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 (F 4 DIB), and 1,4-diiodooctafluorobutane (F 8 DIBut). The crystal structures for the new donor, 2, as well as for six complexes, 1 ·TIE, 1 ·F 4 DIB, 2 ·TIE, 2 ·F 4 DIB, 3 ·(F 4 DIB) 2, and 3 2 · (F 8 DIBut) 2, are reported. Extended chain structures consisting of donor and acceptor molecules are observed in all cases, except that of 3 2 ·(F 8 DIBut) 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 ·F 4 DIB displays an unusual “crosshatched” pattern with each acceptor directly above the diacetylene moiety of another donor along the b -axis. In addition to 1 ·F 4 DIB, 3 2 ·(F 8 DIBut) 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 F 4 DIB 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.