A. Sironi

Interaction of metal ions with humic-like models. Part. I. Synthesis, spectroscopic and structural properties of diaquabis(2,6-dihydroxybenzoato) copper(II) and hexaaquaM(II) bis(2,6-dihydroxybenzoate) dihydrate (M = Mn, Fe, Co, Ni, Cu and Zn)

Abstract Compounds of the type M(2,6-DHB) 2 ·8H 2 O (M = Mn, Fe, Co, Ni, and Zn; 2,6-DHB = 2,6-dihydroxybenzoate ion) and Cu(2,6-DHB) 2 (H 2 O) 2 were prepared and characterized by means of infrared and electronic spectroscopy, electron spin resonance and thermal analysis. For Cu(2,6-DHB) 2 (H 2 O) 2 ( 1 ) and Zn(2,6-DHB) 2 ·8H 2 O ( 2 ) the crystal structure was also determined by single-crystal X-ray diffraction methods. The compound ( 1 ) has a polymeric nature, the coordination around each copper atom being tetragonally-distorted octahedral, with two water oxygens [CuO, 1.966(3) A] and two carboxyl oxygens [CuO, 1.935(2) A] from 2,6-DHB molecules about the square plane and two phenolic groups from adjacent units in the axial positions. The structure of ( 2 ) consists of almost regular octahedral [Zn(H 2 O) 6 ] 2+ cations surrounded by 2,6-DHB anions. The remaining two water molecules are involved in hydrogen bonding with the coordinated water molecules. X-ray data show that all the M(2,6-DHB) 2 ·8H 2 O are isomorphous with ( 2 ). The thermal, spectroscopic and magnetic properties are interpreted on the basis of the crystal structures. In particular, the ESR and absorption data of the copper(II) compounds are compared with those of the salicylate complexes.

A chiral diamondoid 3D lanthanum metal–organic framework displaying blue-greenish long lifetime photoluminescence emission

The compound [La(pmtz)(TzC)(H2O)3](H2O) (pmtz = 5-(pyrimidyl)-tetrazolato, TzC = 5-carboxylato-tetrazolato) has been prepared under hydrothermal conditions and exhibits a 3D diamondoid network. This three-dimensional metal–organic framework has channels with hosted water molecules inside and shows an intense blue-greenish long lifetime photoluminescence emission at room temperature in the solid state with two lifetime decay values of 0.26 and 27 ms.

New tetrahedral cluster compounds of iridium. Synthesis of the anions [Ir4(CO)11X]− (X = Cl, Br, I, CN, SCN) and x-ray structure of [PPh4] [Ir4(CO)11Br]

Abstract [Ir4(CO)11X]− anions are obtained by reaction of halide and pseudo-halide ions with Ir4(CO)12. X-ray determination of the structure of [Ir4(CO)11Br]− shows that the carbonyl arrangement differs from that of the parent Ir4(CO)12, and is similar to that known for Co4(CO)12; one terminal CO group in the basal M3(CO)9 moiety is replaced by the bromide ligand, and two of the bridging CO groups become markedly asymmetric.

P‐RISCON: a real‐space scavenger for crystal structure determination from powder diffraction data

A computer program, P-RISCON, has been designed with the aim of finding the location and orientation of one or more independent fragments of known geometry in the unit cell from low-angle X-ray powder diffraction data only, provided that lattice parameters, space group and a set of integrated intensities are known. A three-dimensional translational search is performed and, if required, rotations of each model about three orthogonal axes are applied, seeking the best match between observed and calculated data. No arbitrary partitioning of the intensity of severely overlapping reflections is required as the integrated intensity of a multiplet can be used as a single observation, thereby introducing very little error in its estimated value. A number of (known) test structures have been solved by this method.

The crystal and molecular structure of trans-chlorocarbonylbis(triphenylphosphine)rhodium(I) in its monoclinic form

Abstract The structure of the title compound, RhCl(CO)(PPh 3 ) 2 , has been investigated in its monoclinic modification. It belongs to space group P 2 1 / n (No. 14), with cell constants a 12.182(3), b 24.285(5), c 11.894(3) A, β 113.10(2)°, Z = 4. The structure was solved by conventional Patterson and Fourier methods, on the basis of 4295 significant counter data, by least-squares methods to a final conventional R values of 0.051. The complex exhibits a square planar coordination, with the two bulky phosphine ligands in mutually trans positions. The mean value of the RhP bond lengths is 2.326 A. The RhCl, RhC and CO bond lengths are 2.371(2), 1.810(7), and 1.144(8) A, respectively. The structure is compared with those of similar species and the small differences observed between the monoclinic and triclinic modifications of this compound are discussed.

Optical spectroscopy of unsolvated and solvated crystalline Alq3

Abstract Three novel unsolvated crystalline phases of tris-(8-hydroxyquinoline)-aluminum(III) (Alq 3 ), namely α-, β- and γ-Alq 3 , have been synthesized and their crystalline structure determined from X-ray diffraction data on powders and single crystals. Both α- and β-Alq 3 crystals are triclinic, space group P-1, but differ for the molecular packings. In the γ-Alq 3 phase, Alq 3 molecules lie about a 3-position of the trigonal P-3 space group. A solvated Alq 3 (C 6 H 5 Cl) 1/2 phase (monoclinic, space group P2 1 / n ) was also isolated. The optical and vibrational properties of these newly isolated crystal phases of Alq 3 have been investigated by absorption, photoluminescence excitation, photoluminescence and Raman spectroscopy. The effect of the different molecular packing on the emission properties has been elucidated, the nature of the photoexcitations clarified, and the vibrational fingerprints of the α- and β-crystalline forms highlighted. The origin of the amorphous nature of the vacuum sublimed thin films is discussed on the basis of the accessibility of many different π–π links between homo- and hetero-chiral Alq 3 molecules.

Interaction of metal ions with humic-like models. Part VII. Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of 2,5-dihydroxybenzoic acid

Abstract Complexes of formula M(2,5-DHB) 2 4H 2 O (M = Mn, Co, Ni, Zn, Cu and Cd; 2,5-DHB = 2,5-dihydroxybenzoate) were prepared and characterized by means of infrared and electronic spectroscopy, and by electron spin resonance. For the Zn complex the crystal and molecular structure was also determined by single-crystal X-ray diffraction analysis. The crystal is orthorhombic, space group Pbca (No. 61), with a = 18.503(4), b = 13.536(3), c = 6.900(2) A, and Z = 4. The final refinement used 877 reflections and gave a residual R value of 0.041. The complex has slightly compressed octahedral coordination, with the zinc atom bound to two monodentate carboxylate groups lying in trans positions and four water molecules. X-ray data and infrared spectra show the Mn, Co, Ni, Zn and Cd complexes to be isostructural with the Zn compound. The electronic, infrared and ESR spectra of the copper(II) complex are consistent with a CuO 4− based chromophore involving two water molecules and two monodentate carboxylate groups in the metal plane, and long axial contacts.

Flexibility in coordinative behavior of propane-1,3-diamine toward Zn(II) and Cd(II) halides:[M(1,3pn)2X2 (M=Zn, Cd; X=Cl, Br,I)].

Abstract A series of compounds of formula M(1,3pn)2X2 (M  Zn(II), Cd(II); 1,3pn=propane-1,3-diamine; X  Cl, Br, I) has been prepared; two of them (M  Zn, X  Cl) and (M  Cd, X  I) have been structurally characterized. The Zn(1,3pn)2Cl2 (I) compound crystallizes in the P21/c space group, with eight formula units in a cell of dimensions: a=12.833(4), b=16.753(9), c=13.010(4) A, β=118.88(3)°. The Cd(1,3pn)2I2 (II) compound crystallizes in the P21/n space group with four formula units in a cell of dimensions: a=12.406(3), b=8.655(2), c=14.372- (4) A, β=113.57(2)°. The structures were solved with the heavy-atom method and refined by full matrix least-squares to R and Rw values of 0.029 and 0.038, 0.042 and 0.058 for I and II respectively. The asymmetric unit of I consists of a dimeric [Zn- (1,3pn)2]24+ moiety, where both Zn ions are tetrahedrally coordinated to four nitrogen atoms belonging to one chelating and two bridging 1,3pn ligands. The dimeric moiety generates an infinite chain upon translation of one cell in the direction of the diagonal (1,0,1). The structure of II shows a polymeric arrangement of octahedral Cd atoms sharing both iodine atoms and 1,3pn ligands. The MN stretching vibrations are discussed and assigned in the light of the known structures.

A test of the suitability of CCD area detectors for accurate electron-density studies

The performance of the Siemens SMART CCD (charge-coupled device) area detector has been tested to assess its suitability for accurate electron-density (ED) determination. 92043 diffraction intensities (14701 unique reflections, 65 h experiment) have been collected on a reference crystal of methyl 2-[(4-butyl-2-methyl-6-oxo-5-{4-[2-(1H-tetrazol-5-yl)phenyl]benzyl }-1,2-dihydropyrimidin-1-yl)methyl]-3-thiophenecarboxylate (C30H30N6O3S) at T = 120 K and compared with those (51485, 14699 unique, 600 h) obtained from a previous collection at T = 18 K on the same crystal using a diffractometer equipped with a conventional detector. Results from spherical and multipolar refinements (agreement factors, standard uncertainties of refined variables and geometries after correction for thermal motion) have also been compared. The λ/2 contamination, which affects area detectors but not well tuned conventional detectors, has been carefully investigated and proved to be a negligible source of errors (which can anyway be easily corrected). The encouraging results of this test prove that area detectors are also well suited for charge-density studies, offering a cheap and fast data-collection mode, without loss of accuracy, which can be exploited for ED studies on large systems.

Crystal structure determination of molecular compounds from conventional powder diffraction data: Trimeric silver(I) 3,5-dimethylpyrazolate

In the absence of single crystals, silver( I ) 3,5-dimethylpyrazolate, [ Ag ( dmpz )] 3 , has been structurally characterized by ab initio X-ray powder diffraction, using conventional laboratory data. Its crystals are triclinic, P 1¯, with a =8.0876(10), b =11.1204(13), c =11.6136(16) A, α=68.293(6), β=78.350(7), and γ=81.243(6)°. The structure has been solved by Patterson, difference Fourier, and geometrical modeling, and ultimately refined by the Rietveld method down to R p =0.068, R wp =0.085, and R F =0.055, for 4300 observations in the 17 Ag ( dmpz ) fragments, with the dmpz ligand bridging, in the exo-bidentate mode, nonbonded Ag…Ag edges.