Solid-State Nuclear Magnetic Resonance Spectroscopic and Quantum Chemical Investigation of ¹³C and ¹⁷O Chemical Shift Tensors, ¹⁷O Nuclear Quadrupole Coupling Tensors, and Bonding in Transition-Metal Carbonyl Complexes and Clusters

Abstract

The carbon-13 and oxygen-17 nuclear magnetic resonance spectroscopic shielding behavior, as well as the oxygen-17 nuclear quadrupole coupling constants (NQCC), in the four metal−CO systems Fe(CO)5, Fe2(CO)9, Ni2(η5-C5H5)2(CO)2, and Rh6(CO)16 have been investigated both experimentally and by density functional calculations. Characteristics of the spectroscopic observables and bonding for the most common types of metal−carbonyl coordination, μ1-, μ2-, and μ3-CO, may thus be compared in detail. There is generally very good agreement between the theoretical predictions and the experimental measurements, including the 17O shift predictions for Fe2(CO)9 and Rh6(CO)16 made previously. Interestingly, the bridging oxygen shift tensor in Fe2(CO)9 has its most deshielded component parallel to the C−O axis. This is highly unusual for carbonyl ligands, but is the normal behavior seen in organic carbonyl groups. To explain this and other observations, the computed shielding tensors and electric field gradients have been broken down into contributions from various localized, delocalized, or mixed sets of molecular orbitals. In addition to the common IGLO procedure, these analyses also include “partial IGLO” and IGLO-Pipek-Mezey methods. The results give new insights into both the magnitudes and orientations of the shielding and nuclear quadrupole coupling tensors. The potential for the combined use of solid-state NMR and quantum chemical methods in various areas of transition metal chemistry is discussed.

Solid state NMR studies of molecular recognition at protein–mineral interfaces

“…This approach basically exploits the fact that the isotropic chemical shifts of the backbone carbonyl, alpha, and beta 13 C spins of each amino acid residue are to varying extents sensitive to the local secondary structure of the protein. Although recent work by Oldfield and coworkers has placed structural interpretation of isotropic 13 C chemical shifts of proteins on a quantitative basis [17][18][19], in the past, analyses of structures using chemical shift data have been done empirically by comparing experimentally observed 13 C chemical shifts for backbone 13 C spins to a large body of data, derived via 13 C Cross Polarization/Magic Angle Spinning (CPMAS) experiments from polypeptides of known secondary structure in the condensed state. An excellent example of this type of analysis is the seminal work by Fernandez et al [20] who studied the structures of polyglutamic acid and polylysine adsorbed to hydroxyapatite and silica using 13 C CPMAS.…”

Oxygen-17 NMR spectroscopy: Basic principles and applications (Part I)

“…Oldfield and collaborators [222] presented a detailed experimental NMR study in the solid state and quantum chemical investigation of both d( 13 C) and d( 17 O) and chemical shift tensor elements in a variety of metal carbonyls containing l 1 , -l 2 , and l 3 -CO ligands (Scheme 3). The SOS-DFPT approach in its local-density Loc1 approximation [223] with IGLO-II and IGLO-III bases was used.…”

“…Accurate shielding polarizabilities can be calculated [227,232,236] by the use of the derivative Hartee-Fock (DHF) approach (Table 12) (Table 12) indicate large contributions from the perpendicular dipole shielding polarizabilities A yy,z with opposite signs for 13 C and 17 O. It was concluded [237] that perturbation of CO by electric fields within proteins is the principal cause for the linear correlation observed between m C@O and d( 13 C) and/or d( 17 O) in heme pro- Table 10 Comparison of experimental a and computed isotropic shifts, d iso , shift tensor elements, d xx , d yy , d zz , and shift anisotropies j d zz À d xx j and jd yy À d xx j [222].…”

Theoretical investigation of Q A −· -ligand interactions in bacterial reaction centers ofRhodobacter sphaeroides

“…It has been shown that density functional theory [3] (DFT) calculations are capable of predicting such HFC tensors for organic radicals [4][5][6][7], whereas the treatment of transition metal systems is also possible but in general much more difficult [7][8][9][10]. There are also systematic DFT studies of QC tensors for different nuclei and molecules that demonstrate the reliability of such theoretical predictions [11][12][13][14][15][16][17][18][19]. These results suggest that quantum chemical calculations based on the (unrestricted) Kohn-Sham formalism can be the missing link between magnetic resonance data and molecular structure.…”

“…60) were used. As in many other studies [11,12,19,27,28] the nuclear quadrupole moments were not calibrated for the applied theoretical methods. Using the above mentioned values for QN it was possible to calculate the QCCs directly from the V= eigenvalues of the EFGs obtained from the computations.…”