skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Solvent effect on the 195 Pt NMR properties in pyridonate-bridged Pt III dinuclear complex derivatives investigated by ab initio molecular dynamics and localized orbital analysis
Title: Solvent effect on the 195 Pt NMR properties in pyridonate-bridged Pt III dinuclear complex derivatives investigated by ab initio molecular dynamics and localized orbital analysis
An ab initio molecular dynamics investigation of the solvent effect (water) on the structural parameters, 195 Pt NMR spin–spin coupling constants (SSCCs) and chemical shifts of a series of pyridonate-bridged Pt III dinuclear complexes is performed using Kohn–Sham (KS) Car–Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations. The indirect solvent effect ( via structural changes) has a dramatic effect on the 1 J PtPt SSCCs. The complexes exhibit a strong trans influence in solution, where the Pt–Pt bond lengthens with increasing axial ligand σ-donor strength. In the diaqua complex, where the solvent effect is more pronounced, the SSCCs averaged for CPMD configurations with explicit plus implicit solvation agree much better with the experimental data, while the calculations for static geometry and CPMD unsolvated configurations show large deviations with respect to experiment. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of 1 J PtPt and 195 Pt chemical shifts. An analysis of 1 J PtPt in terms of localized and canonical orbitals shows that the SSCCs are driven by changes in the s-character of the natural atomic orbitals of Pt atoms, which affect the 'Fermi contact' mechanism.  more » « less
Award ID(s):
1855470
PAR ID:
10253406
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Physical Chemistry Chemical Physics
Volume:
23
Issue:
22
ISSN:
1463-9076
Page Range / eLocation ID:
12864 to 12880
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Journal of the American Chemical Society)
    N-Heterocyclic carbenes (NHCs) are widely used ligands in transition metal catalysis. Notably, they are increasingly encountered in heterogeneous systems. While a detailed knowledge of the possibly multiple metal environments would be essential to understand the activity of metal-NHC-based heterogeneous catalysts, only a few techniques currently have the ability to describe with atomic-resolution structures dispersed on a solid support. Here, we introduce a new dynamic nuclear polarization (DNP) surface-enhanced solid-state nuclear magnetic resonance (NMR) approach that, in combination with advanced density functional theory (DFT) calculations, allows the structure characterization of isolated silica-supported Pt-NHC sites. Notably, we demonstrate that the signal amplification provided by DNP in combination with fast magic angle spinning enables the implementation of sensitive 13C-195Pt correlation experiments. By exploiting 1J(13C-195Pt) couplings, 2D NMR spectra were acquired, revealing two types of Pt sites. For each of them, 1J(13C-195Pt) value was determined as well as 195Pt chemical shift tensor parameters. To interpret the NMR data, DFT calculations were performed on an extensive library of molecular Pt-NHC complexes. While one surface site was identified as a bis-NHC compound, the second site most likely contains a bidentate 1,5-cyclooctadiene ligand, pointing to various parallel grafting mechanisms. The methodology described here represents a new step forward in the atomic-level description of catalytically relevant surface metal-NHC complexes. In particular, it opens up innovative avenues for exploiting the spectral signature of platinum, one of the most widely used transition metals in catalysis, but whose use for solid-state NMR remains difficult. Our results also highlight the sensitivity of 195Pt NMR parameters to slight structural changes. 
    more » « less
  2. (, Magnetic Resonance in Chemistry)
    Abstract The nuclear magnetic resonance (NMR) chemical shift is extremely sensitive to molecular geometry, hydrogen bonding, solvent, temperature, pH, and concentration. Calculated magnetic shielding constants, converted to chemical shifts, can be valuable aids in NMR peak assignment and can also give detailed information about molecular geometry and intermolecular effects. Calculating chemical shifts in solution is complicated by the need to include solvent effects and conformational averaging. Here, we review the current state of NMR chemical shift calculations in solution, beginning with an introduction to the theory of calculating magnetic shielding in general, then covering methods for inclusion of solvent effects and conformational averaging, and finally discussing examples of applications using calculated chemical shifts to gain detailed structural information. 
    more » « less
  3. ; ; ; ; ; ; ; ; (, Chemistry – A European Journal)
    Abstract In this work, we describe the easy synthesis of mercury complexes with the 1,5,9‐trimesityldipyrromethene (MesDPM) ligand. The compounds were characterized using standard analytic methods such as NMR, IR, as well as UV/Vis spectroscopy. The molecular structures in solid state were determined by single‐crystal X‐ray diffraction analysis (SC‐XRD) experiments. In addition, the199Hg NMR chemical shifts were determined by measurements and quantum chemical calculations. 
    more » « less
  4. ; ; ; ; (, Chemical Science)
    Nuclear magnetic resonance (NMR) is one of the primary techniques used to elucidate the chemical structure, bonding, stereochemistry, and conformation of organic compounds. The distinct chemical shifts in an NMR spectrum depend upon each atom's local chemical environment and are influenced by both through-bond and through-space interactions with other atoms and functional groups. The in silico prediction of NMR chemical shifts using quantum mechanical (QM) calculations is now commonplace in aiding organic structural assignment since spectra can be computed for several candidate structures and then compared with experimental values to find the best possible match. However, the computational demands of calculating multiple structural- and stereo-isomers, each of which may typically exist as an ensemble of rapidly-interconverting conformations, are expensive. Additionally, the QM predictions themselves may lack sufficient accuracy to identify a correct structure. In this work, we address both of these shortcomings by developing a rapid machine learning (ML) protocol to predict 1 H and 13 C chemical shifts through an efficient graph neural network (GNN) using 3D structures as input. Transfer learning with experimental data is used to improve the final prediction accuracy of a model trained using QM calculations. When tested on the CHESHIRE dataset, the proposed model predicts observed 13 C chemical shifts with comparable accuracy to the best-performing DFT functionals (1.5 ppm) in around 1/6000 of the CPU time. An automated prediction webserver and graphical interface are accessible online at http://nova.chem.colostate.edu/cascade/. We further demonstrate the model in three applications: first, we use the model to decide the correct organic structure from candidates through experimental spectra, including complex stereoisomers; second, we automatically detect and revise incorrect chemical shift assignments in a popular NMR database, the NMRShiftDB; and third, we use NMR chemical shifts as descriptors for determination of the sites of electrophilic aromatic substitution. 
    more » « less
  5. ; ; (, Chemical Science)
    Co-crystallization of the prominent Fe( ii ) spin-crossover (SCO) cation, [Fe(3-bpp) 2 ] 2+ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ δ − radical anion has afforded a hybrid complex [Fe(3-bpp) 2 ](TCNQ) 3 ·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ RT = 3.1 × 10 −3 S cm −1 , and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ − anions, [Fe(3-bpp) 2 ](TCNQ) 2 ·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy) 2 ](TCNQ) 6 ·2Me 2 CO (4) and [Fe(bzimpy) 2 ](TCNQ) 5 ·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ RT = 9.1 × 10 −2 S cm −1 and 1.8 × 10 −3 S cm −1 , respectively. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email