Automated determination of the extinction symbolviaelectron diffraction data

Nonheme FeIV═O Complexes Supported by Four Pentadentate Ligands: Reactivity toward H- and O- Atom Transfer Processes

Four new pentadentate N5-donor ligands, [N-(1-methyl-2-imidazolyl)methyl-N-(2-pyridyl)-methyl-N-(bis-2-pyridylmethyl)-amine] (L1), [N-bis(1-methyl-2-imidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), (N-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L3), and N,N-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (L4), have been synthesized based on the N4Py ligand framework, where one or two pyridyl arms of the N4Py parent are replaced by (N-methyl)imidazolyl or N-(isoquinolin-3-ylmethyl) moieties. Using these four pentadentate ligands, the mononuclear complexes [FeII(CH3CN)(L1)]2+ (1a), [FeII(CH3CN)(L2)]2+ (2a), [FeII(CH3CN)(L3)]2+ (3a), and [FeII(CH3CN)(L4)]2+ (4a) have been synthesized and characterized. The half-wave potentials (E1/2) of the complexes become more positive in the order: 2a < 1a < 4a ≤ 3a ≤ [Fe(N4Py)(CH3CN)]2+. The order of redox potentials correlates well with the Fe-Namine distances observed by crystallography, which are 2a > 1a ≥ 4a > 3a ≥ [Fe(N4Py)(CH3CN)]2+. The corresponding ferryl complexes [FeIV(O)(L1)]2+ (1b), [FeIV(O)(L2)]2+ (2b), [FeIV(O)(L3)]2+ (3b), and [FeIV(O)(L4)]2+ (4b) were prepared by the reaction of the ferrous complexes with isopropyl 2-iodoxybenzoate (IBX ester) in acetonitrile. The greenish complexes 3b and 4b were also isolated in the solid state by the reaction of the ferrous complexes in CH3CN with ceric ammonium nitrate in water. Mössbauer spectroscopy and magnetic measurements (using superconducting quantum interference device) show that the four complexes 1b, 2b, 3b, and 4b are low-spin (S = 1) FeIV═O complexes. UV/vis spectra of the four FeIV═O complexes in acetonitrile show typical long-wavelength absorptions of around 700 nm, which are expected for FeIV═O complexes with N4Py-type ligands. The wavelengths of these absorptions decrease in the following order: 721 nm (2b) > 706 nm (1b) > 696 nm (4b) > 695 nm (3b) = 695 nm ([FeIV(O) (N4Py)]2+), indicating that the replacement of the pyridyl arms with (N-methyl) imidazolyl moieties makes L1 and L2 exert weaker ligand fields than the parent N4Py ligand, while the ligand field strengths of L3 and L4 are similar to the N4Py parent despite the replacement of the pyridyl arms with N-(isoquinolin-3-ylmethyl) moieties. Consequently, complexes 1b and 2b tend to be less stable than the parent [FeIV(O)(N4Py)]2+ complex: the half-life sequence at room temperature is 1.67 h (2b) < 16 h (1b) < 45 h (4b) < 63 h (3b) ≈ 60 h ([FeIV(O)(N4Py)]2+). Compared to the parent complex, 1b and 2b exhibit enhanced reactivity in both the oxidation of thioanisole in the oxygen atom transfer (OAT) reaction and the oxygenation of C-H bonds of aromatic and aliphatic substrates, presumed to occur via an oxygen rebound process. Furthermore, the second-order rate constants for hydrogen atom transfer (HAT) reactions affected by the ferryl complexes can be directly related to the C-H bond dissociation energies of a range of substrates that have been studied. Using either IBX ester or H2O2 as an oxidant, all four new FeII complexes display good performance in catalytic reactions involving both HAT and OAT reactions.

Hydrogen-atom and oxygen-atom transfer reactivities of iron(IV)-oxo complexes of quinoline-substituted pentadentate ligands

A series of iron(II) complexes with the general formula [Fe^II(L2-Qn)(L)]ⁿ⁺ (n = 1, L = F^-, Cl^-; n = 2, L = NCMe, H₂O) have been isolated and characterized. The X-ray crystallographic data reveals that metal-ligand bond distances vary with varying ligand field strengths of the sixth ligand. While the complexes with fluoride, chloride and water as axial ligand are high spin, the acetonitrile-coordinated complex is in a mixed spin state. The steric bulk of the quinoline moieties forces the axial ligands to deviate from the Fe-N_axial axis. A higher deviation/tilt is noted for the high spin complexes, while the acetonitrile coordinated complex displays least deviation. This deviation from linearity is slightly less in the analogous low-spin iron(II) complex [Fe^II(L1-Qn)(NCMe)]²⁺ of the related asymmetric ligand L1-Qn due to the presence of only one sterically demanding quinoline moiety. The two iron(II)-acetonitrile complexes [Fe^II(L2-Qn)(NCMe)]²⁺ and [Fe^II(L1-Qn)(NCMe)]²⁺ generate the corresponding iron(IV)-oxo species with higher thermal stability of the species supported by the L1-Qn ligand. The crystallographic and spectroscopic data for [Fe^IV(O)(L1-Qn)](ClO₄)₂ bear resemblance to other crystallographically characterized S = 1 iron(IV)-oxo complexes. The hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reactivities of both the iron(IV)-oxo complexes were investigated, and a Box-Behnken multivariate optimization of the parameters for catalytic oxidation of cyclohexane by [Fe^II(L2-Qn)(NCMe)]²⁺ using hydrogen peroxide as the terminal oxidant is presented. An increase in the average Fe-N bond length in [Fe^II(L1-Qn)(NCMe)]²⁺ is also manifested in higher HAT and OAT rates relative to the other reported complexes of ligands based on the N4Py framework. The results reported here confirm that the steric influence of the ligand environment is of critical importance for the reactivity of iron(IV)-oxo complexes, but additional electronic factors must influence the reactivity of iron-oxo complexes of N4Py derivatives.

A Cyclometalated NHC Iridium Complex Bearing a Cationic (η5 -Cyclopentadienyl)(η6 -phenyl)iron Backbone*

Nucleophilic substitution of [(η5 -cyclopentadienyl)(η6 -chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η5 -cyclopentadienyl)(η6 -phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η5 -1,2,3,4,5-pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η5 -cyclopentadienyl)(η6 -phenyl)iron(II)]+ substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X-ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η5 -cyclopentadienyl)(η6 -phenyl)iron(II)]+ unit at the NHC ligand.

Relationship between crystal shape and unit cell shape: crystal shape modification via co-crystallization toward SXRD-suitable crystals

The relationships between the shape and cell parameters were investigated using 131 crystals of secondary aromatic sulfonamides. And, 11 sulfonamides isolated as oils, amorphous, or needle crystals were co-crystallized to obtain block-like crystals.

New luminescent tetracoordinate boron complexes: an in-depth experimental and theoretical characterisation and their application in OLEDs

New luminescent 2-iminopyrrolyl boron complexes with different BX2 moieties are extensively studied via complementary experimental and theoretical methodologies, including application in OLEDs.

High-Spin Mononuclear Iron(III) Complexes with Pentadentate Schiff Base Ligands: Structural Analysis and Magnetic Properties

Various substituted 2-hydroxybenzophenones were combined with aliphatic linear triamines to form pentadentate Schiff base ligands. Twelve new iron(III) complexes with the general formula [Fe(L_n )X].mCH₃ CN (n=1-10; X=N₃ ^- , NCS^- or NCSe^- ; m=0-2) have been synthesized, and spectrally as well as structurally characterized. The structural analysis revealed a notable dependence of coordination polyhedra deformation as well as the spatial configuration of donor atoms on the length and symmetry of the Schiff base ligands. The magnetic properties of the compounds were investigated and the permanent high-spin state (S=5/2) for all reported compounds was established, and allowed calculation of zero-field-splitting parameters as well as coupling constants, which were further confirmed with DFT calculations. The solid-state EPR spectra were recorded at 293 K and 98 K, and in accordance with the magnetic measurements, showed a high-spin state in the measured temperature range.

Paddlewheel-type diruthenium(iii,iii) tetrakis(2-aminopyridinate) complexes with NIR absorption features: combined experimental and theoretical study

Aminopyridinate-bridged Ru₂(iii,iii) complexes with near-infrared absorption features were prepared and characterized by experimental and theoretical techniques.

Playing with Pearson's concept: orthogonally functionalized 1,4-diaza-1,3-butadienes leading to heterobinuclear complexes

By reacting 1,2-diketones and ortho- diphenylphosphinoyl aniline in the presence of zinc(ii) as a templating agent, cationic zinc(ii) complexes of novel phosphine oxide functionalized 1,4-diaza-1,3-butadiene ligands are acessible. Herein the zinc(ii) site is bound to all four donor atoms of the ligand. Depending on the flexibility of the 1,4-diaza-1,3-butadiene backbone, the bonds to zinc(ii) from the 1,4-diaza-1,3-butadiene donors can be broken. Reaction with oxalate cleaves the zinc(ii) coordination completely and makes accessible the free ligands possessing orthogonal (N,N: soft; O,O: hard) sets of donor sites. This allows for the specific coordination of soft and hard Lewis acids and thus for the generation of heterobimetallic complexes, here exemplarily shown for the combination of palladium(ii) (soft) and zinc(ii) (hard) centres.

Introduction of axial chirality at a spiro carbon atom in the synthesis of pentaerythritol-imine macrocycles

Novel chiral macrocyclic polyimines with spiro carbon atoms are described. The key feature of the synthesis is the formation of an axially chiral quaternary carbon atom having four constitutionally identical substituents. This is possible either by the freezing of the labile conformation of a spiro-diboronate moiety or by the diastereomeric fitting of a conformationally stable spiro-acetal moiety into a chiral framework. A general model for the description of this type of axial chirality is proposed.

Benzene-fused bis(acenaphthoBODIPY)s, stable near-infrared-selective dyes

Benzene-fused bis(acenaphthoBODIPY)s prepared by retro-Diels–Alder reaction of bicyclo[2.2.2]octadiene-fused precursors showed strong absorption bands in the near-infrared region and very weak absorptions in the visible region.

Benzene-fused bis(acenaphthoBODIPY)s prepared by retro-Diels–Alder reaction of bicyclo[2.2.2]octadiene-fused precursors showed strong absorption bands in the near-infrared region and very weak absorptions in the visible region.

Total Synthesis, Configuration Assignment, and Cytotoxic Activity Evaluation of Protulactone A

The first total synthesis and absolute configuration assignment of protulactone A (1) has been achieved. Four stereoisomers, 1a, ent-1a, 1b, and ent-1b, of this natural polyketide were prepared by chiral pool synthesis starting from l- and d-arabinose, respectively. The absolute and relative configurations of all isomers were assigned by single-crystal X-ray analysis. Target compounds were screened for their in vitro cytotoxicity toward certain human tumor cells (NCI₆₀ cancer cell line panel).

Reactivity of cationic α-diimine cyclopentadienyl nickel complexes towards AlEt2Cl: synthesis, characterisation and ethylene polymerisation

Cationic α-diimine cyclopentadienyl nickel complexes transform into intermediates upon reaction with AlEt₂Cl giving rise to active ethylene polymerisation catalysts.

Series of high spin mononuclear iron(iii) complexes with Schiff base ligands derived from 2-hydroxybenzophenones

Utilization of 2-hydroxybenzophenone derivatives for the preparation of iron(iii) Schiff base complexes resulted in a series of high-spin, mostly antiferromagnetically coupled systems.

Structural insights intoM2O–Al2O3–WO3(M= Na, K) system by electron diffraction tomography

TheM2O–Al2O3–WO3(M= alkaline metals) system has attracted the attention of the scientific community because some of its members showed potential applications as single crystalline media for tunable solid-state lasers. These materials behave as promising laser host materials due to their high and continuous transparency in the wide range of the near-IR region. A systematic investigation of these phases is nonetheless hampered because it is impossible to produce large crystals and only in a few cases a pure synthetic product can be achieved. Despite substantial advances in X-ray powder diffraction methods, structure investigation on nanoscale is still challenging, especially when the sample is polycrystalline and the structures are affected by pseudo-symmetry. Electron diffraction has the advantage of collecting data from single nanoscopic crystals, but it is frequently limited by incompleteness and dynamical effects. Automated diffraction tomography (ADT) recently emerged as an alternative approach able to collect more complete three-dimensional electron diffraction data and at the same time to significantly reduce dynamical scattering. ADT data have been shown to be suitable forabinitiostructure solution of phases with large cell parameters, and for detecting pseudo-symmetry that was undetected in X-ray powder data. In this work we present the structure investigation of two hitherto undetermined compounds, K5Al(W3O11)2and NaAl(WO4)2, by a combination of electron diffraction tomography and precession electron diffraction. We also stress how electron diffraction tomography can be used to obtain direct information about symmetry and pseudo-symmetry for nanocrystalline phases, even when available only in polyphasic mixtures.

Crystal structure determination and refinementviaSIR2014

SIR2014is the latest program of theSIRsuite for crystal structure solution of small, medium and large structures. A variety of phasing algorithms have been implemented, bothab initio(standard or modern direct methods, Patterson techniques,Vive la Différence) and non-ab initio(simulated annealing, molecular replacement). The program contains tools for crystal structure refinement and for the study of three-dimensional electron-density mapsviasuitable viewers.

Revised stereochemistry of ficifolidione and its biological activities against insects and cells

Ficifolidione (1), a moderately active insecticidal compound from two species of Myrtaceae, and its derivatives were synthesized to evaluate their insecticidal activity. X-ray crystallographic analyses and specific rotation values of ficifolidione and its C-4 (2) demonstrated that the structure of ficifolidione differs from the reported absolute structure; that is, the C-4 configuration of ficifolidione should have an S configuration. The reported insecticidal activity of ficifolidione (1) and its C-4 epimer (2) against adult houseflies (Musca domestica), mosquito larvae (Culex pipiens), and cutworms (Spodoptera litura) was not observed. The cytotoxicities of ficifolidione and its derivatives (1-4) against four cell lines, Sf9, Colon26, HL60, and Vero, were also measured because ficifolidione has a phloroglucinol-derived moiety, a motif that is often present in the structure of cytotoxic chemicals. Compound 1 exhibited IC50 values of ca. 32, 9, 3, and 12 μM for Sf9, Colon26, HL60, and Vero cells, respectively, indicating that ficifolidione possesses selective cytotoxicity against the four cell lines. In HL60 cells treated with 1, DNA fragmentation and the activation of procaspase 3 were observed, suggesting that the cytotoxicity is induced by apoptosis.

Analysis of rapidly synthesized guest-filled porous complexes with synchrotron radiation: practical guidelines for the crystalline sponge method

A detailed set of synthetic and crystallographic guidelines for the crystalline sponge method based upon the analysis of expediently synthesized crystal sponges using third-generation synchrotron radiation are reported. The procedure for the synthesis of the zinc-based metal-organic framework used in initial crystal sponge reports has been modified to yield competent crystals in 3 days instead of 2 weeks. These crystal sponges were tested on some small molecules, with two being unexpectedly difficult cases for analysis with in-house diffractometers in regard to data quality and proper space-group determination. These issues were easily resolved by the use of synchrotron radiation using data-collection times of less than an hour. One of these guests induced a single-crystal-to-single-crystal transformation to create a larger unit cell with over 500 non-H atoms in the asymmetric unit. This led to a non-trivial refinement scenario that afforded the best Flack x absolute stereochemical determination parameter to date for these systems. The structures did not require the use of PLATON/SQUEEZE or other solvent-masking programs, and are the highest-quality crystalline sponge systems reported to date where the results are strongly supported by the data. A set of guidelines for the entire crystallographic process were developed through these studies. In particular, the refinement guidelines include strategies to refine the host framework, locate guests and determine occupancies, discussion of the proper use of geometric and anisotropic displacement parameter restraints and constraints, and whether to perform solvent squeezing/masking. The single-crystal-to-single-crystal transformation process for the crystal sponges is also discussed. The presented general guidelines will be invaluable for researchers interested in using the crystalline sponge method at in-house diffraction or synchrotron facilities, will facilitate the collection and analysis of reliable high-quality data, and will allow construction of chemically and physically sensible models for guest structural determination.

Crystal structure of a four-layered [3.3](3,5)pyridino-phane

The title compound, C40H46N2 {systematic name: 12,30-di-aza-hepta-cyclo[21.13.1.1(5,19).1(6,18).1(10,14).1(24,36).1(28,32)]do-tetra-conta-1(37),5(40),6(41),10(42),11,13,18,23,28,30,32(39),36(38)-dodeca-ene}, has syn-anti-syn geometry wherein the two outer [3.3]meta-cyclo-phane (MCP) moieties have a syn geometry, and contain the facing benzene and pyridine rings at dihedral angles of 26.26 (10) and 26.46 (10)°, respectively. The rings of the central [3.3]MCP unit are not parallel, but orientated at a slight angle of 2.66 (9)°. Three bridging methyl-ene groups are disordered over two sets of sites in a 0.60:0.40 ratio. In the crystal, the mol-ecules are linked by C-H⋯N inter-actions and inter-molecular C-H⋯π short contacts, generating a three-dimensional network.

Crystal structure of 4-(prop-2-yn-yloxy)-2,2,6,6-tetra-methyl-piperidin-1-ox-yl

The structure of a TEMPO derivative with a propyn­yloxy substituent at the 4-position of the piperidine ring is reported. The crystal packing features an unusual C—H⋯π inter­action involving the triple bond of the propyne group which combines with C—H⋯O hydrogen bonds to stack the mol­ecules along the b-axis direction.

The title compound, C₁₂H₂₀NO₂, was synthesized from 4-hy­droxy-2,2,6,6-tetra­methyl­piperidin-1-oxyl (hy­droxy-TEMPO) and propargyl bromide. The six-membered ring adopts a flattened chair conformation and carries a propyn­yloxy substituent in an equatorial orientation at the 4-position. The N—O bond length of the piperidin-1-oxyl unit is 1.289 (3) Å. In the crystal, C—H⋯O hydrogen bonds combine with unusual C—H⋯π inter­actions involving the alkyne unit as acceptor to generate a three-dimensional network.

SIR2011: a new package for crystal structure determination and refinement

SIR2011, the successor ofSIR2004, is the latest program of theSIRsuite. It can solveab initiocrystal structures of small- and medium-size molecules, as well as protein structures, using X-ray or electron diffraction data. With respect to the predecessor the program has several new abilities:e.g.a new phasing method (VLD) has been implemented, it is able to exploit prior knowledge of the molecular geometryviasimulated annealing techniques, it can use molecular replacement methods for solving proteins, it includes new tools like free lunch and new approaches for electron diffraction data, and it visualizes three-dimensional electron density maps. The graphical interface has been further improved and allows the straightforward use of the program even in difficult cases.