A 95Mo and 13C solid-state NMR and relativistic DFT investigation of mesitylenetricarbonylmolybdenum(0) – a typical transition metal piano-stool complex

Abstract

The chemical shift (CS) and electric field gradient (EFG) tensors in the piano-stool compound mesitylenetricarbonylmolybdenum(0), 1, have been investigated via 95 Mo and 13 C solid-state magic-angle spinning (MAS) NMR as well as relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) calculations. Molybdenum-95 (I ¼ 5/2) MAS NMR spectra acquired at 18.8 T are dominated by the anisotropic chemical shift interaction (O ¼ 775 AE 30 ppm) rather than the 2nd-order quadrupolar interaction (C Q ¼ À0.96 AE 0.15 MHz), an unusual situation for a quadrupolar nucleus. ZORA-DFT calculations of the 95 Mo EFG and CS tensors are in agreement with the experimental data. Mixing of appropriate occupied and virtual d-orbital dominated MOs in the region of the HOMO-LUMO gap are shown to be responsible for the large chemical shift anisotropy. The small, but non-negligible, 95 Mo quadrupolar interaction is discussed in terms of the geometry about Mo. Carbon-13 CPMAS spectra acquired at 4.7 T demonstrate the crystallographic and magnetic nonequivalence of the twelve 13 C nuclei in 1, despite the chemical equivalence of some of these nuclei in isotropic solutions. The principal components of the carbon CS tensors are determined via a Herzfeld-Berger analysis, and indicate that motion of the mesitylene ring is slow compared to a rate which would influence the carbon CS tensors (i.e. tens of ms). ZORA-DFT calculations reproduce the experimental carbon CS tensors accurately. Oxygen-17 EFG and CS tensors for 1 are also calculated and discussed in terms of existing experimental data for related molybdenum carbonyl compounds. This work provides an example of the information available from combined multi-field solid-state multinuclear magnetic resonance and computational investigations of transition metal compounds, in particular the direct study of quadrupolar transition metal nuclei with relatively small magnetic moments.

Solid-state 95Mo NMR of mixed-valence polyoxomolybdates (V, VI) with localized or delocalized d1 electrons

“…On the contrary, limited types of the oxidation number of molybdenum have been investigated in solids. So far, solid-state 95 Mo NMR has been reported for Mo VI in mono-and poly-molybdates like M 2 MoO 4 and ðNH 4 Þ 6 Mo 7 O 24 , respectively [7,[10][11][12][13][14], Mo IV in MoX 2 type compounds [15,16] and ½MoðCNÞ 8 4À anions with different symmetry [6], and Mo 0 in complexes [17][18][19]. 95 Mo NMR in metal state has also been reported [8,9,16,20].…”

“…The local density approximation of Vosko-Wilk-Nusair (VWN) augmented with the Becke-Perdew generalized gradient approximation (GGA) was employed for the exchange-correlation functional [6,19] The triple-f doubly polarized (TZ2P) Slater-type ZORA all-electron basis set was used. The Mo and O atomic coordinates were determined so that fMo 16 g and fMo 14 g take averaged structures with T d and C 2v symmetries, respectively, by adapting average bond lengths and bond angles obtained using structural data [34,41].…”

“…95 Mo NMR in metal state has also been reported [8,9,16,20]. NMR parameters of 95 Mo obtained by the NMR measurements have been examined by quantum chemical calculations with or without considering relativistic effect [6,13,19].…”

“…95 Mo ðI ¼ 5=2Þ nuclei with low gyromagnetic ratio ðc ¼ À1:743 Â 10 7 rad s À1 T À1 Þ benefit from such an increased field. Detailed information about local structure around 95 Mo can be obtained through the analysis of solid-state 95 Mo NMR spectra affected by anisotropic interactions such as chemical shift and quadrupole interactions that are usually averaged in liquids [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

95Mo nuclear magnetic resonance parameters of molybdenum hexacarbonyl from density functional theory: appraisal of computational and geometrical parameters

“…This is not as important as observed by Bryce and Wasylishen for the piano-stool compound mesitylenetricarbonylmolybdenum(0). 29 However, the authors attributed to the relativistic effects the difference between a non-relativistic B3LYP calculation using a LANL2DZ basis set with a ZORA calculation using BP86 GGA functional and an all-electron triple-z basis set. This is not rigorous since several parameters differ in these two calculations all the more so since LANL2DZ basis used an effective core potential instead of inner core electrons.…”