First Neutron Diffraction Analysis of an O−H···π Hydrogen Bond: 2-Ethynyladamantan-2-ol

The neutron diffraction analysis of crystals of
2-ethynyladamantan-2-ol (I) provides confirmation of
the
presence of an unusual O−H···π hydrogen bond, together with
more common O−H···O and C−H···O bonds, as
proposed previously. This is first neutron analysis of an
O−H···π hydrogen bond, which is shown to be short
and
linear, with the O−H vector clearly directed towards the mid-point
(X) of the triple bond (O···X = 3.221 Å,
H···X
= 2.258 Å, O−H···X = 179.0°) rather than toward either
of the two alkyne carbon atoms. An exceptionally
short
and straight C−H···O bond is also present in the network which
probably owes its characteristics to a cooperative
effect with an O−H···O hydrogen bond. The three types of
hydrogen bond in this crystal structure link molecules
to form supramolecular synthons which are defined as spatial
arrangements of intermolecular interactions which
incorporate the geometrical and chemical recognition features of
molecules.