Macropolyhedral boron-containing cluster chemistry. Isolation and characterisation of the eighteen-vertex nido-5'-iridaoctaborano[3',8':1,2]-closo-4-iridadodecaborane, [(Co)(PMe(3))(2)IrB16H14Ir(CO)(PMe(3))(2)]

The novel eighteen-vertex macropolyhedral diiridaborane [(CO)(PMe(3))(2)IrB16H14Ir(CO)(PMe(3))(2)] has been isolated in low yield from the products of thermolysis of the nine-vertex. arachno-monoiridaborane [(CO)(PMe(3))(2)HIrB8H12], and examined by single-crystal X-ray diffraction analysis, NMR spectroscopy and mass spectrometry. The macropolyhedral framework consists pf a close-type twelve-vertex {IrB11} subcluster and a nido-type eight-vertex {IrB7} subcluster fused with two boron atoms in common; In addition there is an iridium-boron two-electron two-centre intercluster cross-linkage that is suprafacial to the open nido subcluster. The results are briefly discussed in terms of bonding schemes among individual subclusters.