Br Distances Research Articles

Ventricular Access Utilizing Cutaneous Reference Points: Statistical Analysis and Proposal of a New Ventricular Entry Point

Perform radiologic measurements and analysis of normal brain computed tomography (CT) scans; delineate a new ventricular entry point from cutaneous landmarks, highlighting the potential surgical implications of these findings. Six radiologic distances (AR; BR; AL; BL, C, and D) were measured in normal brain CT scans using Horos software. Statistical analysis of the measurements was performed with minitab18 software based on age, sex, and side. 132 brain CT scans were analyzed, yielding the following mean results: AR distance: 2.1cm; BR distance: 7cm; AL distance: 2.1cm; BL distance: 7.1cm; C distance: 12.4cm; D distance: 7cm; new ventricular entry point: 12.4cm posterior to the nasion, and 2.1cm lateral to the midline. The freehand technique for accessing the lateral ventricles is a common neurosurgical procedure but is often accompanied by complications. To address this, we suggest a novel entry point for ventricular access, determined by cutaneous reference points. This point is situated 12.4cm posterior to the nasion along the midline and 2.1cm lateral to the midline. Although our findings may play a role in presurgical planning for ventricular pathologies, future prospective studies are warranted.

Shortening CN⋯Br–Csp3 halogen bonds via π-stacking

An extremely short N⋯Br distance between a nitrile group and a Csp3-linked bromine atom was encountered in the solid-state and rationalized by DFT calculations, which emphasized the role of π-stacking for bringing both partners at close proximity.

Structural characterization of N-(4-carboxybenzyl)pyridinium bromide: Hydrogen bonding between bromide and a carboxylic acid

The molecular structure of the carboxylic acid, N-(4-carboxybenzyl)pyridinium bromide, (CbpH)Br, has been determined by using X-ray diffraction. Significantly, (CbpH)Br does not exhibit intermolecular hydrogen bonding interactions of the type that are commonly observed between carboxylic acid moieties; instead, the O–H group participates in a hydrogen bond to the bromide anion, i.e. [C(O)OH···Br], with an O···Br distance of 3.199(5) Å and a syn disposition relative to the C=O group. Density functional theory calculations reproduce well the observed structure.

Quintet Dinitrenes with Negative Zero-Field Splitting: Effect of Spin-Orbit Coupling on the Sign of Magnetic Anisotropy.

We report on W-band EPR and quantum chemical investigation of novel organic tetraradicals with negative axial zero-field splitting (ZFS) parameter D. These belong to the class of quintet 1,3,5-tribromophenylene-2,4-dinitrenes bearing different substituents in position 6 of the benzene ring (1b, N3; 1c, F; 1d, CN; 1e; Cl; 1f, Br). Analysis of the W-band EPR spectrum of dinitrene 1c reveals its large negative ZFS parameter D = -0.27 cm-1. Quantum chemical calculations show that negative D gradually grows in the row of 1c(F) < 1b(N3) < 1d(CN) < 1e(Cl) < 1f(Br) dinitrenes due to decreasing of the through-space distance between the nitrene units and neighboring bromine atoms. Shorter steric N···Br distance results in the stronger contribution of the spin-orbit coupling (SOC) to the total ZFS. The sign of D depends on the interplay of three factors: (i) the angle θ between the "easy" z-axes of the dipolar spin-spin (DSS) and spin-orbit (DSOC) interaction tensors, (ii) the ratio of DSOC/DSS values, and (iii) the rhombicity parameters ESS/DSS and ESOC/DSOC. The study demonstrates in which cases organic quintet tetraradicals may have negative ZFS owing to the presence of heavy atoms at appropriate sites nearby the nitrene units and, thus, possess the bistability property as single-molecule magnets.

Metal-free enantiomorphic perovskite [dabcoH2]2+[H3O]+Br- 3 and its one-dimensional polar polymorph.

The structure and stoichiometry of a new metal-free and ammonium-free compound [dabcoH2]2+H3O+Br- 3 (where [dabcoH2]2+ = 1,4-di-aza-bicyclo-[2.2.2]octane dication) correspond to the general formula ABX 3 characteristic of perovskites. In enantiomorphic trigonal polymorph α of [dabcoH2]2+H3O+Br- 3, the corner-sharing [H3O]Br6 octahedra combine into a 3D framework embedding [dabcoH2]2+ dications in pseudo-cubic cages. In the more dense polymorph β, the face-sharing [H3O]Br6 octahedra form 1D polyanionic columns separated by [dabcoH2]2+ dications. These different topologies correlate with different crystal fields around the cations and their different disorder types: orientational disorders of [dabcoH2]2+ dications and H3O+ cations in polymorph α and positional disorder of [H3O]+ cations in polymorph β. The orientational disorder increases the lengths of OH⋯Br hydrogen bonds in polymorph α, but NH⋯Br distances of ordered dabcoH2 dications are longer in polymorph β. The presence of polar [H3O]+ cations in [dabcoH2]2+H3O+Br- 3 polymorphs offers additional polarizability of the centres compared with analogous metal-free [dabcoH2]2+[NH4]+Br- 3 perovskite.

Crystal structure of the two-dimensional coordination polymer poly[di-μ-bromido-bis-(μ-tetra-hydro-thiophene)-dicopper(I)

The polymeric title compound, [Cu2Br2(C4H8S)2] n , CP1, represents an example of a two-dimensional coordination polymer resulting from reaction of CuBr with tetra-hydro-thio-phene (THT) in MeCN solution. The two-dimensional layers consist of two different types of rhomboid-shaped dinuclear Cu(μ2-Br)2Cu secondary building units (SBUs); one with a quite loose Cu⋯Cu separation of 3.3348 (10) Å and a second one with a much closer inter-metallic contact of 2.9044 (9) Å. These SBUs are inter-connected through bridging THT ligands, in which the S atom acts as a four-electron donor bridging each Cu(μ2-Br)2Cu unit in a μ2-bonding mode. In the crystal, the layers are linked by very weak C-H⋯·Br hydrogen bonds with H⋯Br distances of 2.95 Å, thus giving rise to a three-dimensional supra-molecular network.

Diradical character of the bond breaking in the reaction of Br2 with benzene: Reliable barriers using the CR-CC(2,3) method

The transition state for the substitution reaction involving one Br2 species with benzene as a model system has a long Br–Br distance, leading to high multiconfigurational character of the wavefunction in apolar medium. Single reference methods can become erratic on this condition and even the CCSD(T) fails for this system. To describe accurately this reaction, the CR-CC(2,3) method was used because predicts a reliable dissociation curve for the Br2 when compared to MRCISD + Q calculations. The activation barriers for the reaction of one and two Br2 molecules with benzene were calculated with the CR-CC(2,3) method and used as benchmark to evaluate the performance of the functionals B3LYP, M06-2X, M08-HX, ωB97X-D and B2GP-PLYP. The M08-HX and the B2GP-PLYP are the best functionals, with mean absolute deviation close to 3 kcal mol−1.

Multiple Hydrogen Bond-Induced Structural Distortion for Broadband White-Light Emission in Two-Dimensional Perovskites

Low-dimensional hybrid lead-halide perovskites with broadband white-light emission upon near-UV excitation have attracted immense scientific interest due to their potential application for the next...

Influence of the alkali cation size on the Cu2+ coordination environments in (AX)[Cu(HSeO3)2] (A=Na, K, NH4, Rb, Cs; X=Cl, Br) layered copper hydrogen selenite halides

Abstract Using solution evaporation techniques, we succeeded in preparation of new members essentially extending the layered copper hydrogen selenite family, (AX)[Cu(HSeO3)2] with A = Na, K, Rb, Cs, and NH4, and X = Cl and Br. Bromides and chlorides are isostructural in the family of described new compounds crystallizing in three different structure types. (NaX)[Cu(HSeO3)2] and (KX)[Cu(HSeO3)2] (X = Cl, Br) are monoclinic, whereas (AX)[Cu(HSeO3)2] (A = NH4, Rb, Cs; X = Cl, Br) are orthorhombic. Upon the enlargement of the A + ionic radii inserted in the interlayer between the neighboring [Cu(HSeO3)2] slabs, the effective distance is increasing and results in essential elongation of the apical Cu-X (X = Cl, Br) distances. Three different types of CuO4 X n (n = 0–2) polyhedra are formed. The observed trend is an interesting example of the chemical tuning of the Cu2+ coordination environments.

A linear chain of carbazolyl-bis(tetrazole) supported copper(II) dimers held together by bridging tribromide anions

Reaction of NaCzTiPr with CuBr, followed by exposure to air, results in formation of {[Cu(κ3-N3-μ-N’-CzTiPr)(μ-OH)]2[μ-Br3]}x, 2. The structure of 2 in the solid state consists of hydroxo-bridged Cu(II) dimers connected into a linear chain polymer by bridging Br3– units. The Cu(II) centers have axially elongated coordination with a Br3– terminus and a bridging N from a tetrazole on the adjacent Cu forming the ligands on the long axis. The Br3– unit is linear with short Br–Br distances while the Cu–Br–Br angle is close to 90°. The reaction involves oxidation of both the Cu(I) and Br– of CuBr in air.

4-Bromobiphenyl: Long-lived molecular anion formation and competition between electron detachment and dissociation.

Electron attachment to the 4-bromobiphenyl molecule and the decay channels of its molecular anion were investigated by means of Dissociative Electron Attachment (DEA) spectroscopy with two different spectrometers. The first apparatus is equipped with a static magnet mass analyzer (Ufa group) and the second one with a quadrupole mass filter (Prague group). The dominant DEA channel at low electron energy leads to formation of Br- negative fragments. Long-lived (τa = 40 µs at the temperature of 80 °C) molecular negative ions were detected only in the Ufa experiment. We explored the involved potential energy surfaces and found that the molecular anion has two distinct structures with the C-Br distances of 1.92 Å and 2.8 Å. The statistical model based on the Arrhenius approximation fully explains the experimental observations and sheds light on the earlier anion dissociation kinetic studies in solution.

Steric Heavy Atom Effect on Magnetic Anisotropy of Triplet Tribromophenyl Nitrenes.

Previously unknown the steric heavy atom effect on magnetic anisotropy parameters of triplet phenyl nitrenes is reported. The heavy bromine atom effect is revealed by W-band EPR and theoretical investigations of triplet 2,4,6-tribromophenyl nitrenes bearing different substituents in positions 3 and 5 of the phenyl ring (1a, H/H; 1b, CN/CN; 1c, N3/F; 1d, N3/N3; 1e, Cl/Cl; 1f, Br/Br). The zero-field splitting parameters of nitrenes 1a ( D = 0.9930 cm-1, E = 0.0261 cm-1), 1c ( D = 1.244 cm-1, E = 0.030 cm-1), and 1d ( D = 1.369 cm-1, E = 0.093 cm-1), generated by the photolysis of the corresponding azides in frozen methylcyclohexane solution at 5 K, were determined from the W-band EPR spectra. To clarify the origin of considerable differences in the experimental D values of nitrenes 1a, 1c, and 1d, extensive DFT and CASSCF calculations of these nitrenes as well as of model nitrenes 1b, 1e, and 1f were performed. The calculations show that all nitrenes have nearly the same magnitudes of the spin-spin interactions ( DSS ∼ 1 cm-1), but drastically differ in the spin-orbit coupling parameter (from DSOC = 0.087 cm-1 for 1a to DSOC = 0.765 cm-1 for 1f). Comprehensive analysis of various computational data showed that the magnitude of DSOC of nitrenes 1a-f is the function of the N···Br distance between the nitrene nitrogen and the neighboring bromine atoms. The more bulky substituents are located in positions 3 and 5 of nitrenes 1a-1f, the smaller the N--Br distance and the larger DSOC. These features indicate that the heavy atom effect on magnetic anisotropy of triplet phenyl nitrenes originates from the through-space rather than through-bond electronic interactions between the bromine atoms and the nitrene unit.

Structural, spectroscopic and theoretical studies of 6-hydroxyquinolinium bromide monohydrate

Molecular structure and properties of 6-hydroxyquinolinium bromide monohydrate have been characterized by X-ray diffraction, B3LYP/6-311++G(d,p) calculations and FTIR spectroscopy. Centrosymmetric cyclamers R44(8) of OH⋯Br− bonding two molecules of water and two bromide anions mediate the aggregation of 6-hydroxyquinolinium cations into ribbons. In the absorption spectrum, the 3250–2500 cm−1 region has been attributed to ν⋯O(w), νNH⋯Br- and νBr-⋯HO(w) vibrations. The N⋯Br, O(6)⋯O(w) and O(w)⋯Br distances, of 3.289(2), 2.647(2) and 3.343(2) Å, respectively, have been reproduced in the theoretically optimized models. The experimental and computed spectra of mono- and dihydrates are consistent in the fingerprint region. The potential energy distributions (PED) have been used to assigned bands in the vibrational spectrum.

Functionalization of poly(bis‐thiophene methine)s via facile C–C bulk polymerization and their application as chemosensors for acid detection

ABSTRACTUp to now, 3,4‐ethylenedioxythiophene (EDOT) or its modified analogs are indispensable units or subunits in all successful monomers for polythiophene synthesis through solid‐state polymerization (SSP). Here, a more open thiophene‐(CH(R))‐thiophene platform was developed successfully and corresponding poly(bis‐thiophene methine)s were obtained via C–C SSP or melt‐state polymerization (MSP), that is, bulk polymerization. Meanwhile, the observation of quite long effective Br–Br distance of 5.634 Å, which is more than 50% of halogen's double van der Waals radius (2rw), would help us to understand powerful capability of modulation of molecule movement and reaction under SSP. In addition, these polymers were further employed as acid sensors and they show highly sensitive response to HCl, MeSO3H, BF3‐OEt2, and HNO3. The detailed experiment reveals that P1 has the detection limit of 3.35 × 10−5 M for HCl. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1676–1683

Halogen Bonds in Square Planar 2,5‐Dihalopyridine–Copper(II) Bromide Complexes

Halogen bonding in self‐complementary 1:2 metal–ligand complexes obtained from copper(II) bromide (CuBr2) and seven 2,5‐dihalopyridines were analyzed using single‐crystal X‐ray diffraction. All presented discrete complexes form 1D polymeric chains connected with C–X···Br–Cu halogen bonds (XB). In (2‐chloro‐5‐X‐pyridine)2·CuBr2 (X = Cl, Br, and I) only the C5‐halogen and in (2‐bromo‐5‐X‐pyridine)2·CuBr2 (X = Cl, Br, and I) both C2‐ and C5‐halogens form C–X···Br–Cu halogen bonds with the X acting as the XB donor and copper‐coordinated bromide as the XB acceptor. The electron‐withdrawing C2‐chloride in (2‐chloro‐5‐X‐pyridine)2·CuBr2 complexes has only a minor effect on the C5–X5···Br–Cu XBs, and the X5···Br distances follow the expected order I5 &lt; Br5 &lt; Cl5 with RXB values of 0.91, 0.94, and 0.99, respectively. In (2‐bromo‐5‐X‐pyridine)2·CuBr2 complexes, due to the polarization of both halogens, the C2–X2···Br–Cu and C5–X5···Br–Cu RXB values are very similar [0.92–0.99] as a result of the competition between C2‐ and C5‐halogens for XB formation. In addition to the classical halogen bonds, the square‐planar CuII complexes exhibit C2–X2···Cu (X = Cl and Br) contacts perpendicular to the Br–Cu–Br plane with shorter C2–Br2···Cu than C2–Cl2···Cu contacts. These interactions induce a pseudo‐octahedral geometry for CuII ions. Notably, C2–X2···Br–Cu halogen bonds and the additional C2–X2···Cu contacts are slightly enhanced by the C5‐halogen electronegativity.

Halogen bonding in a series of Br(CF2)nBr-DABCO adducts (n = 4, 6, 8).

Halogen bonding (XB) is a highly-directional class of intermolecular interactions that has been used as a powerful tool to drive the design of crystals in the solid phase. To date, the majority of XB donors have been iodine-containing compounds, with many fewer involving brominated analogues. We report the formation of adducts in the vapour phase from a series of dibromoperfluoroalkyl compounds, BrCF2(CF2)nCF2Br (n = 2, 4, 6), and 1,4-diazabicyclo[2.2.2]octane (DABCO). Single-crystal X-ray diffraction studies of the colourless crystals identified 1,4-diazabicyclo[2.2.2]octane-1,4-dibromoperfluorobutane (1/1), C4Br2F8·C6H12N2, (I), 1,4-diazabicyclo[2.2.2]octane-1,6-dibromoperfluorohexane (1/1), C6Br2F12·C6H12N2, (II), and 1,4-diazabicyclo[2.2.2]octane-1,8-dibromoperfluorooctane (1/1), C8Br2F16·C6H12N2, (III), each of which displays a one-dimensional halogen-bonded network. All three adducts exhibit N...Br distances less than the sum of the van der Waals radii, with butane analogue (I) showing the shortest N...Br halogen-bond distances yet reported between a bromoperfluorocarbon and a nitrogen base [2.809 (3) and 2.818 (3) Å], which are 0.58 and 0.59 Å shorter than the sum of the van der Waals radii.

Rotational Dynamics of Diazabicyclo[2.2.2]octane in Isomorphous Halogen-Bonded Co-crystals: Entropic and Enthalpic Effects.

Based on rotational dynamics measurements carried out with isomorphic co-crystals formed by halogen-bonding (XB) between tritylacetylene halides (TrX) and diazabicyclo[2.2.2]octane (dabco), we were able to distinguish the sources of the enthalpic and entropic components in the rotational free energy barrier. We describe the formation of the 1:1 co-crystals (TrX···N(R)3N) obtained from 1 equiv of dabco and 1 equiv of either TrI or TrBr, respectively, to give 4a and 4b instead of the potential 2:1 complexes. The co-crystals were prepared by solvent evaporation and mechanochemical synthesis. No co-crystal with TrCl was obtained, reflecting the weaker nature of the TrCl···NR3 interaction. Single-crystal X-ray diffraction confirmed structures that resemble a spinning top on a tripod and revealed that the two XB co-crystals are isomorphous, with slightly different C-X···NR3 (X = I, Br) distances and packing interactions. Quadrupolar-echo 2H NMR experiments with 2H-labeled samples showed that fast rotation of dabco in these co-crystals follows a six-fold potential energy surface with three lowest energy minima. Variable-temperature 1H NMR spin-lattice relaxation (VT 1H T1) data revealed rotational dynamics with indistinguishable pre-exponential factors and small but distinguishable activation energies. The activation energy of 4b (Ea = 0.71 kcal mol-1) is the lowest reported in the field of amphidynamic crystals. Using the Eyring equation, we established that their activation entropy for rotation is small but negative (ΔS⧧ = -3.0 cal mol-1 K-1), while there is almost a 2-fold difference in activation enthalpies, with 4a having a higher barrier (ΔH⧧ = 0.95 kcal mol-1) than 4b (ΔH⧧ = 0.54 kcal mol-1). Analysis of the rotator cavity in the two co-crystals revealed subtle differences in steric interactions that account for their different activation energies.

Theoretical Investigation of the Te4Br2 Molecule in Ionic Liquids

Material synthesis in ionic liquids, at or near room temperature, is currently a subject of immense academic interest. In order to illuminate molecular‐level details and the underlying chemistry, we carried out molecular simulations of a single Te4Br2 molecule dissolved in the ionic liquid 1‐ethyl‐3‐methylimidazolium chloride, as well as in the ionic liquid mixed with aluminum chloride. Although the ethyl side chain is much too short to show detailed microheterogeneity, significant structuring with the small chloride anions is seen in case of the pure ionic liquid. In the case of the mixture, formation of larger anionic clusters is distinctly observed and analyzed. Due to the tendency of ionic liquids to dissociate, there is a pronounced shift to elongated Te–Br distances in both investigated solvents. However, only in the AlCl3‐containing liquid, we observe the reaction of the open chain‐like Te4Br2 molecule to a closed square‐like Te4Br+ and AlCl3Br– ion. The molecular arrangement of the [Te4]2+ unit shows negligible deviation from that in the experimental crystal structure.

The non-isomorphous crystal structures of NHC-Au-Cl and NHC-Au-Br (NHC is 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene).

Gold monochloride and monobromide can be transformed into monomeric complexes by ligands such as CO, PPh3 or Me2S, and such ligand-stabilized gold monochloride compounds have been investigated as catalysts, luminescent materials and anticancer drugs, especially when coordinated to a lipophilic benzyl-substituted N-heterocyclic carbene (NHC) ligand. The triclinic structures of NHC-Au-Cl {chlorido(1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)gold, [AuCl(C29H24N2)]} and NHC-Au-Br {bromido(1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene)gold, [AuBr(C29H24N2)]}, determined by X-ray crystallography at 100 K, have one and four molecules, respectively, in their asymmetric units. The chloride compound shows an almost linear C-Au-Cl fragment [179.76 (8)°], with an Au-C distance of 1.976 (3) Å and an Au-Cl distance of 2.3013 (6) Å, while the bromide compound shows surprisingly large geometry deviations, from 1.969 (12) to 2.016 (10) Å for the Au-C distance and from 2.4279 (14) to 2.4796 (12) Å for the Au-Br distance, in the four independent molecules.

Iridium complexes [p-Tol4Sb]+[p-Tol4Sb(DMSO)]+[IrBr6]2– and [p-Tol4Sb(DMSO)]+[IrBr4(DMSO)2]–: Synthesis and structure

The complex [p-Tol4Sb]+[p-Tol4Sb(DMSO)]+[IrBr6]2– (I) has been synthesized by the reaction between tetra(para-tolyl)stibonium bromide and sodium hexabromoiridate(IV) in dimethyl sulfoxide. In a solution, complex I is slowly converted into [p-Tol4Sb(DMSO)]+[IrBr4(DMSO)2]– (II). The antimony atoms in the [p-Tol4Sb]+ cation of complex I have a distorted tetrahedral coordination: СSbС angles are 106.5(3)°–111.1(3)°, and Sb–С bonds range within 2.083(7)–2.097(7) A. The antimony atoms in [p-Tol4Sb(DMSO)]+ cations have a distorted trigonal bipyramidal coordination to oxygen and carbon atoms in axial positions. The axial OSbC and equatorial СSbC angles are, respectively, 172.5(4)° and 107.6(3)°, 115.9(3)°, 120.0(3)° for I; 177.2(9)° and 113.7(9)°, 116.9(9)°, 117.8(9)° for II. The Sb–C and Sb–O distances are 2.086(7)–2.117(8) and 2.945(9) A (I), 2.09(2)–2.16(2) and 2.60(2) A (II). The trans-BrIrBr angles in the octahedral [IrBr6]2– and [IrBr4(DMSO)2]– anions range within 178.79(3)°–179.49(3)° and 176.6(4)°–178.79(15)°, respectively. The Ir–Br distances are 2.4686(9)–2.4925(9) A and 2.463(5)–2.500(4) A, respectively, and the Ir–S distances are 2.291(7) and 2.340(5) A.