Solid‐State NMR Spectroscopy Proves the Presence of Penta‐coordinated Sc Sites in MIL‐100(Sc)

Abstract

Advanced solid-state NMR methods and first-principles calculations demonstrate for the first time the formation of penta-coordinated scandium sites. These coordinatively unsaturated sites were shown during the thermal activation of scandium-based metal-organic frameworks (MOFs). A Sc NMR experiment allows their specific observation in activated Sc BTB (H BTB=1,3,5-tris(4-carboxyphenyl)benzene) and MIL-100(Sc) MOFs. The assignment of the ScO groups is supported by the DFT calculations of NMR parameters. The presence of ScO Lewis acid sites in MIL-100(Sc) explains furthermore its catalytic activity. The first NMR experiment to probe C- Sc distances is also introduced. This advanced solid-state NMR pulse sequence allows the demonstration of the shrinkage of the MIL-100(Sc) network when the activation temperature is raised.

The β‐Agostic Structure in (C5Me5)2Sc(CH2CH3): Solid‐State NMR Studies of (C5Me5)2Sc−R (R=Me, Ph, Et)

“…[3] In their studies of s-bond metathesis reactions involving Cp* 2 ScÀR, Bercaw and co-workers isolated Cp* 2 ScÀEt. [8] Solid-state 45 Sc NMR has been used to study small molecules, [9] crystalline porous materials, [10] and glassy solids. [6] Though THF-free Cp* 2 LnÀEt complexes are rare,C p* 2 YÀEt was recently isolated and analysis of the solid-state structure obtained from X-ray diffraction studies unambiguously establishes the b-agostic structure in this complex.…”

“…[4] The solid-state structure of Cp* 2 ScÀEt was disordered, [5] and solution 1 Ha nd 13 CNMR data did not conclusively identify a b-agostic structure.T he b-agostic structure in Cp* 2 Sc À Et is supported by the presence of low energy C À Hbands in the IR spectrum, and the unexpected slow ethylene insertion kinetics compared to other Cp* 2 ScÀRcomplexes. [8] Solid-state 45 Sc NMR has been used to study small molecules, [9] crystalline porous materials, [10] and glassy solids. [7] Solid-state NMR spectroscopy could, in principle,d ifferentiate between the non-agostic and Sc···H À Ca gostic structures of Cp* 2 Sc À Et (Figure 1).…”

“…[7] Solid-state NMR spectroscopy could, in principle,d ifferentiate between the non-agostic and Sc···H À Ca gostic structures of Cp* 2 Sc À Et ( Figure 1). [8] Solid-state 45 Sc NMR has been used to study small molecules, [9] crystalline porous materials, [10] and glassy solids. Static central transition (CT) solid-state NMR of quadrupolar nuclei is arich source of information for studies of complex structures.…”

“…Static central transition (CT) solid-state NMR of quadrupolar nuclei is arich source of information for studies of complex structures. [8] Solid-state 45 Sc NMR has been used to study small molecules, [9] crystalline porous materials, [10] and glassy solids. [11] Theb road NMR powder patterns from these experiments are dominated by the interaction of the nuclear electric quadrupole moment, eQ, with the electric field gradient (EFG) tensor, which is reported as the quadrupolar coupling constant (C q )i nM Hz.…”

The β‐Agostic Structure in (C5Me5)2Sc(CH2CH3): Solid‐State NMR Studies of (C5Me5)2Sc−R (R=Me, Ph, Et)

“…Static central transition (CT) solid‐state NMR of quadrupolar nuclei is a rich source of information for studies of complex structures . Solid‐state 45 Sc NMR has been used to study small molecules, crystalline porous materials, and glassy solids . The broad NMR powder patterns from these experiments are dominated by the interaction of the nuclear electric quadrupole moment, eQ , with the electric field gradient (EFG) tensor, which is reported as the quadrupolar coupling constant ( C q ) in MHz.…”