Reaction of Tetracopper(I)-Phosphonitocavitand with PhSeSiMe3: Synthesis and Structure of a Polyanionic Cluster [pyH]6[(CuCl)9(μ3-SePh)5(μ4-SePh)]

Treatment of tetracopper(I)-phosphonitocavitand [1·Cu₄(μ-Cl)₄(μ₄-Cl)] (2) (1 = tetraphosphonitocavitand [rccc-2,8,14,20-tetrakis-(iso-butyl)-phosphonitocavitand (C₄₄H₄₈O₈P₄Ph₄)]) with PhSeSiMe₃ in THF at low temperature afforded a novel polyanionic cluster [pyH]₆[(CuCl)₉(μ₃-SePh)₅(μ₄-SePh)] (4) as a major product along with a new tetracopper(I)-phosphonitocavitand (3) with a centered μ₃-Cl. Molecular structure of anionic cluster in 4 consists of six PhSe⁻ bridging ligands containing five μ₃-SePh and one exceptional μ₄-SePh bridging nine copper atoms, of which eight copper atoms have trigonal coordination geometry and the other has distorted tetrahedral geometry. Dedicated to Professor Han-Qin Liu on the occasion of his 70th birthday.     

The neomycin biosynthetic gene cluster of Streptomyces fradiae NCIMB 8233: characterisation of an aminotransferase involved in the formation of 2-deoxystreptamine

The biosynthetic gene cluster of the 2-deoxystreptamine (DOS)-containing aminoglycoside antibiotic neomycin has been cloned for the first time by screening of a cosmid library of Streptomyces fradiae NCIMB 8233. Sequence analysis has identified 21 putative open reading frames (ORFs) in the neomycin gene cluster (neo) with significant protein sequence similarity to gene products involved in the biosynthesis of other DOS-containing aminoglycosides, namely butirosin (btr), gentamycin (gnt), tobramycin (tbm) and kanamycin (kan). Located at the 5'-end of the neo gene cluster is the previously-characterised neomycin phosphotransferase gene (apH). Three genes unique to the neo and btr clusters have been revealed by comparison of the neo cluster to btr, gnt, tbm and kan clusters. This suggests that these three genes may be involved in the transfer of a ribose moiety to the DOS ring during the antibiotic biosynthesis. The product of the neo-6 gene is characterised here as the L-glutamine : 2-deoxy-scyllo-inosose aminotransferase responsible for the first transamination in DOS biosynthesis, which supports the assignment of the gene cluster.     

Perfluororganocadmium-verbindungen als sehr wirksame perfluoralkylierungs- und perfluorphenylierungsmittel zur darstellung von perfluororganozinn- und -blei-verbindungen [1]

Perfluoroorgano tin and lead compounds can be prepared in high yields from the reactions of (CH₃)₃SnOCOCF₃ and (CH₃)₃Pb(OCOCF₃) with perfluoroorgano cadmium complexes. (CH₃)₃SiOCOCF₃ reacts with (CF₃)₂Cd complexes — probably via the intermediate (CH₃)₃SiCF₃ and CF₂ elimination — to form (CH₃)₃SiF and CF₃CdOCOCF₃ complexes. While the reaction of (CF₃)₂Cd·D with (CH₃)₃SnONO₂ yields CF₃NO as the only volatile product, (R_f)₂Cd·D (R_f  C₂F₅, iC₃F₇) forms R_fCdONO₂·D and (CH₃)₃SnR_f. The preparations and properties of the partly new compounds as well as the n.m.r. spectra are described.     

Peculiar structure of the HOOO(-) anion

The HOOO(-) anion (1) can adopt a triplet state (T-1) or a singlet state (S-1), where the former is 9.8 kcal/mol (DeltaH(298) = 10.3 kcal/mol) more stable than the latter. S-1 possesses a strong O-OOH bond with some double bond character and a weakly covalent OO-OH bond (1.80 A) according to CCSD(T)/6-311++G(3df,3pd) calculations (the longest O-O bond ever found for a peroxide). In aqueous solution, S-1 adopts a geometry closely related to that of HOOOH (OO(O), 1.388 A; (O)OO(H), 1.509 A; tau(OOOH), 78.3 degrees ), justifying that S-1 is considered the anion of HOOOH. Dissociation into HO anion and O(2)((1)Delta(g)) requires 15.4 (DeltaH(298) = 14.3; DeltaG(298) = 8.9) kcal/mol. Structure T-1 corresponds to a van der Waals complex between HO anion and O(2)((3)Sigma(g)(-)) having a binding energy of 2.7 (DeltaH(298) = 2.1) kcal/mol. Modes of generating S-1 in aqueous solution are discussed, and it is shown that S-1 represents an important intermediate in ozonation reactions.     

XVI. (2,5-C4Bu2RHN)MCl3 (M = Ti, Zr, Hf; R = H, SiMe3)—Azacyclopentadienyl-Komplexe der Gruppe 4-Metalle

The azacyclopentadienyl compounds (2,5-C₄^tBu₂RHN)MCl₃ (M = Ti, Zr, Hf; R = H, SiMe₃) have been prepared as stable solids from the lithiated pyrroles and MCl₄. The π-coordination of the azacyclopentadienyl ligands, as suggested from ¹³ C NMR data, has been confirmed for (2,5-C₄^tBu₂H₂N)TiCl₃ by an X-ray diffraction study.     

A π-acceptor series for phosphines from51V N.M.R. data on [η5-CpV(CO)3L] complexes

Summary Qualitative molecular orbital considerations of the complexes [⁵-CPV(CO)₃ L] (L = substituted phosphane, SbPh₃, AsPh₃, CN^–) suggest that s' V chemical shift parameters () obtained for these compounds should correlate with the -acceptor abilities of L. Based on observed r-values, the ligands are arranged in sequence of their -acceptor ability, which lies in the order P(OR)₃ > CN^– > PR'₃3 SbPh₃ PPhF₂ > P(i-Bu)₃ P(NR ₂ )₃ > PPh₃ > AsPh₃ Nuclear spin-spin coupling constants J (⁵¹V-³¹ P), line widths H and i.r. data in the (CO) region are also presented.P(OR)₃ = P(OEt)₃, 4-Ethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]-octane; R = Me, n-Pr; R = Me, Et.     

The Yellow Polymorphs of Mercuric Iodide (HgI2)

HgI₂ crystallizes under ambient conditions from various solvents and by sublimation into three concomitant polymorphs whose colors are red, orange, and yellow. The orange and yellow phases are metastable and transform into the red phase when touched. A phase transition from red to yellow occurs at 400 K. The reverse transition from yellow to red shows a huge hysteresis. We established that the structures of the metastable yellow^M phase (determined by single‐crystal X‐ray diffraction) and the high‐temperature yellow^HT phase (determined by powder synchrotron X‐ray diffraction and second‐harmonic generation) are different, albeit closely related. Both show analogous packings of I? Hg? I molecules, which are straight in the first and bent with an angle of ca. 160° in the second. The red and orange phases are tetrahedral semiconductor structures that sublime even at room temperature. The growth of the yellow^M phase from 2‐chloroethanol and the kinetics of the reconstructive phase transition red to yellow^HT and back were studied by optical microscopy, Raman spectroscopy in solution, luminescence, and powder synchrotron X‐ray diffraction as a function of time at various temperatures. Both yellow phases grow by accretion of HgI₂ molecules, present in the solution or liberated from the red crystals, on the surface of the crystal. In contrast, the reverse transformation from yellow to red occurs in the bulk of the crystal, presumably by migration of Hg in the packing of I and subsequent rearrangement of I. The displacement parameters of Hg in both structures are considerably larger than those of I and apparently not dominated by disorder effects.     

Some non-existence results on divisible difference sets

In this paper, we shall prove several non-existence results for divisible difference sets, using three approaches:

1. character sum arguments similar to the work of Turyn [25] for ordinary difference sets,
2. involution arguments and
3. multipliers in conjunction with results on ordinary difference sets.

Among other results, we show that an abelian affine difference set of odd orders (s not a perfect square) inG can exist only if the Sylow 2-subgroup ofG is cyclic. We also obtain a non-existence result for non-cyclic (n, n, n, 1) relative difference sets of odd ordern.     

Unified treatment of fermions and bosons

Dirac's matrices can be interpreted as an 8-rank covariant antisymmetric tensor field on an 11-dimensional manifold (space-time ×S ⁷) enforcing a linkage between the Lorentz transformation and rotations ofS ⁷, conferring spinorial properties on any quantity having an index in the inner spaceS ⁷.