Volume 62, Issue 2

Monophasic La 6 C 2 Br 9 was prepared by heating a mixture of LaBr 3 , lanthanum metal and carbon in a molar ratio of 3 : 3 : 2 at 840 °C for 5 d. The crystal structure was investigated by X-ray single crystal diffraction (space group C2/c, a = 14.234(3), b = 10.858(2), c = 14.588(3) Å , β = 106.80(3) °). In the structure the La atoms form edge-sharing double tetrahedra. The La tetrahedra are centered by single carbon atoms. The yellow crystals of La 6 C 2 Br 9 are transparent and electrically insulating.

The title compounds are formed by reaction of Dyl 3 , Dy metal and C in stoichiometric amounts in closed Ta ampoules, Dy 10 (C 2 ) 2 I 18 at 930 °C 7days, Dy 4 (C 2 )I 6 at 950 °C for 6 days and Dy 12 (C 2 ) 3 I 17 at 900 °C for 11 days as pure samples according to X-ray powder diffraction. Dy 10 (C 2 ) 2 I 18 crystallizes in space group P2 1/c with a = 10.470(2), b = 17.152(3), c = 13.983(3) Å and β = 121.14(3)°, Dy 4 (C 2 )I 6 in Pnnm with a = 13.622(3), b = 14.335(3) and c = 8.396(2) Å , and Dy 12 (C 2 ) 3 I 17 in C2/c with a = 19.149(4), b = 12.069(2), c = 18.595(4) Å , and β = 90.54(3)°. The crystal structure of Dy 10 (C 2 ) 2 I 18 is composed of Dy double octahedra centered by (C2) 6− groups (ethanide) with the iodide ions above the edges and the corners of the Dy 10 (C 2 )2 units. In Dy 4 (C 2 )I 6 the Dy atoms form chains of trans-edge sharing octahedra with embedded (C 2 ) groups. In the structure of Dy 12 (C 2 ) 3 I 17 alternately cis-, trans-edge-condensed Dy 6 octahedra centered by (C 2 ) groups occur. The iodine atoms surround the chains like in the M 6 X 12 cluster and interconnect neighboring chains.

Four new arsenides of rhodium and zinc were prepared by heating mixtures of the elements at high temperatures (1000 - 1200 °C) and investigated by single crystal X-ray methods. EuRh 2 As 2 (a = 4.067(1), c = 11.319(2) Å ) and BaRh 2 As 2 (a = 4.053(1), c = 12.770(3) Å ) crystallize with the well-known ThCr 2 Si 2 -type (I4/mmm; Z = 2). Due to the rigid layers of RhAs 4 tetrahedra, and to the atomic size of europium and barium, the As-As distances between the layers with values of 2.97 and 3.66 Å, respectively, are very long. SrRh 2 As 2 is polymorphic and undergoes two phase transitions at about 190 and 282 °C. Main features of the three crystal structures are also layers of RhAs 4 tetrahedra. At room temperature α-SrRh 2 As 2 (a = 5.676(1), b = 6.178(2), c = 11.052(2) Å ) probably crystallizes with the BaNi 2 Si 2 -type (Cmcm; Z = 4), whereas β -SrRh2As2 (a = 5.760(3), b = 6.067(4), c = 11.264(5) A° , Fmmm, Z = 4) forms a new orthorhombically distorted variant of the ThCr 2 Si 2 -type. Single crystals grown in a flux of lead and quenched at high temperature show that the γ -phase (a = 4.112(1), c = 11.431(6) Å ) crystallizes with the ThCr 2 Si 2 -type. The same is true for the high temperature modification of BaZn 2 As 2 (β -phase; a = 4.120(1), c = 13.578(1) Å ), whereas the already known α-BaZn 2 As 2 forms the α-BaCu 2 S 2 -type (Pnma; Z = 4) consisting of a 3D-network of edge- and vertex-sharing ZnAs 4 tetrahedra with Ba atoms in the voids of this network.

The magnesium compounds RE 4 Co 2 Mg 3 (RE = Pr, Gd, Tb, Dy) were prepared by induction melting of the elements in sealed tantalum tubes. The samples were studied by powder X-ray diffraction. The structures of the gadolinium and of the terbium compound were refined from single crystal diffractometer data: Nd 4 Co 2 Mg 3 -type, P2/m, Z = 1, a = 754.0(4), b = 374.1(1), c = 822.5(3) pm, β = 109.65(4)°, wR2 = 0.0649, 730 F 2 values for Gd 4 Co 2 Mg 3 and a = 750.4(2), b = 372.86(6), c = 819.5(2) pm, β = 109.48(3)°, wR2 = 0.0398, 888 F 2 values for Tb 4 Co 2 Mg 3 with 30 variables each. The RE 4 Co 2 Mg 3 structures are 3 : 1 intergrowth variants of distorted CsCl and AlB 2 related slabs of compositions REMg and RECo 2 . Characteristic structural features (exemplary for Tb 4 Co 2 Mg 3 ) are relatively short Tb-Co (271 pm), Co-Co (232 pm) and Mg-Mg (314 pm) distances. The latter are a geometrical constraint of the distortion of the REMg and RECo 2 slabs. Chemical bonding analysis (ELF and ECOV data) for Gd 4 Co 2 Mg 3 reveals strong Gd-Co bonding followed by Mg-Co, while the Mg-Mg interactions can be considered as weak. The Co-Co contacts are only weakly bonding. The bonding and antibonding states are almost filled.

The intermetallic compounds RE 2 Au 2 Sn (RE = Y, Dy-Tm, Lu) and RE 2 Au 2 In (RE = Ho, Lu) were synthesized from the elements via arc-melting and subsequent annealing at 1070 K for 10 days. Depending on the size of the rare earth element, the compounds crystallize with the Mo 2 B 2 Fetype (space group P4/mbm) or the Er 2 Au 2 Sn structure (space group P42/mnm), a superstructure of Mo 2 B 2 Fe. Temperature dependent susceptibility measurements of Y 2 Au 2 Sn, Lu 2 Au 2 Sn, and Lu 2 Au 2 In indicate Pauli paramagnetism compatible with the metallic behavior deduced from resistivity measurements. Ho 2 Au 2 In and RE 2 Au 2 Sn (RE = Dy-Tm) show Curie-Weiss behavior above 50 K with experimental magnetic moments close to the free ion values of the trivalent rare earth elements. The compounds Ho 2 Au 2 In, Dy 2 Au 2 Sn, Ho 2 Au 2 Sn, and Er 2 Au 2 Sn, undergo magnetic ordering at 20(1) (F), 16(1) (AF), 8(1) (AF), and 4.5(1) K (AF), respectively. Tm 2 Au 2 Sn remains paramagnetic down to 2 K.

The hexagonal scandium compounds ScAuSi (P6̄m2, a = 421.7(1), c = 680.7(1) pm) and ScAuGe (P63mc, a = 431.03(9), c = 685.5(1) pm) were synthesized in X-ray pure form via arc-melting of the elements. The structures are derived from the AlB 2 -type. The gold and silicon (germanium) atoms build up strongly puckered layers of Au 3 Si 3 and Au 3 Ge 3 hexagons. Due to a different puckering pattern and stacking sequence of the hexagons, the ScAuGe structure has one and the ScAuSi structure two crystallographically independent scandium sites, which can be unambiguously distinguished on the basis of 45 Sc- 29 Si magnetic dipole-dipole interactions measured in a site selective fashion on an isotopically enriched material by solid state NMR.

The binary alkaline earth trielides of the composition A II M III 2 exhibit a puzzling variety of structure types ranging from electron precise Zintl compounds like CaIn 2 and KHg 2 (both with networks of four-bonded M − entities) and the AlB 2 structure type (with graphite analogue M sheets) to the cubic Laves phases e. g. of CaAl 2 . The examination of the phase stabilities of mixed compounds AM1 III x M2 III 2−x of two trielides allows to separate the stability ranges in a structure map by taking the electronegativity differences of M III and A II (Δ EN) and the radius ratios (RR = rM/rA) into account: The CaIn2-type is stable at comparatively large RR, for example over the whole range CaGa 2 -CaIn 2 and even up to CaAl 0.6 Ga 1.4 and CaAl 1.2 In 0.8 , and in SrIn 2 , together with a limited substitution of In by Al or Ga. The KHg 2 -type is observed in a region of lower RR: In BaIn 2 , a substitution of In by 50% Al and 30% Ga is possible without a general structure change, in SrAl 2 this holds for a content of up to 50% In. At high Δ EN and low RR values (e. g. Sr/Ba-Ga), the ideal AlB 2 structure type exhibits a distinct stability range; only for small RR around CaAl 2 the MgCu 2 -type is stable. FP-LAPWband structure calculations of the binary trielides allow to explain the structural changes qualitatively. In the case of the electron precise phases forming the CaIn 2 , KHg 2 or AlB 2 structure type, details of the bonding situation (such as M-M distances) as well as differences to other isoelectronic compounds can be rationalized taking the incomplete charge transfer from the alkaline earth towards the triel elements into account. This causes a partial depopulation of some of the bonding and a population of predominantly antibonding states.

A new organic/inorganic salt formed by mixed-valence dibenzotetrathiafulvalene (DBTTF) radical cations and the spherical Keggin-type polyoxometalate anions [H 3 BW 12 O 40 ] 2− was obtained by electrochemical oxidation of the donor in an acetonitrile and a 1,2-dichloroethane solution containing the polyanion. The compound has been characterized by X-ray diffraction, elemental analysis, EPR, IR and Raman spectroscopy. X-Ray diffraction experiments have revealed that the compound consists of heteropolyanions, water molecules and DBTTF radical cations. The organic radicals form trimers and dimers via π-π stacking; moreover, the polyoxoanions and the organic donors are also held together by hydrogen bonding interactions. In their packing arrangement, a three-dimensional supramolecular network with one-dimensional channels along the b axis is established with uncoordinated water molecules residing in the channels.

The unsymmetrical complexes Ni(dmdt)(dmio) and Ni(dmstfdt)(dmio) (dmdt = dimethyltetrathiafulvalenedithiolate, dmstfdt = dimethyldiselenadithiafulvalenedithiolate, dmio = 1,3-dithiol-2-one- 4,5-dithiolate) were prepared and characterized analytically and spectroscopically. The complexes exhibit strong third-order nonlinear optical response in the visible and near-infrared spectral regions.

A new copper(II) complex with a (bdpg-His) ligand was prepared and its structural properties were investigated both in crystalline and in solution states; (bdpg-His) = N,N-bis(2-pyridylmethyl) carnosine methylester. In the solid state, the complex has a dimeric structure, but in solution it partially dissociates into monomeric species, which have an imidazole moiety as an anchor group. This complex can prevent the precipitation of aggregated amyloid beta-peptide induced by zinc(II) ions, and affects the structure of the superoxide dismutase molecule, leading to the loss of the dimeric structure; these effects are probably due to the free imidazole group of the complex in solution.

The new tetraalkylammonium tetrathiomolybdates (Me 4 N) 2 [MoS 4 ] (1) and (nBu 4 N) 2 [MoS 4 ] (2) were prepared via a direct salt substitution using (NH 4 ) 2 [MoS 4 ] as starting material. Compound 1 crystallises in the non-centrosymmetric orthorhombic space group P2 1 2 1 2 1 with a = 8.9233(4), b = 15.5210(9) and c = 37.255(3) Å. Compound 2 crystallises in the orthorhombic space group Fdd2 with a = 28.9142(18), b = 35.7811(10) and c = 15.6774(17) Å. The structures of both compounds consist of slightly distorted [MoS 4 ] 2− tetrahedra and tetraalkylammonium cations which are packed in different ways. Single crystals of (Et 4 N) 2 [MoS 4 ] (3) were also investigated giving the lattice parameters a = 14.0346(7) and c = 12.5143(8) Å. A very strong disorder prevented a successful structure refinement and only the anion and one cation could be located. It is remarkable that the disorder of parts of the alkyl groups decreases with increasing chain length, in correlation with the IR and Raman vibrations of the [MoS 4 ] 2− tetrahedron showing a slight shift to lower energy with increasing alkyl chain length. The most prominent IR band of [MoS 4 ] 2− is broad but not split, indicating that the distortion of the tetrahedra is small.

Strontium hydroxide octahydrate Sr(OH) 2 · 8 H 2 O crystallizes in the tetragonal space group P4/ncc with cell constants a = 9.017(1) and c = 11.603(1) Å . The crystal structure has been refined from 2656 diffractometer data up to 2ϑ = 60° to an R value of 0.0303. With the new diffraction data it was possible to localize the positions of all hydrogen atoms for the first time and to describe the hydrogen bonding scheme in detail. The Sr 2+ ions are square antiprismatically coordinated by eight water molecules. These {Sr(H 2 O) 8 } 2+ coordination polyhedra are linked with each other via hydrogen bonds in a way that linear columns parallel to the c axis result. The two hydroxyl anions of the asymmetric unit are linked by weak hydrogen bonds and are not coordinated to strontium atoms. Like the strontium atoms, they form linear chains parallel to the c axis. Both, {Sr(H 2 O) 8 } 2+ columns and OH - chains, are interconnected through two types of additional hydrogen bonds.

Boron-nitrogen compounds were studied with respect to indirect nuclear 15 N- 11 B spin-spin coupling ( 1 J( 15 N, 11 B)). Some new experimental data were determined for aminoboranes and tetra-Npyrrolylborate, and a variety of compounds with B-N single, double and triple bonds were examined using DFT methods for the calculation of 1 J( 15 N, 11 B) at the B3LYP/6-311+G(d,p) level of theory. The calculations predict magnitude and sign of 1 J( 15 N, 11 B) reasonably well, and the Fermi contact term was found to be dominant. A positive sign of 1 J( 15 N, 11 B) was calculated in the case of 1-azacloso- dodecaborane(12), in contrast to all other compounds studied.

The reaction of the tridentate ligand-precursor molecule 1, o-HO-p-MeO-C 6 H 3 -C(Ph)=N-(o-C 6 H 4 )-OH, with diorganodichlorosilanes Me 2 SiCl 2 , Ph 2 SiCl 2 and PhAllSiCl 2 yields pentacoordinate silicon complexes R,R′Si[o-O-p-MeO-C 6 H 3 -C(Ph)=N-(o-C 6 H 4 )-O] (2a′: R, R′ = Me; 2b: R, R′ = Ph; 2c: R = Ph, R′ = All). 2b and 2c have pentacoordinate silicon atoms in the solid state as well as in chloroform solution. Surprisingly, for 2a an isomer 2a′ with Si-tetracoordination is preferred in the solid state, while the Si-pentacoordinated isomer 2a may dominate in solution. The hypercoordinate allylsilane 2c with a C=X→Si moiety is stable in solution and does not undergo a 1,3-allyl-shift-reaction.

The most widely used criterion for the evaluation of chemical bonding, especially of weak bonding, are interatomic distances shorter than the sum of the van derWaals radii, d(X···Y)<Σr(vdW)[X,Y]. The shortcomings of these radii are, however, so serious, that illicit conclusions are easily arrived at. It is proposed to discard the ‘shorter than Σr(vdW)’ criterion altogether and to rely on alternative criteria.

Several new 4’-O-substituted derivatives of 3,4,5-trimethoxy-4’-hydroxystilbene were synthesized and characterized by their IR and NMR spectra. The crystal structure of ethyl {4-[(E)-2-(3,4,5-trimethoxyphenyl) vinyl]phenoxy}acetate, one of these stilbene derivatives, has been solved by singlecrystal X-ray structure analysis. The results show that all carbon and oxygen atoms in the molecule are nearly coplanar except C(16), and molecules stack to a column arrangement owing to C-H···π interactions. Pairs of these columns are linked by other molecules, and these linker molecules themselves also produce a column along the other direction. A puckered cyclic tetramer R 4 4 (46) is formed and the tetramer propagates itself via intermolecular hydrogen bonds and C-H···π interactions. In this way, molecules are interrelated and assembled to a two-dimensional layer structure.

The 1,2,3,4-tetrahydro-isoquinolin-4-one 4 reacts as an α-amino ketone with periodate to give various products, the major compound being 1-hydroxy-1,2-dihydro-3,4-isoquinolinedione 12. Upon stepwise oxidation with Hg(II)-EDTA the 4-hydroxyisoquinolinium ion 14 is detected as an intermediate and its further oxidation with periodate gives rise to an almost identical product spectrum. Because 12 represents a carbinolamide with an additional 4-carbonyl group, this type was examined first. Acid catalysis was used because the reactive species mostly are iminium ions. With cyclic 1,3- dicarbonyl compounds, 1-substituted derivatives 17a, b are formed.With linear species 1-substitution is also observed, but the tautomeric forms 19a - c are obtained. The stable enones 24a, b result from alkyl ketones by ready autoxidation of the primary products. Base catalysis induces a ring contraction of 12 to the hydroxycarboxylic acid 25. Reaction of 12 with aniline and phenylhydrazine yields the easily oxidizable 1-substitution products 28 and 31.

4-Nitrophenyl-1-piperidinostyrene (4) reacts with an aromatic diazonium salt to afford the arylhydrazonal 6. The latter condenses with active methylene compounds to yield pyridazine derivatives, and with hydroxylamine hydrochloride to produce oxadiazole and 1,2,3-triazole derivatives. Compound 12 was reacted with chloroacetonitrile to afford 4-aminopyrazoles 15.

The investigation of a dichloromethane extract of flower heads of Achillea clypeolata collected in Bulgaria led to the isolation of one guaiane (4,10,11-trihydroxy-guaiane, 1), four eudesmanes (4(15)-eudesmene-1β ,11-diol, 2, clypeotriol, 3, 3-epi-clypeotriol, 4, cryptomeridiol, 5), one diterpene (sugeroside, 6) and two phenolic compounds (centaureidin, 7 and scopoletin, 8). Their structures were elucidated by UV/vis, EI- and CI-MS as well as by one- and two-dimensional NMR experiments. 4,10,11-Trihydroxy-guaiane (1) and 3-epi-clypeotriol (4) are reported here for the first time.

A new eudesmane sesquiterpene glycoside, named funingensin A (1), together with a novel cyclic ether based on the cadalane skeleton, named funingensin B (2), were isolated from the roots of Parepigynum funingense. Their structures were elucidated by spectroscopic methods, including oneand two-dimensional NMR (COSY, HMQC, HMBC and ROESY).

Biotransformation of the diterpene jatrophone (1) by Aspergillus niger ATCC 16404 afforded the new diterpene 9β -hydroxyisabellione (2). The compounds were characterized by spectroscopic analysis. The cytotoxicity of the compounds as IC 50 values on AGS and lung fibroblasts was 2.4 and 2.8 μM for compound 1 and 53.1 and 260 μM for 2, respectively. Microbial transformation of 1 into compound 2 strongly reduced the cytotoxicity and enhanced the selectivity against AGS cells.

Recent phytochemical studies on the ethanolic extract of Artocarpus nobilis, collected from Sri Lanka, have resulted in the isolation of two new cycloartane-type triterpenoids, artocarpuate A (1) and artocarpuate B (2). Structures of these new compounds were established with the aid of extensive NMR spectroscopic studies. Compounds 1 and 2 were found to exhibit weak acetylcholinesterase inhibitory activity.

An unusual and complex tropane alkaloid pattern has been detected in the root bark of Astripomoea malvacea and in the whole plant of Falkia repens (Convolvulaceae) by GC-MS analysis. The specific profile of both species is characterized by the presence of aliphatic 3- acyloxytropanes/-nortropanes (exclusively in A. malvacea; predominantly in F. repens in cooccurrence with a few aromatic as well as arylalkyl acyl congeners). The principal alkaloid of A. malvacea, astrimalvine A N-oxide [3β -(3-tigloyloxy-2-methylbutyryloxy)tropane N-oxide], isolated and structurally elucidated by detailed spectroscopic analysis, represents the first N-oxide of a 3β -tropanol derivative in the Convolvulaceae. Its minor tertiary congener astrimalvine B [3β -(3-hydroxy-2-methylbutyryloxy)tropane] turned out to be a metabolite of both convolvulaceaous species. This is the first phytochemical report on the African genera Astripomoea and Falkia.

Phytochemical examination of the methanolic extract from fruit bodies of an unidentified Vietnamese Phellinus species led to the isolation of four compounds, one of which is a new steroid, 25-hydroxy-ergosta-7,24(28)-dien-3β -ol, named phellinol, together with senexonol, trametenolic acid B and ergosta-4,6,8(14),22-tetraen-3-one. Their structures were determined by 2D NMR, MS, IR and UV spectroscopy. In addition, the absolute configuration of senexonol was established by X-ray crystallographic analysis of its p-bromobenzoate derivative as 22(R)-hydroxy-4(S),14(S)- dimethyl-cholesta-8,24-dien-3-one. All compounds moderately suppressed the lipopolysaccharide (LPS)-induced production of nitric oxide (NO) in RAW 264.7 cells.