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).