Solvent effects on 15N NMR coordination shifts

¹⁵N NMR chemical shift became a broadly utilized tool for characterization of complex structures and comparison of their properties. Despite the lack of systematic studies, the influence of solvent on the nitrogen coordination shift, Δ¹⁵N_coord, was hitherto claimed to be negligible. Herein, we report the dramatic impact of the local environment and in particular that of the interplay between solvent and substituents on Δ¹⁵N_coord. The comparative study of CDCl₃ and CD₃CN solutions of silver(I)‐bis(pyridine) and silver(I)‐bis(pyridylethynyl)benzene complexes revealed the strong solvent dependence of their ¹⁵N NMR chemical shift, with a solvent dependent variation of up to 40 ppm for one and the same complex. The primary influence of the effect of substituent and counter ion on the ¹⁵N NMR chemical shifts is rationalized by corroborating Density‐Functional Theory (nor discrete Fourier transform) calculations on the B3LYP/6–311 + G(2d,p)//B3LYP/6–31G(d) level. Cooperative effects have to be taken into account for a comprehensive description of the coordination shift and thus the structure of silver complexes in solution. Our results demonstrate that interpretation of Δ¹⁵N_coord in terms of coordination strength must always consider the solvent and counter ion. The comparable magnitude of Δ¹⁵N_coord for reported transition metal complexes makes the principal findings most likely general for a broad scale of complexes of nitrogen donor ligands, which are in frequent use in modern organometallic chemistry. Copyright © 2012 John Wiley & Sons, Ltd.