Klaus Eichele: Publication Abstracts 1992 [ Go Home ]

Die Zahl der ueber das N-Atom koordinierten Thiocyanatoliganden ist nur eine aus einer ganzen Fuelle von Informationen, die dem ¹¹³Cd-Festkoerper- NMR-Spektrum von (NnPr₄)[Cd(SCN)₃] entnommen werden koennen. So scheint beispielsweise auch die Aufspaltung der gut aufgeloesten Multiplettsignale, die von direkten und indirekten ¹¹³Cd,¹⁴N-Kopplungen herruehrt, ein direktes Mass fuer die Cd-N-Abstaende zu sein. Loesungs- NMR-Spektren von Metallthiocyanaten liefern dagegen nur sehr wenige Strukturinformationen.

The number of the N-bound thiocyanato ligands is only a part of the wealth of information that can be extracted from the Cd-113 NMR spectrum of solid (NnPr₄)[Cd(SCN)₃]. For instance, the splitting in the well-resolved multiplet signals, which results from direct and indirect Cd-113, N-14 coupling appears to be a measure of the Cd-N distances. In contrast, NMR studies of metal thiocyanates in solution are rather uninformative.

The C-13 CP/MAS NMR spectrum of [(n-C₃H₇)₄][Cd(SCN)₃], indicates the presence of three nonequivalent thiocyanate ligands, in agreement with the results of a recent single-crystal X-ray diffraction study. Examination of the C-13 MAS line shapes allows direct measurement of the indirect spin-spin coupling constants, ¹J(N-14,C-13) = 16(1) Hz and ²J(Cd-111/113,C-13) = 75(5) Hz, for the unique N-bonded thiocyanate ligand. This is the first reported measurement of ¹J(N-14,C-13) and ²J(Cd-111/113,C-13) in the solid state. Possible reasons for the failure to observe ¹J(N-14,C-13) values in previous high-resolution C-13 CP/MAS NMR studies are summarized.

The P-31 chemical shift tensors of bis(phosphine) complexes of the type [M][Ph₂P-(CH₂)_n-PPh₂] ([M] = (OC)₄Mo, (OC)₄W, Cl₂Pt; n = 1-5) and of fac-(OC)₃Mo{PPh(CH₂CH₂PPh₂)₂] were determined by solid-state NMR techniques and correlated with structural features of the compounds. d(P-31), ¹J(M,P) and d(M) show a dependence on the ring size in the solution NMR spectra of the four- to six-membered chelates; for larger rings this dependence vanishes. A model for the orientation of the P-31 shift tensor principal components within the molecular frame is proposed. Each tensor component displays a different dependence on the ring size; the isotropic shift is dominated by the component perpendicular to the ring plane. Changes in this component are explained in terms of variations of the M-P-C angles. Generally speaking, the behavior of each of the tensor components must be regarded as a complex interplay of all six bond angles at phosphorus. The crystal structure of (OC)₄W[Ph₂P(CH₂)₄PPh₂] (2d) was determined by X-ray diffraction. Crystals of 2d are monoclinic, space group P2₁/n, a = 1202.8(1) pm, b = 1531.8(1) pm, c = 1654.1(2) pm, b = 104.72(1) deg, and Z = 4.

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