Two-Dimensional and Three-Dimensional Coordination Polymers of Hexakis(4-cyanophenyl)[3]radialene: The Role of Stoichiometry and Kinetics

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.