Crystal Engineering through Halogen Bonding. 2. Complexes of Diacetylene-Linked Heterocycles with Organic Iodides

The bis(aryl)diacetylenes 1,4-bis(3-quinolyl)-1,3-butadiyne (1), 1,4-bis(4-isoquinolyl)-1,3-butadiyne (2),
and 1,4-bis(3-pyridyl)-1,3-butadiyne (3) form strongly halogen bonded complexes with organic iodides, including
tetraiodoethylene (TIE), 1,4-diiodotetrafluorobenzene (F4DIB), and 1,4-diiodooctafluorobutane (F8DIBut). The crystal
structures for the new donor, 2, as well as for six complexes, 1·TIE, 1·F4DIB, 2·TIE, 2·F4DIB, 3·(F4DIB)2, and 32·
(F8DIBut)2, are reported. Extended chain structures consisting of donor and acceptor molecules are observed in all
cases, except that of 32·(F8DIBut)2, which forms a molecular adduct. In most cases, the complexes segregate into
columns of donors and acceptors, as is typical for this class of complexes. However, 1·F4DIB displays an unusual
“crosshatched” pattern with each acceptor directly above the diacetylene moiety of another donor along the b-axis.
In addition to 1·F4DIB, 32·(F8DIBut)2 also exhibits packing that does not consist of segregated stacks (i.e., the acceptor
in the chain sits on top of one end of the donor and the uncomplexed F4DIB sits on top of the other end). Neither
diacetylene 2, nor any of the complexes, pack in a manner that would allow for topotactic polymerization of the
diacetylene moiety.