Sabine Strobel

The Laccase-Catalyzed Domino Reaction between Catechols and Heterocyclic 1,3-Dicarbonyls and the Unambiguous Structure Elucidation of the Products by NMR Spectroscopy and X-ray Crystal Structure Analysis

The laccase-catalyzed reaction between catechols and heterocyclic 1,3-dicarbonyls (pyridinones, quinolinones, thiocoumarins) using aerial oxygen as the oxidant delivers benzofuropyridinones, benzofuroquinolinones, and thiocoumestans in a simple fashion, highly regioselectively with yields ranging from 55 to 98%. With barbituric acid derivatives the exclusive formation of dispiropyrimidinone derivatives takes place. The unambiguous and complete structure elucidation of all reaction products has been achieved by means of NMR spectroscopic methods (HSQMBC and band-selective HMBC) as well as by X-ray crystal structure analysis.

A Five-Center Redox System: Molecular Coupling of Two Noninnocent Imino-o-benzoquinonato-Ruthenium Functions through a π Acceptor Bridge

Combining the concepts of noninnocent behavior of metal/ligand entities and the coupling of redox-active moieties via an electronically mediating bridge led to the synthesis and the structural, electrochemical, and spectroscopic characterization of [Cl(Q)Ru(mu-tppz)Ru(Q)Cl](n) where Q(o) is 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone and tppz(o) is 2,3,5,6-tetrakis(2-pyridyl)pyrazine, the available oxidation states being Ru(II,III,IV), Q(o,*-,2-), and tppz(o,*-,2-). One-electron transfer steps between the n = (2-) and (4+) states were studied by cyclic voltammetry and by EPR, UV-vis-NIR spectroelectrochemistry for the structurally characterized anti isomer of [Cl(Q)Ru(mu-tppz)Ru(Q)Cl](PF(6))(2), 2(PF(6))(2), the only configuration obtained. The combined investigations reveal that 2(2+) is best described as [Cl(Q(*-))Ru(III)(mu-tppz(o))Ru(III)(Q(*-))Cl](2+) with antiferromagnetic coupling between the ruthenium(III) and the iminosemiquinone components at each end. A metal-based spin as evident from large g factor anisotropy (EPR) and an intense intervalence absorption band at 1850 nm in the near-infrared (NIR) suggest that oxidation occurs at both iminosemiquinones to yield two Ru(II,III)-bonded quinones, implying redox-induced electron transfer. Reduction takes place stepwise at the metal centers yielding iminosemiquinone complexes of Ru(III,II) as evident from radical complex EPR spectra with small (99,101)Ru hyperfine contributions. After complete metal reduction to ruthenium(II) the bridging ligand tppz is being reduced stepwise as apparent from typical NIR absorption bands around 1000 nm and from small g anisotropy of the monoanion [Cl(Q(*-))Ru(II)(mu-tppz(*-))Ru(II)(Q(*-))Cl](-). A structure-based DFT calculation confirms the Ru-Cl character of the HOMO and the iminoquinone-dominated LUMO and illustrates the orbital interaction pattern of the five electron transfer active components in this new system.

An Odd‐Electron Complex [Ruk(NOm)(Qn)(terpy)]2+ with Two Prototypical Non‐Innocent Ligands

Six combinations of oxidation states are conceivable for the paramagnetic title complex. Single-crystal X-ray diffraction, spectroscopic analysis (IR, EPR at conventional and high frequency), and DFT calculations establish that it is the iminosemiquinone radical structure that is formed: [Ru(k)(NO(m))(Q(n))(terpy)](2+) (k = 2+, m = 1+, n = 1-).

YF[MoO4] and YCl[MoO4]: Two halide derivatives of yttrium ortho-oxomolybdate: Syntheses, structures, and luminescence properties

The halide derivatives of yttrium ortho-oxomolybdate YX[MoO 4] (X = F, Cl) both crystallize in the monoclinic system with four formula units per unit cell. YF[MoO 4] exhibits a primitive cell setting (space group P21/ c; a = 519.62(2) pm, b = 1225.14(7) pm, c = 663.30(3) pm, beta = 112.851(4) degrees ), whereas the lattice of YCl[MoO 4] shows face-centering (space group C2/m; a = 1019.02(5) pm, b = 720.67(4) pm, c = 681.50(3) pm, beta = 107.130(4) degrees ). The two compounds each contain crystallographically unique Y (3+) cations, which are found to have a coordination environment of six oxide and two halide anions. In the case of YF[MoO 4], the coordination environment is seen as square antiprisms, and for YCl[MoO 4], trigon-dodecahedra are found. The discrete tetrahedral [MoO 4] (2-) units of the fluoride derivative are exclusively bound by six terminal Y (3+) cations, while those of the chloride compound show a 5-fold coordination around the tetrahedra with one edge-bridging and four terminal Y (3+) cations. The halide anions in each compound exhibit a coordination number of two, building up isolated planar rhombus-shaped units according to [Y 2F 2] (4+) in YF[MoO 4] and [Y 2Cl 2] (4+) in YCl[MoO 4], respectively. Both compounds were synthesized at high temperatures using Y2O3, MoO3, and the corresponding yttrium trihalide in a molar ratio of 1:3:1. Single crystals of both are insensitive to moist air and are found to be coarse shaped and colorless with optical band gaps situated in the near UV around 3.78 eV for the fluoride and 3.82 eV for the chloride derivative. Furthermore, YF[MoO 4] seems to be a suitable material for doping to obtain luminescent materials because the Eu (3+)-doped compound shows an intense red luminescence, which has been spectroscopically investigated.

Yttrium(III) oxomolybdates(VI) as potential host materials for luminescence applications: an investigation of Eu3+-doped Y2[MoO4]3 and Y2[MoO4]2[Mo2O7]

Two ternary yttrium(III) oxomolybdates(VI) are investigated, both structurally and spectroscopically. The crystal structure of Y2[MoO4]3 was solved at room temperature in the orthorhombic space group Pba2 (a = 1030.21(3), b = 1032.41(3), c = 1057.25(3) pm, Z = 4). In the unit cell, three discrete ortho-oxomolybdate(VI) units [MoO4]2− and two Y3+ cations, both with CN = 7 featuring a monocapped trigonal-prismatic oxygen environment, can be distinguished. Y2[MoO4]2[Mo2O7] crystallizes monoclinically in the space group P21/c (a = 681.85(2), b = 959.13(3), c = 1052.99(3) pm, β = 105.586(2)°) with two formula units per unit cell. In this compound the anionic environment of the crystallographically unique Y3+ cations also comprises seven oxygen atoms forming a monocapped trigonal prism. Furthermore, the crystal structure features both tetrahedral [MoO4]2− and pyroanionic [Mo2O7]4− entities, the latter in staggered conformation, with the bridging oxygen atom between the two vertex-shared [MoO4]2− tetrahedra residing on an inversion centre. Besides self-activated emission, resulting from the oxomolybdate(VI) units (maximum at around 600 nm), both compounds have the potential to be used as luminescence host materials, shown by spectroscopic studies involving Eu3+ as a sensitive probe. The emission spectra of Y2[MoO4]3:Eu3+ and Y2[MoO4]2[Mo2O7]:Eu3+ are dominated by the Eu3+-typical 5D0 → 7F2 transition at 614 nm. In the excitation spectra, aside from 4f-interconfigurational Eu3+ transitions at lower energies, broad charge-transfer (CT) bands due to O2− → Eu3+ or O2− → Mo6+ transitions dominate at higher energies. Comparing the diffuse reflectance spectra (DRS) of the undoped with the Eu3+-doped materials, the O2− → Mo6+ LMCT process proves to be crucial for the position of the broad CT band in the excitation spectra of both yttrium oxomolybdates(VI).

Rare-Earth Metal(III) Oxide Selenides M4O4Se[Se2] (M = La, Ce, Pr, Nd, Sm) with Discrete Diselenide Units: Crystal Structures, Magnetic Frustration, and Other Properties

The rare-earth metal(III) oxide selenides of the formula La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were synthesized from a mixture of the elements with selenium dioxide as the oxygen source at 750 degrees C. Single crystal X-ray diffraction was used to determine their crystal structures. The isostructural compounds M4O4Se[Se2] (M=La, Ce, Pr, Nd, Sm) crystallize in the orthorhombic space group Amm2 with cell dimensions a=857.94(7), b=409.44(4), c=1316.49(8) pm for M=La; a=851.37(6), b=404.82(3), c=1296.83(9) pm for M=Ce; a=849.92(6), b=402.78(3), c=1292.57(9) pm for M=Pr; a=845.68(4), b=398.83(2), c=1282.45(7) pm for M=Nd; and a=840.08(5), b=394.04(3), c=1263.83(6) pm for M=Sm (Z=2). In their crystal structures, Se2- anions as well as [Se-Se]2- dumbbells interconnect {[M4O4]4+} infinity 2 layers. These layers are composed of three crystallographically different, distorted [OM4]10+ tetrahedra, which are linked via four common edges. The compounds exhibit strong Raman active modes at around 215 cm(-1), which can be assigned to the Se-Se stretching vibration. Optical band gaps for La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were derived from diffuse reflectance spectra. The energy values at which absorption takes place are typical for semiconducting materials. For the compounds M4O4Se[Se2] (M=La, Pr, Nd, Sm) the fundamental band gaps, caused by transitions from the valence band to the conduction band (VB-CB), lie around 1.9 eV, while for M=Ce an absorption edge occurs at around 1.7 eV, which can be assigned to f-d transitions of Ce3+. Magnetic susceptibility measurements of Ce4O4Se[Se2] and Nd4O4Se[Se2] show Curie-Weiss behavior above 150 K with derived experimental magnetic moments of 2.5 micro B/Ce and 3.7 micro B/Nd and Weiss constants of theta p=-64.9 K and theta p=-27.8 K for the cerium and neodymium compounds, respectively. Down to 1.8 K no long-range magnetic ordering could be detected. Thus, the large negative values for theta p indicate the presence of strong magnetic frustration within the compounds, which is due to the geometric arrangement of the magnetic sublattice in form of [OM4]10+ tetrahedra.

Einkristalle von CuPrS2 im A— und Pr2S3 im C—Typ bei Versuchen zur Synthese ternärer Kupfer(I)—Praseodym(III)—Sulfide

Derbe, gelblichgrune Einkristalle des ternaren Kupfer(I)-Praseodym(III)-Sulfids CuPrS2 entstehen bei der Umsetzung der Elemente (Kupfer, Praseodym und Schwefel) im molaren Verhaltnis von 1:1:2 innerhalb von sieben Tagen bei 800°C in evakuierten Quarzglasampullen, wenn aquimolare Mengen an CsCl als Flusmittel zugegen sind. Versuche zur Darstellung von CuPr3S5 oder CuPr5S8 liefern unter analogen Reaktionsbedingungen statt der erhofften Zielverbindungen stets zweiphasige Gemenge aus CuPrS2 und Pr2S3 (C—Typ). Die Kristallstruktur von CuPrS2 (monoklin, P21/c; a = 655, 72(6); b = 722, 49(6); c = 686, 81(6)pm, β = 98, 686(7)°; Z = 4) weist parallel (100) angeordnete gewellte Schichten {[Cu(S1)3/3(S2)1/1]3—} aus eckenverknupften Doppeln ([Cu2S6]10—) zweier [CuS4]7—-Tetraeder mit gemeinsamer Kante auf, die durch Pr3+-Kationen in uberkappt-trigonal-prismatischer Siebenerkoordination von S2—-Anionen dreidimensional vernetzt werden. Die Metall-Schwefel-Abstande in den [CuS4]-Einheiten uberstreichen mit 233 (Cu—S2) und 236 (Cu—S1) sowie 247 (Cu—S1′) und 248pm (Cu—S1″) ein recht weites Intervall, wahrend jene (Pr—S: 284—304pm) in den [PrS7]-Polyedern vergleichsweise eng beieinanderliegen. C—Pr2S3 kristallisiert gemas Pr2, 677□0, 333S4 mit Z = 4 in einer kationendefekten Th3P4-Struktur (kubisch, I4¯3d; a = 857, 68(7) pm; Z = 5, 333 fur Pr2S3). Entsprechend der Niggli-Formel {PrS8/5, 333} ist Pr3+ von acht S2— in Abstanden von 287 (4×) und 307pm (4×) trigondodekaedrisch koordiniert. Weder die Einkristallrontgenstrukturanalyse noch Elektronenstrahl-Mikrosondenuntersuchungen zeigen eine Evidenz fur den Einbau von Cu+-Kationen in diese Kristallstruktur. Single Crystals of A—type CuPrS2 and C—type Pr2S3 from Attempts to Synthesize Ternary Copper(I) Praseodymium(III) Sulfides Coarse, yellowish-green single crystals of the ternary copper(I) praseodymium(III) sulfide CuPrS2 form within seven days at 800°C by oxidation of elemental copper and praseodymium with sulfur (molar ratio: 1:1:2) in evacuated silica tubes when equimolar quantitites of CsCl are present as flux. Attempts to synthesize CuPr3S5 or CuPr5S8 under analogous conditions always yield two-component mixtures of CuPrS2 and Pr2S3 (C type) instead of the desired target compounds. The crystal structure of CuPrS2 (monoclinic, P21/c; a = 655.72(6), b = 722.49(6), c = 686.81(6)pm, β = 98.686(7)°; Z = 4) exhibits undulated layers {[Cu(S1)3/3(S2)1/1]3—} parallel (100) which consist of vertex-linked pairs of two [CuS4]7— tetrahedra ([Cu2S6]10—) sharing a common edge. Their three-dimensional cross-linkage is achieved by Pr3+ cations in monocapped trigonal prismatic coordination of seven S2— anions each. The metal sulfur distances in the [CuS4] units cover with 233 (Cu—S2) and 236 (Cu—S1) as well as 247 (Cu—S1′) and 248pm (Cu—S1″) a rather broad interval, whereas those (Pr—S: 284—304 pm) within the [PrS7] polyhedra lie relatively closer together. According to Pr2.677□0.333S4 (with Z = 4), C—Pr2S3 crystallizes in a cation-deficient Th3P4-type structure (cubic, I4¯3d; a = 857.68(7) pm; Z = 5.333 for Pr2S3). In conformity with the Niggli formula {PrS8/5.333} Pr3+ is surrounded trigon-dodecahedrally by eight S2— at distances of 287 (4×) and 307pm (4×). Neither the X-ray single-crystal structure refinement nor electron-beam microprobe analyses leave any evidence for the incorporation of Cu+ cations into this crystal structure.

Ruthenate-ferrites AMRu5O11 (A = Sr, Ba; M = Ni, Zn): Distortion of kagome nets via metal–metal bonding

Abstract Crystals of the three novel oxorhutenates SrNiRu5O11 (a = 11.7374(2) Å, c = 13.2088(4) Å), SrZnRu5O11 (a = 11.7271(2) Å, c = 13.4246(4) Å), and Sr0.63(1)Ba0.37ZnRu5O11 (a = 11.7245(4) Å, 13.5268(4)) were obtained applying a flux-growth technique. A superstructure of the R-type ferrite crystal structure with doubled hexagonal a-axis (space group P63/m, Z = 8) originates from Ru—Ru pair formation within the kagome nets extending in (001). No indication for an intermixing of 3d metals at the Ru sites was observed.

Münzmetall-Lanthanid-Chalkogenide: II. Kupfer(I)-Lanthanid(III)- Sulfide der Zusammensetzung CuMS2 (M = Dy – Lu) im orthorhombischen B-Typ / Coinage Metal Lanthanide Chalcogenides: II. Copper(I) Lanthanide(III) Sulfides of the Composition CuMS2 (M = Dy – Lu) with the Orthorhombic B-Type Structure

Single crystals of the ternary copper(I) lanthanide(III) sulfides with the composition CuMS2 (M = Dy - Lu) are formed within seven days at 750 °C by oxidation of elemental copper and lanthanide metal with sulfur (molar ratio: 1 : 1 : 2, evacuated silica tubes) in equimolar quantities of CsCl, CsBr or CsI as fluxing agents. The CuYS2-type crystal structures (orthorhombic, Pnma, Z = 4; e. g. CuDyS2: a = 1342.51(9), b = 397.96(3), c = 627.43(5) pm and CuLuS2: a = 1315.06(9), b = 391.04(3), c = 624.18(5) pm) exhibit chains of cis edge-linked [CuS4]7− tetrahedra with the composition 1∞{[Cu(S1)3/3(S2)1/1]3−} which run parallel to [010] and show hexagonal rod packing. Charge compensation and three-dimensional interconnection of these anionic strands occur via octahedrally coordinated M3+ cations surrounded by six S2− anions. These [MS6]9− octahedra share vertices and edges to form a three-dimensional network 3∞{[M(S1)3/3(S2)3/3]−} with the ramsdellite-type topology of γ-MnO2. The metal sulfur distances within the [MS6] polyhedra are very similar (M-S: 263 - 279 pm), whereas those within the [CuS4] units cover the ranges 227 - 230 (Cu-S2) and 231 - 233 (Cu-S1) as well as 250 - 252 pm (Cu-S1′, 2×). The present work is the first comprehensive X-ray single crystal diffraction study of the complete isotypic B-type series CuMS2 (M = Dy - Lu).

Garnet-type Mn3Cr2(GeO4)3

Single crystals of garnet-type trimanganese(II) dichromium(III) tris[orthogermanate(IV)], MnII 3CrIII 2(GeO4)3, were obtained by utilizing a chemical transport reaction. Corresponding to the mineral garnet with the general formula A II 3 B III 2(SiO4)3, each of the four elements occupies only one crystallographically distinct position. Mn2+ occupies the respective A position (Wyckoff site 24c, site symmetry 2.22), being surrounded by eight O atoms that form a distorted cube [d(Mn—O) = 2.291 (2) and 2.422 (2) Å, 4× each], while Cr3+ on the B position (Wyckoff site 16a, site symmetry .-3.) is situated in a slightly distorted octahedron of six O2− anions [d(Cr—O) = 1.972 (2) Å, 6×]. In addition, the O atoms on general site 96h form isolated [GeO4]4− tetrahedra with Ge4+ on site 24d [site symmetry -4..; d(Ge—O) = 1.744 (2) Å, 4×].