Estimation for rotational barriers of unsymmetrical tert-amide-containing pyridine ligands and their silver(I) complexes

Abstract

Structures of silver(I) complexes with unsymmetrical tert-amide-containing pyridine ligand isomers (1a-1d) are reported. Because these ligands exist as s-cis and s-trans forms in solution, the ratios of s-cis and s-trans forms in solution and their rotational barriers were estimated by 1H NMR experiments. Despite the presence of s-cis and s-trans-form in solution, silver(I) complexes with these ligands were all s-trans form in the solid-state. Because of the semi-flexible properties of isomers (1a-1d), various ligand shapes showed the coordination networks depending on the direction of the pyridine nitrogen. For example, on the silver(I) triflate complexations, the tertiary amide incorporating two 4‑pyridyl units (1a) yields a wavy 2D coordination polymer. On the other hand, the complexation of 1b afforded double-stranded 1D coordination polymer. Furthermore, the complexations of 1c and 1d afforded 2D coordination polymer and cyclic dimer, respectively. The complexations of isomers (1a-1d) with AgBF4 instead of AgOTf were also investigated. As a result, the AgBF4 complexations of 1a, 1c, and 1d gave 1D, 2D, and 1D structures, respectively.