⁹⁵Mo NMR: a useful tool for structural studies in solution

Abstract

Oxomolybdenum(VI) complexes containing diverse ligands from an electronic and topological point of view have been analysed by means of (95)Mo NMR in solution with the purpose of using this technique as a tool to study their coordination chemistry and reactivity. The relationship between the electronic density on the metal tuned by the electron-donor ability of the coordinated ligands and the (95)Mo chemical shift has been proved for mono- and bimetallic complexes showing a hexa- or hepta-coordination around the metal centre. The different origins of the signal broadening (associated either to the symmetry of the metallic polyhedron or to the presence of isomers or to the ligand de-coordination) have been also considered to rationalise the obtained data.

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

“…During geometry optimizations, only atomic positions have been relaxed. Calculations using a cubic supercell have also been carried out for a single Mo(CO) 6 complex. Although larger supercells have been considered, calculations were proven to converge in EFG a n dC Sv a l u e sw i t ha ne d g eo f1 2Å length of the cubic cell.…”

“…This tends to prove that SR US-PP takes into account most of the scalar relativistic effects in the case of molybdenum. Quadrupolar parameters have also been calculated using the crystal structure of Mo(CO) 6 ; C Q and Z Q values are equal to 622 kHz and 0.25, respectively. The influence of neighbouring molecular units on the calculation of these quadrupolar parameters is significant, even if molybdenum hexacarbonyl is a molecular crystal, weaker but significant interactions occur between molecular units.…”

“…32 Moreover, since molybdenum hexacarbonyl has been used as a benchmark molecule in several previous theoretical studies using different computational approaches, this broadens the scope of the present study. It is noteworthy to mention that for the first time: (i) since structural parameters often play a part in NMR computations, their influence has been examined: 95 Mo NMR parameters have been computed for Mo(CO) 6 using the geometry determined by X-ray diffraction experiments at first, 33 the influence of geometry optimization has been studied subsequently; (ii) not only DFT calculations of an isolated Mo(CO) 6 molecule have been carried out but also periodic DFT calculations in order to evaluate the influence of neighbouring molecules on the NMR properties.…”

“…2 Experimental details 2.1 Crystal structure of Mo(CO) 6 Molybdenum hexacarbonyl crystallizes in an orthorhombic cell in space group Pnma (no. 62).…”

“…These problems can now be overcome by the use of specific pulse schemes, magic angle spinning (MAS) 4 and the development of high-magneticfield spectrometers. 95 Mo NMR spectroscopy has been successfully used in the field of organometallic chemistry, [5][6][7] homogeneous and zeolite catalyses, [8][9][10][11] inorganic materials, [12][13][14] glass, [15][16][17] superconducting materials, 18 agricultural products, 19 etc. Because of its lower quadrupolar moment, the 95 Mo nucleus is generally preferred to 97 Mo.…”