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A Hybrid Solid State NMR and Electron Microscopy Structure Determination Protocol for Engineering Advanced Para-crystalline Optical Materials.

Research paper by Brijith B Thomas, Jeroen J Rombouts, Gert T GT Oostergetel, Karthick Babu Sai Sankar KB Gupta, Francesco F Buda, Koop K Lammertsma, Romano R Orru, Huub J M HJ de Groot

Indexed on: 25 Jan '17Published on: 25 Jan '17Published in: Chemistry - A European Journal



Abstract

We demonstrate hybrid MAS NMR and TEM for de novo structure determination of para-crystalline materials with a bioinspired fused naphthalene diimide (NDI) - salphen - phenazine prototype light harvesting compound.  Starting from chiral building blocks with C2 molecular symmetry we determine the asymmetric unit by MAS NMR, index low resolution TEM diffraction data, resolve reflection conditions, and show for the first time ability to determine the space group from reciprocal space data using our hybrid approach. Transfer of molecular C2 symmetry into P2/c packing symmetry provides a connection across length scales to overcome both lack of long range order and missing diffraction phase information. Refinement with heteronuclear distance constraints confirms the racemic P2/c packing that is scaffolded by molecular recognition of salphen zinc in a pseudo-octahedral environment with bromide, and with alkyl chains folding along the phenazine. The NDI light harvesting stacks run orthogonal to the intermolecular electric dipole moment present in the solid. Finally, we determine the orientation of flexible lamellae on an electrode surface.