ONE-DIMENSIONAL STACKING OF BIFUNCTIONAL DITHIAADIAZOLYL AND DISELENADIAZOLYL RADICALS - PREPARATION AND STRUCTURAL AND ELECTRONIC-PROPERTIES OF 1,3-[(E2N2C)C6H4(CN2E2)] (E = S, SE)

The preparation and solid-state characterization of the 1,3-phenylene-bridged bis(dithiadiazolyl) and bis(diselenadiazolyl) diradicals 1,3-[(E2N2C)C6H4(CN2E2)] (E = S, Se) are reported. The isomorphous crystals of 1,3-[(E2N2C)C6H4(CN2E2)] so obtained are tetragonal, space group I4(1)/a. Stacks of diradical molecules, linked vertically in a zigzag fashion through alternate ends by long E---E contacts (mean 3.140/3.284 angstrom for E = S/Se), are arranged in pinwheellike clusters about the 4(1) and 4BAR axes, producing complex patterns of interstack E---E contacts. Both compounds show the presence of spin defects in the lattice, and there is a very large enhancement in the paramagnetism of the sulfur compound at high temperatures. The selenium compound is a semiconductor, with a room temperature conductivity of 2 x 10(-4) S cm-1. Solid-state NMR experiments find enhanced relaxation times, which have their origin in the presence of a mobile paramagnetic defect. Extended Huckel band structure calculations show the materials to be semiconductors, with band gaps of about 1.0/0.8 eV for E = S/Se. Although the compounds adopt a columnar structure, the calculations indicate significant interactions between the stacks and the materials exhibit well-developed three dimensionality. The enhanced paramagnetism in the sulfur compound is attributed to the presence of thermally generated phase kinks in the lattice, whereas the selenium compound is classified as an intrinsic semiconductor.