Monday, May 04, 2009

Marcel's Update

Can. J. Chem. 87(1): 348–360 (2009)

Probing solid iminobis(diorganophosphine chalcogenide) systems with multinuclear magnetic resonance

Bryan A. Demko and Roderick E. Wasylishen

Abstract: A 31P and 77Se solid-state NMR investigation of the iminobis(diorganophosphine chalcogenide) HN(R2PE)2 (R = Ph,iPr; E = O, S, Se) systems is presented. The NMR results are discussed in terms of the known HN(R2PE)2 structures available from X-ray crystallography. The phosphorus chemical shift tensors are found to be sensitive to the nature of the alkyl and chalcogen substituents. The nature of the R group also influences the selenium chemical shift tensors of HN(R2PSe)2 (R = Ph, iPr), which are shown to be sensitive to hydrogen bonding in the dimer structure of HN(Ph2PSe)2 and to the presence of disorder in the case of HN(iPr2PSe)2. Scalar relativistic ZORA DFT nuclear magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. A theoretical investigation into the effect of the E-P···P-E “torsion” angle on the phosphorus and selenium chemical shift tensors of a truncated HN(Me2PSe)2 system indicates that the electronic effect of the alkyl group on the respective nuclear magnetic shielding tensors are more important than the steric effect of the E-P···P-E torsion angle.
Key words: iminobis(diorganophosphine chalcogenide), solid-state NMR, 31P NMR, 77Se NMR, ZORA DFT.

Can. J. Chem. 87(4): 563–570 (2009)

Measurement and calculation of 13C and 15N NMR chemical-shift tensors of a push–pull ethylene

Saeed K. Amini, Mohsen Tafazzoli, Hilary A. Jenkins, Gillian R. Goward, and Alex D. Bain

Abstract: Methyl 3-dimethylamino-2-cyanocrotonate (MDACC) has a remarkably weak carbon–carbon double bond. It has strong electron-withdrawing groups on one end and electron-donating groups on the other: a so-called push–pull ethylene. To investigate this unusual electronic structure, we have determined the crystal structure and measured both the 13C and 15N NMR chemical-shift tensors. These measurements are supplemented by shielding-tensor calculations done with density functional methods. The large difference (approximately 100 ppm) between isotropic chemical shifts of the two alkenyl carbons reflects a large charge release from the electron-donating side of C=C double bond to the electron-withdrawing groups. Comparison of the calculated orientations of the principal components of the alkenyl carbons obtained from ab initio calculations shows that the primary changes in charge density occur in the molecular plane. On the other hand, smaller charge density changes above and below the plane of the C=C double bond establish the conjugation of donor and acceptor groups with π* and π molecular orbitals of the central double bond, respectively, which lowers the barrier to rotation about this bond.
Key words: density functional methods, NMR, shielding anisotropy, CSA, push–pull ethylenes, crystal structure.

J. Mater. Chem., 2009, 19, 1151 – 1159

Sol-gel synthesis of sodium-modified AlPO4–SiO2 glasses and structural characterization by solid state NMR

Rashmi R. Deshpande, Long Zhang and Hellmut Eckert

Abstract: Sodium aluminophosphosilicate gels and glasses along the composition line (Na2O)x–[(AlPO4)0.5(SiO2)0.5]1-x were synthesized via the sol-gel process using sodium acetate, aluminium lactate, phosphoric acid and tetraethyl orthosilicate (TEOS) as precursors. The structural evolution from solution to gel and to the final glass was monitored by 27Al, 31P, 29Si and 23Na magic-angle spinning (MAS) NMR. In the solution state aluminium forms a mixture of octahedral coordinated complexes coordinated to lactate, water and phosphate units with varying degrees of polymerization. With increasing temperature up to about 150 °C the lactate ligands are successively replaced by phosphate, resulting in an increased extent of Al–O–P linking. Annealing the xerogel at 400 °C results in a glassy network containing mostly four-coordinated Al species (Al(IV)), in addition to small concentrations of Al(V) and Al(VI). While the distribution of Al coordination numbers remains constant, the compositional trend of the 27Al chemical shift indicates a gradual replacement of Al–O–P linkages by Al–O–Si linkages with increasing sodium content. This conclusion is confirmed by 27Al{31P} Rotational Echo Double Resonance (REDOR) experiments, which reveal a reduction in the number of Al–O–P linkages. Concomitantly, the interaction of Na with the phosphate species is successively increased as indicated by 31P chemical shift trends and 31P{23Na} REDOR results. The results illustrate that the network segregation found in pure AlPO4–SiO2 sol-gel glasses can be overcome, at least partially, by introduction of the network modifier Na2O.

J. Mater. Chem., 2009, 19, 2683 – 2694

Solid state NMR investigation of photoresist molecular glasses including blend behavior with a photoacid generator

David L. VanderHart, Vivek M. Prabhu, Anuja De Silva, Nelson M. Felix and Christopher K. Ober

Abstract: We have examined four molecular glass (MG) materials that show promise as photoresists for extreme-ultraviolet (EUV) lithography. These glass-forming materials were investigated by proton and 13C solid state nuclear magnetic resonance (NMR) techniques in the bulk state as pure materials and as mixtures with (5 or 10) % by mass of the photoacid generator (PAG), triphenylsulfonium perfluorobutanesulfonate. The 13C techniques gave information about crystallinity, purity, and the qualitative existence of multiple phases. Proton studies focused on using spin diffusion to characterize the intimacy of mixing of the PAG and MG blends. The four MGs were largely aromatic materials containing several hydroxyl groups that were partially protected by t-butoxycarbonyl (t-BOC) groups. In two cases, this fraction was varied and the impact on mixing noted. Phase separation of the PAG into PAG-rich larger domains was never seen; the PAG was always finely distributed and the maximum size for any PAG clustering was estimated; however, in some cases, the average local concentration of PAG appeared to vary. Crystallinity was only seen associated with the underivatized materials implying that the mixing of the PAG with any derivatized MG was not restricted by crystallization. It was also noted that some very strong hydrogen bonds exist in three of the four underivatized materials and were eliminated or weakened upon partial derivatization with t-BOC.

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