Syntheses, structures and photoluminescent properties of silver(I) complexes with in situ generated hexahydropyrimidine derivatives

Two new linear and V-shaped tetradentate ligands, namely 1,4-bis(2-hexahydropyrimidyl)benzene (L) and 1,3-bis(2-hexahydropyrimidyl)benzene (L′), and their silver(I) complexes, [Ag2L(μ-ONO2)](NO3) · 2H2O (1), [Ag2L(μ-pn)](NO3)2 (2), [Ag2L(μ-pn)](ClO4)2 (3) and [Ag4L′2(H2O)](NO3)4 · 5H2O (4) (pn=1,3-diaminopropane) have been synthesized in situ and structurally characterized by single-crystal X-ray diffraction. 1 and 2 were obtained from the same reaction solution but different crystallization conditions. 1 is an one-dimensional chain featuring cuboid tetranuclear silver(I) units interconnected through monoatomic nitrate bridges. Both 2 and 3 are ribbon-like helical compounds in which each L ligand acts in a tetradentate bridging mode to interconnect four metal atoms, and each pn ligand functions in a bidentate bridging mode to link a pair of metal atoms. 4 shows a truncated square-pyramidal tetranuclear motif arose by the V-shaped L′ ligand. Close Ag⋯Ag separations (2.901–2.939 Å) assisted by bis(hexahydropyrimidine) bridges were observed in 1 and 4, indicating metal–metal interactions. Photoluminescence of 1–4 has also been observed in the solid state and solution at room temperature and low temperature, respectively.