Syntheses, structural diversity and photo-physical properties of copper(I) and silver(I) coordination polymers based on the pyridine-4-amidoxime ligand

Three new complexes, [{Cu(L)I}2]n (1), [Ag(L)]n·nClO4 (2) and [{Ag(L)(CF3COO)}2]n (3), have been synthesised and characterized by different physico-chemical methods with the aim of exploring the ligating properties of pyridine-4-amidoxime (L). Single crystal X-ray structure analysis reveals that 1 is a 2D coordination polymer, while 2 and 3 are wavy 1D chains in spite of the same coordination mode adopted by the ligand. The crystal structures also show that the coordination geometry of the metals is different in each complex, being tetrahedral in 1, but distorted trigonal planar and distorted linear in 2 and 3, respectively. The asymmetric units of 1 and 3 consist of two independent metal centres and each is associated with a counter anion of the metal salt used, while the asymmetric unit of 2 is cationic in nature, the perchlorate anion being non-coordinated. Structural diversities are also evident as the 2D structure of 1 is stabilized by O–H⋯I interactions, while several classical and non-classical hydrogen bonds lead to 3D supra-molecular structures for complexes 2 and 3. The solid state fluorescence of L and of its complexes were studied revealing that both 1 and 2 show a broad emission band with a maxima at 525 and 522 nm, respectively, strongly red shifted when compared to the free ligand band (463 nm), while 3 is found surprisingly to be non-emissive.