Carboxylic-substituted polychlorotriphenylmethyl radicals, new organic building-blocks to design nanoporous magnetic molecular materials

In this review, we will give a short overview of a new type of magnetic nanoporous molecular materials developed in our group, based on the use of open-shell organic polychlorotriphenylmethyl (PTM) radicals as building-blocks. First, from a geometrical point of view, PTMDC and PTMTC acidic radicals can be considered expanded versions of the isophtalic and trimesic acid molecules, respectively, where the benzene-1,3-diyl and benzene-1,3,5-triyl units has been replaced by an sp2 hybridized carbon atom decorated with two or three 4-substituted 2,3,5,6-tetrachlorophenyl rings. Therefore, according with their related trigonal symmetries and functionalities, PTMDC and PTMTC radicals are expected to yield similar open-frameworks structures than isophtalic and trimesic acid. Second, polychlorinated triphenylmethyl radicals have their central carbon atom, where most of the spin density is localized, sterically shielded by the six bulky chlorine atoms that increase astonishingly its lifetime and thermal and chemical stabilities. Furthermore, the intrinsic molecular bulkiness and rigidity of this family of radicals is also expected to prevent a close packing of molecular units in the solid state. And third, the monocarboxylic PTMMC radical has allowed to confirm the excellent conditions of PTM radicals to magnetically interact between them and with transition metal ions through the carboxylic groups. Indeed, a recently reported family of monomeric complexes using PTMMC radical has confirmed the feasibility of this type of carboxylic-substituted radicals to magnetically interact with metal ions (Fig. 1). Thus, in this review, we will focus our attention to the recent results on the use of carboxylic-substituted PTM radicals for the obtaining of the first examples of metal-organic and purely organic molecular radical-based materials with combined interesting porosity characteristics and magnetic properties.