A Study of Transition‐Metal Organometallic Complexes Combining 35Cl Solid‐State NMR Spectroscopy and 35Cl NQR Spectroscopy and First‐Principles DFT Calculations

A series of transition‐metal organometallic complexes with commonly occurring metal? chlorine bonding motifs were characterized using ³⁵Cl solid‐state NMR (SSNMR) spectroscopy, ³⁵Cl nuclear quadrupole resonance (NQR) spectroscopy, and first‐principles density functional theory (DFT) calculations of NMR interaction tensors. Static ³⁵Cl ultra‐wideline NMR spectra were acquired in a piecewise manner at standard (9.4 T) and high (21.1 T) magnetic field strengths using the WURST‐QCPMG pulse sequence. The ³⁵Cl electric field gradient (EFG) and chemical shielding (CS) tensor parameters were readily extracted from analytical simulations of the spectra; in particular, the quadrupolar parameters are shown to be very sensitive to structural differences, and can easily differentiate between chlorine atoms in bridging and terminal bonding environments. ³⁵Cl NQR spectra were acquired for many of the complexes, which aided in resolving structurally similar, yet crystallographically distinct and magnetically inequivalent chlorine sites, and with the interpretation and assignment of ³⁵Cl SSNMR spectra. ³⁵Cl EFG tensors obtained from first‐principles DFT calculations are consistently in good agreement with experiment, highlighting the importance of using a combined approach of theoretical and experimental methods for structural characterization. Finally, a preliminary example of a ³⁵Cl SSNMR spectrum of a transition‐metal species (TiCl₄) diluted and supported on non‐porous silica is presented. The combination of ³⁵Cl SSNMR and ³⁵Cl NQR spectroscopy and DFT calculations is shown to be a promising and simple methodology for the characterization of all manner of chlorine‐containing transition‐metal complexes, in pure, impure bulk and supported forms.     

Spin‐Polarized Structures and Solid‐State NMR Spectroscopy of Paramagnetic Compounds

On an atomic scale and with high sensitivity, solid‐state NMR spectroscopy can provide information about the electronic spin density and coupling mechanisms in paramagnetic compounds. The picture shows how the hyperfine splitting collapses through relaxation. Insights into which compounds are suitable and which approximations have to be made are given.

     

Solid‐State 73Ge NMR Spectroscopy of Simple Organogermanes

Germanium‐73 is an extremely challenging nucleus to examine by NMR spectroscopy due to its unfavorable NMR properties. Through the use of an ultrahigh (21.1 T) magnetic field, a systematic study of a series of simple organogermanes was carried out. In those cases for which X‐ray structural data were available, correlations were drawn between the NMR parameters and structural metrics. These data were combined with DFT calculations to obtain insight into the structures of several compounds with unknown crystal structures.     

Solid‐State 17O NMR Spectroscopy of Paramagnetic Coordination Compounds

High‐quality solid‐state ¹⁷O (I=5/2) NMR spectra can be successfully obtained for paramagnetic coordination compounds in which oxygen atoms are directly bonded to the paramagnetic metal centers. For complexes containing V^III (S=1), Cu^II (S=1/2), and Mn^III (S=2) metal centers, the ¹⁷O isotropic paramagnetic shifts were found to span a range of more than 10 000 ppm. In several cases, high‐resolution ¹⁷O NMR spectra were recorded under very fast magic‐angle spinning (MAS) conditions at 21.1 T. Quantum‐chemical computations using density functional theory (DFT) qualitatively reproduced the experimental ¹⁷O hyperfine shift tensors.