  The existence of flavor exotic $QQ\bar{q}\bar{q}$ molecular-type states is
investigated. An attractive force between two {\it pseudoscalar} $H =
(Q\bar{q})$ heavy meson is generated by (correlated) two-pion exchange. The
emergence of a (loosely) bound state depends crucially on the value of the
coupling constant $g$ of the $H^*H\pi$ vertex. For a $g$ value calculated from
the experimental upper limit on the width of the $D^*$ meson the considered
mechanism alone is strong enough to generate a bound state in the $BB$ system
while the $DD$ system is very close to become bound. Such states, if exist, are
stable with respect to strong interactions. They may be observed as stable
scalar particles with the mass $M\approx 2\,m_H$ and flavor quantum number $\pm
2$.
