A reversible metal framework rearrangement in high-nuclearity osmium–platinum cluster compounds. X-Ray crystal structures of [Os<sub>6</sub>Pt(CO)<sub>17</sub>(µ<sub>3</sub>-NCMe)(C<sub>8</sub>H<sub>12</sub>)], [Os<sub>6</sub>Pt(CO)<sub>17</sub>(µ<sub>4</sub>-NCMe)(C<sub>8</sub>H<sub>12</sub>)](C<sub>8</sub>H<sub>12</sub>= cyclo-octa-1,5-diene), and [Os<sub>6</sub>(CO)<sub>19</sub>(µ<sub>3</sub>-NCMe)]: compounds with novel metal–acetonitrile bonding modes