  Kontsevich has proven that the Lie homology of the Lie algebra of symplectic
vector fields can be computed in terms of the homology of a graph complex. We
prove that the Leibniz homology of this Lie algebra can be computed in terms of
the homology of a variant of the graph complex endowed with an action of the
symmetric groups. The resulting isomorphism is shown to be a
Zinbiel-associative bialgebra isomorphism.
