A multinuclear magnetic resonance study of crystalline tripotassium tetracyanocuprate

Direct NMR observation of copper-63/65 nuclei in solid K3Cu(CN)(4) provides the first experimental example of anisotropic copper chemical shielding. A xially symmetric by virtue of the space group symmetry, the shielding tenso r spans 42 ppm, with the greatest shielding when the unique axis is perpend icular to the applied magnetic field. The nuclear quadrupole coupling const ant is also appreciable, C-Q(Cu-63) = -1.125 MHz, reflecting a deviation of the Cu(CN)(4)(3-) anion from pure tetrahedral symmetry. Spin-spin coupling to C-13 nuclei in an isotopically enriched sample is quantified by line-sh ape simulations of both C-13 and Cu-63/65 magic-angle spinning (MAS) NMR sp ectra to be 300 Hz. It is shown that this information is also directly avai lable by 63/65Cu triple-quantum (3Q) MAS NMR. The relative merits of these three approaches to characterizing spin-spin couplings involving half-integ er quadrupolar nuclei are discussed. Chemical shielding tensors for nitroge n-15 and carbon-13 are obtained from NMR spectra of nonspinning samples, an d are compared to those of tetrahedral group 12 tetracyanometallates. Final ly, (2)J(Cu-63/65,N-15) detected in N-15 MAS experiments are found to be 19 and 20 Hz for the two crystallographically distinct cyanide ligands.