As part of our studies of ligands containing an electron-deficient [3]-radialene core we discovered that the hexadentate ligand hexa(4-cyanophenyl)[3]-radialene 1 forms 6,3-connected 2-D coordination polymers on reaction with silver(I). Compounds {[Ag(1)](PF 6 ) · 2(CH 3 NO 2 )} n 2 and {[Ag(1)](ClO 4 ) · 2(CH 3 NO 2 )} n 3, which are the first coordination polymers of 1, readily crystallize from solutions of the silver salt and 1 in noncoordinating nitromethane solvent and were characterized by X-ray crystallography. In these structures the ligand is hypodentate, coordinating only through four nitrile N-donors to act as a 3-connecting center. The distorted tetrahedral silver also acts as a 3-connecting center. In the extended structure the anions lie in pockets above and below the [3]-radialene core of the ligands, forming moderate and weak hydrogen bonds with four different molecules of 1. The anions are in close proximity to the electron-deficient [3]-radialene core of 1, forming weak anion-π interactions.

SummaryThe syntheses of three new [3]radialenes – hexakis(3,5-dimethylpyrazolyl)-, hexakis(3-cyanophenyl)-, and hexakis(3,4-dicyanophenyl)[3]radialene (1–3) – are reported. Compound 3 is obtained in five steps with an excellent yield of 76% in the key step. Compared to that, the respective steps of the syntheses of 1 and 2 result in lower yields. All compounds adopt a double bladed propeller conformation in solution. Compound 3 is considerably more electron deficient than previously reported hexaaryl[3]radialenes, with reduction potentials of −0.06 and −0.45 V in CH2Cl2. The compounds mostly display red fluorescence with large Stokes shifts.

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(CH 3 NO 2 )} n (X = ClO 4 , 2a; X = PF 6 , 2b) upon reaction with AgClO 4 and AgPF 6 . 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), {[Cu 2 (1) 2 ](X) 2 •Y(CH 3 NO 2 )} n (X = BF 4 , Y = 20, 4a; X = PF 6 , Y = 14, 4b) and {[Cu(1)](X)•2(CH 3 NO 2 )} n (X = BF 4 , 5a; X = PF 6 , 5b), are reported, along with two further examples of the (6,3) network {[Ag(1)](X)•2(CH 3 NO 2 )} n (X = BF 4 , 2c; X = SbF 6 , 2d), and an 8-fold interpenetrated (10,3)-b net formed from 1 and AgClO 4 , {[Ag 3 (1)](ClO 4 ) 3 •CH 3 NO 2 } 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(CH 3 CN) 4 ]BF 4 and [Cu(CH 3 CN) 4 ]PF 6 gave isostructural coordination polymers. In each experiment, a three-dimensional (3-D) network with a (4.6 2 )(4 2 .6)(4 3 .6 6 .8 6 ) 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.

Coordination polymers and discrete metallo-supramolecular assemblies of hexaaryl[3]radialene compounds exhibit intriguing structures with short anion to π-centroid distances in the solid-state. Furthermore, these [3]radialene compounds display useful photophysical and electrochemical properties that make them ideal as potential platforms for anion receptors. In this study, hexafluoro[3]radialene was optimized to the MP2/aug-cc-pVTZ level of theory, and its complexes with halide anions were optimized to HF/6-31G++(d,p), MP2/6-31G++(d,p), M06-2X/6-31G++(d,p), and M06-2X/6-311G++(d,p) levels of theory. Hexafluoro[3]radialene was shown to have properties (large positive Qzz and areas of positive electrostatic surface potential) comparable to other compounds that show anion-π interactions. The interaction energies of complexes of hexafluoro[3]radialene with halide anions were calculated and found to be favorable and equivalent to those of fluorinated aromatic compounds. A series of synthetically accessible hexaaryl[3]radialenes were optimized to HF/6-31G++(d,p) theory and their complexes with halides optimized to the M06-2X/6-31G++(d,p) level of theory. The calculated properties of the electron-deficient hexaaryl[3]radialenes also show large positive Qzz quadrupole moments and two areas of positive potential; at the [3]radialene core and the acidic aryl hydrogen atoms. The interaction energies of the complexes of hexaaryl[3]radialenes and halide anions were found to follow the trend F(-) > Cl(-) ≈ Br(-) and correlate with the electron-deficient nature of the [3]radialene. Close contacts were observed between the anion and the radialene core and the aryl hydrogen atoms, suggesting a combination of anion-π and hydrogen bonding is important. Mass spectrometry was used to experimentally observe the complexes of a number of hexaaryl[3]radialenes with F(-), Cl(-), and Br(-) predicted computationally. Anion-[3]radialene complexes were successfully detected, and the stability of the complexes in tandem MS/MS experiments was found to support the computational results.