Porous metal-organic polyhedra (MOPs), constructed from heterometallic Pd(II)-M(II) (M = Cu, Ni, Zn) paddlewheel nodes and 5-tert-butyl-1,3-benzenedicarboxylate organic links, were prepared in which the Pd(II) ions preferentially line the inner surface of the cage molecules. Careful activation produces co-ordinatively unsaturated 3d transition metal sites on the external MOP surfaces giving rise to H2 adsorption enthalpies in excess of -12 kJ mol(-1).