Unprecedented 3D Nanoporous Magnetic Material Formed by C-H---F Interactions Between a Planar Pd(II)-Phenoxyl Radical Cationic Complexes and SbF6 Anions

Laurent Benisvy, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Galina Zats, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Ohad Fleker, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Ronit Lavi, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Yossi Gofer, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Maylis Orio, Laboratoire de Spectrochimie Infrarouge et Raman, Lille University, Villeneuve d'Ascq , France
Dmitry Yufit, Chemistry, Durham University, Durham, UK
Galina Romanenko, Interantional Tomography Center, Novossibirsk University, Novossibirsk, Russia
Victor Ovcharenko, Interantional Tomography Center, Novossibirsk University, Novossibirsk, Russia
Elena Benisvy-Aharonovich, Chemistry, Bar-Ilan University, Ramat Gan, Israel

In the last two decades, inspired by the unique Cu(II)-Tyrosyl radical moiety at the active site of Galactose oxidase (GO)¹, [A fungal enzyme that catalyse the two-electrons oxidation of a wide variety of primiray alcohols to their corresponding aldehydes]; chemists have joined efforts to synthesise and characterise persistent transition metal - phenoxyl radical complexes.²  Whist the reactivity of phenoxyl radical complexes is crucial for catalysis, their limited stability consitute a major drawback to metal-based magnetic materials. Indeed, persistent phenoxyl radical complexes are scarce and only a few have been isolated and crystallographically characterised. In a continous search for a suitable ligand framework capable of sustaining a phenoxyl radical state, we have recently designed a suitably protected N,O-phenol-pyrazole pro-ligand (LH) that has allowed stable Cu(II) and Ni(II) phenoxyl radical complexes to be isolated.³ Herein, we report, using the LH, the synthesis and characterisation of the neutral square planar palladium(II) complex, PdL₂ (1), together with the product of its one-electron oxidation with Ag[SbF₆] (1[SbF₆]). Our combined spectroscopic, and theoretical studies clearly indicate that the cation 1⁺ consists of a Pd(II)-phenoxyl radical cation in which the unpaired electron is fully delocalised over the two phenoxyl rings. Most remarkably, the X-ray structure of 1[SbF₆] displays an unprecedented 3D nano-porous structure, that appears to be formed by the supramolecular assembly of helixes formed through C-H---F close contacts between the planar cations 1⁺ and the SbF₆ anions. Such porous material is magnetically active and displays a high surface area that is further illustrated by HR-SEM images.

To the best of our knowledge this is the first example of a nanopourous metal-radical based  material formed by non-coordinative interactions.

References:

1. J. W. Wittaker, Chem. Rev., 2003, 103, 2347.

2. C. T. Lyons, T. D. P. Stack, Coord. Chem. Rev., 2013, 257, 528.

3. (a) G. Zats, L. Benisvy et al., Dalton Trans., 2011, 40, 10889; (b) Dalton. Trans., 2012, 41, 47.