113Cd Shielding Tensors of Monomeric Cadmium Compounds Containing Nitrogen Donor Atoms. 3. Syntheses, Crystal Structure, and 113Cd NMR Spectroscopy of the Six-Coordinate Complexes [HB(pz)3]2Cd, [HB(3-Phpz)3]2Cd, and [B(pz)4]Cd[HB(3-Phpz)3] (pz = pyrazolyl)
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All possible mixed-ligand complexes of the formula LL’Cd (L, L’ = [HB(pz)3]-, [HB(3,5-Me2pz)3]-, [B(pz)4]-, [HB(3-Phpz)3]- (pz = pyrazolyl)) were prepared by the reaction of a 1/1/1 molar ratio of the desired ligand salts and CdCl2. The new symmetrical complex [HB(3-Phpz)3]2Cd was prepared from 2 equiv of the ligand salt and CdCl2. The solid state structures of [HB(pz)3]2Cd (1), [HB(3-Phpz)3]2Cd (4), and [B(pz)4]Cd[HB(3-Phpz)3] (10) have been characterized by X-ray crystallography. All three are pseudo-octahedral, but the structures of both 4 and 10 are distorted by a rotational movement of one ligand relative to the other ligand. Because of this rotation with 4 and 10, the trans N-Cd-N bond angles are significantly distorted from 180°, leading to one set of cis, interligand N-Cd-N angles that average 89.3 and 92.4° and another that average 100.6 and 105.7°, respectively. The Cd-N bond distances (average 2.33 Å) for 1 are similar to those observed earlier in the structures of [HB-(3,5-Me2pz)3]2Cd, [B(pz)4]2Cd and [B(3-Mepz)4]2Cd, but the Cd-N distances are longer in 4 (average 2.39 Å) and in 10 ([HB(3-Phpz)3]- ligand average 2.39 Å and the [B(pz)4]- ligand 2.36 Å). The solution 113Cd NMR chemical shifts for complexes containing the [HB(3-Phpz)3]- are substantially more shielded than the other complexes in the series. A regression analysis of the solution 113Cd NMR chemical shifts for all of these complexes for the shift caused by each ligand relative to Cd(C104)2 shows a good correlation of the calculated and observed chemical shifts of these complexes. These shift values (ligand/ligand shift, δ) are [HB(pz)3]-/97.3, [HB(3,5-Me2pz)3]-/101.7, [B(pz)4]-/107.4, and [HB(3-Phpz)3]-/44.9. The principal components of the 113Cd shielding tensor were determined from CP/MAS data. The σ33 element was found to be relatively independent of the Cd—N bond lengths while the opposite is true of σ11. This accounts for the dependence of the shielding anisotropies upon the bond distances. The respective chemical shift anisotropies and asymmetry parameters for 1 (both line shapes), 4, and 10 are -238.7, -228.4, -138.5, and -220.8 ppm and 0.55, 0.65, 0.26, and 0.15 ppm. © 1995, American Chemical Society. All rights reserved.
author list (cited authors)
Reger, D. L., Myers, S. M., Mason, S. S., Darensbourg, D. J., Holtcamp, M. W., Reibenspies, J. H., Lipton, A. S., & Ellis, P. D.
complete list of authors
Reger, Daniel L||Myers, Sheila M||Mason, Scott S||Darensbourg, Donald J||Holtcamp, Matthew W||Reibenspies, Joseph H||Lipton, Andrew S||Ellis, Paul D