Role and Effect of Anions in the Construction of Silver Complexes Based on a Pyridylimidazole Ligand with L-Type Coordination Vectors and Their Photoluminescence Properties

Abstract

Three anion-dependent Ag(I) coordination complexesspecifically, [Ag 2 (pyim) 2 (NO 3 ) 2 ] (1), {[Ag(pyim) 2 ]• ClO 4 •CH 3 OH•(H 2 O) 1.25 } n (2), and [Ag 4 (pyim) 4 ]•(CF 3 SO 3 ) 4 ( 3)were prepared by the reaction of the corresponding silver salts with a rigid ditopic N-terphenyl-substituted 2-(4-pyridyl)imidazole (pyim) ligand possessing an "L"-type coordination vector. Complex 1, in which the nitrate anion acts as a monodentate terminal ligand, exhibits a discrete cyclic dimer structure, whereas complex 2, incorporating a perchlorate anion with weak coordination ability, displays an anion-free one-dimensional (1D) looped chain structure resulting from the Ag sharing of consecutive cyclic dimers. When using a trifluoromethanesulfonate (triflate) as a counteranion with moderate affinity toward the metal center, the resulting complex 3 exhibits an unusual cyclic tetramer structure. In 3, the triflate anions act as bridges between adjacent cyclic tetramers via the weak interaction with the Ag(I) ions, yielding a parquet-like two-dimensional (2D) framework. All three complexes display violet-blue emission, with maxima ranging from 388 to 396 nm. Furthermore, in solution, complex 2 exhibits a substantial emission enhancement, resulting in an emission intensity nearly 2 orders of magnitude greater than those of both the free ligand and the two other Ag(I) complexes, 1 and 3. Counteranions possessing different abilities to coordinate to Ag(I) play important roles in the structural diversity and photoluminescence properties of 1−3.

Crystal structure of a one-dimensional looped-chain silver(I) coordination polymer:catena-poly[[silver(I)-bis{μ-4-[1-(5′-isopropyl-[1,1′:3′,1′′-terphenyl]-2′-yl)-1H-imidazol-2-yl]pyridine-κ2N:N′}] nitrate methanol monosolvate monohydrate]

“…1, the Ag I atom is coordinated by two pyridine N atoms and two imidazole N atoms from four individual i-pro-pyim ligands, giving rise to a highly distorted tetrahedral geometry with bond angles falling in the range of 100.33 (19)-122.76 (19) ( Table 1). The average Ag-N distance is 2.31 Å , similar to that found in the related perchlorate salt (Lee et al, 2016).…”

“…However, there are relatively few reports of the structures of metal complexes that exhibit coordination of pyridylimidazole (pyim) ligands with an L-type coordination sphere, which is similar to a phenylimidazole system. Recently, Ag I coordination polymers built from pyim ligands have attracted much attention due to their structural diversity and photoluminescence properties which have been shown to depend on the nature of the counter-anion (Lee et al, 2016). The structural topology of Ag I is quite sensitive to both the counter-anion and solvent molecules (Durá et al, 2014).…”

“…The coordination ISSN 2056-9890 polymer is obtained by addition of the ligand to AgNO 3 in methanol/acetonitrile. The title nitrate salt is closely related to the perchlorate salt (Lee et al, 2016).…”

“…The i-pro-pyim ligand was synthesized according to literature procedures (Lee et al, 2016). Crystals of the title compound were obtained by combining AgNO 3 with the i-pro-pyim ligand in a 1:1 molar ratio in a mixture of methanol/acetonitrile (1:1) and allowing the solution to evaporate slowly at room temperature.…”

Meso‐Helical Ag(I) Coordination Polymer Based on a Pyridylimidazole Ligand

“…On the basis of such consideration, we selected N ‐terphenyl‐substituted 2‐(4‐pyridyl)imidazole (pyim) with two orthogonal binding sites as a “L”‐type ligand. Our group has recently reported that the supramolecular motives, cyclic dimer and tetramer, and looped‐chains are generated by the control of counter‐anions possessing different coordination abilities in the reaction of pyim with several silver salts . Herein, we report a fascinating, infinite meso ‐helical Ag(I) coordination polymer based on “L”‐type pyim ligand (Scheme ).…”