What's new in stable radical chemistry?

Abstract

Many kinds of radicals are stable enough to isolate, handle, and store without any special precautions. The diversity in molecular architectures of these stable radicals is sufficiently large that the common factors governing radical stability/persistence, geometric and electronic structure, association/dimerization preferences, and reactivity have generally not been well articulated or appreciated. This review provides a survey of the major classes of stable or persistent organic/organomain group radicals with a view to presenting a unified description of the interdependencies between radical molecular structure and properties.

Interface-engineered templates for molecular spin memory devices

“…Our calculations show that the distance between the phenalenyl rings in the magnetic molecule and the molecule above is ~3.26 Å, which is smaller than the sum of the van der Waals radii of the carbon atoms 11 . This suggests a weak chemical bonding of the molecular π-dimer.…”

Clotrimazole Scaffold as an Innovative Pharmacophore Towards Potent Antimalarial Agents: Design, Synthesis, and Biological and Structure–Activity Relationship Studies

“…Although the replacement of a phenyl ring by a piridyl ring in a triphenylmethyl radical does not change dramatically its stability, however, the pyridyl group delocalizes radicals less than the phenyl ring. 14 On these bases, to increase the ability to stabilize a radical intermediate and, consequently, the antimalarial activity, we planned to replace the 4-pyridyl by a 7-chloroquinolin-4-yl system (a pyridine with a fused 4-Cl benzo group at C2-C3), which stabilizes the radical by a higher π delocalization. Accordingly, the 7-Cl-quinoline derivative 4m, although lacking the favorable electron-withdrawing substituent on the phenyl ring (see paragraph (d), Halogen vs Methoxy Substituents at the Trityl System), was endowed with a higher antimalarial activity against both CQ-R and CQ-S strains than 4j, in perfect agreement with its electronic properties.…”

Synthesis, Structure and Solid State Properties of Cyclohexanemethylamine Substituted Phenalenyl Based Molecular Conductor

“…The radicals 2, 4 and 13 crystallize as weakly bound, paramagnetic π-dimers but the conductivities of these compounds (σ RT = 1.4 × 10 −6 S/cm (2), 0.4 × 10 −6 S/cm (4), and 0.5 ×10 −6 S/cm (13)) are much lower than those of 1 and 3, because of the orientation of the molecules in the crystal lattice [43,44]. The n-octyl (6) and cyclooctyl (10) radicals can be crystallized as both a σ-dimer and a π-dimer-these latter structures are weakly bound (paramagnetic, 6) and strongly bound (diamagnetic, 10) dimers; both compounds show low conductivity: σ RT = 1 × 10 −5 (6), and 1 × 10 −6 S/cm (10) [45][46][47]. …”

“…Phenalenyl (PLY), a polycyclic odd-alternant hydrocarbon with a planar D 3h symmetric π-electronic system, is one of the fundamental delocalized neutral radicals [9,10]. Because of its simple and highly symmetric structure, and its intriguing properties in solution and in the crystalline state, it has fascinated researchers for some time [6,7,11,12]. It was first proposed in 1975 that phenalenyl has the potential to serve as a building block for molecular conductors [13][14][15].…”

“…and phenalenyl based radical conductors have been the subject of number recent reviews [6][7][8]. Phenalenyl (PLY), a polycyclic odd-alternant hydrocarbon with a planar D 3h symmetric π-electronic system, is one of the fundamental delocalized neutral radicals [9,10].…”