Abstract

The iodinated analogue of imidazobenzodiazepine, imidazenil (1), has been prepared with the aim of radiolabelling it with iodine-123 and including it in a study to determine the role of benzodiazepine receptors in neurodegenerative diseases using single photon emission computer tomography (SPECT) imaging. A comparison of the bromo- and iodo-derivatives, as well as the conformational changes resulting from bromine–iodine substitution are described, and it is concluded that the substitution has no clear effect on the geometry. Crystal structures of (1) and iodoimidazenil (2) have been determined by X-ray diffraction methods and refined to R values of 0.059 (3817 F) and 0.048 (1318 F), respectively. The crystals of imidazenil are triclinic, space group P1^–,a 12.537(4), b 18.211(6), c 7.852(2) Å, α 91.07(2), β 106.26(2), γ 77.86(2)°, Z 4, and those of iodoimidazenil are monoclinic, space group P2₁/a, a 12.185(2), b 7.558(2), c 18.287(2) Å, β 95.23(1)°, Z 4.