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

초록

Three anion-dependent Ag(I) coordination complexes-specifically, [Ag-2(pyim)(2)(NO3)(2)] (1), {[Ag(pyim)(2)]ClO4 center dot CH3OH center dot(H2O)(1.25)}(n) (2), and [Ag-4(pyim)(4)]center dot(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.

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