Synthesis, Structure, and Physical Properties of a Partial π‐Stacked Phenalenyl‐Based Neutral Radical Molecular Conductor

Abstract

We report the synthesis, crystallization, and solid-state characterization of the 3,7-ethoxy-substituted spirobiphenalenyl-boron neutral radical 22. The radical is distinguished by its low disproportionation energy and one-dimensional structure. We show that our strategy of substitution of OEt group at the active positions of the phenalenyl units changes the crystal packing from its previously known OMe analogue and the solid-state properties are dictated by the partial π-stack structure and the oxygen atoms at the 3,7-positions and can be best rationalized in terms of the resonating valence bond model. Magnetic susceptibility measurements show that in the solid state the radical remains paramagnetic but there is significant spin-spin interaction between the molecules. Band structure calculations reflect efficient overlap between the molecules along the π stack and show evidence of interactions between the spin-bearing oxygen atoms. The room temperature electrical conductivity (σ(RT)=2.0×10(-2) S cm(-1)) of 22 is higher than that observed in previously known one-dimensional phenalenyl radicals.

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

“…An ORTEP drawing of 11 with atom numbering scheme is shown in Figure 2. The structure is similar to the previously reported benzyl analog 7 [48], but different from the recently reported low E 2−1 radical 22 [53]. A comparison of relevant crystal parameters pertaining to compounds 7 and 11 (Table 1) reveals that the volume of the unit cell for the radical 11 is higher (3048 Å 3 ) than that of the radical 7 (2784 Å 3 ).…”

“…It may be noted that the low E 2−1 radical 22 adopts similar kind of π-step structure where the molecules pack in a continuous array of partially π-stacked neighboring PLY units along b-axis and similar to the radicals 7 and 11 there are no significant inter-molecular C· · · C interactions in 22 (less than 3.4 Å) along other axes. The extended Hückel theory (EHT) predicts that the radical (22) has a band dispersion more than 0.5 eV along the packing axis and the room temperature conductivity is 10 times higher than that of radical 7 and 11 [53]. The combination of electrical and magnetic properties observed for 11 is typical of a Mott insulator [57][58][59], in which the unpaired spins are localized due to dominance of the Coulomb interaction U over the transfer integral t. Thus the magnetic data are well described in terms of a one dimensional S = 1/2 antiferromagnetic Heisenberg chain with J = 6.3 cm −1 ( Figure 7) [55].…”

Pressure-Induced Conductivity in a Neutral Nonplanar Spin-Localized Radical

“…[6][7] In view of the importance of obtaining crystals of singlecomponent molecular conductors, the use of neutral organic radicals as building blocks for molecular conductors has appeared as alternative due to the possibility that the unpaired electrons can serve as charge carriers without the need of a previous doping process. 8 Phenalenyl-based radicals, developed by Haddon,[9][10][11][12][13][14][15][16][17] and thiazolyl-based radicals, by Oakley, [18][19][20][21][22] are good examples of such materials. The solid state electronic structure of this kind of crystals is best described in terms of the half-filled band (f = 1/2) Mott-Hubbard model, with one electron associated with each radical site.…”

Synthesis, structure and solid state properties of benzannulated phenalenyl based neutral radical conductor

“…Θ = −5 K indicating antiferromagnetic interaction. The low fraction of Curie spins per molecule indicates that the paramagnetism in 19 is partially quenched because of the dimeric structure of the radical that has a π–π separation 0.340 nm; similar behavior is observed in the alkoxy substituted phenalenyl radicals, and the ethyl and butyl radicals ( 1 and 3 ) that show variable spin counts over the whole temperature range . Below 50 K, the fraction of unpaired spins further decreases (Fig.…”