Macropolyhedral boron-containing cluster chemistry: Models for intermediates en route to globular and discoidal megaloborane assemblies. Structures of [nido-B10H12(nido-B5H8)2] and [(CH2CH2C5H4N)-arachno-B10H10(NC5H4-closo-C2B10H10)] as determined by sync

A {B20H28} species, from the oligomerisation of B5H9, has a central nido {B10H12} core with two nido {B5H8} units bound to it at mutually adjacent positions. [(CH2CH2C5H4N)-arachno-B10H10(NC5H4-closo-C2B10H10)], a by-product from the reaction of [B10H12(NCMe)2] with ortho-ethynyl-pyridine, has mutually linked closo {C2B10} and arachno {B10} cluster units conjoined to a central aromatic pyridine unit; the arachno {B10} residue is also fused to an organyl double-ring structure involving a second pyridyl moiety. Both species model possible steps to globular megaloborane synthesis via the assembly of boron hydride units around a central cluster core, as well as having other interesting features. The small size of the crystals for both compounds necessitated the use of synchrotron X-radiation for sufficient diffracted-beam intensity for crystallographic analysis.