  A phenomenological estimate is derived such that the binding energies of
dimesons are expressed as combinations of masses of different mesons and
baryons. The estimate is almost model-independent, the only major assumptions
being that the wave functions of the two light quarks in $\Lambda_c$,
$\Lambda_b$ and in the $\bar{c}\bar{c}qq$ and $\bar{b}\bar{b}qq$ dimesons are
very similar, and that for heavy quarks the $QQ$ interaction is half as strong
as the $Q\bar{Q}$ interaction. We get $\bar{b}\bar{b}qq$ (I=0, J=1) bound by
about 100 MeV and $\bar{c}\bar{c}qq$ unbound.
