The various preparative procedures described in the literature for ReOCl3(PPh3)2 were repeated. The standard methods were found to yield a yellow triclinic material ([Formula: see text] a = 11.793, b = 14.300, c = 16.422 Å, α = 64.04°, β = 84.31°, γ = 87.32°, R = 0.064). The unit cell contains three discrete monomeric molecules with the trans-bis(phosphine) configuration, one of which has its Cl-Re=O unit disordered over two opposite directions. Recrystallization in CH2Cl2 yielded crystals of the bright green monoclinic polymorph (C2/c, a = 24.347, b = 9.604, c = 15.666 Å, β = 116.77°, R = 0.025) containing the same monomeric molecule, but with a different conformation of the PPh3 ligands and a different packing pattern. These two polymorphs actually correspond to "isomers" 1 and 2 described by Johnson, Lock, and Wilkinson in 1964. Attempts to prepare their third "isomer" yielded powders containing ReOCl3(PPh3)2 (green polymorph) and ReNCl2(PPh3)2. The IR and 31P NMR spectra of these samples are discussed.
The bidirectional upstream element of the adenovirus-2 major late promoter binds a single monomeric molecule of the upstream factor.
