  We explore molecular states of two open heavy-quark mesons (Q qbar)-(qbar Q)
in a quark-based model in terms of a four-body non-relativistic Hamiltonian
with pairwise effective interactions. Molecular states are found in the
combinations of {D, D*, B, B*} with {Dbar, Dbar*, Bbar, Bbar*}, including a
weakly-bound D-Dbar* state near the threshold which may be qualitatively
identified as the 3872 state observed recently by the Belle Collaboration.
