TY - JOUR
T1 - Multimodal Structure Solution with 19F NMR Crystallography of Spin Singlet Molybdenum Oxyfluorides
AU - Ding, Fenghua
AU - Griffith, Kent J.
AU - Koçer, Can P.
AU - Saballos, Richard J.
AU - Wang, Yiran
AU - Zhang, Chi
AU - Nisbet, Matthew L.
AU - Morris, Andrew J.
AU - Rondinelli, James M.
AU - Poeppelmeier, Kenneth R.
N1 - Funding Information:
This work was supported by funding from the National Science Foundation (DMR-1904701). K.J.G. was supported by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. R.J.S., J.M.R., and powder diffraction at the J. B. Cohen X-ray Diffraction Facility were supported by the MRSEC program (DMR-1720139) at the Materials Research Center of Northwestern University (NU). Single-crystal X-ray, solid-state NMR, and FT-IR measurements were acquired at Northwestern University’s Integrated Molecular Structure Education and Research Center (IMSERC), which is supported by grants from NSF-NSEC, NSF-MRSEC, NSF DMR-0521267, the KECK Foundation, the State of Illinois, and NU. Raman and EDS measurements made use of the EPIC and SPID facilities of NU’s NU ANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the MRSEC program, the International Institute for Nanotechnology (IIN), the Keck Foundation, and the State of Illinois through the IIN. Computations were performed using the Extreme Science and Engineering Discovery Environment (XSEDE) Stampede 2 at the Texas Advance Computing Center (allocation TG-DMR110085), which is supported by NSF grant number ACI-1548562 and also Athena at HPC Midlands+, which was funded by the EPSRC through grant EP/P020232/1 (via the EPSRC RAP call of spring 2019). C.P.K. thanks the Winton Programme for the Physics of Sustainability and EPSRC for financial support.
PY - 2020/7/15
Y1 - 2020/7/15
N2 - Complex crystal structures with subtle atomic-scale details are now routinely solved using complementary tools such as X-ray and/or neutron scattering combined with electron diffraction and imaging. Identifying unambiguous atomic models for oxyfluorides, needed for materials design and structure-property control, is often still a considerable challenge despite their advantageous optical responses and applications in energy storage systems. In this work, NMR crystallography and single-crystal X-ray diffraction are combined for the complete structure solution of three new compounds featuring a rare triangular early transition metal oxyfluoride cluster, [Mo3O4F9]5-. After framework identification by single-crystal X-ray diffraction, 1D and 2D solid-state 19F NMR spectroscopy supported by ab initio calculations are used to solve the structures of K5[Mo3O4F9]·3H2O (1), K5[Mo3O4F9]·2H2O (2), and K16[Mo3O4F9]2[TiF6]3·2H2O (3) and to assign the nine distinct fluorine sites in the oxyfluoride clusters. Furthermore, 19F NMR identifies selective fluorine dynamics in K16[Mo3O4F9]2[TiF6]3·2H2O. These dual scattering and spectroscopy methods are used to demonstrate the generality and sensitivity of 19F shielding to small changes in bond length, on the order of 0.01 Å or less, even in the presence of hydrogen bonding, metal-metal bonding, and electrostatic interactions. Starting from the structure models, the nature of chemical bonding in the molybdates is explained by molecular orbital theory and electronic structure calculations. The average Mo-Mo distance of 2.505 Å and diamagnetism in 1, 2, and 3 are attributed to a metal-metal bond order of unity along with a 1a21e4 electronic ground state configuration for the [Mo3O4F9]5- cluster, leading to a rare trimeric spin singlet involving d2 Mo4+ ions. The approach to structure solution and bonding analysis is a powerful strategy for understanding the structures and chemical properties of complex fluorides and oxyfluorides.
AB - Complex crystal structures with subtle atomic-scale details are now routinely solved using complementary tools such as X-ray and/or neutron scattering combined with electron diffraction and imaging. Identifying unambiguous atomic models for oxyfluorides, needed for materials design and structure-property control, is often still a considerable challenge despite their advantageous optical responses and applications in energy storage systems. In this work, NMR crystallography and single-crystal X-ray diffraction are combined for the complete structure solution of three new compounds featuring a rare triangular early transition metal oxyfluoride cluster, [Mo3O4F9]5-. After framework identification by single-crystal X-ray diffraction, 1D and 2D solid-state 19F NMR spectroscopy supported by ab initio calculations are used to solve the structures of K5[Mo3O4F9]·3H2O (1), K5[Mo3O4F9]·2H2O (2), and K16[Mo3O4F9]2[TiF6]3·2H2O (3) and to assign the nine distinct fluorine sites in the oxyfluoride clusters. Furthermore, 19F NMR identifies selective fluorine dynamics in K16[Mo3O4F9]2[TiF6]3·2H2O. These dual scattering and spectroscopy methods are used to demonstrate the generality and sensitivity of 19F shielding to small changes in bond length, on the order of 0.01 Å or less, even in the presence of hydrogen bonding, metal-metal bonding, and electrostatic interactions. Starting from the structure models, the nature of chemical bonding in the molybdates is explained by molecular orbital theory and electronic structure calculations. The average Mo-Mo distance of 2.505 Å and diamagnetism in 1, 2, and 3 are attributed to a metal-metal bond order of unity along with a 1a21e4 electronic ground state configuration for the [Mo3O4F9]5- cluster, leading to a rare trimeric spin singlet involving d2 Mo4+ ions. The approach to structure solution and bonding analysis is a powerful strategy for understanding the structures and chemical properties of complex fluorides and oxyfluorides.
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U2 - 10.1021/jacs.0c04019
DO - 10.1021/jacs.0c04019
M3 - Article
C2 - 32530621
AN - SCOPUS:85088179733
VL - 142
SP - 12288
EP - 12298
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 28
ER -