A new porous coordination polymer (PCP), formulated as {[La-2(III)(mu(3)-OH)(CH3COO)(2)(H2O)][Cu-I(dmdcbpy)(2)]center dot 9H(2)O} (La2Cu center dot 9H(2)O; H(2)dmdcbpy: 6,6'-dimethyl-5,5'-dicarboxy-2,2'bipyridine), was synthesized and characterized by X-ray diffraction and vapor-adsorption isotherms. The porous framework of La2Cu consists of a 3-D coordination network of the Cu(I)-metalloligand and the tetranuclear La-4 cluster {La-4(mu(3)-OH)(2)(CH3COO)(4)(H2O)(2)}. La2Cu exhibits reversible guest adsorption desorption for various vapors, with reversible structural transformations.