Polyhedral iridaborane chemistry: Elements of the 10-vertex closo–isonido–isocloso continuum: Molecular structures of [(PPh3)2HIrB9H9(PPh3)], [(PPh3)(Ph2PC6H4)IrB9H7(PPh3)], [(PPh3)(Ph2PC6H4)HIrB9H6Cl(PPh3)], [(PPh3)(Ph2PC6H4)HIrB9H6(PPh3)2] and [(PPh3)(P

There is experimental difficulty in the isolation and structural definition of examples of compounds of the isonido 10-vertex cluster structure in order that they may be adduced to the pattern of behaviour associated with the 10-vertex closo–isonido–isocloso structural continuum in boron-containing cluster chemistry. By contrast, the closo and isocloso extremes are well recognised, with several definitive examples. An approach involving the synergic application of crystallography (using single-crystal X-ray diffraction analysis and HYDEX), multi-element NMR spectroscopy, and DFT calculations of structure and nuclear magnetic shielding, has been used to delineate and define two basic variants in the quadrilaterally open-faced 10-vertex ‘isonido’ {IrB9} metallaborane system. Type A variants, as in [7,7,7-(PPh3)2H-μ-3,7-H-isonido-7-IrB9H8-9-(PPh3)] (2), have an Ir–H–B bridging hydrogen atom involving a boron atom off the open face, and an Ir–H non-bridging linkage. Type B variants, as in [8-Cl-7-(PPh3)-μ-7P,10C-(Ph2P-ortho-C6H4)-isonido-7-IrB9H6-9-(PPh3)] (5), have no cluster-bridging hydrogen atoms and no Ir–H unit. Previously unreported single-crystal X-ray diffraction analyses are given for isonido type-A [7-(PPh3)-μ-7P,10C-(Ph2P-ortho-C6H4)-7-H-μ-3,7-H-isonido-7-IrB9H8-9-(PPh3)] (10), classical closo [7-(PPh3)-μ-7P,10C-(Ph2P-ortho-C6H4)-7-H-closo-7-IrB9H6-3,9-(PPh3)2] (13) and classical nido [6-(PPh3)-μ-6P,5C-(Ph2P-ortho-C6H4)-6-H-nido-6-IrB9H12] (15). Overall, the work well demonstrates the synergic usage of NMR spectroscopy, single-crystal X-ray crystallography (including HYDEX calculations) and DFT calculations of structure and nuclear shielding, to resolve ambiguous problems of chemical constitution in polyhedral boron-containing cluster chemistry, an approach that should have wider applicability.