Nanometer-sized molybdenum-iron oxide capsule-surface modifications: external and internal.

The cluster {(Mo)Mo5}12Fe(III)30 1 a present in compound 1 (cluster diameter approximately 2.3 nm), which belongs to the family of nanoscale spherical porous {(Mo)Mo5}12{Linker}30 capsules that allow a new type of nanochemistry inside their cavities as well as unprecedented aggregation processes under gaseous, solution, and solid-state conditions, is the starting material for the present investigation. In solution it reacts with LnCl3 x nH2O (Ln = Ce, Pr) thereby replacing six Fe(III) ions with Ln(III) ions to form compounds 2 (Ce) and 3 (Pr). During metal-cation exchange, some of the pentagonal {(Mo)Mo5O21(H2O)6}6- units, which are connected to the Fe(III) centers in 1 a, decompose, thus leading to a temporary capsule opening and uptake of the formed smaller molybdate units into the capsule cavities. In 2 and 3, the pentagonal units are connected via 24 Fe(III) and six Ln(III)-type linkers/spacers representing together the capsule skeletons, which are structurally well-defined in contrast to the capsule contents. The new capsules self-associate into single-layer blackberry-type structures, thus extending the variety of these types of assemblies; the assembly process, that is, the size of the final species, can be controlled by the pH, which allows the generation of differently sized nanoparticles. Magnetic properties of the two new nanomaterials 2 and 3 are also determined.