Solvent effects on 15N NMR coordination shifts

Area of Science:

• Inorganic Chemistry
• Nuclear Magnetic Resonance Spectroscopy
• Computational Chemistry

Background:

• Nitrogen-15 (15) NMR chemical shift is a key tool for characterizing complex structures.
• The influence of solvent on the nitrogen coordination shift (Δ(15)N(coord)) was previously considered negligible.

Purpose of the Study:

• To investigate the impact of the local environment, specifically solvent and substituent interplay, on Δ(15)N(coord).
• To demonstrate the strong solvent dependence of (15)N NMR chemical shifts in silver complexes.

Main Methods:

• Comparative study of silver(I)-bis(pyridine) and silver(I)-bis(pyridylethynyl)benzene complexes in CDCl(3) and CD(3)CN solutions.
• Density-Functional Theory (DFT) calculations at the B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) level to rationalize findings.

Main Results:

• Observed significant solvent-dependent variations in (15)N NMR chemical shifts, up to 40 ppm for the same complex.
• Demonstrated that solvent, substituents, and counter ions collectively influence Δ(15)N(coord).
• DFT calculations supported the observed experimental trends.

Conclusions:

• Interpretation of Δ(15)N(coord) requires consideration of solvent and counter ion effects.
• Cooperative effects are crucial for a comprehensive understanding of coordination shifts and silver complex structures in solution.
• Findings are likely general for various nitrogen donor ligand complexes used in organometallic chemistry.