Polymorphism of 1,3-Phenylene Bis(diselenadiazolyl). Solid-State Structural and Electronic Properties of β-1,3-[(Se₂N₂C)C₆H₄(CN₂Se₂)]

The solid-state characterization of a second or β-phase of the 1,3-phenylene-bridged diselenadiazolyl diradical 1,3-[(Se₂N₂C)C₆H₄(CN₂Se₂)] is reported. Crystals of this β-phase are monoclinic, space group P2₁/n, with a = 9.108 (6), b = 15.233 (13), c = 16.110 (5) Å, β = 103.37 (5)°, Z = 8. The crystal structure consists of chain-like arrays of discrete dimers (4 per unit cell), although one intradimer Se-Se linkage is notably longer (3.411 Å) than the other three (3.125, 3.196, 3.204 Å). The dimer units lie in chains that are linked by a complex three-dimensional array of Se-Se contacts. Variable-temperature single-crystal conductivity measurements on this phase indicate a band gap of 0.77 eV. Consistent with the conductivity measurements, extended Hückel band structure calculations suggest a relatively isotropic electronic structure.