~(113)Cd Shielding Tensors of Monomeric Cadmium Compounds Containing Nitrogen Donor Atoms. 2. Syntheses, Crystal Structures, and ~(113)Cd NMR Spectroscopy of the Six-Coordinal Complexes [HB(pz)_3]_2Cd, [HB(3-Phpz)_3]_2Cd, and [B(pz)_4]Cd[HB(3-Phpz)_3]

摘要

All possible mixed-ligand complexes of the formula LL′Cd (L, L′ = [HB(pz)_3]~-, [HB(3,5-Me_2pz)_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 CdCl_2. The new symmetrical complex [HB(3-Phpz)_3]_2Cd was prepared from 2 equiv of the ligand salt and CdCL_2. 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 A) for 1 are similar to those observed earlier in the structures of [HB-(3,5-Me_2pz)_3]_2Cd, [B(pz)_4]_2Cd and [B(3-Mepz)_4]_2Cd, but the Cd-N distances are longer in 4 (average 2.39 A) and in 10 ([HB(3-Phpz)_3]~- ligand average 2.39 A and the [B(pz)_4]~- ligand 2.36 A). The solution ~(113)Cd 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 ~(113)Cd NMR chemical shifts for all of these complexes for the shift caused by each ligand relative to Cd(ClO_4)_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-Me_2pz)_3]~-/101.7, [B(pz)_4]~-/107.4, and [HB(3-Phpz)_3]~-/44.9. The principal components of the ~(113)Cd shielding tensor were determined from CP/MAS data. The σ_(33) element was found to be relatively independent of the Cd-N bond lengths while the opposite is true of σ_(11). 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.