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Metallaprism
Metallaprisms, otherwise known as metalla-assemblies or complex metallacycles, are large organometallic assemblies derived from arene ruthenium building blocks. Osmium (a ruthenium anologue) metallaprisms have also been constructed, but due to the cost of osmium it is general procedure to first prepare the ruthenium anologue with sure success. These structures are generally prepared in tetracationic and hexacationic forms and are isolated as triflate salts (triflate acting as the counterion). Due to the large conformationally flexible cavity that is characteristic of metallaprisms, in which they are able to host a variety of guest molecules, they have been shown to be effective as drug delivery agents.



Recent Activity
These assemblies began to gain popularity circa the year 2000 when Severin and co-workers were able to selectively complex Li+ cations in water using arene ruthenium metallacycles. This lead to the discovery of several other applications. One such application, designed by Stang ''et. al''., was a series of arene ruthenium mellaprisms with a relatively high affinity for nitroaromatic compounds were shown to have great potential as sensors. This was achieved through the exploitation of the large cavity of the conformationally flexible metallaprism. This large cavity is apparent, and distinct in all metallaprisms. It has been shown that signiture structures are achievable for an adaptable metalla-assembly by the addition of an appropriate guest molecule. The guest molecule is encapsulated into the hydrophobic cavity of the metallaprism. The host-guest properties of water-soluble arene ruthenium assemblies have also been used to deliver guest molecules to cancer cells. Various guest molecules have been encapsulated in the hydrophobic cavity of metallaprisms. A few examples of these host-guest systems were used to deliver bioconjugate derivatives, metal complexes , and photosensitizers. A general scheme of the host-guest assembly can been seen in the osmium-based metallaprism-guest molecule assembly shown below.



Synthesis and Characterization
Though a variety of metallaprisms have been synthesized with different characteristics to be able to host various guest molecules, described here is the synthesis of [(η6-p-cymene)6Ru6(μ3-tpt-κN)2(μ-C6HRO4- κO)3]6+. The synthesis occurs in two steps. Two equivalents of silver triflate is first added to the dinuclear complex (η6-p- cymene)2Ru2(μ-C6HRO4-κO)Cl2 ([1]) to remove the chlorine ligands. This results of the formation of a coordinatively unsaturated intermediate (not shown because it could not be isolated), which then reacts with two equivalents of 2,4,6-tri(pyridine-4-yl)-1,3,5-triazine, otherwise known as the tpt ligand, to form the metallaprism [2]6+. The metalla-assembly is hexacationic and is isolated as a triflate salt ([2][CF3SO3]6). The structure of the metalla-assembly was characterized using Infrared Spectroscopy, Nuclear Magnetic Resonance, Electrospray Ionization-Mass Spectrometry, and elemental analysis. An osmium analogue of the metallaprism was also prepared by the same group.