The perchlorotriphenylmethyl (PTM) radical

Abstract

In spite of the considerable understanding and development of perchlorotriphenylmethyl (PTM) radical derivatives, the preparation of crystals of the pure unsubstituted PTM radical, C19Cl15, suitable for single-crystal X-ray diffraction has remained a challenge since its discovery, and only two studies dealing with the crystal structure of the unsubstituted PTM radical have been published. In one study, the radical forms clathrates with aromatic solvents [Veciana, Carilla, Miravitlles & Molins (1987). J. Chem. Soc. Chem. Commun. pp. 812-814], and in the other the structure was determined ab initio from powder X-ray diffraction data [Rius, Miravitlles, Molins, Crespo & Veciana (1990). Mol. Cryst. Liq. Cryst. 187, 155-163]. We report here the preparation of PTM crystals for single-crystal X-ray diffraction and their resolution. The structure, which shows monoclinic symmetry (C2/c), revealed a nonsymmetric molecular propeller conformation (D3 symmetry) caused by the steric strain between the ortho-Cl atoms, which protect the central C atom (sp(2)-hybridization and major spin density) and give high chemical and thermal persistence to the PTM. The supramolecular structure of PTM shows short Cl...Cl intermolecular interactions and can be described in terms of layers formed by rows of molecules positioned in a head-to-tail manner along the c axis.

Self‐Assembled Architectures with Segregated Donor and Acceptor Units of a Dyad Based on a Monopyrrolo‐Annulated TTF–PTM Radical

“…These difference values go from 0.33–0.35 Å for 10 A and 10 B to 0.17 Å for 2 A and 2 B at 300 K; this demonstrates that the PTM radical unit in dyad 2 induces a higher electron‐withdrawing effect over the rest of the molecule, in contrast with what is observed in compound 10 . On the other hand, the average of the distance between the central C23 atom of PTM and the C20, C24, and C30 atoms is about 1.54 Å in 10 and 1.46 Å in 2 ; this shows a partial double‐bond character in 2 , which indicates weak delocalization of the unpaired electron into the aromatic rings, as reported for other PTM derivatives 44…”

“…These difference values go from 0.33-0.35 f or 10 A and 10 B to 0.17 f or 2A and 2B at 300 K; this demonstrates that the PTM radical unit in dyad 2 induces ah igher electron-withdrawing effect over the rest of the molecule, in contrast with what is observed in compound 10.O nt he other hand, the average of the distance between the central C23 atom of PTM and the C20, C24, and C30 atoms is about 1.54 i n10 and 1.46 i n2; this shows ap artial double-bond character in 2,w hich indicates weak delocalization of the unpaired electron into the aromatic rings, as reported forother PTM derivatives. [44] Molecules of radical dyad 2 are arranged as shown in Figure 7, formingr egular 1D chains of equivalent molecules (2A or 2B), in which the MPTTF subunits form ah erringbone structure along the b axis with short Cl···Cl contacts in the range of 3.30-3.49 a nd S···S short contacts of 3.95 and3 .90 for 2A and 2B,r espectively (see Ta ble S3 in the Supporting Information). However,t his supramolecular assembly is different over the a axis, where there is no overlap between the S atoms and stacking is governed by S···Cl and S···C(pyrrole) interactions of 3.52 and 3.45 , respectively,w itha lternating molecules of 2A and 2B (Figure 8a nd Figure S14 in the Supporting Information).…”

Structural control over spin localization in triarylmethyls

“…1 This discovery launched the eld of radical chemistry at the beginning of the twentieth century and, since then, more than hundred triarylmethyl (TAM) derivatives have been synthesized. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] All molecules in this class possess a main skeleton composed of three aryl rings bonded to a central carbon atom, where their unpaired electron mainly resides (Fig. 1).…”

A redox-active radical as an effective nanoelectronic component: stability and electrochemical tunnelling spectroscopy in ionic liquids

“…[15][16][17] The charge transport through self-assembled monolayers 18,19 and single-molecule junctions 20 incorporating PTM radicals have been studied before, but the different redox states (radical and anion) were not addressed. Since the structure of both components of the redox pair is almost identical, 21 the inner reorganization energy associated with the structural change upon reduction/oxidation is expected to be low. In addition, bulky redox systems are expected to show low outer-sphere reorganization energy associated with the surrounding solvent, and indeed their current enhancement efficiency in redox-active molecular junctions is typically high.…”