. The resulting boule consisted of a polycrystalline exterior shell of the columbite structure – columbite is the thermodynamically stable form of NiNb2O6 under ambient conditions – and a core region consisting of transparent yellow-green single crystals up to 5 mm×2 mm×1 mm in dimension of the previously unidentified phase. The crystal structure, solved from single crystal x-ray diffraction data, is described in the P42/n space group. Interestingly, this is not a subgroup of P42/mnm, the rutile space group. The Ni2+ ions form layers which are displaced such that interlayer magnetic frustration is anticipated. Magnetic susceptibility data shows a broad maximum at approximately 22 K and evidence for long range antiferromagnetic order at approximately 14 K, obtained by Fisher heat capacity analysis as well as heat capacity measurements. The susceptibility data for T > 25 K are well fit by a square lattice S = 1 model, consistent with the Ni sublattice topology.

InAsSb pillars were investigated for multispectral photodetection in the long wavelength infrared (LWIR) region. An InAs0.19Sb0.81 thin film was successfully grown on Si (1 0 0) substrate, utilizing an AlSb buffer layer to alleviate the large lattice mismatch. X-ray diffraction studies showed a majority [1 0 0] orientation of the as-grown films, with minor orientations arising as a result of twinning. Arrays of InAsSb pillars with diameters ranging from 1700 nm to 4000 nm were fabricated by a top-down reactive ion etching process. The arrays showed resonant optical absorption peaks in the LWIR region from 8 to 16 μm wavelength, dependent on the pillar diameter. The peak absorptance wavelength increased by 0.46 μm for each 100 nm increase in pillar diameter, demonstrating the multispectral tunability of such arrays.

Despite their versatility, the application of telluradiazoles as supramolecular building blocks is considerably constrained by their sensitivity to moisture. Albeit more robust, their selenium analogues form weaker supramolecular interactions. These, however, are enhanced when one nitrogen atom is bonded to an alkyl group. Here we investigate general methods for the synthesis of such derivatives. Methyl, iso-propyl and tert-butyl benzo-2,1,3-selenadiazolium cations were prepared by direct alkylation or cyclo-condensation of the alkyl-phenylenediamine with selenous acid. While the former reaction only proceeds with the primary and tertiary alkyl iodides, the latter is very efficient. Difficulties reported in earlier literature are attributable to the formation of adducts of benzoselenadiazole with its alkylated cations and side reactions initiated by aerobic oxidation of iodide. However, the cations themselves are resilient to oxidation and stable in acidic to neutral aqueous medium. X-ray crystallography was used in the identification and characterization of the following compounds: [C6H4N2(R)Se](+)X(-), (R = CH(CH3)2, C(CH3)3; X = I(-), I3(-)], [C6H4N2(CH3)Se](+)I(-), and [C6H4N2Se][C6H4N2(CH3)Se]2I2. Formation of SeN secondary bonding interactions (chalcogen bonds) was only observed in the last structure as anion binding to selenium is a strong competitor. The relative strengths of those forces and the structural preferences they enforce were assessed with DFT-D3 calculations supplemented by AIM analysis of the electron density.

The widespread emergence of antibiotic drug resistance has resulted in a worldwide healthcare crisis. In particular, the extensive use of β-lactams, a highly effective class of antibiotics, has been a driver for pervasive β-lactam resistance. Among the most important resistance determinants are the metallo-β-lactamases (MBL), which are zinc-requiring enzymes that inactivate nearly all classes of β-lactams, including the last-resort carbapenem antibiotics. The urgent need for new compounds targeting MBL resistance mechanisms has been widely acknowledged; however, the development of certain types of compounds-namely metal chelators-is actively avoided due to host toxicity concerns. The work herein reports the identification of a series of zinc-selective spiro-indoline-thiadiazole analogues that, in vitro, potentiate β-lactam antibiotics against an MBL-carrying pathogen by withholding zinc availability. This study demonstrates the ability of one such analogue to inhibit NDM-1 in vitro and, using a mouse model of infection, shows that combination treatment of the respective analogue with meropenem results in a significant decrease in bacterial burden in contrast to animals that received antibiotic treatment alone. These results support the therapeutic potential of these chelators in overcoming antibiotic resistance.

Iodine oxidation of bis[2-(hydroxyiminomethyl)phenyl] dichalcogenides yields benzo-1,2-chalcogenazole 2-oxides. Annulated derivatives of iso-tellurazole N-oxides spontaneously aggregate into cyclic tetra- and hexamers through Te⋯O chalcogen bonding; the structures of the co-crystals with benzene and CH2Cl2 illustrate the ability of these macrocycles to interact with small guest molecules. The selenium congener crystallizes forming a supramolecular polymer. VT NMR indicates that both compounds aggregate in solution but only at low temperature in the selenium case. The different abilities of these molecules to engage in supramolecular interactions are interpreted on the basis of their electronic properties evaluated with DFT-D3 calculations.

The synthesis of a rigid 4,5-bis(triphenylphosphinimino)-2,7-di-tert-butyl-9,9-dimethylxanthene {(Ph3PN)2XT} ligand is outlined, along with a modified synthesis for previously reported 1,8-bis(triphenylphosphinimino)naphthalene {(Ph3PN)2NAP}. Reaction of neutral (Ph3PN)2XT with [Y(CH2SiMe3)3(THF)2] resulted in double cyclometallation, yielding the base-free monoalkyl complex, [({Ph2(C6H4)PN2XT)Y(CH2SiMe3)] (1). Layering a concentrated THF solution of 1 with hexanes at −28 °C afforded THF-coordinated [({Ph2(C6H4)PN}2XT)Y(CH2SiMe3)(THF)]·2THF (1-THF·2THF), with a distorted pentagonal bipyramidal geometry and approximately meridional coordination of the pentadentate {Ph2(C6H4)PN}2XT dianion. Similarly, (Ph3PN)2NAP reacted with [Y(CH2SiMe3)3(THF)2] to afford a THF-coordinated monoalkyl complex, [{(Ph2(C6H4)PN)2NAP}Y(CH2SiMe3)(THF)] (2-THF). Layering a DME solution of 2-THF with hexanes at −28 °C afforded X-ray quality crystals of [[{(Ph2(C6H4)PN)2NAP}Y(CH2SiMe3)(κ2-DME)]·hexane (2-DME·hexane), with a highly distorted pentagonal bipyramidal geometry and a facial coordination mode of the tetradentate {Ph2(C6H4)PN}2NAP dianion.

The two title complexes as well as the dimeric complex [Ru(II)(η5-C5H5)(6,6′-diamino-2,2′-bipyridine)]2(OTf)2 have been synthesized and characterized by NMR and single-crystal X-ray crystallography. The direct structural comparison of the 2,2′-bipyridine and 6,6′-diamino-2,2′-bipyridine complexes suggests that the electronic and steric environments of the ruthenium centers in both complexes are essentially equivalent, providing for a unique opportunity to probe the influence of the noncoordinated amine substituent on the relative reactivity and catalytic activity of the complexes. Opposite to what would be anticipated on the basis of steric effects, the bulkier amine-substituted ligand results in a catalyst showing substantially higher activity in the hydrogenation of cyclohexanone in acidic medium, which is attributed to the operation of a metal–ligand bifunctional hydrogenation mechanism mediated by the amine substituents in their protonated form acting as proton shuttles.

Treatment of β-naphthil dihydrazone, 1, with silver oxide yields di(β-naphthyl)acetylene, 2, which undergoes Diels-Alder cycloaddition with tetra(β-naphthyl)cyclopentadienone, 4, to give hexa(β-naphthyl)benzene, 5, upon decarbonylation. Molecules 1, 2 and 4 have been characterised by X-ray crystallography, but hexa(β-naphthyl)benzene exhibits rotational disorder of the peripheral substituents. Nevertheless, calculations at the density functional level reveal the favoured structure of 5 to be a molecular propeller, in which the eight possible rotamers are essentially iso-energetic. Variable-temperature NMR spectroscopy studies yield a naphthyl rotational barrier of approximately 17 kcal mol

Under aprotic conditions, the reaction of 4-amino-1,2-naphthoquinone with excess S2Cl2 generates 4,5-dioxo-naphtho[1,2-d][1,2,3]dithiazol-2-ium chloride in a typical Herz condensation. By contrast, prior literature reports an imine (NH) product, 4,5-dioxo-1H-naphtho[1,2-d][1,2,3]dithiazole, for the same reaction performed in acetic acid. Herein, the cation product is isolated with four different counter-anions (Cl(-), GaCl4(-), FeCl4(-) and OTf(-)). Reduction of the cation generates a neutral radical 1,2,3-dithiazolyl-o-naphthoquinone, with potential ligand properties. Further reduction generates a closed shell anion, isolated as a water-stable Li(+) complex and exhibiting O,O-bidentate chelation. The hydroxy (OH) isomer of the original imine (NH) product is reported, and this can be readily deprotonated and acylated (OAc). All species are structurally characterized. Solution redox behaviour and EPR are discussed where appropriate.

Two-dimensional X-ray diffraction was employed, to provide a complete understanding of the energy efficiency improvement of organic photovoltaics by AC electric field alignment. Two distinguishable poly (3-hexylthiophene) (P3HT) nanostructures were found in the form of two separated layers, one of which is highly oriented and the other randomly distributed. The finding helps to analyze the crystallite arrangements not only in the interface in the bulk heterojunction, but also those closer to the substrate. The highly oriented P3HT layer, although located near the substrate, was found to enhance the device efficiency, by increasing the short circuit current and decreasing the series resistance.

The use of high-strength polymer in automotive structural components is limited by insufficient understanding of microscopic aspects of deformation for accurate numerical predictions of the mechanical behavior during forming processes. One approach to meeting these critical data needs is a careful examination of the structure property relationships that directly influence formability. Different hot forming processes (solid-state extrusion, axial feed hot oil tube forming, and biaxial ball stretching test) are utilized in this work for investigating the effect of process conditions on the molecular orientation of polypropylene (PP) tubes. White-Spruiell representation of orientation factors based on the results form X-ray diffraction (XRD) patterns is utilized to analyze the development of orientation under extrusion and various forming conditions. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Reaction of [(BDPP)ThCl 2 (dme)] ( 1 ) with 2 equivalents of MeMgBr in OEt 2 , followed by filtration and layering a toluene solution with hexanes at −30 °C yielded a single large crystal of [{(BDPP)ThX(μ-X) 2 Mg(OEt 2 )(μ-Me)} 2 ]·2 toluene (X = Br 0.73–0.87 /Cl 0.13–0.27 ; 3 ·2 toluene). This product is the result of halide exchange to form a partially brominated neutral thorium species, which is adducted with MeMgX(OEt 2 ). The complex is then tetrametallic as a result of Mg–Me–Mg bridges. The structure of complex 3 provides direct insight into the process by which halide exchange takes place between electrophilic metal halide complexes and Grignard reagents. This reactivity stands in stark contrast to the reactions of 1 and [(XA 2 )ThCl 2 (dme)] ( 2 ) with PhCH 2 MgCl. In these cases the expected dialkyl products, [LTh(CH 2 Ph) 2 ] [L = BDPP ( 4 ) and XA 2 ( 5 )], were formed under most conditions. However, addition of a PhCH 2 MgCl solution to 2 at −78 °C and warming to room temperature after 5 minutes gave [(XA 2 )Mg(dme)] ( 6 ), the product of ancillary ligand transfer from thorium to magnesium, in 30–50% yield.