R. K. Sheline

Analysis of the Infrared Spectra of Metal Carbonyls

A simplified normal coordinate treatment of the CO stretching vibrations is applied to metal carbonyls of various complexity. Infrared data to compute force constants directly are available for the following three groups of compounds: cyclopentadienyl manganese tricarbonyl and its derivatives [CpMn(CO)3−xLx, x=0→2], the substituted nickel carbonyls [Ni(CO)4−xLx, x=1→3], and some molybdenum carbonyl derivatives [sym‐Mo(CO)3L3 and cis‐Mo(CO)2L4]. When there are more force constants than observable frequencies in a molecule, the assumption is made that the effects of ligands on force constants are additive. In this way, many additional frequencies are obtained while only a few new force constants are introduced. This method has been used on two additional groups of compounds: Fe(CO)5−x(PF3)x and Mn2(CO)10—x(PF3)x. Excellent agreement between calculated and experimentally observed frequencies is found in all five groups of compounds. In some cases the effective force constants obtained may be interpreted as a...

Oxygen‐17 Quadrupole Coupling Parameters for Water in Its Various Phases

Analysis of 17O NMR data in D217O ice yields a quadrupole coupling constant, e2qQ / h = 6.66 ± 0.10MHz, and an asymmetry parameter, η = 0.935 ± 0.01. Comparison with the data for liquid and gas indicates a temperature dependence of the 17O quadrupole coupling constant in the liquid and explains the unusual linewidth behavior for liquid D217O. Charge distributions in the water molecule in both the solid and gaseous states have been obtained by a valence‐shell atomic‐orbital population analysis based on the experimental data for the 17O quadrupole coupling parameters and the molecular dipole moment. The results were used to calculate the quadrupole coupling constant for the deuterium nucleus. Good agreement with experimental data was obtained for both the solid and gaseous states. Comparison of the calculations for the two phases suggests that the intermolecular effects in ice are mostly electrostatic.

Anisotropic Chemical Shifts in Trigonal Cobalt Carbonyls Containing Metal–Metal Bonds

The 59Co NMR was studied in a number of single crystals and solutions of cobalt carbonyl complexes X3MCo(CO)4 (M=Si, Ge, Sn, Pb; X=Cl, Br, I, C6H5) containing metal–metal bonds. The z component of the chemical shift as determined by single crystal measurements in I3GeCo(CO)4, Br3SnCo(CO)4, and (C6H5)3SnCo(CO)4 was found to be constant within the series and showed a paramagnetic contribution of at least 3.6‰. As ligand field theory predicts no paramagnetic shift in this case, the data showed that for low oxidation state complexes the chemical shift can only be explained using MO theory. Good agreement with experiment was obtained using MO coefficients for the isoelectronic Fe(CO)5. The paramagnetic contributions to the x and y components of the shift vary considerably within the series (3.3‰–5.0‰). These variations were attributed to differences in the metal–metal bonds. It was found that for a given X the shifts do not vary linearly as the atomic weight of M is changed. This was attributed to differences ...

Quadrupole Coupling and Anisotropic Chemical Shifts in Some Manganese Carbonyls

Single crystals of a number of manganese carbonyls were studied by broadline NMR at room temperature. In the pentacarbonylhalides, Mn(CO)5X, the 55Mn quadrupole coupling constants (e2qQ / h) are 13.86 MHz (X is Cl), 17.46 MHz (X is Br), and 19.85 MHz (X is I). The asymmetry parameters are only 0.024–0.043, indicating rather high symmetry of the molecules in the solid. The halogen NMR was also observed and analyzed to give values for the quadrupole coupling parameters; 35Cl: e2qQ / h = 36.07 MHz, 81Br: e2qQ / h = 226.7 MHz, 127I: e2qQ / h = 927 MHz with η values of 0.03–0.06. The z axes of the field‐gradient tensor at the manganese sites were found to lie along the Mn–X bond. The anisotropic chemical shifts of 55Mn in these compounds and (C5H5)Mn(CO)3 were also determined. In the Mn(CO)5X series the shift anisotropy decreases in the order Cl>Br>I (σzz − σxx = 1.3‰, 1.2‰, 1.0‰). The z component of the shift tensor was found to be constant within the series, but different from the isotropic shift in Mn(CO)6+...

Single‐Crystal Broad‐Line 59Co and 55Mn NMR in CoMn(CO)9

The 59Co and 55Mn NMR was studied in a single crystal and solution of CoMn(CO)9. Two pairs of independent crystallographic sites were found related by the twofold axis and the mirror plane of the monoclinic crystal. The z axes of the 59Co and 55Mn electric‐field‐gradient tensors were found to be coaxial. The 59Co quadrupole coupling parameters were determined to be (1) e2qQ/h=129.15 MHz, η=0.1558 and (2) e2qQ/h=128.44 MHz, η=0.0937. The z component of the chemical shift was found to be identical with that for the compounds X3MCo(CO)4 (M is Si, Ge, Sn, and Pb; X is Cl, Br, I, C6H5) which have near C3ν symmetry. The 55Mn quadrupole coupling parameters were determined as (1) e2qQ/h= ∼ 20 MHz, η undetermined and (2) e2qQ/h=19.940 MHz, η=0.004. The z component of the chemical shift was found to be identical with that for the manganese pentacarbonyl halides which have approximate C4ν symmetry. The structure of CoMn(CO)9 has not been determined by x‐ray crystallography as it always forms twin crystals, but the q...

Quadrupole Coupling and Anisotropic Chemical Shift in Dicobalt Octacarbonyl at Liquid Nitrogen Temperature

The single‐crystal broadline 59Co NMR of dicobalt octacarbonyl was studied at liquid nitrogen temperature. Using these data, the complete orientation of the electric‐field gradient tensor system was determined for both crystallographically independent sites. The z axis of the electric‐field gradient tensor was within 6° of the terminal carbonyl opposite the missing bridging carbonyl. This direction agrees well with the value predicted by considering Co2(CO)8 to have both threefold and fourfold distortions at the cobalt site, but disagrees with a bent bond interpretation for Co2(CO)8. An anisotropic chemical shift was found at liquid nitrogen temperature. The anisotropy was small (0.5‰) and the z component was more paramagnetically shifted than the x and y components, as expected from the threefold and fourfold distortions at the cobalt site. A two‐circle goniometer for determination of the NMR parameters at liquid nitrogen temperature is described.

Quadrupole Coupling and Anisotropic Chemical Shift in Re2(CO)10, Mn2(CO)10, and ReMn(CO)10

Single crystals of the bimetallic carbonyls Mn2(CO)10, Re2(CO)10, and ReMn(CO)10 were studied at room temperature by broadline NMR. Earlier work on the orientation of the principal axis system of the electric field‐gradient tensor in Re2(CO)10 and Mn2(CO)10 was corrected. The z axis of the tensor in Re2(CO)10 was found to lie within 6° of the Re–Re bond. In Mn2(CO)10 the y axis of the field gradient tensor was within 10° of the Mn–Mn bond. The coupling constant and asymmetry parameter for 55Mn in MnRe(CO)10 were determined as e2qQ/h=8.6 MHz and η=0.61. The z axis of the field gradient tensor at the 55Mn site was within 2° of the Mn–Re bond. The orientation of the principal axis system of the field gradient tensor in Mn2(CO)10 and Re2(CO)10 was determined at liquid nitrogen temperature. The angle between the z axis and the Re–Re bond in Re2(CO)10 was found to double by going from room temperature to liquid nitrogen temperature. The orientation of the principal axis system in Mn2(CO)10 was unchanged within ...

Single Crystal Broad‐Line 55Mn NMR in Adducts of Manganese Pentacarbonyl, X3M–Mn(CO)

Single crystals of four members of the series X3M–Mn(CO)5 [X3M is (C6H5)3Pb, (C6H5)3Sn, (C6H5)3Ge, and Cl3Sn] were grown and the 55Mn broad‐line NMR was studied at room temperature. The 55Mn quadrupole coupling constants (e2qQ/h) are 7.3 MHz [Cl3Sn–Mn(CO)5], 12.04 MHz [(C6H5)3Pb–Mn(CO)4], 18.33 MHz [(C6H5)3Sn–Mn(CO)5], and 24.636 MHz [(C6H5)3Ge–Mn(CO)5]. The quadrupole coupling constants are related to the electronegativities and are discussed by comparison to empirical predictions derived from NQR data on the similar X3M–Co(CO)4 series. The asymmetry parameters are in the range 0.11–0.37. For (C6H5)3Ge–Mn(CO)5, the anisotropic chemical shift tensor was determined and the charge distribution around the manganese was found to be isotropic.

Quadrupole Coupling in Dicobalt Octacarbonyl

The pure nuclear quadrupole resonance spectrum of 59Co in dicobaltoctacarbonyl was studied in the temperature range of − 196 to − 30°C. At liquid‐nitrogen temperature, the quadrupole coupling parameters for the two independent crystallographic sites are (A)e2qQ / h = 90.18 ± 0.15 MHz, η = 0.3149 ± 0.001 and (B)e2qQ / h = 89.30 ± 0.15 MHz, η = 0.4837 ± 0.001. The asymmetry parameters for the two sites approach each other with increasing temperature. To understand the observed parameters, the environment of the cobalt atom in Co2(CO)8 is described in terms of an octahedron with distortions along its three and fourfold axes. Defining two corresponding axially symmetric field gradient tensors with z components qa and qb, a quadratic equation relating the ratio qa / qb to the observed asymmetry parameter η is derived. The calculated field gradient with the z axis along the Co–Co direction is in reasonable agreement with the observed quadrupole splitting in Fe2(CO)9. The difference in the η values for the two s...

Orientation of the Electric‐Field‐Gradient Tensor in Crystalline Dirhenium Decacarbonyl

The orientation of the principal‐axis system of the field‐gradient tensor in a single crystal of Re2(CO)10 was studied at room temperature. The z and y axes were determined independently from curves of constant frequency for the + 32 ↔ + 52 and − 32 ↔ − 12 transitions at a magnetic field of 2 kG. Two sets of principal axes related by the twofold axis and mirror plane of the monoclinic crystal were found. The rhenium–rhenium bond coincides with the intersection of the two y–z planes and forms an angle of 25° with the z axes. The deviation of the z axes from the Re–Re bond is attributed to distortions of the molecule in the solid due to nearest‐neighbor interactions of carbonyl groups. The total field‐gradient tensor is described as the sum of an axially symmetric tensor with z axis along the Re–Re bond—dominated by intramolecular contributions—and a second axially symmetric tensor arising from the distortion of the molecule in the lattice with z axis in the y–z plane of the total field‐gradient system at a...