An overview of studies on the highly dispersed uranium oxide species occluded within mesoporous MCM-41 and MCM-48 host materials

In this article we have consolidated our recent studies on anchoring of uranyl groups and encapsulation of highly dispersed nano-particles of -U₃O₈ in mesoporous MCM samples. The size of uranium oxide crystallites and the binding of uranyl groups at framework sites of host matrix depended on the preparation method, viz. wet impregnation, exchange of template cations, and the hydrothermal route. These uranium species contributed individually to the catalytic oxidation of organic molecules, such as methanol, toluene and benzyl alcohol; the uranyl groups playing a more important role at lower reaction temperatures. Also, the size and the lattice oxygen of uranium oxide crystallites played a vital role, not only in the lowering of reaction onset temperature but also in deciding the nature and the reactivity of the transient surface species formed during the oxidation of above mentioned organics. For instance, the results of in situ IR spectroscopy experiments have shown that while larger-size U₃O₈ crystallites help in the growth of certain oxymethylene (–OCH₂) and polymerized oxymethylene (–OCH₂)_n species, adsorption of methanol on smaller size particles helped in the additional formation of formate-type complexes. Thus, a relationship was found between the size of uranium oxide crystallites, the nature of the transient species formed and the catalytic conversion of methanol to form CO₂, CO and methane. In addition, the uranyl ions anchored within the pore system of host matrix are found to serve as efficient heterogeneous photocatalysts for the sunlight-assisted deep oxidation of organic molecules in the vapor phase and at room temperature. The reaction mechanisms, accounting for the catalytic properties of occluded UO_x species without and in the presence of radiation, are discussed in the light of the above mentioned results.     

Kinetics and mechanism of the beta- to alpha-CuAlCl(4) phase transition: a time-resolved (63)Cu MAS NMR and powder X-ray diffraction study

The beta and alpha phases of CuAlCl(4) have been characterized by solid-state (27)Al and (63)Cu magic angle spinning nuclear magnetic resonance. The very short spin--lattice relaxation times of the copper spins, and the sensitivity of the I = 3/2 (63)Cu nucleus to the small differences in the local structure of Cu in the two phases, allowed (63)Cu spectra to be acquired in very short time periods (1 min), in which the beta and alpha phases were clearly resolved. This time resolution was exploited to follow the phase transition from the pseudohexagonal close-packed beta-CuAlCl(4) into the pseudocubic close-packed alpha-CuAlCl(4), which occurs above 100 degrees C. In situ time-resolved (63)Cu MAS NMR and synchrotron X-ray diffraction experiments were used to measure the kinetics of this phase transition as a function of temperature. The transformation was shown to be a first-order phase transition involving no intermediate phases with an activation energy of 138 kJ/mol. The kinetic data obey a first-order Avrami--Erofe'ev rate law. A one-dimensional growth mechanism is proposed that involves a combination of Cu(+) ion self-diffusion and a translational reorganization of the close-packed anion layers imposed by the periodic rotations of [AlCl(4)](-) tetrahedra. This beta to alpha phase transformation can be induced at ambient temperatures by low partial pressures of ethylene.     

Tetraphenyl-and tetratolylantimony complexes with N,N-dialkyldithiocarbamate ligands: Synthesis, X-ray diffraction analysis, and 13C and 15N CP/MAS NMR studies

Crystalline tetraphenylantimony and tetratolylantimony complexes with N,N-dialkyldithiocarbamate ligands [Sb(C₆H₅)₄(S₂CNR₂)] (R = CH₃, C₂H₅, and C₃H₇ and R₂ = (CH₂)₆) were synthesized by ligand exchange reactions and studied by ¹³C and ¹⁵N CP/MAS NMR spectroscopy. X-ray diffraction analysis revealed that the complex [Sb(n-CH₃-C₆H₄)₄{S₂CN(C₃H₇)₂}] exists as the single molecular form, while [Sb(C₆H₅)₄{S₂CN(CH₂)₆}] exists as two molecular conformers. The ¹³C and ¹⁵N signals were assigned to the positions of the atoms in the isomeric structures [Sb(C₆H₅)₄{S₂CN(CH₂)₆}] in terms of different degrees of double bonding in the formally single =N-C(S)S-bond.     

Polyvinyl- and polyphenylsilsesquioxanes and their films: an investigation by X-ray diffractometry, positron diagnostics, and 29Si NMR spectroscopy

Polyvinyl- and polyphenylsilsesquioxanes (RSiO_1,5) _n were synthesized by hydrolytic polycondensation. The cross section surface areas of the polymer chain were measured and the sizes of ??traps?? of the free and ordered volumes and the ratio of the T₂ and T₃ units in (RSiO_1,5) _n were determined by time positron diagnostics, ²⁹Si NMR spectroscopy, and X-ray diffractometry. The density of polyvinyl- and polyphenylsilsesquioxanes was determined picnometrically and from the X-ray phase analysis data, and the content of hydroxyl groups was found by thermogravimetry. The cross section surface area of the silsesquioxane chains containing vinyl and phenyl radicals at Si were calculated by the Miller-Boyer method. The elementary volumes of the chain segments determined by different methods were compared. The geometric models for ??traps?? of the free volume were proposed. The optical properties and morphology of the polyvinylsilsesquioxane films were studied by atomic force microscopy and UV spectroscopy.     

Structural insights into the polymorphism of amyloid-like fibrils formed by region 20-29 of amylin revealed by solid-state NMR and X-ray fiber diffraction

Many unrelated proteins and peptides can assemble into amyloid or amyloid-like nanostructures, all of which share the cross-beta motif of repeat arrays of beta-strands hydrogen-bonded along the fibril axis. Yet, paradoxically, structurally polymorphic fibrils may derive from the same initial polypeptide sequence. Here, solid-state nuclear magnetic resonance (SSNMR) analysis of amyloid-like fibrils of the peptide hIAPP 20-29, corresponding to the region S (20)NNFGAILSS (29) of the human islet amyloid polypeptide amylin, reveals that the peptide assembles into two amyloid-like forms, (1) and (2), which have distinct structures at the molecular level. Rotational resonance SSNMR measurements of (13)C dipolar couplings between backbone F23 and I26 of hIAPP 20-29 fibrils are consistent with form (1) having parallel beta-strands and form (2) having antiparallel strands within the beta-sheet layers of the protofilament units. Seeding hIAPP 20-29 with structurally homogeneous fibrils from a 30-residue amylin fragment (hIAPP 8-37) produces morphologically homogeneous fibrils with similar NMR properties to form (1). A model for the architecture of the seeded fibrils is presented, based on the analysis of X-ray fiber diffraction data, combined with an extensive range of SSNMR constraints including chemical shifts, torsional angles, and interatomic distances. The model features a cross-beta spine comprising two beta-sheets with an interface defined by residues F23, A25, and L27, which form a hydrophobic zipper. We suggest that the energies of formation for fibril form containing antiparallel and parallel beta-strands are similar when both configurations can be stabilized by a core of hydrophobic contacts, which has implications for the relationship between amino acid sequence and amyloid polymorphism in general.     

Testing the limits of sensitivity in a solid-state structural investigation by combined X-ray powder diffraction, solid-state NMR, and molecular modelling

A solid state structural investigation of ethoxzolamide is performed on microcrystalline powder by using a multi-technique approach that combines X-ray powder diffraction (XRPD) data analysis based on direct space methods with information from (13)C((15)N) solid-state Nuclear Magnetic Resonance (SS-NMR) and molecular modeling. Quantum chemical computations of the crystal were employed for geometry optimization and chemical shift calculations based on the Gauge Including Projector Augmented-Wave (GIPAW) method, whereas a systematic search in the conformational space was performed on the isolated molecule using a molecular mechanics (MM) approach. The applied methodology proved useful for: (i) removing ambiguities in the XRPD crystal structure determination process and further refining the derived structure solutions, and (ii) getting important insights into the relationship between the complex network of non-covalent interactions and the induced supra-molecular architectures/crystal packing patterns. It was found that ethoxzolamide provides an ideal case study for testing the accuracy with which this methodology allows to distinguish between various structural features emerging from the analysis of the powder diffraction data.     

Incorporation of aluminum in the calcium silicate hydrate (C-S-H) of hydrated portland cements: a high-field 27Al and 29Si MAS NMR investigation

The calcium silicate hydrate (C-S-H) phase resulting from hydration of a white Portland cement (wPc) in water and in a 0.3 M NaAlO(2) solution has been investigated at 14 and 11 hydration times, respectively, ranging from 6 h to 1 year by (27)Al and (29)Si MAS NMR spectroscopy. (27)Al MAS NMR spectra recorded at 7.05, 9.39, 14.09, and 21.15 T have allowed a determination of the (27)Al isotropic chemical shift (delta(iso)) and quadrupolar product parameter (P(Q) = C(Q)) for tetrahedrally coordinated Al incorporated in the C-S-H phase and for a pentacoordinated Al site. The latter site may originate from Al(3+) substituting for Ca(2+) ions situated in the interlayers of the C-S-H structure. The spectral region for octahedrally coordinated Al displays resonances from ettringite, monosulfate, and a third aluminate hydrate phase (delta(iso) = 5.0 ppm and P(Q) = 1.20 MHz). The latter phase is tentatively ascribed to a less-crystalline aluminate gel or calcium aluminate hydrate. The tetrahedral Al incorporated in the C-S-H phase has been quantitatively determined from (27)Al MAS spectra at 14.09 T and indirectly observed quantitatively in (29)Si MAS NMR spectra by the Q(2)(1Al) resonance at -81.0 ppm. A linear correlation is observed between the (29)Si MAS NMR intensity for the Q(2)(1Al) resonance and the quantity of Al incorporated in the C-S-H phase from (27)Al MAS NMR for the different samples of hydrated wPc. This correlation supports the assignment of the resonance at delta(iso)((29)Si) = -81.0 ppm to a Q(2)(1Al) site in the C-S-H phase and the assignment of the (27)Al resonance at delta(iso)((27)Al) = 74.6 ppm, characterized by P(Q)((27)Al) = 4.5 MHz, to tetrahedrally coordinated Al in the C-S-H. Finally, it is shown that hydration of wPc in a NaAlO(2) solution results in a C-S-H phase with a longer mean chain length of SiO(4) tetrahedra and an increased quantity of Al incorporated in the chain structure as compared to the C-S-H phase resulting from hydration of wPc in water.     

Thermal decomposition of monocalcium aluminate decahydrate (CaAl2O4.10H2O) investigated by in-situ synchrotron X-ray powder diffraction, thermal analysis and 27Al, 2H MAS NMR spectroscopy

The stability of monocalcium aluminate decahydrate, with the nominal composition CaAl(2)O(4).10H(2)O (CAH(10)), has a decisive role for the strength development and durability of cementitious materials based on high alumina cements. This has prompted an investigation of the thermal transformation of crystalline monocalcium aluminate decahydrate in air to an amorphous phase by in-situ synchrotron X-ray powder diffraction in the temperature range from 25 to 500 degrees C, by DTA/TGA, and (2)H, (27)Al MAS NMR spectroscopy. The decomposition includes the loss of hydrogen-bonded water molecules in the temperature range up to 175 degrees C, coupled with a reduction of the unit cell volume from 1928 A(3) at 25 degrees C, to 1674 A(3) at 185 degrees C. Furthermore, X-ray diffraction shows that CaAl(2)O(4).10H(2)O starts to transform to an amorphous phase at approximately 65 degrees C. This phase is fully developed at approximately 175 degrees C and it converts to crystalline CaAl(2)O(4) when heated to 1300 degrees C. The thermal decomposition in the temperature range from approximately 65 to approximately 175 degrees C involves both formation of an amorphous phase including AlO(4) tetrahedra and structural changes in the remaining crystalline phase.     

New applications of electron diffraction in the pharmaceutical industry: polymorph determination by using a combination of electron diffraction and synchrotron X-ray powder diffraction techniques.

Electron diffraction has been recently used in the pharmaceutical industry to study the polymorphism in crystalline drug substances. While conventional X-ray diffraction patterns could not be used to determine the cell parameters of two forms of the microcrystalline GP IIb/IIIa receptor antagonist roxifiban, a combination of electron single-crystal and synchrotron powder diffraction techniques were able to clearly distinguish the two polymorphs. The unit-cell parameters of the two polymorphs were ultimately determined using new software routines designed to take advantage of each technique's unique capabilities. The combined use of transmission electron microscopy (TEM) and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large-unit-cell, micron-sized) polymorphic pharmaceutical compounds.     

A novel cadmium aminophosphonate: X-ray powder diffraction structure, solid-state IR and NMR spectroscopic determination of the fine structure of the organic moieties

A new divalent cadmium phosphonate, Cd2Cl2(H2O)4(H2L), has been synthesized from the ethylenediamine-N,N'-bis(methylenephosphonic acid) (H4L). The obtained microcrystalline compound has been characterized by solid-state IR spectra and 13C, 31P, and 113Cd CP MAS NMR. The static 13P NMR spectra have been also recorded to give the delta11, delta22, and delta33 chemical shift parameters for both compounds. The spectral data, collected for Cd2Cl2(H2O)4(H2L), are in an agreement with its X-ray powder diffraction structure solved with the cell dimensions a = 16.6105(10), b = 7.1572(4), and c = 6.8171(4) A and beta = 98.327(4) degrees. The octahedral coordination sphere of the cadmium atoms consists of two phosphonate oxygen atoms, two water oxygen atoms, and the two chlorine atoms. Cadmium atoms are bridged by the chlorine atoms forming four-membered rings. The phosphorus atoms exhibit a tetrahedral coordination with two oxygen atoms bonded to the cadmium atoms with P-O distances of 1.503(10) and 1.504(10) A. The third oxygen atom, showing a longer P-O distance (1.546(9) A), is not bonded to the metal center, nor is it bonded to a proton. The combined IR and NMR proton-phosphorus cross-polarization kinetic data together with the X-ray data confirm that the cadmium phosphonate has the zwitterionic structure (NH2(+)CH2P(O2Cd2)O-) similar to the initial aminophosphonic acid H4L.     

A study of the adsorption activities of silanol surface structures on a fused silica model substrate by combining 29Si CP MAS NMR and inverse gas chromatographic data

The possibilities of inverse gas-solid chromatography (IGC) in obtaining chromatographic data on fumed silica were examined. Aerosil A-200, a fused silica model substrate in ²⁹Si nuclear magnetic resonance analysis, was trimethylsilylated to different degrees. IGC was used to very reproducibly determine the free specific energies of adsorption of several functionalized probe solutes. Hydrogen bonding solutes have a free specific energy of adsorption that is at least about 50% higher than that of non-hydrogen bonding probe solutes. NMR was used in combination with elemental analysis to calculate surface concentrations of the different chemical surface structures. IGC data and surface concentrations were combined in order to determine the contribution of each type of surface structure to the total free specific adsorption energy. It could be concluded that residual silanols from the reaction of dihydroxydi-siloxysiloxane (Q₂ groups) with trimethylchlorosilane possess a higher adsorption activity than the silanols initially present.     

Structural understanding of a molecular material that is accessed only by a solid-state desolvation process: the scope of modern powder X-ray diffraction techniques

Many molecular materials cannot be prepared as a "pure" (nonsolvate) crystalline phase by conventional crystal growth from solution due to the facile formation of solvate structures. In such cases, it may be possible to obtain the pure phase by a solid-state desolvation process, although such processes are generally associated with loss of crystal integrity, yielding a microcrystalline powder of the pure phase. This paper demonstrates the utility of modern powder X-ray diffraction techniques for obtaining structural understanding in such cases, focusing on a particular member of a structural family that is of wider relevance within the context of crystal engineering and design.     

Adducts of zinc and copper(II) dimethyland diethyldithiocarbamates with piperidine: Synthesis, EPR, solid-state natural abundance 13C and 15N CP/MAS NMR and single-crystal X-ray diffraction studies

Crystalline adducts of zinc and copper(II) dimethyl-and diethyldithiocarbamates with piperidine (Pip) of the general formula [M{NH(CH₂)₅}(S₂CNR₂)₂] (M = Zn and ⁶³Cu; R = CH₃ and C₂H₅) were obtained. Their structures and spectroscopic characteristics were studied by X-ray diffraction analysis, EPR spectroscopy, and solid-state natural abundance ¹³C and ¹⁵N MAS NMR spectroscopy. The most substantial differences between the adducts of the formula [Zn{NH(CH₂)₅}(S₂CNR₂)₂] (R = CH₃ and C₂H₅) were found in the spatial orientations of the coordinated heterocycles and the geometries of the zinc polyhedra. The individual character of the EPR spectra of magnetically diluted isotope-substituted copper(II) adducts was determined by computerassisted modeling. The adducts of copper(II) and zinc dimethyldithiocarbamates proved to exist as two isomers. The coordination polyhedra of copper(II) and zinc are intermediate between a tetragonal pyramid (TP) and a trigonal bipyramid (TBP). The contributions from the TBP/TP components to the coordination polyhedra were quantitatively estimated from X-ray diffraction data. The ¹³C and ¹⁵N NMR signals were assigned to the positions of the atoms of the =NC(S)S^? groups in the resolved (according to X-ray diffraction data) molecular structures of the adducts.     

Structures of polynuclear thallium(I) and copper(II)-thallium(I) complexes with dialkyldithiocarbamates: 13C and 15N CP/MAS NMR, EPR, and X-ray diffraction studies

A comparative study of polynuclear thallium complexes with dialkyldithiocarbamates [Tl₂{S₂CNR₂}₂]_n (R = CH₃, i-C₃H₇, C₄H₉, and i-C₄H₉; R₂ = (CH₂)₆) was performed by solid-state ¹³C and ¹⁵N CP/MAS NMR spectroscopy. The dithiocarbamate groups were found to be structurally equivalent in the complexes studied. An increase in the positive inductive effect of alkyl substituents at the N atom increased ¹⁵N chemical shifts as a result of a combination of positive inductive effect of the alkyl substituents and the mesomeric effect of=NC(S)S-groups. The first representative of thallium(I) complexes with a cyclic dithiocarbamate ligand [Tl₂{S₂CN(CH₂)₆}₂]_n was obtained. Its molecular structure was determined from X-ray diffraction data. The β-form of the isotope-substituted complex [^63/65CuTl₂{S₂CN(CH₂)₆}₄] was obtained and examined by EPR spectroscopy. The EPR spectra were modeled at the second order of the perturbation theory. The spin density at the thallium atoms was calculated and its distribution over the AOs of thallium was determined.     

The effect of dehydration on the position of cesium cations in the structure of CsNaFAU(Y) studied by powder X-ray diffraction and magic-angle spinning NMR spectroscopy

The influence of dehydration on the position of sodium and cesium cations obtained by ion exchange in the structure of FAU(Y) was studied by powder X-ray diffraction using synchrotron radiation and ²³Na and ¹³³Cs magic-angle spinning NMR spectroscopy. The sodium and cesium cations were found to be mobile in the hydrated samples. In dehydrated zeolites CsNaFAU(Y), cesium is predominantly localized in four crystallographic ion-exchange positions located in the large cavities and sodalite cages.     

Phase evolution in lithium disilicate glass-ceramics based on non-stoichiometric compositions of a multi-component system: structural studies by 29Si single and double resonance solid state NMR

The crystallization mechanism of a high-strength lithium disilicate glass-ceramic in the SiO(2)-Li(2)O-P(2)O(5)-Al(2)O(3)-K(2)O-(ZrO(2)) system, used as restorative dentistry material, has been examined on the basis of quantitative (29)Si magic angle spinning (MAS) and (29)Si{(7)Li} rotational echo double resonance (REDOR) NMR spectroscopy. Crystallization occurs in two stages: near 650 °C a significant fraction of the Q(3) units disproportionates into crystalline Li(2)SiO(3) and Q(4) units. Upon further annealing of this glass-ceramic to 850 °C the crystalline Li(2)SiO(3) phase reacts with the Q(4) units of the softened residual glass matrix, resulting in the crystallization of Li(2)Si(2)O(5). The NMR experiments provide detailed insight into the spatial distribution of the lithium ions suggesting the absence of lithium ion clustering in the residual glassy component of the final glass-ceramic. (31)P MAS-NMR spectra indicate that phosphate acts as a lithium ion scavenger, resulting in the predominant formation of orthophosphate (P(0)) and some pyrophosphate (P(1)) groups. Crystallization of Li(2)SiO(3) occurs concomitantly with the formation of a highly disordered Li(3)PO(4) phase as evidenced from strong linebroadening effects in the (31)P MAS-NMR spectra. Well-crystallized Li(3)PO(4) is only formed at annealing conditions resulting in the formation of crystalline lithium disilicate. These results argue against an epitaxial nucleation process previously proposed in the literature and rather suggest that the nucleation of both lithium metasilicate and lithium disilicate starts at the phase boundary between the disordered lithium phosphate phase and the glass matrix.     

Metals in organic syntheses: XIV. NMR,IR, and reactivity studies on the olefin hydroformylation catalyzed by Pt-Sn complexes

Among the several hydrides formed when trans-[PtHClL₂] (L = PPh₃) reacts with Sncl₂, only trans-[PtH(SnCl₃)L₂] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl₃)L₂]. At −10°C, cis-[PtEt(SnCl₃)L₂] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable.At −50°C, a mixture of trans-[PtHClL₂] and trans[PtH(SnCl₃)L₂] reacts with ethylene to give cis-[PtEtClL₂] and cis-[PtEt(SnCl3)L₂] and this has been attributed to the catalytic activity of SnCl₂ which dissociates from cis-[PtEt(SnCl₃)L₂] at this temperature.Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl₃)L₂], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L₂]⁺ SnCl₃⁻. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L₂], trans-[Pt(SnCl₃)(COEt)L₂], trans-[PtCl(COEt)l₂ · SnCl₂], and trans-[Pt(COEt)(CO)L₂]⁺ SnCl₃⁻. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL₂] with SnCl₂.Trans-[PtH(SnCl₃)L₂] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl₃)(CO)₂L₂], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl₃)L₂] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl₃)L₂] is allowed to react with CO.The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.     

Solid state NMR method for the determination of 3D zeolite framework/sorbate structures: 1H/29Si CP MAS NMR study of the high-loaded form of p-xylene in ZSM-5 and determination of the unknown structure of the low-loaded form

A general protocol is described for structure determinations of organic sorbate-zeolite complexes based on the selective, through-space, distance-dependent transfer of magnetization from protons in selectively deuterated organics to framework silicon nuclei. The method was developed using the known structure of the high-loaded ZSM-5/p-xylene complex containing p-xylene-d(6) or p-xylene-d(4). It was then applied to determine the unknown structure of the low-loaded ZSM-5/p-xylene complex using NMR alone. For the high-loaded complex improved data were obtained below 273 K, where slow motions and exchange processes of the p-xylene are eliminated. The general approach was validated by the exact agreement of the experimental (1)H-(29)Si CPMAS spectra obtained at a specific contact time and the complete 24-line spectra simulated using 1/T(CP) vs M(2) correlations from only the six clearly resolved resonances. For the low-loaded complex the (29)Si resonances were assigned at 267 K, and variable contact time CP experiments were carried out between 243 and 173 K using the same specifically deuterated p-xylenes. All possible locations and orientations of the p-xylene guests were sampled, and those solutions that gave acceptable linear 1/T(CP) vs M(2) correlations were selected. The optimum p-xylene location in this temperature range was determined to be in the channel intersection with the long molecular axis parallel to [0,1,0] (ring center fractional coordinates {-0.009, 0.250, 0.541}) with the ring plane oriented at an angle of 30 +/- 3 degrees about the crystallographic b axis. A subsequent single-crystal X-ray study confirmed this predicted structure.     

Synthesis of four different antimony(III) O,O'-dialkyldithiophosphates: characterization by 31P CP/MAS NMR, single-crystal X-ray diffraction, and adsorption at a stibnite surface (Sb2S3)

Four different dialkyldithiophosphate (DTP) ions, (RO)(2)PSS(-) (R=C(3)H(7), iso-C(3)H(7), iso-C(4)H(9), and cyclo-C(6)H(11)), have been adsorbed on the surface of synthetically prepared stibnite, Sb(2)S(3), and studied by means of (31)P CP/MAS NMR. Corresponding individual [Sb{S(2)P(OR)(2)}(3)] complexes have also been synthesized and used for comparison with the surface-adsorbed DTP species. The results show that a low concentration of collector at the surface leads to a chemisorbed monolayer of DTP on the mineral surface. At high concentration of DTP, a surface precipitate of Sb(DTP)(3) is formed. (31)P CP/MAS NMR and chemical shift anisotropy data indicate that the SPS bite angle of the chemisorbed DTP groups on the surface is larger than in the corresponding precipitated complexes and the coordination of the ligands differs. Using single-crystal X-ray diffraction technique, the molecular structure of a solvated form of crystalline O,O'-di-cyclo-hexyldithiophosphate antimony(III) complex has been resolved. In this novel molecular structure, the central antimony atom S,S'-anisobidentately coordinates three structurally non-equivalent DTP groups, and therefore, the geometry of the [SbS(6)] chromophore can be approximated by a distorted octahedron. Besides that, useful correlations between (31)P CSA parameters and structural data on this complex were also established.     

1-Methylphenanthro[3,4-b]thiophene: Determination of the tertiary structure in solution and in the crystalline state by NMR spectroscopy and X-ray diffraction

1-Methylphenanthro[3,4-b]thiophene was prepared by the photocyclization of 1-(4′-methyl-2′-thienyl)-2-(2″-naphthyl)ethene. The ¹H and ¹³C-nmr spectra were assigned using two-dimensional ¹H/¹³C heteronuclear chemical shift correlation and relayed coherence transfer (RELAY) experiments. From nuclear Overhauser difference spectra, the H11-C1 methyl-H intramolecular distance was determined to be 2.10 Å. The molecule crystallized from chloroform in the monoclinic system, space group P2₁/c. A total of 3536 unique reflections were measured and the structure was solved by direct methods and refined to a final R = 0.049. The molecule is helical with both chiral forms observed in the crystal. The H11-C1 methyl-H distance in the crystal was 2.12(3)Å in excellent agreement with the distance measured in solution by NOE techniques.