Two-dimensional and three-dimensional coordination polymers of hexakis (4-cyanophenyl)[3] radialene: the role of stoichiometry and kinetics

Abstract

Hexakis(4-cyanophenyl)[3]radialene (1) is a hexadentate ligand that has previously been shown to form isomorphous honeycomb two-dimensional (2-D) coordination polymers {[Ag(1)](X)·2(CH3NO2)}n (X = ClO4, 2a; X = PF6, 2b) upon reaction with AgClO4 and AgPF6. Within these coordination polymers, close contacts were observed between the anions and the electron-deficient [3]radialene core. Here the synthesis and characterization of four new coordination polymers of 1 and copper(I), {[Cu2(1)2](X)2·Y(CH3NO2)}n (X = BF4, Y = 20, 4a; X = PF6, Y = 14, 4b) and {[Cu(1)](X)·2(CH3NO2)}n (X = BF4, 5a; X = PF6, 5b), are reported, along with two further examples of the (6,3) network {[Ag(1)](X)·2(CH3NO2)}n (X = BF4, 2c; X = SbF6, 2d), and an 8-fold interpenetrated (10,3)-b net formed from 1 and AgClO4, {[Ag3(1)](ClO4)3·CH3NO2}n (3). Coordination polymers 2a–2d were synthesized using low ratios of ligand to metal, 1:1 to 1:3, whereas other examples described herein (compounds 3, 4, and 5) were obtained via the use of a considerably higher ligand-to-metal salt ratio, in the range of 1:6 to 1:18. Reaction of 1 with [Cu(CH3CN)4]BF4 and [Cu(CH3CN)4]PF6 gave isostructural coordination polymers. In each experiment, a three-dimensional (3-D) network with a (4.62)(42.6)(43.66.86) topology (4a and 4b) formed first, while a honeycomb two-dimensional (2-D) coordination polymer, with a fully cross-linked bilayer (5a and 5b) crystallized second. Unlike the case for the Ag(I) coordination polymers, the rate of crystallization rather than the stoichiometry of the reactions dictated the structure of the final product for the Cu(I) compounds. The presence of radialene–anion interactions within these coordination polymers is also discussed, with anion-π interactions being observed to be of lesser significance relative to weak C–H···anion hydrogen bonding.