Journal of Physical Chemistry B, Vol.108, No.26, 9060-9069, 2004
Solid-state Zr-91 NMR of bis(cyclopentadienyl)dichlorozirconium(IV)
The first solid-state Zr-91 NMR spectra of an organometallic zirconium complex, bis(cyclopentadienyl)dichlorozirconium(IV) (CP2ZrCl2), are presented. Overlapping static and magic-angle spinning (MAS) Zr-91 NMR spectra Of Cp2ZrCl2 and a zirconium oxide NMR rotor are presented to explore the possibility of conducting Zr-91 NMR experiments using standard ZrO2 rotors. Quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) Zr-91 NMR experiments on static and MAS samples, in combination with analytical and numerical spectral simulations, are used to extract Zr-91 quadrupolar coupling constants and asymmetry parameters. The first example of zirconium chemical shielding anisotropy is reported for Cp2ZrCl2, with a span of Omega = 475(45) ppm and a skew of -0.55(5) (i.e., delta(11) = 306 ppm, delta(22) = -62 ppm, and delta(33) = -169 ppm). Comparison of conventional static and MAS Zr-91 Hahn echo NMR spectra with those acquired using the recently reported double frequency sweep/QCPMG and rotor-assisted population transfer/QCPMG pulse sequences demonstrate an order of magnitude gain in sensitivity for Cp2ZrCl2. Restricted Hartree-Fock and hybrid density functional theory calculations reveal that anisotropic zirconium chemical shielding tensors can be calculated with good accuracy using non-relativistic theory with large all-electron basis sets. The Zr-91 quadrupolar parameters for Cp2ZrCl2 are C-Q = 6.35(10) MHz and eta(Q) = 0.3(1). Reasonable agreement is obtained between calculated Zr-91 electric field gradient tensors and experimental results.