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Solvent effects on 15N NMR coordination shifts

Artikel i vetenskaplig tidskrift
Författare Roland Kleinmaier
Sven Arenz
Alavi Karim
Anna-Carin Carlsson
Mate Erdelyi
Publicerad i Magnetic resonance in chemistry : MRC
Volym 51
Nummer/häfte 1
Sidor 46-53
ISSN 1097-458X
Publiceringsår 2013
Publicerad vid Svenskt NMR-centrum vid Göteborgs universitet
Institutionen för kemi och molekylärbiologi
Sidor 46-53
Språk en
Länkar dx.doi.org/10.1002/mrc.3907
Ämnesord Fourier Analysis, Magnetic Resonance Spectroscopy, methods, Nitrogen Isotopes, Solvents, chemistry
Ämneskategorier Kemi, Molekylärbiologi

Sammanfattning

(15)N 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, Δ(15)N(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 Δ(15)N(coord). The comparative study of CDCl(3) and CD(3)CN solutions of silver(I)-bis(pyridine) and silver(I)-bis(pyridylethynyl)benzene complexes revealed the strong solvent dependence of their (15)N 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 (15)N 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 Δ(15)N(coord) in terms of coordination strength must always consider the solvent and counter ion. The comparable magnitude of Δ(15)N(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.

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