A. E. Goeta

X-ray and neutron diffraction studies of the non-linear optical compounds MBANP and MBADNP at 20 K: charge-density and hydrogen-bonding analyses

Neutron-diffraction studies of the compounds 5-nitro-2-[[1-phenylethyl]amino]pyridine (methylbenzylaminonitropyridine, hereafter MBANP) and 3,5-dinitro-2-[[1-phenylethyl]amino]pyridine (methylbenzylaminodinitropyridine, hereafter MBADNP) are presented, and a charge-density study of the latter is reported. The studies were conducted in order to relate the structural attributes of these materials to their physical properties. MBANP exhibits a second-harmonic generation (SHG) output, chi(2), over eight times higher than that of MBADNP, despite their very similar molecular characteristics and the seemingly more SHG-favourable molecular features present in MBADNP. The neutron-diffraction studies show that intramolecular hydrogen bonding is responsible for this apparent discrepancy. The charge-density study on MBADNP confirms this and reveals that the pyridine group is the principal moiety responsible for the SHG effect on the molecular scale. Moreover, the strong intramolecular hydrogen bond present in MBADNP is proven to result from an electrostatic interaction. The dipole moment of MBADNP is also deduced from the charge-density study.

Experimental evidence for the amino-group non-planarity in nitroanilines: neutron diffraction study of 2-methyl-5-nitroaniline at 100 K

An appreciable degree of pyramidalization of the amine N atom is observed in the title compound. The existence of polar chains, induced by N-H.O synthons, is confirmed. C-H.O interactions, not noted in a previous X-ray study, were found to stabilize further the known head-to-tail assembling of the chains. The structure can be described as non-polar (101) layers, embodying chains interlinked by centrosymmetric dimers, connected by C(aryl)-H.pi interactions. The latter are not present in m-nitroaniline, 2-methyl-4-nitroaniline and other related compounds with chains built from similar N-H.O synthons and assembled head-to-head. This finding implies that an obvious relationship between molecular recognition patterns and crystal structures should not be assumed.

4-[Bis(4-hydroxy-3,5-dimethylphenyl)methyl]pyridinium chloride and bromide.

The isostructural title salts, 4-[bis(4-hydroxy-3,5-dimethylphenyl)methyl]pyridinium chloride and bromide, C22H24NO2+.Cl- and C22H24NO2+.Br-, exhibit extended hydrogen-bonded ribbons in the solid state. The halide ions form hydrogen bonds to the pyridinium NH+ group and to the phenol OH groups of the cation. These bonds are coplanar to within 0.1 A and form a T configuration at the anion.

Hydroxycalciomicrolite, Ca1.5Ta2O6(OH), a new member of the microlite group from Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil

Abstract Hydroxycalciomicrolite, Ca1.5Ta2O6(OH) is a new microlite-group mineral found in the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil. It occurs as isolated octahedral and as a combination of octahedral and rhombic dodecahedral crystals, up to 1.5 mm in size. The crystals are yellowand translucent, with a white streak and vitreous to resinous lustre. The mineral is brittle, with a Mohs hardness of 5-6. Cleavage is not observed and fracture is conchoidal. The calculated density is 6.176 g cm-3. Hydroxycalciomicrolite is isotropic, ncalc. = 2.010. The infrared and Raman spectra exhibit bands due to O-H stretching vibrations. The chemical composition determined from electron microprobe analysis (n = 13) is (wt.%): Na2O 0.36(8), CaO 15.64(13), SnO2 0.26(3), Nb2O5 2.82(30), Ta2O5 78.39(22), MnO 0.12(2), F 0.72(12) and H2O 1.30 (from the crystal structure data), O = F -0.30, total 99.31(32), yielding an empirical formula, (Ca1.48Na0.06Mn0.01)Σ1.55(Ta1.88Nb0.11Sn0.01)Σ2.00O6.00[(OH)0.76F0.20O0.04]. Hydroxycalciomicrolite is cubic, with unit-cell parameters a = 10.4205(1) Å, V = 1131.53(2) Å3 and Z = 8. It represents a pyrochlore supergroup,microlite-groupmineral exhibiting P4332 symmetry, instead of Fd3̅m. The reduction in symmetry is due to long-range ordering of Ca and vacancies on the A sites. This is the first example of such ordering in a natural pyrochlore, although it is known from synthetic compounds. This result is promising because it suggests that other species with P4332 or lower-symmetry space group can be discovered and characterized.

2-(4-Chloro­anilino)- and 2-(4-methoxy­anilino)-1,2-diphenyl­ethanone

The title compounds, C20H16ClNO and C21H19NO2, adopt syn orientations of the C=O and N-H bonds but, like their analogues, form no strong intermolecular hydrogen bonds.

6α-Chloro-3α-hydroxymethyl-2,2-dimethylpenam 1,1-Dioxide

In the title compound (6-chloro-3-hydroxymethyl-2,2-dimethyl-5-oxo-2,3,6,6a-tetrahydro-5H-azeto[2,1-b]thiazole 1,1-dioxide, C 8 H 12 ClNO 4 S), the 2-azetidinone ring is non-planar. The thiazolidine ring has a conformation that can be classified as C3, with 2α-CH 3 pseudo-equatorial, 2β-CH 3 axial and 3α-R axial. The N atom has a pyramidal bonding arrangement. The structure is stabilized by O-H...O hydrogen bonds along the direction of the c axis.

2-Acetylphenyl 1-Naphthoate

The crystal structure of the title compound, C 19 H 14 O 3 , an intermediate in the synthesis of 2-naphthylchromones, has been determined by X-ray diffraction. The title molecule, which can be viewed as the fusion of 1-naphthoic acid and acetophenone, is not planar. The dihedral angle between the benzene and naphthalene planes is 77.39 (7)°. Two intramolecular C-H...O bonds and a short intramolecular O...O distance of 2.719 (2) A have been observed.

3‐Aryloxypropiononitriles Intermediates: Crystal and Molecular Structure of 2‐ and 4‐(2‐Bromoethoxy)diphenylmethanes

The crystal structure of 2- and 4-(2-bromoethoxy)diphenylmethanes (I and II respectively), intermediates in a novel synthesis of substituted 3-aryloxypropiononitriles, have been determined by single crystal X-ray diffraction at room temperature (r.t.) and at 150K. No significant changes in the crystal structure of I and II have been observed in going from r.t. to 150K. In both compounds the bromoethoxy group presents a gauche conformation and shows a short Br...O intramolecular interaction that allows to explain the very good reaction yields obtained in the novel synthesis. The three-dimensional structure of I is stabilized by two intermolecular hydrogen bonds and that of II by six. This difference in the crystal packing of I and II explains the variation in the m.p. The analysis of 1 H and 13 C NMR spectra suggests that the molecular conformations in solution are similar to those found in solid state.