Structure Determination for the Crystalline Phase of Triphenyl Phosphite by Means of Multi-Dimensional Solid-State NMR and X-Ray Diffraction

Abstract

Triphenyl Phosphite, Structure Determination, Solid-State NMR The crystalline phase of triphenyl phosphite P(OCöH5)3 was investigated by means of 11P solid-state NMR and X-ray diffraction in a temperature range between 170 K and its melting point (Tm = 293 K). ID MAS NMR spectra exhibit one sharp central resonance indicating only one crystallographically unique molecule in the unit cell. A theoretical analysis concerning the shape of 2D exchange spectra for 1 = 1 /2 nuclei is presented. It is shown that if the exchange is caused by radio-frequency driven spin-diffusion, this technique allows to discriminate rota tional symmetry elements in crystalline solids. Used on crystalline triphenyl phosphite, 3-fold symmetry could be revealed clearly. Structure determination based on X-ray single crystal diffraction data collected at 191 K shows that triphenyl phosphite crystallises in hexagonal metric with space group R3 (w R i = 8.3%, Z = 18) and one molecule in the asymmetric unit.This result is in excellent agreement with the NMR spectroscopic data. The lattice parameters at 200 K were determined to a = 37.887(1) and c = 5.7567(2) Ä (V = 7156(1) A3) by refining an X-ray powder-diffraction pattern. The structure of triphenylphosphite can be described as a close rod packing. The rods are formed by ecliptically arranged triphenylphosphite molecules. Due to the 3-fold rotoinversion axis the orientation of molecules in neighboured rods is anti parallel.

A Concerted Approach for the Determination of Molecular Conformation in Ordered and Disordered Materials

“…Bigger differences up to 168 for dihedral angles occur where packing effects account for a distortion of the phenyl rings. [40] As expected gas-phase www.chemeurj.org optimizations of polymorph c1 do not reproduce this feature and always result in C s symmetry (compare the phenyl rings C1 and C3 of structures c1 and I in Figure 2). For c2 the comparison between experiment and calculation in general shows deviations of 0.01-0.05 for bond lengths, 18 for angles and 18 for dihedral angles.…”

“…Even though built up by a small molecule (see Figure 1) the accessible solidstate phases include two different crystalline (c1 [40] and c2 [41] ) and two amorphous states (aI and aII). [39] Of the crystalline phases c1 is the commonly found modification whereas c2 can only be crystallized from an ionic liquid.…”

“…Changes about dihedral angles of AE 68 are well in agreement with the atomic displacement parameters found for the crystal structure of c1. [40] Thus even for the crystalline phase one can expect that the 2D spectrum results from an ensemble of molecules with small structural deviations from a mean arrangement which is represented by structure c1 DFT . It should be noted that whereas librational dynamics leads to a partial averaging of the CSA tensor (which is expected to be small at 190 K) the here observed differences in the spectral shape clearly account for a structural distribution representing static disorder in the crystalline phase.…”

“…The ellipsoids represent the traceless symmetric part of the second rank tensor which is characterized via the asymmetry parameter h and the coupling constant d. The orientation of the 13 C tensor with respect to the corresponding phenyl moiety is nearly identical in all Figure 2. Top: Conformers of the crystalline phases c1 [40] and c2; [41] Bottom: DFT calculated minimum structures; 13 C ab initio anisotropies are depicted as tensor ellipsoids for the labeled positions (see also Figure 1). À1 and refer to the energy of structure I.…”

“…The emersion of these three signals in the experiment accounts for the broken C s symmetry due to packing effects in the crystal. [40,44] Furthermore Table 4 shows the ab initio calculated values of conformer c1…”