Electron microscopy investigations on structures of ZrO2‐rich phases in the quasibinary system ZrO2‐Zr3N4

Slowly cooled nitrided zirconia samples were investigated and characterized by means of transmission electron microscopy (TEM). Besides the well‐known different modifications of ZrO₂ some ZrO₂‐rich oxynitride phases could be further found, called β‐type phases. An overview regarding the formation of such different structural modifications could be gained, supported by previously performed measurements using powder X‐ray diffractometry (XRD). Similar to fast cooled nitrided zirconia samples Zr(N,O), the slowly cooled ones also contain different kinds of ZrO₂ precipitates, which can be obviously emphasized by using the methods of diffraction contrast. A super cell was successively built, derived from the unit cells of the β and β′ phase, in order to explain the structure of the observed modulated β″ phase. Agreements from the comparisons between experimental high resolution images and the simulated ones of such modulated structures confirm the suggested starting points. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phosphazene cations

Cations derived from (NPCl2)3, hexachloro-cyclo-triphosphazene, the weakly basic precursor of phosphazene polymers, have been prepared using strongly electrophilic reagents based on carborane anions. N-protonated, N-methylated, and N-silylated adducts of (NPCl2)3 have been isolated and characterized by X-ray crystallographic and spectroscopic methods. The normally potent chloride-abstracting silyl reagents of the type R3Si(carborane) are unable to abstract chloride from (NPCl2)3, even though the coordinatively unsaturated N2P2Cl5+ cation is widely accepted as a reactive intermediate in the ring-opening polymerization of (NPCl2)3.     

Synthesis of extended polyphosphacumulenes

Addition of two equivalents of (Me(3)Si)(2)CLiCl to the C-[(diphenyl) (diisopropylamino)phosphonio]-P-(diisopropylamino)phosphaalkene 2 affords the 1sigma(4),3sigma(3)-diphosphabuta-1,2,3-triene E1 in 55 % yield. Derivative E1 was fully characterized, including a single-crystal X-ray diffraction study. Alkylation of E1 with methyl trifluoromethanesulfonate gives rise to the first C-phosphonio-bis(methylene)phosphorane 5, which was isolated in 84 % yield. Because the second carbon center is also nucleophilic, cumulene E1 reacts as a "pincer" with BF(3)OEt(2), leading to the formation of a novel four-membered PCBC heterocycle 6 with a betaine-like structure. Addition of three equivalents of P-[diphenyl(diisopropylamino)]methylene phosphorane to (diisopropylamino)dichlorophosphane, followed by addition of one equivalent of CCl(4), and subsequent deprotonation with lithium hexamethyldisilazide gave rise to 1sigma(4),3sigma(3),5sigma(4)-triphosphapenta-1,2,3,4-tetraene F1, which was isolated in 62 % yield.     

Supramolecular fullerene-porphyrin chemistry. Fullerene complexation by metalated "jaws porphyrin" hosts

Porphyrins and fullerenes are spontaneously attracted to each other. This new supramolecular recognition element is explored in discrete, soluble, coordinatively linked porphyrin and metalloporphyrin dimers. Jawlike clefts in these bis-porphyrins are effective hosts for fullerene guests. X-ray structures of the Cu complex with C60 and free-base complexes with C70 and a pyrrolidine-derivatized C60 have been obtained. The electron-rich 6:6 ring-juncture bonds of C60 show unusually close approach to the porphyrin or metalloporphyrin plane. Binding constants in toluene solution increase in the order Fe(II) < Pd(II) < Zn(II) < Mn(II) < Co(II) < Cu(II) < 2H and span the range 490-5200 M-1. Unexpectedly, the free-base porphyrin binds C60 more strongly than the metalated porphyrins. This is ascribed to electrostatic forces, enhancing the largely van der Waals forces of the pi-pi interaction. The ordering with metals is ascribed to a subtle interplay of solvation and weak interaction forces. Conflicting opinions on the relative importance of van der Waals forces, charge transfer, electrostatic attraction, and coordinate bonding are addressed. The supramolecular design principles arising from these studies have potential applications in the preparation of photophysical devices, molecular magnets, molecular conductors, and porous metal-organic frameworks.     

Synthesis and characterization of the SO(2)N(3)(-), (SO(2))(2)N(3)(-), and SO(3)N(3)(-) anions

SO(2) solutions of azide anions are bright yellow, and their Raman spectra indicate the presence of covalently bound azide. Removal of the solvent at -64 degrees C from CsN(3) or N(CH(3))(4)N(3) solutions produces yellow (SO(2))(2)N(3)(-) salts. Above -64 degrees C, these salts lose 1 mol of SO(2), resulting in white SO(2)N(3)(-) salts that are marginally stable at room temperature and thermally decompose to the corresponding azides and SO(2). These anions were characterized by vibrational and (14)N NMR spectroscopy and theoretical calculations. Slow loss of the solvent by diffusion through the walls of a sealed Teflon tube containing a sample of CsSO(2)N(3) in SO(2) resulted in white and yellowish single crystals that were identified by X-ray diffraction as CsSO(2)N(3).CsSO(3)N(3) with a = 9.542(2) A, b = 6.2189(14) A, c = 10.342(2) A, and beta = 114.958(4) degrees in the monoclinic space group P2(1)/m, Z = 2, and Cs(2)S(2)O(5).Cs(2)S(2)O(7).SO(2), respectively. Pure CsSO(3)N(3) was also prepared and characterized by vibrational spectroscopy. The S-N bond in SO(2)N(3)(-) is much weaker than that in SO(3)N(3)(-), resulting in decreased thermal stability, an increase in the S-N bond distance by 0.23 A, and an increased tendency to undergo rotational disorder. This marked difference is due to SO(3) being a much stronger Lewis acid (pF(-) value of 7.83) than SO(2) (pF(-) value of 3.99), thus forming a stronger S-N bond with the Lewis base N(3)(-). The geometry of the free gaseous SO(2)N(3)(-) anion was calculated at the RHF, MP2, B3LYP, and CCSD(T) levels. The results show that only the correlated methods correctly reproduce the experimentally observed orientation of the SO(2) group.     

Isolating benzenium ion salts

When partnered with carborane anions, arenium ions are remarkably stable. Previously investigated only at subambient temperatures in highly superacidic media, protonated benzene is readily isolated as a crystalline salt, thermally stable to >150 degrees C. Salts of the type [H(arene)][carborane] have been prepared by protonating benzene, toluene, m-xylene, mesitylene, and hexamethylbenzene with the carborane superacid H(CB(11)HR(5)X(6)) (R = H, Me; X = Cl, Br). They have been characterized by elemental analysis, X-ray crystallography, NMR and IR methods. Solid-state (13)C NMR spectra are similar to those observed earlier in solution, indicating that lattice interactions are comparable to solution solvation effects. The acidic proton(s) of the arenium cations interact weakly with the halide substituents of the anion via ion pairing. This is reflected in the dependence of the C-H stretching frequency on the basicity of the carborane anion. Bond lengths in the arenium ions are consistent with predominant cyclohexadienyl cation character, but charge distribution within the cation is less well represented by this resonance form. Structural and vibrational comparison to theory is made for the benzenium ion (C(6)H(7)(+)) with density functional theory at B3LYP/6-31G and B3P86/6-311+G(d,p) levels. The stability of these salts elevates arenium ions from the status of transients (Wheland intermediates) to reagents. They have been used to bracket the solution-phase basicity of C(60) between that of mesitylene and xylene.     

Thin-layer chromatographic and column liquid chromatographic analyses of morphine in urine via dabsylation

A semiquantitative screening method for morphine in urine and a quantitative assay method for the drug were developed. In the semiquantitative method, morphine in urine was directly reacted with 4-dimethylaminoazobenzene-4'-sulphonyl chloride (dabsyl chloride) in a slightly alkaline medium. The orange-coloured dabsyl morphine was separated by silica gel thin-layer chromatography and the spot intensity was visually compared with that of the standards. The limit of detection is 0.075 microgram/ml. In the quantitative method, morphine was extracted from urine before dabsylation. The dabsylation reaction is very fast and is complete within 5-10 min at room temperature. Dabsylation yield is maximum at a dabsyl chloride concentration of 6.2 mM. Total recovery of morphine using the extraction and dabsylation procedures described is 66%. Dabsyl morphine, thus formed, was analysed using high-performance liquid chromatography by monitoring its absorbance at 436 nm on a normal-phase mu Porasil column. The limit of quantitation using high-performance liquid chromatography is 0.26 microM (0.075 microgram/ml), which corresponds to 10.5 pmol of injected dabsyl morphine. Quantitative assay was also carried out by thin-layer chromatography on silica gel followed by densitometry. The limit of quantitation is 1.3 microM (0.375 microgram/ml).     

Light-mediated C-C sigma-bond driven crystallization of a phenalenyl radical dimer

Polymorphism-the phenomenon that a given compound forms more than one crystalline arrangement of the molecules in the solid state- plays a crucial role in understanding organic conductors, superconductors, and magnets. We have found that solutions of a new phenalenyl radical can give rise to two (nonpolymorphic) crystalline forms depending on whether the crystallization is allowed to proceed in the presence or absence of light. In both cases the crystals take the form of black shining blades and are indistinguishable by optical microscopy. We have fully characterized these crystalline forms, and we show that they differ by the presence or absence of a C-C sigma-bond between the unpaired electrons of the parent radical. These molecular forms crystallize from the same solvent to give rise to a sigma-dimerized insulator and a monomeric radical semiconductor as dictated by the presence or absence of light.     

Air- and water-stable catalysts for hydroamination/cyclization. Synthesis and application of CCC-NHC pincer complexes of Rh and Ir

The scope of CCC-NHC pincer complex synthetic methodology by metalation/transmetalation has been extended to Ir. Structural characterization revealed that it is isomorphous with the Rh complex. Both Rh and Ir complexes are efficient catalysts for the hydroamination/cyclization of secondary amines in the presence of air and/or water.