title: Phenalenyl-based neutral radical molecular conductors: substituent effects on solid-state structures and properties.
abstract: We report the preparation, crystallization, and solid-state characterization of cycloheptyl and cyclooctyl-substituted spirobiphenalenyl radicals and the corresponding sigma-dimer of the cyclooctyl derivative. The crystal structure shows that the cycloheptyl radical (9) is monomeric in the solid state, with the molecules packed in an unusual one-dimensional (1-D) fashion that we refer to as a pi-chain structure, whereas the cyclooctyl variant exists both as pi-dimer 10 and sigma-dimer 10d. The neutral radical 9 shows the temperature-independent Pauli paramagnetism characteristic of a metal with a magnetic susceptibility, chip approximately 4.5x10(-4) emu/mol and is assigned a resonating valence bond (RVB) ground state. We highlight the relationship between the magnetic properties of the Heisenberg antiferromagnet and the RVB ground state in 1-D and further elucidate the electronic structure of this new class of compounds. Magnetic susceptibility measurements show that 10 is a diamagnetic pi-dimer, whereas 10d is a diamagnetic sigma-dimer. Extended Hückel calculations for 9 indicate that the solid is a one-dimensional organic metal with a bandwidth of about 0.4 eV. Pressed pellet conductivity measurements indicate values of sigmaRT=1.5x10(-3) S/cm for compound 9 and sigmaRT=1.0x10(-6) S/cm for compound 10. The structural results and transport properties are discussed in the light of extended Hückel theory band structure calculations and DFT investigations of the electronic structure of related compounds.
authors.affiliation: Department of Chemistry, University of California, Riverside, California 92521-0403, USA.
authors.forename: Sushanta K
authors.initials: SK
authors.lastname: Pal
authors.forename: Mikhail E
authors.initials: ME
authors.lastname: Itkis
authors.forename: Fook S
authors.initials: FS
authors.lastname: Tham
authors.forename: Robert W
authors.initials: RW
authors.lastname: Reed
authors.forename: Richard T
authors.initials: RT
authors.lastname: Oakley
authors.forename: Bruno
authors.initials: B
authors.lastname: Donnadieu
authors.forename: Robert C
authors.initials: RC
authors.lastname: Haddon