Silver coordination polymers with tri- and hexacyanoethyl-functionalized macrocyclic ligands

Abstract

Tri- and hexa-cyanoethyl functionalized 17- (L¹) and 42-membered (L²) macrocyclic compounds were obtained by [1 + 1] (for L¹) or [2 + 2] (for L²) cyclocondensation of the corresponding dialdehyde and diethylenetriamine, followed by hydrogenation by KBH₄ and subsequent cyano-functionalization with acrylonitrile. They react with silver nitrate, leading to the formation of [AgL¹](NO₃) (1) and of the metal–organic coordination polymers [Ag₂(NO₃)₂L¹]_n (2) and {[Ag₂L²](NO₃)₂}_n (3). The complexes were characterized by elemental analysis, ¹H NMR, ¹³C NMR, IR spectroscopies, and ESI-MS; moreover, L², 1, 2 and 3 were also characterized by single crystal X-ray diffraction. The metal cation in 1 is pentacoordinated with a N₃O₂ coordination environment; in 2, the metal cations display N₄O₂ octahedral and N₂O₃ square-pyramid coordination and in 3 they are in square-planar N₄ sites. In 1, the ligand acts as a pentadentate chelator, and in the other two cases, the ligands behave as octadentate chelators in a 1κ³N:κ²O,2κN,3κN,4κN (in 2) or 1κ³N,2κ³N,3κN,4κN fashion (in 3). The cyanoethyl strands of the ligands are directly involved in the formation of the 2D frameworks of 2 and 3, which in the former polymer can be viewed as a net composed of hexametallic 36-membered macrocyclic rings and in the latter generates extra hexametallic 58-membered cyclic sets that form zig-zag layers. The thermal analytical and electrochemical properties of these silver complexes were also studied.