Well-Designed Strategy To Construct Helical Silver(I) Coordination Polymers from Flexible Unsymmetrical Bis(pyridyl) Ligands: Syntheses, Structures, and Properties

In
this Article, self-assembly of AgX (X = NO3– and ClO4–) salts and four flexible
unsymmetrical bis­(pyridyl) ligands, namely, N-(pyridin-2-ylmethyl)­pyridin-3-amine
(L1), N-(pyridin-3-ylmethyl)­pyridin-2-amine
(L2), N-(pyridin-4-ylmethyl)­pyridin-2-amine
(L3), and N-(pyridin-4-ylmethyl)­pyridin-3-amine
(L4), results in the formation of eight helical silver­(I)
coordination polymers, [Ag­(L)­(NO3)]n [L = L1 (1), L2 (2), L3 (3), L4 (4)] and [Ag­(L)­(ClO4)]n [L = L1 (5), L2 (6), L3 (7), L4 (8)], which have been characterized
by elemental analysis, IR, TG, PL, and powder and single-crystal X-ray
diffraction. The alternating one-dimensional (1-D) left- and right-handed
helical chains are included in achiral complexes 1–3 and 5–8. By contrast, the
ligand L4 only alternately bridges Ag­(I) cation to form
the 1-D right-handed helical chain in complex 4. The
pitches of these helical chains locate in the range 5.694(5)–17.016(6)
Å. Meanwhile, the present four unsymmetrical bis­(pyridyl) ligands
in the eight complexes present diverse cis–trans and trans–trans conformation
and facilitate the construction of helical structures. Moreover, the
solid-state luminescent emission intensities of the perchlorate-containing
complexes are stronger than those of nitrate-containing complexes
at room temperature.