Synthesis, structures and photoluminescence properties of silver(i) complexes with N,N′-di(pyrazin-2-yl)pyridine-2,6-diamine

Abstract

Four silver complexes with N,N′-di(pyrazin-2-yl)pyridine-2,6-diamine (H2dpzpda) as ligand, [Ag2(H2dpzpda)2](ClO4)2 (1), [Ag2(H2dpzpda)2(ClO4)2] (DMF)2 (2), [Ag2(H2dpzpda)2](CF3SO3)2 (3), and [Ag2(H2dpzpda)(DMF)4](PF6)2·DMF (4) have been synthesized and structurally characterized by elemental analyses, IR spectroscopy and single-crystal X-ray diffractometer methods. The single-crystal X-ray determination revealed that the molecular structures 1 and 3 are all cationic bimetallic supramolecular rectangles, [Ag2(H2dpzpda)2]2+, in which two H2dpzpda ligands adopt bis-monodentate bridging mode connecting two linearly coordinated silver(I) ions. For 2, adjacent rectangles are then mutually linked via the Ag⋯Ag interaction to form an infinite 1D chain. The structure of complex 4 can be best described as a 1D ladder-like infinite chain, which is constructed via two crystallographically independent Ag(I) ions connected by the H2dpzpda ligand with a tetra-monodentate bridging mode. The emission of 1 and 3 is ascribed to a intra-ligand-based π*–π transition, while the emission origin of 4 is likely arising from inter-ligand charge-transfer transition. The emission of complex 2 is attributed to a inter-ligand charge-transfer transition. Moreover, two-photon excitation emission (TPEF) and two-photon absorption cross section of complex 2 were measured from TPEF via confocal microscope and Z-scan methods, for which two-photon cross section in solid state was deduced to be 43.4 ± 2.2 GM (800 nm).