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

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 .