Insight into the structure of silver cyanide from 13C and 15N solid-state NMR spectroscopy

The structure of silver cyanide has been investigated by solid-state multinuclear magnetic resonance spectroscopy. Carbon-13 and nitrogen-15 NMR spectra of magic-angle-spinning (MAS) and stationary powder samples of isotopically enriched (AgCN)-C-13, (AgCN)-C-13-N-15, and (AgCN)-N-15 have been acquired at the external applied magnetic field strengths 4.7, 7.05, and 9.4 T. Axially symmetric carbon and nitrogen chemical shift (CS) tensors provide evidence for linearity of the polymeric (-Ag-CN-)(n) chains. A two-site model is required to successfully simulate the C-13 MAS NMR line shape, which is dominated by indirect nuclear spin-spin coupling between Ag-109/107 and C-13 nuclei. In combination with relativistic zeroth-order regular approximation density functional theory (ZORA-DFT) calculations on model AgCN fragments, the C-13 MAS NMR results show that 30 +/- 10% of the silver sites are disordered, that is, either -NC-Ag-CN- or -CN-Ag-NC-, and 70 10% of the silver sites are ordered, that is, -NC-Ag-NC-. Effective dipolar coupling data extracted from C-13 NMR spectra of stationary samples allow an upper limit of 1.194 Angstrom to be placed on the carbon-nitrogen internuclear distance. After incorporation of the effects of anisotropic indirect nuclear spin-spin coupling and motional averaging on the NMR-derived distance, a corrected value of r(CN) = 1.16 +/- 0.03 Angstrom is obtained. This work provides an example of the type of information which may be obtained from solid-state NMR studies of disordered materials and how such information may complement that available from diffraction studies.