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. [ABSTRACT FROM AUTHOR]