Magnetism and phase relations of the PrAl2CaAl2, GdAl2CaAl2 systems

The magnetic properties and phase relations of the ternary systems Pr_1?xCa_xAl₂ and Gd_1?xCa_xAl₂ are reported. The first system exhibits complete miscibility whereas the second shows a miscibility gap extending from x = 0.5 to 0.8. The ternaries were examined magnetically to ascertain whether antiferromagnetism could be produced by replacing the trivalent rare earth ion with divalent Ca. Results for the (Pr, Ca)Al₂ system give some indication that the exchange changes sign when 80% or more of the Pr is replaced by Ca. The α-phase (Gd-rich) alloys in the (Gd,Ca)Al₂ system are ferromagnetic with Curie temperatures only modestly reduced from that of GdAl₂. The β-phase (Ca-rich) alloys in this system are paramagnetic to 4.2°K. The evidence suggests that PrAl₂ and CaAl₂ are electronically similar in regard to band structure and both differ in band structure from GdAl₂.     

Straightforward synthesis of enantiopure 2-aminomethyl and 2-hydroxymethyl pyrrolidines with complete stereocontrol

A practical synthesis of 2-aminomethyl- and 2-hydroxymethyl-3,4-dihydroxypyrrolidines via stereocontrolled addition of TMSCN and LiCH₂OMOM to chiral 3,4 dihydro-2H-pyrroline N-oxides is reported.     

Vibrational spectroscopic studies on 1,3-dithiacyclohexane and some 2-substituted 1,3-dithia-2-boracyclobexanes

Infrared and Raman spectra are reported for 1,3-dithiacyclohexane and 2-X-1,3-dithia-2-boracyclohexanes, where X = Cl, Br or Ph. Assignments are made in each case assuming a molecular symmetry of C_s. The assignments of ring modes for the dithiaboracyclohexanes are almost all very close to those for the corresponding dithiaboracyclopentanes.     

Supertetrahedral polyanionic network in the first lithium phosphidoindate Li3InP2 – structural similarity to Li2SiP2 and Li2GeP2 and dissimilarity to Li3AlP2 and Li3GaP2

Phosphide-based materials have been investigated as promising candidates for solid electrolytes, among which the recently reported Li₉AlP₄ displays an ionic conductivity of 3 mS cm⁻¹. While the phases Li–Al–P and Li–Ga–P have already been investigated, no ternary indium-based phosphide has been reported up to now. Here, we describe the synthesis and characterization of the first lithium phosphidoindate Li₃InP₂, which is easily accessible via ball milling of the elements and subsequent annealing. Li₃InP₂ crystallizes in the tetragonal space group I4₁/acd with lattice parameters of a = 12.0007(2) and c = 23.917(5) Å, featuring a supertetrahedral polyanionic framework of interconnected InP₄ tetrahedra. All lithium atoms occupy tetrahedral voids with no partial occupation. Remarkably, Li₃InP₂ is not isotypic to the previously reported homologues Li₃AlP₂ and Li₃GaP₂, which both crystallize in the space group Cmce and feature 2D layers of connected tetrahedra but no supertetrahedral framework. DFT computations support the observed stability of Li₃InP₂. A detailed geometrical analysis leads to a more general insight into the structural factors governing lithium ion mobility in phosphide-based materials: in the non-ionic conducting Li₃InP₂ the Li ions exclusively occupy tetrahedral voids in the distorted close packing of P atoms, whereas partially filled octahedral voids are present in the moderate ionic conductors Li₂SiP₂ and Li₂GeP₂.

Li₃InP₂ exhibits a polyanionic framework of corner-sharing InP₄ tetrahedra and DFT computations reveal the stability trend for indium in the tetragonal structure compared to the orthorhombic structure of the lighter homologues.     

Lifetime measurements of the 2p 3d 3 D 1, 2, 3 0 and 2p 3d 1 P 1 0 levels in NII by beam-foil-laser spectroscopy

Accurate lifetimes measured by means of the cascade-free method based on laser excitation of a fast ion beam preexcited in a carbon foil are reported for four 2p 3d levels in NII. The lifetime results are: τ(2p 3d ³ D ₁ ⁰ )=0.209±0.007 ns, τ(2p 3d ³ D ₂ ⁰ )=0.219±0.007 ns, τ(2p 3d ³ D ₃ ⁰ )=0.217±0.005 ns, and τ(2p 3d ¹ P ₁ ⁰ )=0.410±0.017 ns. These results are compared to theoretical and experimental lifetimes reported previously.     

The influence of the purine 2-amino group on DNA conformation and stability-II: Synthesis and physical characterization of d[CGT(2-NH2)ACG], d[CGU(2-NH2)ACG], and d[CGT(2-NH2)AT(2-NH2)ACG]

Synthesis of an N-protected derivative of 2-amino-2'-deoxyadenosine (dA') from 2'-deoxyguanosine is reported. The syntheses of several oligodeoxynucleotides containing this modified nucleoside are described, together with physical characterization via melting studies and CD conformational analysis. As expected, the 2-amino group is seen to add to the duplex stability. Although the sequence d(TA')₃ was found to undergo a salt-induced conformational transition, mixed sequences such as d(CGTA'CG) did not display this behavior. All guanine residues present in these sequences were O⁶ protected, either with the cyanoethyl group or the 4-nitrophenylethyl group, to eliminate guanine degradation during phosphorylation and condensation reactions. Procedures for the introduction and removal of these O⁶ protecting groups are described.     

Structural chemistry of Ba2CdS3, Ba2CdSe3, BaCdS2, BaCu2S2 and BaCu2Se2

The structures of all compounds were determined from three dimensional single crystal X-ray diffraction data and refined by least squares. Ba₂CdS₃ and Ba₂CdSe₃ are isostructural, Pnma, a = 8.9145(6)Å, b = 4.3356(2)Å, c = 17.2439(9)Å for the former compound and a = 9.2247Å, b = 4,4823(6)Å, c = 17.8706(11)Å for the latter, z = 4, R = 0.0751 and R = 0.0462, respectively. The compounds are isostructural with the previously reported Mn analogues and with K₂AgI₃. Cd ions are in tetrahedral environment and the tetrahedra form infinite linear chains by corner sharing. Ba ions are in 7-fold coordination in which 6 anions form a trigonal prism and 1 anion caps one of the rectangular faces. BaCdS₂, Pnma, a = 7.2781(3)Å, b = 4.1670(1)Å, c = 13.9189(6)Å, z = 4, R = 0.0685. Cd ions can be considered to have a triangular planar coordination with CdS distances of 2.47 and 2.53 Å (twice). Two additional S ions are at 2.89 and 3.22 Å to complete a triangular bipyramidal configuration. Ba is in 7-fold coordination with the anions forming a trigonal prism which is capped on one rectangular face. The compound is isostructural with BaCdO₂ and is related to the structure of BaMnS₂. BaCdSe₂ could not be prepared. BaCu₂S₂ and BaCu₂Se₂ are isostructural, Pnma, a = 9.3081(4)Å, b = 4.0612(3)Å, c = 10.4084(5)Å for the sulfide and a = 9.5944(6)Å, b = 4.2142(4)Å, c = 10.7748(8)Å for the selenide, z = 4, R = 0.0634 and 0.0373, respectively. Ba ions are in the usual 7-fold, capped hexagonal prism, coordination. However, 9 Cu ions also can be considered to form a trigonal prism with all rectangular faces capped, around Ba since the BaCu distances range from 3.24 to 3.54 Å for the sulfide and from 3.37 to 3.67 Å for the selenide. One of the Cu ions is in a very distorted tetrahedral environment and the second one is located in a more regular tetrahedral configuration of the anions. Two independent infinite chains of tetrahedra are present. They are formed by sharing of two adjacent edges of each tetrahedron and then these chains in turn are linked by corner sharing into a three-dimensional network of tetrahedra.     

Infrared spectra of Ag2BrNO3 and Ag2ClNO3

The infrared spectra of Ag₂BrNO₃ and Ag₂ClNO₃ are reported. Vibration assignments are proposed on the basis of the group theoretical analysis and D_2h symmetry. Factor group, site and TO-LO splittings are observed. The internal and external mode frequencies are correlated with those of AgNO₃ and KNO₃(II).     

Photodissociation of H2O2 at 248 nm: translational anisotropy and oh product state distributions

Ground-state OH(X²Π) fragments, from the photodissociation of H₂O₂ at 248 nm, have been probed by laser-induced fluorescence. Nascent product rotational distributions and polarisation-dependent Doppler lineshapes are reported. The high translational anisotropy (β = −1 at low N″) indicates a prompt repulsion along the O-O axis. Polarisation-dependent Doppler lineshapes are interpreted as a correlation between the fragment recoil velocity v and angular momentum J_OH, the product rotation being aligned along v. Product rotation is generated by an axial torsion about the O-O axis, consistent with a change in dihedral angle in the upper state.     

Vibrational spectroscopy of gaseous 1-methylcyclopentadiene and 2-methylcyclopentadiene

The infrared and fifth vibrational overtone (6v_CH) spectra of gaseous 1-methylcyclopentadiene and 2-methylcyclopentadiene are reported.     

Reactivity of 2-halo-2H-azirines. Part 3: Dehalogenation of 2-halo-2H-azirine-2-carboxylates

The dehalogenation of 2-halo-3-phenyl-2H-azirine-2-carboxylates is described. Using sodium borohydride and tributyltin hydride 3-phenyl-2H-azirine-2-carboxylates were obtained in moderate yields. The synthesis of a new 2-bromo-2H-azirines with a chiral auxiliary, 10-phenylsulfonylisobornyl 2-bromo-3-phenyl-2H-azirine-2-carboxylate, is reported. Its dehalogenation led to 10-phenylsulfonylisobornyl 2H-azirine-2-carboxylate as single stereoisomer together with the formation of 10-phenylsulfonylisobornyl acetate.     

Compressibility and structural behavior of pure and Fe-doped SnO2 nanocrystals

We have performed high-pressure synchrotron X-ray diffraction experiments on nanoparticles of pure tin dioxide (particle size ∼30 nm) and 10 mol % Fe-doped tin dioxide (particle size ∼18 nm). The structural behavior of undoped tin dioxide nanoparticles has been studied up to 32 GPa, while the Fe-doped tin dioxide nanoparticles have been studied only up to 19 GPa. We have found that both samples present at ∼13 GPa a second-order structural phase transition from the ambient pressure tetragonal rutile-type structure (P4₂/mnm) to an orthorhombic CaCl₂-type structure (space group Pnnm). No phase coexistence was observed for this transition. Additionally, pure SnO₂ presents a phase transition to a cubic structure at ∼24 GPa. The evolution of the lattice parameters with pressure and the room-temperature equations of state are reported for the different phases. The reported results suggest that the partial substitution of Sn by Fe induces an enhancement of the bulk modulus of SnO₂. Results are compared with previous studies on bulk and nanocrystalline SnO₂. The effects of pressure on Sn-O bonds are also analyzed.     

Synthesis and structural characterization of cis-Pt(SH)2(PPh3)2 and related alkyl and aryl thiolato complexes

The synthesis and spectroscopic characterization of the complexes cis-Pt(SR)₂(PPh₃)₂ (R = H. Me, n-Bu and Ph) are reported, together with the single crystal X-ray crystallographic characterization of cis-Pt(SH)₂(PPh₃)₂. The ability of these complexes to act as bidentate ligands towards other metal centres is also briefly described.     

Synthesis,Antiprotozoal Activity,and Cheminformatic Analysis of 2-Phenyl-2H-Indazole Derivatives

Indazole is an important scaffold in medicinal chemistry. At present, the progress on synthetic methodologies has allowed the preparation of several new indazole derivatives with interesting pharmacological properties. Particularly, the antiprotozoal activity of indazole derivatives have been recently reported. Herein, a series of 22 indazole derivatives was synthesized and studied as antiprotozoals. The 2-phenyl-2H-indazole scaffold was accessed by a one-pot procedure, which includes a combination of ultrasound synthesis under neat conditions as well as Cadogan’s cyclization. Moreover, some compounds were derivatized to have an appropriate set to provide structure-activity relationships (SAR) information. Whereas the antiprotozoal activity of six of these compounds against E. histolytica, G. intestinalis, and T. vaginalis had been previously reported, the activity of the additional 16 compounds was evaluated against these same protozoa. The biological assays revealed structural features that favor the antiprotozoal activity against the three protozoans tested, e.g., electron withdrawing groups at the 2-phenyl ring. It is important to mention that the indazole derivatives possess strong antiprotozoal activity and are also characterized by a continuous SAR.     

The conductance of divalent Ions in H2O at 10 and 25°C and in D2O

Precise conductance measurements are reported for potassiumm-benzenedisulfonate and ferricyanide, for calcium, strontium, barium, and manganese chloride, and for manganese and potassium sulfate in D₂O at 25°C. Measurements were also carried out in water at 10 and 25°C for all the salts with the exception of K₃Fe(CN)₆ at 10°C. Two runs are reported for sodium sulfate in water at 25°C. Limiting conductances of these ions are discussed in terms of solvent structural effects. The association constant for MnSO₄ is found to be the same in H₂O and D₂O.     

Hydrogen bond studies: Part 118. A deuteron magnetic resonance study of BeSO4· 4D2O and Li2SO4· D2O

The electric field gradient (EFG) tensors at the deuterons in the water molecules in BeSO₄ · 4D₂O at 25°C are reported. The quadrupole coupling constants (e²Q/h) and asymmetry parameters (η) for the two independent deuterons are 181.1(4) and 194.8(3) kHz, and 0.226(4) and 0.123(3), respectively. The EFG tensor corresponding to the smallest e²qQ/h is considerably distorted by the beryllium ion, which causes a high η value as well as a deviation of the y-principal axis by 21.8(6)° from the normal to the water molecule plane. A redetermination of the EFG tensors at the deuterons in the water molecule in Li₂SO₄ · D₂O at 25°C and ?110°C is also reported. The e²Q/h and η values for the two deuterons are 236.6(1.2) and 239.8(1.1) kHz, and 0.091(8) and 0.126(7), respectively, at ?110°C. The corresponding e²qQ/h and η values for the averaged EFG tensor at 25°C are 125.8(1.1) kHz and 0.813(13), respectively. The results are in good agreement with those from the pioneer work by Ketudat and Pound, 20 years ago on the same compound.     

Vibrational spectroscopic studies on some 2-substituted 1,3-dithi a-2-boracyclopentanes

Infrared and Raman spectra are reported for 2-X-1,3-dithia-2-boracyclopentanes, where X = Br, Cl, Ph or NMe₂. In all cases the vibrations of the heterocyclic ring unit can be assigned in terms of C₂ symmetry, corresponding to a “twisted-ring” conformation similar to that found for the related molecule 1,3-dithiolan-2-thione. The internal modes of the B-Ph unit are in agreement with C_2v “local” symmetry, while those for B-NMe₂ suggest a considerably lower symmetry.     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Stereoselective synthesis of (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one

A stereoselective synthesis of (6S)-5,6-dihydro-6-[(2R)-2-hydroxy-6-phenylhexyl]-2H-pyran-2-one is reported. The strategy utilizes an olefin cross-metathesis, syn-benzylidene acetal formation and a preferential (Z)-Wittig olefination reaction and lactonization as the key steps.     

Preparation of cis-Mo(CO)2(Ph2P(CH2)nPPh2)2 (n = 1, 2, 3) from cis-dicarbonylbis(norbornadiene)molybdenum and crystal structure of [cis-Mo(CO)2(Ph2P(CH2)3PPh2)2]

The complexes cis-Mo(CO)₂(Ph₂P(CH₂)_nPPh₂)₂ (n = 1, 2, 3) are synthesized by heating benzene solutions of cis-dicarbonylbis(norbornadiene)molybdenum and the corresponding diphosphines. The X-ray structural analysis of cis-Mo(CO)₂(Ph₂P(CH₂)₃PPh₂)₂ is reported, with the following crystal data: C₅₆H₅₂MoO₂P₄·2CH₂Cl₂·0.5C₆H₁₄, mol wt. 1189.81, monoclinic, space group P2₁/n, a 15.643(2), b 21.453(7), c 17.105(3) Å, β 100.75(1)°, V 5639.59 ų, Z = 4, D_c 1.39, D_m 1.36 g/cm³.