The Crystal and Molecular Structures of 2,5-Bis(2'-pyridyl)-pyrazine (BPPZ) and Some 3d Transition-Metal Complexes

The symmetrical ligand 2,5-bis(2'-pyridyl)pyrazine (BPPZ) exists in the extended form with a dihedral angle between the pyrazine and the pyridine rings of 7.88°. BPPZ forms symmetrical bis(bidenate) complexes with MnII, FeII, and CuII. The dihedral angles between the best planes through the planar pyrazine ring and the pyridine ring are 2.6° in the MnII complex, 4° in the FeII complex, and 8.5° in the CuII complex. The metal-Npy bond distances are shorter than standard values and similar in length to the metal-Npz distances

AgI, CdII, and HgII complexes with 2,5-bis(pyridyl)pyrazine ligands: syntheses, spectral analyses, single crystal, and powder X-ray analyses

2,5-Bis(4-pyridyl)pyrazine (4-bppz) and 2,5-bis(3-pyridyl)pyrazine (3-bppz) have been synthesized and characterized spectroscopically and crystallographically. 4-bppz [unit cell: a = 7.319(1), b = 5.746(1), c = 12.756(2) Å, β = 93.16(1)° space group: P21/a] was characterized by X-ray single crystal diffraction methods while the structure of 3-bppz [unit cell: a = 10.9148(4), b = 4.5722(1), c = 11.4462(2) Å, β = 109.571(2)° space group: P21/c] was determined from laboratory X-ray powder diffraction data. In these compounds, the pyrazine ring contains two symmetrically attached pyridine substituents with the nitrogen atom in the para positions for 4-bppz and in the meta positions for 3-bppz. Both compounds possess Ci symmetry with the pyridine rings twisted by 17.7° (4-bppz) and 2.6° (3-bppz) with respect to the pyrazine ring. 4-bppz was used in the formation of coordination compounds with silver(I) and cadmium(II). The silver(I) complex [Ag(OAc)(4-bppz)] n (1) [unit cell: a = 8.472(1), b = 13.051(1), c = 19.063(2) Å, β = 109.96(1)° space group: P21/c] is characterized by the formation of a perfectly linear chain containing the silver ions bridged by the ligand molecule, the latter using its pyridine nitrogen donor atoms for coordination. A pair of chains is interconnected by silver-silver interactions, the silver coordination sphere being completed by acetate anions. A similar one-dimensional coordination polymer, [Cd(OAc)2(4-bppz)(MeOH)] n (2) [unit cell: a = 8.680(1), b = 10.035(1), c = 13.445(1) Å, α = 77.35(1), β = 71.17(1), γ = 80.14(1)° space group: $$P\bar 1$$ ], was obtained by the reaction of 4-bppz with Cd(OAc)2. Ligand 3-bppz forms an analogous cadmium(II) complex, [Cd(OAc)2(3-bppz)(MeOH)] n (3) [unit cell: a = 9.306(1), b = 9.733(1), c = 11.550(1) Å, α = 87.86(1), β = 76.73(1), γ = 85.91(1)° space group: $$P\bar 1$$ ], containing the molecules arranged in double zigzag chains. The reaction of 3-bppz with HgI2 leads surprisingly to a binuclear complex, [Hg2I4(3-bppz)2] (4) [unit cell: a = 17.555(1), b = 12.973(1), c = 16.195(1) Å, β = 115.32(1)° space group: C2/c]. Two ligand molecules are bridged by two mercury(II) ions forming a cyclic structure, the tetrahedral coordination sphere of the metal being completed by iodide anion

AgI, CdII, and HgII complexes with 2,5-bis(pyridyl)pyrazine ligands: syntheses, spectral analyses, single crystal, and powder X-ray analyses

2,5-Bis(4-pyridyl)pyrazine (4-bppz) and 2,5-bis(3-pyridyl)pyrazine (3-bppz) have been synthesized and characterized spectroscopically and crystallographically. 4-bppz [unit cell: a = 7.319(1), b = 5.746(1), c = 12.756(2) Å, β = 93.16(1)° space group: P21/a] was characterized by X-ray single crystal diffraction methods while the structure of 3-bppz [unit cell: a = 10.9148(4), b = 4.5722(1), c = 11.4462(2) Å, β = 109.571(2)° space group: P21/c] was determined from laboratory X-ray powder diffraction data. In these compounds, the pyrazine ring contains two symmetrically attached pyridine substituents with the nitrogen atom in the para positions for 4-bppz and in the meta positions for 3-bppz. Both compounds possess Ci symmetry with the pyridine rings twisted by 17.7° (4-bppz) and 2.6° (3-bppz) with respect to the pyrazine ring. 4-bppz was used in the formation of coordination compounds with silver(I) and cadmium(II). The silver(I) complex [Ag(OAc)(4-bppz)] n (1) [unit cell: a = 8.472(1), b = 13.051(1), c = 19.063(2) Å, β = 109.96(1)° space group: P21/c] is characterized by the formation of a perfectly linear chain containing the silver ions bridged by the ligand molecule, the latter using its pyridine nitrogen donor atoms for coordination. A pair of chains is interconnected by silver-silver interactions, the silver coordination sphere being completed by acetate anions. A similar one-dimensional coordination polymer, [Cd(OAc)2(4-bppz)(MeOH)] n (2) [unit cell: a = 8.680(1), b = 10.035(1), c = 13.445(1) Å, α = 77.35(1), β = 71.17(1), γ = 80.14(1)° space group: $$P\bar 1$$ ], was obtained by the reaction of 4-bppz with Cd(OAc)2. Ligand 3-bppz forms an analogous cadmium(II) complex, [Cd(OAc)2(3-bppz)(MeOH)] n (3) [unit cell: a = 9.306(1), b = 9.733(1), c = 11.550(1) Å, α = 87.86(1), β = 76.73(1), γ = 85.91(1)° space group: $$P\bar 1$$ ], containing the molecules arranged in double zigzag chains. The reaction of 3-bppz with HgI2 leads surprisingly to a binuclear complex, [Hg2I4(3-bppz)2] (4) [unit cell: a = 17.555(1), b = 12.973(1), c = 16.195(1) Å, β = 115.32(1)° space group: C2/c]. Two ligand molecules are bridged by two mercury(II) ions forming a cyclic structure, the tetrahedral coordination sphere of the metal being completed by iodide anion

Rhodium(iii) complexes containing C4-bound N-heterocyclic carbenes: synthesis, coordination chemistry, and catalytic activity in transfer hydrogenation

Direct metalation of C2-protected diimidozolium salts with RhCl₃ or [RhCl(cod)]₂ and KI afforded a series of new rhodium(III) complexes with abnormally C4-bound, cis-chelating NHC ligands. The complexes were isolated as dimetallic species containing two (μ²-I)₃-bridged rhodium(III) centers. In the presence of coordinating ligands such as CH₃CN, PPh₃, or dppe, the dimeric structure is readily cleaved and yields monometallic complexes. Crystallographic analysis of representative structures indicates a higher trans influence of abnormally C4-bound carbenes as compared to normal NHCs. The exceptionally strong donor ability of carbenes in such a C4 coordination mode increases the catalytic activity of the rhodium center and allows for efficient transfer hydrogenation of ketones in iPrOH/KOH

Multi-Modal X-ray Imaging and Analysis for Characterization of Urinary Stones

Backgound: The composition of stones formed in the urinary tract plays an important role in their management over time. The most common imaging method for the non-invasive evaluation of urinary stones is radiography and computed tomography (CT). However, CT is not very sensitive, and cannot differentiate between all critical stone types. In this study, we propose the application, and evaluate the potential, of a multi-modal (or multi-contrast) X-ray imaging technique called speckle-based imaging (SBI) to differentiate between various types of urinary stones. Methods: Three different stone samples were extracted from animal and human urinary tracts and examined in a laboratory-based speckle tracking setup. The results were discussed based on an X-ray diffraction analysis and a comparison with X-ray microtomography and grating-based interferometry. Results: The stones were classified through compositional analysis by X-ray diffraction. The multi-contrast images obtained using the SBI method provided detailed information about the composition of various urinary stone types, and could differentiate between them. X-ray SBI could provide highly sensitive and high-resolution characterizations of different urinary stones in the radiography mode, comparable to those by grating interferometry. Conclusions: This investigation demonstrated the capability of the SBI technique for the non-invasive classification of urinary stones through radiography in a simple and cost-effective laboratory setting. This opens the possibility for further studies concerning full-field in vivo SBI for the clinical imaging of urinary stones

Diastereoselective synthesis of coordination compounds: a chiral tripodal ligand based on bipyridine units and its ruthenium(II) and iron(II) complexes

The enantiomerically pure chiral tris-chelating ligand (+)-(7S,10R)-L(L) comprising three 4,5-pinenobipyridine subunits connected through a mesityl spacer has been synthesized. Complexes of L with RuII and FeII have been prepared and characterised. NMR spectroscopy indicates that only one diastereoisomer is formed, and the CD spectra show that the complexes have the Λ configuration on the metal centre. The X-ray crystal structure of the iron complex shows that in the octahedral complex, the ligand L coils around the metal and confirms the absolute configuration. The RuII and FeII compounds were also characterised by mass spectrometry, electronic absorption, and, in the case of Ru(II), fluorescence spectroscopy. The photostability of the ruthenium compound was checked by photochemical experiments

Crystal structures of <i>trans</i>-di­chlorido­tetra­kis­[1-(2,6-diiso­propyl­phen­yl)-1<i>H</i>-imidazole-Κ<i>N</i>³]iron(II), <i>trans</i>-di­bromido­tetra­kis­[1-(2,6-diiso­propyl­phen­yl)-1<i>H</i>-imidazole-Κ<i>N</i>³]iron(II) and <i>trans</i>-di­bromido­tetra­kis­[1-(2,6-diiso­propyl­phen­yl)-1<i>H</i>-imidazole-Κ<i>N</i>³]iron(II) diethyl ether disolvate

The title compounds, [FeCl₂(C₁₅H₂₀N₂)₄], (I), [FeBr₂(C₁₅H₂₀N₂)₄], (II), and [FeBr₂(C₁₅H₂₀N₂)₄]·2C₄H₁₀O, (IIb), respectively, all have triclinic symmetry, with (I) and (II) being isotypic. The FeII atoms in each of the structures are located on an inversion center. They have octa­hedral FeX₂N₄ (X = Cl and Br, respectively) coordination spheres with the FeII atom coordinated by two halide ions in a trans arrangement and by the tertiary N atom of four aryl­imidazole ligands [1-(2,6-diiso­propyl­phen­yl)-1H-imidazole] in the equatorial plane. In the two independent ligands, the benzene and imidazole rings are almost normal to one another, with dihedral angles of 88.19 (15) and 79.26 (14)° in (I), 87.0 (3) and 79.2 (3)° in (II), and 84.71 (11) and 80.58 (13)° in (IIb). The imidazole rings of the two independent ligand mol­ecules are inclined to one another by 70.04 (15), 69.3 (3) and 61.55 (12)° in (I), (II) and (IIb), respectively, while the benzene rings are inclined to one another by 82.83 (13), 83.0 (2) and 88.16 (12)°, respectively. The various dihedral angles involving (IIb) differ slightly from those in (I) and (II), probably due to the close proximity of the diethyl ether solvent mol­ecule. There are a number of C-H***Missing image substitution***halide hydrogen bonds in each mol­ecule involving the CH groups of the imidazole units. In the structures of compounds (I) and (II), mol­ecules are linked via pairs of C-H...halogen hydrogen bonds, forming chains along the a axis that enclose R₂²(12) ring motifs. The chains are linked by C-H...π inter­actions, forming sheets parallel to (001). In the structure of compound (IIb), mol­ecules are linked via pairs of C-H...halogen hydrogen bonds, forming chains along the b axis, and the diethyl ether solvent mol­ecules are attached to the chains via C-H...O hydrogen bonds. The chains are linked by C-H...π inter­actions, forming sheets parallel to (001). In (I) and (II), the methyl groups of an isopropyl group are disordered over two positions [occupancy ratio = 0.727 (13):0.273 (13) and 0.5:0.5, respectively]. In (IIb), one of the ethyl groups of the diethyl ether solvent mol­ecule is disordered over two positions (occupancy ratio = 0.5:0.5)

Improved thermal stability of an organic zeolite by fluorination

The thermal stability of an organic zeolite material, namely 2,4,6-tris(4-bromo-3,5-difluorphenoxy)-1,3,5-triazin (Br-3,5-DFPOT), was improved by fluorination of 2,4,6-tris(4-bromophenoxy)-1,3,5-triazin (BrPOT). The open pore structure (van der Waals diameter of 10.5Å) of the modified zeolite was observed up to 110°C in comparison to 70°C for BrPOT. Nitrogen sorption at low temperature showed a type I isotherm and derived pore volumes thereof are in agreement with structural data. It was observed here that Br-3,5-DFPOT crystals preserving the open pore structure could only be obtained below a typical size of about 50μm. The improved thermal stability of the fluorinated system is attributed to an enhancement of the strength of the Br3-syntho

Multiscale and multimodal X-ray analysis: Quantifying phase orientation and morphology of mineralized turkey leg tendons

Fibrous biocomposites like bone and tendons exhibit a hierarchical arrangement of their components ranging from the macroscale down to the molecular level. The multiscale complex morphology, together with the correlated orientation of their constituents, contributes significantly to the outstanding mechanical properties of these biomaterials. In this study, a systematic road map is provided to quantify the hierarchical structure of a mineralized turkey leg tendon (MTLT) in a holistic multiscale evaluation by combining micro-Computed Tomography (micro-CT), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD). We quantify the interplay of the main MTLT components with respect to highly ordered organic parts such as fibrous collagen integrating inorganic components like hydroxyapatite (HA). The microscale fibrous morphology revealing different types of porous features and their orientation was quantified based on micro-CT investigations. The quantitative analysis of the alignment of collagen fibrils and HA crystallites was established from the streak-like signal in SAXS using the Ruland approach and the broadening of azimuthal profiles of the small and wide-angle diffraction peaks. It has been in general agreement that HA crystallites are co-aligned with the nanostructure of mineralized tissue. However, we observe relatively lower degree of orientation of HA crystallites compared to the collagen fibrils, which supports the recent findings of the structural interrelations within mineralized tissues. The generic multiscale characterization approach of this study is relevant to any hierarchically structured biomaterials or bioinspired materials from the μm-nm-Å scale. Hence, it gives the basis for future structure-property relationship investigations and simulations for a wide range of hierarchically structured materials