Alkynolpyridines and Their Complexes with Triphenylphosphine Oxide

2,6-Bis(3-methyl-butyn-3-ol)pyridine (1) and 2-bromo-6-[3-methyl-butyn-3-ol]pyridine (2) form complexes with triphenylphosphine oxide, 1·2tppo and 2·tppo, respectively. Hydrogen bonding dominates the crystal
packing in 1, but in the complexes phenyl embraces play a major role. Hydrogen bonding between the hydroxyl end
groups of 1 link the molecules into infinite chains, and the chains are cross-linked through hydrogen bonding between
one hydroxyl group and the pyridine nitrogen atom to form layers. In 1·2tppo the hydroxyl groups are terminated
through O−H···OP interactions, but the chain structure is perpetuated sextuple embraces. The loosely associated
chains pack so that the pyridyl rings of one chain are inserted into cavities of the next. Replacement of one of the
alkynol arms by a bromine atom in 2·tppo results in formation of a dimer through C−H···O interactions. Phenyl
embraces coupled with C−H···N and C−H···Br interactions extend the structure in two dimensions, and the resulting
layers stack normal to this plane. Thermal analysis of the complexes reveals that decomposition of 1·2tppo occurs
through simultaneous loss of both components, while the monoalkynol pyridine diffuses out of the complex first in
2·tppo.