1,721,088 research outputs found
X-ray crystallography: one century of Nobel Prizes
No full textIn 2012, the United Nations General Assembly declared 2014 the International Year of Crystallography. Throughout the year 2014 and beyond, all the crystallographic associations and societies active all over the world are organizing events to attract the wider public toward crystallography and the numerous topics to which it is deeply interlinked. To increase awareness of modern crystallography and to diminish its halo of exoticism, the present commentary focuses on the fundamental contributions of X-ray crystallography during the last century in chemistry, physics, and medicine, as witnessed by the numerous Nobel Prizes that involved it
Enclosing the functional properties of pyrazolato-based coordination polymers within a structural frame: the role of laboratory X-ray powder diffraction
No full textAb initio X-ray powder diffraction structural analyses from laboratory data have been widely employed in the characterization of coordination polymers not affording single crystals of suitable quality to undergo conventional structural determinations. This is particularly true for coordination polymers built upon strong ligand-to-metal bonds, as those formed by anionic, nitrogen-based heterocycles - pyrazolates, imidazolates, pyrimidinolates and more complex moieties derived therefrom. More than one hundred species belonging to this class have been structurally characterized in the last three decades, affording key, otherwise inaccessible stereochemical and supramolecolar features. This contribution summarizes our most recent experience in the XRPD structural characterization of pyrazolato-based coordination polymers, devoting a special consideration to the methodologies and tricks which allowed us to juxtapose the structural description of these materials to their physico-chemical and, above all, functional properties
Fundamentals of Powder Diffraction
No full textIn this contribution we provide the theoretical and experimental basis of powder diffraction methods, which, in the last decades, have been widely used for qualitative and quantitative phase analyses, materials characterization and lately, for structural analyses of polycrystalline species and in situ and real time characterization of chemical reactions and phase transformations
Coordination chemistry of 2-pyrimidinolate: Synthesis and characterization of a neutral tetrameric rhodium(I) derivative
No full textA novel metal-organic complex of analytical Rh(COD)(2-pymo) formulation (COD = 1,5-cyclooctadiene, 2-Hpymo = 2-hydroxypyrimidine) has been prepared by reacting [Rh(COD)Cl]2 with 2-Hpymo. While direct syntheses in a variety of solvents (acetone, toluene or methanol) typically afforded amorphous powders, recrystallization from methanol allowed to perform a single crystal data collection on the CH3OH solvate. The crystal structure of the latter [tetragonal, P-42c, a = 13.9780(2), c = 14.4980(10) Å, V = 2832.7(6) Å^3] contains cyclic [Rh(COD)(2-pymo)]4 tetramers, in which distorted square planar metal atoms are bridged by n1-μ2-N,N′-exo-bidentate 2-pymo ligands in 1,3-alternate disposition. Upon dissolving both the amorphous and the crystalline (solvated) species in CD2Cl2, variable temperature NMR spectra confirmed the presence of identical (tetrameric) species, thus excluding the existence of other oligomers of different nuclearity in the amorphous powders
Coordination polymers and metal-organic frameworks based on poly(pyrazole)-containing ligands
No full textIn the past two decades, the vast classes of coordination polymers (CPs) and metal-organic frameworks (MOFs) have received deep attention in both the academic and industrial realms, as they can possess different functional properties of economic, technological and/or environmental interest, such as luminescence, electric conductivity, magnetism, catalytic activity, gas storage or separation, drug delivery - to mention only a few. Within this vast landscape, this review proposes a survey on those transition metal containing CPs and MOFs built up with poly(pyrazole)- and poly(pyrazolate)-based ligands, in which up to three N-donor heterocyclic rings are organized on rigid or flexible cores. The overview has been restricted to the most recurrent transition metals, namely copper, zinc, cobalt, nickel, cadmium, silver and iron. For each material, mentioning of the synthetic method(s) yielding to its isolation is complemented by a description of its thermal behaviour, of the main structural aspects and, whenever investigated, of its functional properties
2-(2-Hydroxyaryl)cinnamic amides: a new class of axially chiral molecules
No full textThe syntheses of several differently substituted amides formally derived from a chiral amine, either E-2-(2-hydroxyphenyl)cinnamic acid or both E- and Z-2-(2-hydroxynaphthyl)cinnamic acid, are reported. These molecules display a restricted rotation about the C2-Caryl bond. The barriers to rotation about the C2-Caryl bond were measured by the dynamic 1H NMR and were found to vary between 11.8 and 24.5 kcal mol-1, depending on the substitution. In particular, E-2-(2-hydroxynapthyl)cinnamic amides, displayed a high barrier to rotation (ΔGc‡ = 24.4 kcal mol-1) and could be isolated in both diastereomerically pure forms at room temperature. The X-ray structure of one E-2-(2-hydroxynapthyl)cinnamic amide, was resolved, enabling for the determination of the absolute configuration of the chiral axis (aR)
X-ray powder diffraction characterization of the elusive tetraphosphine Si(CH2PPh2)4 silane
No full textX-ray powder diffraction data for the tetraphosphinic Si(CH2PPh2)4 silane are reported. Its crystal and molecular structures were determined by simulated annealing and full-profile Rietveld refinement methods. Si(CH2PPh2)(4) was found to have tetragonal symmetry with P-42(1)c space group. The lattice parameters were determined to be a = 17.211(2) angstrom, c = 7.553(1) angstrom, V = 2237.5(5) angstrom^3. The crystal structure was found to contain isolated Si(CH2PPh2)(4) molecules. In each Si(CH2PPh2)(4) molecule, the central Si atom was fixed at the -4 symmetric position bearing four CH2PPh2 branches. This environment was confirmed by P-31 CP/MAS NMR measurements. Thermo-diffractometric measurements in the 20-120 degrees C range were also used to estimate the linear and volumetric thermal expansion coefficients (d ln V/ dT=1.8 x 10^-4 K^-1, typical for very "soft" materials
Synthesis and characterisation of new polynuclear copper(I) pyrazolate complexes and their catalytic activity in the cyclopropanation of olefins
No full textThe reaction of [Cu(CH3CN)4](BF4) with racemic pyrazole-3,5-dicarboxylic acid di-sec-butyl ester (3,5-dicarbo-sec-butoxypyrazole, Hdcsbpz) or with pyrazole-3,5-di-ter-butyl (3,5-di-ter-butylpyrazole, Hdtbpz) quantitatively yields the new [Cu(dcsbpz)]4 and [Cu(dtbpz)]4 complexes, respectively. Crystals of [Cu(dcsbpz)]4 are triclinic, P1̄, a = 10.9748(7), b = 11.8399(8), c = 26.5575(17) Å, α =100.605(2), β = 90.783(2), γ = 105.362(2)°; [Cu(dtbpz)]4·CH2Cl2 is monoclinic, P21/n, a = 10.902(3), b = 19.200(3), c = 25.772(4) Å, β = 93.86(2)°. Both species contain cyclic tetrameric molecules, with the heterocyclic ligands binding in the common N,N′-exo-bidentate mode; however, the shape and geometry of the inner Cu4 moiety is remarkably different, as highlighted, for example, by the absolute values of the 1,2 and 1,3 (non-bonding) Cu⋯Cu interactions. These polynuclear copper(I) pyrazolate complexes catalyse the conversion of alkenes into the corresponding cyclopropane derivatives with interesting diastereomeric excesses. Aiming at the evaluation of their catalytic activities, a systematic study of the cyclopropanation reactions in the presence of ethyl diazoacetate has been performed
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