The tetratungstate polyoxoanion-supported organometallic compound 2CH(3)CN subset of(n-Bu4N)(2)[(lr( 1,5-COD))(6)W4O16]. 2CH(3)CN (2CH(3)CN subset of 1 . 2CH(3)CN) is reported, a complex which exhibits an unusual ''methyl-first'' CH3CN inclusion (''subset of'') chemistry. The synthesis of 2CH(3)CN subset of 1 . 2CH(3)CN was accomplished by the reaction of 3 equiv of [Ir(1,S-COD)Cl](2) with 4 equiv of (n-Bu4N)(2)WO4; an X-ray diffraction single-crystal structure shows that the four tungsten atoms in of 2CH(3)CN subset of 1 . 2CH(3)CN are located in tetrahedral positions and combine with four bridging oxygens to yield a tungsten-oxygen cubane structure. The cubane core tungsten atoms are capped by six surrounding Clr(1,S-COD)](+) groups in an octahedral arrangement relative to the cube, with each [Ir(1,S-COD)](+) group coordinated by two terminal oxygen atoms from the tetratungstate unit. Two sets of flexible acetonitrile-binding cavities, formed between each three of the six [Ir(1,S-COD)](+) groups, form a roughly tetrahedral array surrounding the cube. This host-guest complex binds acetonitrile methyl-first, that is, with the methyl group rather than the nitrile group oriented toward a cubane core oxygen atom. The C-Me... O nonbonded distances fall in the range 3.10-4.46 Angstrom for C-Me...-(mu(2)-O) and 3.08-4.02 Angstrom for C-Me...(mu(3)-O) Acetonitrile-free 1 was also prepared, and its possible acetonitrile and toluene complexation in benzene and methylene chloride solution was studied by NMR. No binding between acetonitrile or toluene and I in solution is observed, even when using greater than 300 mol equiv of guest relative to 1. Therefore, the host-guest interaction between 1 and acetonitrile appears to be weak (K-eq ( 10 M-1), possibly being limited to the solid state.