Iodine Substituted Tetrathiafulvalene Radical Cation Salts with [M(isoq)₂(NCS)₄]^- Anions where M = Cr^III, Ga^III:  Role of I···S and S···S Contacts on Structural and Magnetic Properties

The preparation, crystal structures, extended Hückel theory band structure, and density functional theory (DFT) calculations and conducting and magnetic properties of seven new charge-transfer salts, formulated as (D)₂[M^III(isoq)₂(NCS)₄], where D = DIET (diiodo(ethylenedithio)tetrathiafulvalene), DIETS (diiodo(ethylenedithio)diselenadithiafulvalene), M = Cr, Ga, and isoq = isoquinoline, are reported. For each donor two different phases called a and b were obtained. Crystal data for (DIET)₂[Cr(isoq)₂(NCS)₄] (1) are as follows: phase a, triclinic P1̄, a = 9.8645(6) Å, b = 10.3255(8) Å, c = 13.7712(8) Å, α = 87.905(5)°, β = 75.981(5)°, γ = 80.712(2)°; phase b, triclinic P1̄, a = 10.6760(5) Å, b = 11.3000(6) Å, c = 11.3930(9) Å, α = 101.256(2)°, β = 96.755(2)°, γ = 97.342(5)°. All compounds exhibit semiconductive behavior with room-temperature resistivity ranging from 2 × 10³ to 5 × 10⁴ Ω cm. Donors in the mixed-valence-state form dimers. They are connected to anions through very short I···S contacts (S2···I2 = 3.248(2) Å for 1a). The magnetic measurements and spin density DFT calculations revealed that iodine atoms are good structural agents but are poor magnetic mediators to promote superexchange interactions between the donors and the inorganic anions. Our analyses reveal also that in these charge-transfer salts the magnetic interactions between spin carriers are mainly ensured by short intermolecular S···S contacts.