Molecular metals normally require charge transfer between two different chemical species. We prepared crystals of [Ni(tmdt) 2 ] (tmdt, trimethylenetetrathiafulvalenedithiolate) and carried out crystal structure analyses and resistivity measurements. The analyses and measurements revealed that these single-component molecular crystals are metallic from room temperature down to 0.6 kelvin. Ab initio molecular orbital calculations suggested that π molecular orbitals form conduction bands. The compact molecular arrangement, intermolecular overlap integrals of the highest occupied and lowest unoccupied molecular orbitals, and tight-binding electronic band structure calculation revealed that [Ni(tmdt) 2 ] is a three-dimensional synthetic metal composed of planar molecules.

https://science.sciencemag.org/content/sci/291/5502/285.full.pdf

A Three-Dimensional Synthetic Metallic Crystal Composed of Single-Component Molecules

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.

What's new in stable radical chemistry?

Single-component molecular metals with extended-TTF dithiolate ligands.

http://lib.fibopt.ru/Articles/PAPER/Elsevier/CCRev-2007-251-1007.pdf

Stretching bonds in main group element compounds—Borderlines between biradicals and closed-shell species

This review describes recent advances in the development of thiazyl radicals, particularly dithiadiazolyl (RCNSSN) and dithiazolyl (RCSNSCR) as molecule-based materials. Particular emphasis is placed on their potential applications as molecular conductors, magnets and switchable materials and incorporates an overview of the structure–property relationships required in these molecular systems.

Thiazyl radicals: old materials for new molecular devices

The preparation and purification of the heterocyclic diradical benzo-1,2:4,5-bis(1,3,2-dithiazolyl) (BBDTA) is described. Crystals of BBDTA, grown by fractional sublimation at 120-180 °C/10-3 Torr, are monoclinic, space group P21/c, with a ) 4.144(2), b ) 9.0344(13), and c ) 10.7424(16) A,‚ ) 91.11(3)°, and Z ) 2. The crystal structure consists of discrete, unassociated molecules of BBDTA. The molecules form slipped stacks along the x direction, with the mean molecular plane making an angle of 32.4° to the x axis. The interplanar separation between consecutive molecules along the stacking direction is 3.49 A. The ESR spectrum of BBDTA is solvent dependent, displaying signals attributable to partially associated materials ( not exchange coupled) and to free diradical (exchange coupled). Ab initio molecular orbital calculations suggest a small (ca. 0.5 kcal/mol) separation between the triplet and singlet diradical states. Cyclic voltammetry on BBDTA and the related benzo-1,3,2-dithiazolyl BDTA, coupled with gas phase photoelectron studies on BDTA, establish that both compounds are strong electron donors. Magnetic susceptibility measurements show that BBDTA is essentially diamagnetic up to room temperature; variable temperature single-crystal conductivity measurements provide a band gap of 0.22 eV. The transport properties are discussed in the light of extended Huckel band structure calculations, which suggest a highly three-dimensional electronic structure for bulk BBDTA in the solid state.

https://pure.rug.nl/ws/files/3624920/1997JAmChemSocBarclaySupp.pdf

The heterocyclic diradical benzo-1,2:4,5-bis(1,3,2-dithiazolyl). electronic, molecular and solid state structure

Condensation of oxamidrazone with sulfur dichloride in acetonitrile affords 4,4‘-bis(1,2,3,5-dithiadiazolium) dichloride in moderate yield. Reduction of this salt with triphenylantimony yields the diradical 4,4‘-bis(1,2,3,5-dithiadiazolyl) [S2N2C−CN2S2], which has been isolated and characterized in the solid state as its dimer [S2N2C−CN2S2]2. The diradical is disjoint, and ab initio molecular orbital methods confirm a very small energy gap (<0.5 kcal/mol) between the triplet and diradical singlet states, regardless of the torsion angle about the central C−C bond. In accord with these theoretical predictions the ESR spectrum of the diradical consists (in CHCl3 at 273 K) of a simple five-line pattern (aN = 0.50 mT, g = 2.011), i.e., there is no observable exchange coupling between the two centers. In the solid state, the dimer [S2N2C−CN2S2]2 forms a slipped stack structure, with a mean intradimer S−S distance of 3.078 A and mean interdimer S- - -S contact of 3.761 A. Cosublimation of the diradical with iodi...

/pdf/preparation-and-characterization-of-the-disjoint-diradical-4-4dtz4muiu6.pdf

Preparation and Characterization of the Disjoint Diradical 4,4‘-Bis(1,2,3,5-dithiadiazolyl) [S2N2C−CN2S2] and Its Iodine Charge Transfer Salt [S2N2C−CN2S2][I]

The condensation of diaminobenzenedithiol with sulfur monochloride leads to the chloride salt of the radical cation of 3,6-dichlorobenzo(1,2-d:4,5-d')bis(1,2,3-dithiazole), dichloro-(BB-123-DTA)(Cl), which can be reduced to neutral dichloro-(BB-123-DTA) with triphenylantimony. A similar condensation with selenium tetrachloride leads, upon reduction, to the corresponding bis(1,2,3-thiaselenazole) dichloro-(BB-123-TSA). The crystal and molecular structures of both compounds have been determined by X-ray diffraction. Both compounds, which are formally antiaromatic 16﷿-systems, exhibit internal bond lengths consistent with a quinoid formulation. The radical cations of both rings have been characterized by ESR spectroscopy; for dichloro-(BB-123-DTA) + g ) 2.0114 and aN ) 0.201 mT, while for dichloro-(BB-123-TSA) + g ) 2.021 and aN ) 0.44 mT. Further oxidation of both rings affords the corresponding dications, both of which have been characterized crystallographically as their AlCl 4 - salts. The structural features of these compounds are consistent with those expected for dithiazolylium (or thiaselenazolylium) derivatives. The structure and redox chemistry of the benzo(1,2-d:4,5-d')bis(1,2,3-dithiazole) framework is discussed in the light of the results of ab initio calculations.

J.D. Goddard

Papers

The heterocyclic diradical benzo-1,2:4,5-bis(1,3,2-dithiazolyl). electronic, molecular and solid state structure

Preparation and Characterization of the Disjoint Diradical 4,4‘-Bis(1,2,3,5-dithiadiazolyl) [S2N2C−CN2S2] and Its Iodine Charge Transfer Salt [S2N2C−CN2S2][I]

Benzo-Bridged Bis(1,2,3-dithiazoles) and Their Selenium Analogues. Preparation, Molecular and Electronic Structures, and Redox Chemistry