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, [Ag2(pyim)2(NO3)2] (1), {[Ag(pyim)2]·ClO4·CH3OH·(H2O)1.25}n (2), and [Ag4(pyim)4]·(CF3SO3)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. [ABSTRACT FROM AUTHOR]