A systematic survey of zeolites Y containing tris(2,2’-bipyridine)ruthenium(II) with various levels of loading was undertaken. Almost pure Ru(bpy)(3)(2+) was obtained whenever the loading was less than approximately one complex per two supercages. At higher loading an increasing amount of byproducts corresponding formally to Ru(bpy)n(NH3)(6-2n)(2+), n < 3, was found. This dependence of the yield of the "ship-in-a-bottle" synthesis of Ru(bpy)(3)(2+) in zeolite Y on the ruthenium exchange degree was interpreted in terms of transport problems and in terms of sterical fitting between host zeolite Y supercages and guest Ru(bpy)(3)(2+). For high loadings, we observed a tendency of Ru(bpy)(3)(2+) accumulate toward the surface of the zeolite microcrystals instead of a random distribution in the bulk. The consequence of this was to slow down the bpy diffusion during the in situ complexation process and finally to prevent the reaction from being completed at high loading levels.