Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal.

A detailed description of the procedures utilized in the nonroutine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder

Trapping x‐ray radiation damage from homolytic Se–C bond cleavage in BnSeSeBn crystals (Bn=benzyl, CH2C6H5)

Irradiation of dibenzyl diselenide BnSeSeBn with X-ray or UV-light cleaves the Se-C and the Se-Se bonds, inducing stable and metastable radical states. They are inevitably important to all natural and life sciences. Structural changes due to X-ray-induced Se-C bond-cleavage could be pin-pointed in various high-resolution X-ray diffraction experiments for the first time. Extended DFT methods were applied to characterize the solid-state structure and support the refinement of the observed residuals as contributions from the BnSeSe • radical species. The X-ray or UV-irradiated crystalline samples of BnSeSeBn were characterized by solid-state EPR. This paper provides insight that in the course of X-ray structure analysis of selenium compounds not only organo-selenide radicals like RSe • may occur, but also organo diselenide BnSeSe • radicals and organic radicals R • are generated, particularly important to know in structural biology

Expanding the scope of Cu(I) Catalyzed “Click Chemistry” with abnormal NHCs: three-fold click to Tris-Triazoles

Ho NKT, Reichmann SO, Rottschäfer D, Herbst-Irmer R, Ghadwal R. Expanding the scope of Cu(I) Catalyzed “Click Chemistry” with abnormal NHCs: three-fold click to Tris-Triazoles. Catalysts. 2017;7(9): 262.Cationic copper(I) complexes [Cu(aIPrPh)(IPr)]I (3) and [Cu(aIPrPh)2]I (4) featuring an abnormal N-heterocyclic carbene (aNHC) (aIPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl- imidazol-4-ylidene) and/or an NHC (IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) ligand(s) are reported. Treatment of Cu(aIPrPh)I (2) with IPr affords complex 3. Reaction of (IPrPh)I (1) (IPrPh = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazolium) with CuI in the presence of K{N(SiMe3)2} leads to the formation of 4. Complexes 3 and 4 represent rare examples of mixed aNHC-NHC and bis-aNHC metal complexes, respectively. They are characterized by elemental analysis, NMR spectroscopic, and mass spectrometric studies. The solid-state molecular structures of 3 and 4 have been determined by single crystal X-ray diffraction analyses. The catalytic activity of 2, 3, and 4 has been investigated in the [3+2] cycloaddition of alkynes and organic azides, affording triazole derivatives in an almost quantitative yield. Notably, complexes 2, 3, and 4 are excellent catalysts for the three-fold cycloaddition of a tris-azide with various alkynes. This catalytic protocol offers a high yield access to tris-triazoles in a shorter reaction time and considerably reduces the experimental work-up compared to the classical synthetic method

Fundamental characterization, photophysics and photocatalysis of a base metal iron(II)-cobalt(III) dyad

A new base metal iron-cobalt dyad has been obtained by connection between a heteroleptic tetra-NHC iron(II) photosensitizer combining a 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine with 2,6-bis(3-methyl-imidazol-2-ylidene)-4,4′-bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)-cobalt(III) assembly has been extensively characterized by ground- and excited-state methods like X-ray crystallography, X-ray absorption spectroscopy, (spectro-)electrochemistry, and steady-state and time-resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited-state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability. Transient absorption spectroscopy after excitation into the metal-to-ligand charge transfer absorption band suggests a relaxation cascade originating from hot singlet and triplet MLCT states, leading to the population of the $^{3}$MLCT state that exhibits the longest lifetime. Finally, decay into the ground state involves a $^{3}$MC state. Attachment of cobaloxime to the iron photosensitizer increases the $^{3}$MLCT lifetime at the iron centre. Together with the directing effect of the linker, this potentially makes the dyad more active in photocatalytic proton reduction experiments than the analogous two-component system, consisting of the iron photosensitizer and Co(dmgH)$_2$(py)Cl. This work thus sheds new light on the functionality of base metal dyads, which are important for more efficient and sustainable future proton reduction systems

Substituted pyrazolo[3,4-d]pyrimidines : microwave assisted, solvent free synthesis and biological evaluation

A simple and efficient method has been developed for the synthesis of various pyrazolo[3,4-d]pyrimidines using microwave irradiation under solvent-free conditions. The advantages of applying microwave irradiation compared with the classical method were demonstrated. The structures of all the compounds were confirmed by the usual techniques and in two cases by X-ray analysis. The compounds did not display appreciable ability to inhibit xanthine oxidase activity. Screening for antifungal activity showed that some derivatives were active against four fungi, with more significant results for Botrytis.FEDERFundação para a Ciência e Tecnologia (FCT) - I&D 226/2003, POCTI-SFA-3-686), SFRH/BPD/20816/ 2004)Xunta de Galicia - PGIDIT05PXIB26201PR,PR405A098/59-

Unusual formation of a N-heterocyclic germylene via homolytic cleavage of a C-C bond

Deutsche Forschungsgemeinschaft [RO 224/60-1]; Danish National Research Foundation [DNRF93]; Centre for Materials Crystallography; Norwegian Research Council through the CoE Centre for Theoretical and Computational Chemistry (CTCC) [179568/V30]; China Scholarship Council; Norwegian Supercomputing Program (NOTUR) [NN4654K]Reaction of the monoanionic radical salt IP center dot-K+ (IP = (Py)CH(=NR); Py = C5H4N, R = 2,6-iPr(2)C(6)H(3); alpha-iminopyridine) with GeCl2(dioxane) afforded compound (IPGeCl)(2) (1) which produced red blocks of IPGe: (2), when treated with KC8 in toluene. 1 is a digermylene formed via C-C coupling between two carbon-centered radicals. 2 can be considered as an analogue of a N-heterocyclic carbene, which exhibits a five-membered GeC2N2 ring with one CQC double bond. 2 is formed by two-electron reduction of 1 with cleavage of the two Ge-Cl bonds and the central C-C single bond

Kristallographische Datenbanken Systematische Ueberpruefung von Strukturen auf hoehere Symmetrie und Untersuchungen zur Konformation von 1,3-Oxazolidinen und Phenylsulfonamiden

SIGLEAvailable from TIB Hannover: DW 1519 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman