Self-Assembly, Reorganization, and Photophysical Properties of Silver(I)−Schiff-Base Molecular Rectangle and Polymeric Array Species

A self-assembly of AgClO4 with a Schiff-base ligand N,N‘-bis(pyridin-2-ylmethylene)benzene-1,4-diamine (1) gave
a 1D zigzag polymeric array [{Ag2(C18H14N4)2}(ClO4)2(CH3CN)]n (3), while the self-assembly of AgClO4 with 3,3‘-dimethyl-N,N‘-bis(pyridin-2-ylmethylene)biphenyl-4,4‘-diamine (2) afforded the molecular rectangle [{Ag2(C26H22N4)2}(ClO4)2] (4). The structures of 3 and 4 were characterized by single-crystal X-ray diffraction analysis. Structural
data for 3 indicate that the Ag(I) ion is coordinated by two ligands of 1 in a distorted tetrahedral fashion thereby
leading to a 1D zigzag polymeric array. The zigzag chains are interdigitated with weak π−π stacking interactions.
The structure of 4 consists of a discrete molecular rectangle where the silver atom has a distorted square-planar
coordination with the pyridyl ligands and azomethine nitrogen atoms of 2. An intramolecular π−π interaction between
the phenyl rings of adjacent Schiff-base 2 functions to stabilize the rectangular architecture. The Ag(I)−Schiff-base
coordination polymer 3 is not stable in solution. The degradation and reorganization of 3 to form a [2 × 2] grid
architecture [{Ag4(C26H22N4)4}(ClO4)4] (3g) was supported in a FAB-MS study. The rectangular structure of 4 remains
intact in solution at ambient temperature. The complexes 3g and 4 exhibit unusual luminescence behavior in
solution at room temperature with significantly red-shifted emission in the visible region.