M. A. Monge

(NH4)2Ge7O15: A Microporous Material Containing GeO4 and GeO6 Polyhedra in Nine‐Rings

GeO4tetrahedra and GeO6octahedra, which form nine-rings (see sketch on the right), feature in the unprecedented structure of the microporous solid, (NH4)2Ge7O15. This compound provides the first evidence that in the GeO2/NH4+ system the cubic (NH4)3HGe7O16⋅n H2O is not the only existing phase, but depending on the GeO6/GeO4 ratio, differently charged frameworks can be generated.

Structure-directing and template roles of aromatic molecules in the self-assembly formation process of 3D holmium-succinate MOFs.

Two new holmium-succinate frameworks have been synthesized by hydrolysis in situ of the succinylsalicylic acid under different hydrothermal conditions. Compound 1, [Ho(2)(C(4)H(4)O(4))(3)(H(2)O)(2)]·0.33(C(7)H(6)O(3)), P ̅i space group, has a novel structure composed by 1D-SBUs consisting of [HoO(9)] chains of polyhedra linked by the succinate ligands giving a 3D framework. Compound 2, [Ho(2)(C(4)H(4)O(4))(3)(H(2)O)(2)], also belonging to the P ̅i space group, has a denser structure. The role of the in-situ-generated salicylic acid on formation of both structures is studied by means of a synthesis design methodology. A topological study of the new holmium succinate compounds in comparison with the previously reported 3D holmium-succinate framework is performed here.

Polarization and local disorder effects on the properties of Er 3+ -doped XBi(YO 4 ) 2 , X=Li or Na and Y=W or Mo, crystalline tunable laser hosts

Pure and Er-doped ([Er]crystal≤2.4 × 1020 cm−3), NaBi(WO4)2 (NBW), NaBi(MoO4)2, and LiBi(MoO4)2 crystals have been grown by the Czochralski method. The three crystal hosts have similar structural and optical properties. The noncentrosymmetric space group I4¯ (No. 82) crystallographic structure has been established through 300 K single-crystal x-ray and neutron (for NBW only) diffraction. Er3+ energy levels were determined experimentally and simulated in the S4 symmetry through a crystal-field analysis. With this background, the large spectroscopic bandwidths observed were ascribed to the presence of two 2b and 2d sites for Er3+ and to different short-range Na+ and Bi3+ distributions around both sites. The radiative properties of Er3+ are described by the Judd-Ofelt theory achieving branching ratios and radiative lifetimes for transitions useful as laser channels. The 4I13/2—>4I15/2 laser channel (λ≈1.5 μm) shows a peak emission cross-section σEMI(λ≈1530 nm)≈0.5×10−20 cm2 and a quantum efficiency η∞0.68 to 0.74. The laser emission is envisaged to be tunable by Δλ≈100 nm.

Copper complexes with multidentate ligands derived from l-proline. X-ray crystal structure of {[Cu(N,N′-bis[(S)-prolyl]ethylenediamine)]ClO4}2·(MeCN)2

Abstract The reaction of [Cu(CH 3 CN) 4 ]X (X=ClO 4 , PF 6 ) with multidentate ligands N , N ′-bis[( S )-prolyl]ethylenediamine ( 1 ), N , N ′-bis[( S )- N -benzylprolyl]ethylenediamine ( 2 ), N , N ′-bis{[( S )-pyrrolidin-2-yl]methyl}ethylenediamine ( 3 ), N , N ′-bis-{[( S )- N -benzyl-pyrrolidin-2-yl]methyl}ethylenediamine ( 4 ) gives copper complexes which were characterised by analytical (elemental analysis, and mass spectroscopy) and FT IR, NMR and electronic spectroscopies. The {[Cu( N , N ′-bis[( S )-prolyl]ethylenediamine)]ClO 4 } 2 ·(MeCN) 2 complex was characterised by X-ray crystallography. This new family of Cu-complexes catalyse the cyclopropanation of styrene with ethyl and t -butyl diazoacetate to yield cis / trans 2-phenylcyclopropan-1-carboxylates in good yields and selectivity against dimerisation and low ee (

Single-crystal growth of superconducting Bi2Sr2CaCu2O8 using rotary crucibles

Crystals grown using static and rotary crucibles from mixtures of analytical grade Bi2O3, Sr(OH)2·8H2O, CaCO3 and CuO had nominal compositions Bi2SrmCanCupOq (1.5 < m ≤ 2.0, 0.2 < n ≤ 2.0, 1.8 < p < 3.0), were characterized by X-ray powder diffraction and scanning electron microscopy, and contained intergrown crystals of Bi2Sr2CaCu2O8 (2212) and Bi2Sr2CuO6 (2201) in various relative amounts, together with crystals of CuO, (Sr, Ca)2CuO3 and Sr(Cu, Bi)O2. The intergrowths of 2212 and 2201 with highest 2212 contents were obtained from melts at 980°C of mixtures with m = p = 2 and n = 1, using rotary crucibles and a cooling rate of 0.5°C h-1. After being recrystallized, crystals of 2212 appeared free of even traces of 2201, were orthorhombic, had cell dimensions of a = 5.404(2) A, b = 5.418(4) A and c = 30.80(3) A, and showed a superconducting transition at 90 K as indicated by magnetization measurements. The crystal structure of one orthorhombic Sr(Cu, Bi)O2 crystal of unit-cell constants a = rm3.4865(5) A, b = rm16.176(2) A and c = rm3.8818(4) A was refined in the space group Cmcm arriving at the composition Sr(Cuin0.85Bi0.15)O 2.225, R = 0.037, and the main distances and angles which are given.

Unusual Magnetic Behaviors and Electronic Configurations Driven by Diverse Co(II) or Mn(II) MOF Architectures

Five novel metal organic frameworks were obtained by hydro-solvothermal reactions using the hexafluorisopropylidenebis(benzoic) acid (H2hfipbb) as linker and Co(II) or Mn(II) ions as connectors. [Co2(Hhfipbb)(TEA)], compound 1 (TEA = triethanolamine trianion) with a three-dimensional (3D) framework, and a tpu net; [Co1.5(hfipbb)2]·HN(CH2CH3)3 and [Co3(hfipbb)2]·2{HN(CH2CH3)3}, compounds 2 and 2-a, respectively, both with two-dimensional structure, sql topologies, and different layer packings. Compounds 3 and 4, having the general formula [M2(hfipbb)2]·C7H8, where M = Co (3) or Mn (4), have 3D frameworks with an sqc topology. A deep analysis of the magnetic measurements reveals different striking magnetic behaviors resulting from diverse secondary building unit and framework architectures. Compound 1 presents canted antiferromagnetic chains, compound 2 contains ferromagnetic linear trimeric clusters, and compound 3 exhibits ferromagnetic chains. For the three compounds, a 3D canted antiferromagnetic structure takes place at ∼8 K by means of weak magnetic interactions between the mentioned magnetic units. Such long-range magnetic order is precluded with the application of a high enough magnetic field. Compound 4 evidenced intrachain antiferromagnetic interactions.

Alternation of TaO and TeO layers in a three-dimensional array: Crystal structure of Ta2Te2O9

Abstract Single crystals of monoclinic Ta2Te2O9 were grown by slow cooling of Ta2O5TeO2 melts. Ta2Te2O9 crystallizes in space group P2 1 c (No. 14), Z = 4, with a = 7.100(1), b = 7.486(2), c = 14.625(5) A and β = 102.98(2)°. The structure has been solved by X-ray single-crystal techniques up to a final R value of 0.061 using 1184 observed reflections. Ta2Te2O9 is three-dimensional, with infinite puckered layers of composition (Te4O12)n parallel to the ab plane, alternating along the c axis with infinite sheets constituted by nearly regular TaO6 octahedra sharing corners. The two kinds of tellurium atoms are four- and five-fold oxygen coordinated, the nonbonded pair being directed towards the vacant positions of a trigonal bipyramid and a strongly deformed octahedron, respectively. The structure of Ta2Te2O9 is compared with those known in the systems M2O5TeO2 (M = V, Nb).

Crystal growth of Ba2Cu3RO7 − x (R = Y, Nd, Gd, Yb)

Abstract Two methods of growing Ba 2 Cu 3 RO 7 − δ ( R = Y , Nd, Gd, Yb) crystals were followed. In the first method a molten and water quenched mass of molar ratios Ba : Cu : R = 2 : 3 : 1 is introduced into the furnace at 1040°C, soaked at this temperature for 5 h and cooled at 25°C h -1 . In the second, a mixture of CuO and BaO 2 (72 : 28) is employed as a flux and the crystals are grown by cooling from 1010°C at 5°C h -1 or 15°C h -1 . CuBaR 2 O 5 crystals are also grown. The first method leads to euhedral crystals, better formed than those grown using fluxes. The shape and growth mode of the crystals grown by the second method are accounted for by the presence of helicoidal dislocations of the same sign or by means of a Frank-Read mechanism. X-ray diffraction data for BaCuGd 2 O 5 and Ba 2 Cu 3 GdO 7 − x are included.

Crystal growth of superconducting LiTi2O4

Crystals of LiTi2O4, a member (s = 1) of the hypothetical LisTi(III)4-3sTi(IV)2s-1O4 (0.50≤s≤1.33) spi nel series, were grown by two methods: electrolysis (30 mA, 100 mV) of a bath containing a suspension of TiO2 (anatase) in molten LiBO2, and chemical reduction by addition of a metal, Zr, more electropositive than Ti, on the indicated suspension. LiTi2O4 crystals were characterized by energy dispersive spectroscopy (EDS), X-ray powder diffraction and scanning electron microscopy. Electrolysis led to crystal aggregates of about 1 mm3, grown on the cathode and to skeletal crystals, 0.15 mm3, of cubic morphology related to the development of growth spirals in the three directions. The reduction using Zr plates gave rise to rows of twinned crystals as well as to isolated crystals showing planar faces unequally developed. The crystal structure of LiTi2O4 was anisotropically refined by single-crystal X-ray diffraction in space group Fd3m(No. 227), with a = 8.372(1) A, V = 586.8(1) A3, Li and Ti at tetrahedral and octahedral sites, respectively, an oxygen parameter u = 0.2628(3) and, as a consequence, practically equal Li-O and Ti-O distances. As is shown by AC susceptibility measurements, electrotically grown crystals as well as those grown on Zr plates are very similar in their superconducting transitions, with Tc (onset) of 11.5 K, transition widths of 1.5 K, and diamagnetic shieldings of 65–70%. Magnetization measurements up to 2 T at 6 K on electrolytically grown crystals show a lower critical field Hc1 of 250 Oe and a critical current of 106 A cm-2.

A novel microporous Ge-material containing nine-rings ☆

Abstract (NH4)2Ge7O15 is the first microporous material containing nine-rings constituted by tetrahedral and octahedral germanium species. Its channel structure is characterized by a nine-ring channel running along the [001] direction. These channels are lined forming cages which are capped by six-rings giving rise to smaller tunnels in [110] [010] directions. Two, related by inversion center, NH4+ cations are housed in each cage bonded to several oxygen atoms of the framework through hydrogen bonds. The paper reports the full structural data as well as thermal stability conditions and the first catalytic essays.