Crystal Structures of Tetrabromoethylene and of 1:1 Pyrazine Adducts of Tetrabromo- resp. Tetraiodoethylene.

The crystal structure of 2-amino-3-chloropyrazine, C4H2N2ClNH2

“…Cromer (1957) observed a symmetrical lengthening of the ring C-C separations to 1.43 A in tetramethylpyrazine. Monosubstitution in pyrazine-2-carboxyamide (Takaki, Sasada & Watanabe, 1960), complex formation between AgNO3 and pyrazine (Vranka & Amma, 1966), and the formation of adducts of pyrazine with tetrabromo-and tetra-iodoethylene (Dahl & Hassel, 1968), do not change the C-C distance from that of pyrazine.…”

N6,N6-Dimethyladenine–tetraiodoethene (2/1)

“…In these chains the molecules are held together by N9--H9...N3 hydrogen bonds between two N6,N6-dimethyladenine mol-ecules situated around a centre of symmetry, and by N...I interactions, where two I atoms of a tetraiodoethene molecule are bonded to the N7 atoms of two N6,N6-dime~yladenine molecules. The N...I distance is 3.173 (4)A, which is 0.194,~, longer than in a similar complex between pyrazine and tetraiodoethene (Dahl & Hassel, 1968), and the angle N...I---C is 172.6 (1) °. In the complex between 9-cyclohexyladenine and iodine there are monomeric units, and I is bonded to N 1 with a nearly linear N...I--I arrangement and an N...I distance of 2.520,4,.…”

trans-2,3-Diiodo-2-butene-1,4-diol

“…[symmetry code: (i) 23--x, 3 _ y, -~ A search in the Cambridge Structural Database (Allen & Keunard, 1993) for diiodated double/aromatic bonds (no disorder, R _< 0.10, atom coordinates reported) revealed a total of 15 structures, of which only two have an iodinated non-cyclic double bond, namely, tetraiodoethylene (Haywood & Shirley, 1977) 9nd a pyrazinetetraiodoethylene complex (Dahl & Hassel, 1968). The present structure thus presents the first diiodinated noncyclic double bond.…”