A world beyond hydrogen bonds? -Chalcogen-chalcogen interactions yielding tubular structures.

It is shown that tubular structures arise in the solid state through close chalcogen-chalcogen (X...X) contacts. As examples a variety of cyclic systems containing sulfur and selenium centers is presented. Common to all of them are close contacts between the chalcogen centers of neighboring stacks giving rise to a zigzag or ladder-type arrangement. In the case of cyclic systems of ring size 24-33 the resulting tubes are able to include hydrocarbons as guest molecules. For 2,7-ditelluraocta-3,5-diyne (17) the close contacts between the tellurium centers of the acyclic C(2) symmetric building blocks generate a helical arrangement in which n-hexane was included. The favored X...X contacts can be traced back to np(X)-sigma*(X[bond]C) interactions.