Three-Dimensional Structure Determination of Surface Sites

Abstract

The spatial arrangement of atoms is directly linked to chemical function. A fundamental challenge in surface chemistry and catalysis relates to the determination of three-dimensional structures with atomic-level precision. Here we determine the three-dimensional structure of an organometallic complex on an amorphous silica surface using solid-state NMR measurements, enabled through a dynamic nuclear polarization surface enhanced NMR spectroscopy approach that induces a 200-fold increase in the NMR sensitivity for the surface species. The result, in combination with EXAFS, is a detailed structure for the surface complex determined with a precision of 0.7 Å. We observe a single well-defined conformation that is folded toward the surface in such a way as to include an interaction between the platinum metal center and the surface oxygen atoms.

Materials Characterization by Dynamic Nuclear Polarization-Enhanced Solid-State NMR Spectroscopy

“…29 Si solid-state NMR is useful to confirm molecules are covalently grafted to the support and obtain information about the conformation of molecules on the surface. 26,27 Notably, Emsley and co-workers recently showed that by combining DNP-enhanced 2D HETCOR experiments and REDOR-based dipolar coupling measurements it was possible to determine the three-dimensional structure of molecules grafted onto silica surfaces ( Figure 3A). 27 DNP-enhanced 2D 29 Si- 29 Si correlation experiments were used to observe the bonding/connectivity of silicon atoms at the silica surface ( Figure 3B) 28 and probe the spatial distribution of organic fragments on functionalized silica surfaces.…”

Structural Insights into Peptides Bound to the Surface of Silica Nanopores

“…This includes the monitoring of organic reactions on silica surfaces and the fast characterization of the surface functionalization of silica materials . Finally, these techniques have been employed to investigate the binding sites of transition‐metal complexes on surface‐modified silica materials, as well as for the three‐dimensional structure determination of an organometallic complex on an amorphous silica surface …”

“…[15] Finally,t hese techniques have been employed to investigate the binding sites of transition-metal complexes on surface-modified silica materials, [16] as well as for the three-dimensional structured etermination of an organometallic complex on an amorphoussilica surface. [17] In the present work, the detailed solid-state NMR characterization of our previously published peptide-silica hybrid model system [6] is presented. The model system is composed of highly ordered (3-aminopropyl)triethoxysilane (APTES)-functionalized silica materiala st he organic-inorganic support (SBA-15), which is functionalized with the dipeptide Gly-Phe.…”

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

“…Fore xample, DNP SENS together with computational chemistry provides detailed structural information about the arrangement of atoms at the surface of materials, [590] specific structures and coordination environments, [591][592][593] and even the 3D conformation of surface species. [594,595] Similarly,EXAFS (extended X-ray adsorption spectroscopy) seems to be particularly wellsuited to provide unique information about single-site catalysts under ab road range of operating conditions (temperature and pressure), since such catalysts mainly contain one type of surface sites, [43] and can be complemented by other spectroscopic methods such as IR, Raman, and UV/ Visspectroscopy. [596] Although still rarely used to study singlesite catalysts,o perando XAS combined with complementary spectroscopic methods and computational approaches will help to understand well-defined systems and, by comparison, provide insights into the corresponding industrial catalysts.In particular,s ingle-site catalysts prepared by SOMC provide ideal benchmarks for both advanced spectroscopic and computational methods, [597] akey step in determining possible surface structures and refining of models.T ogether with surface science techniques,which bridge the pressure gap,one can foresee that SOMC will provide amolecular-level understanding of the surface sites of industrial catalysts that will allow ultimately the bridging of model systems and industrial catalysts.…”