IntroductionCarboranes such aso-,m-, andp-C2B10H12[1,2-, 1,7-, 1,12-dicarbadodecaborane(12)] (hereaftero-,m-, andp-carborane) are twelve-vertex icosahedral cages with applications in a number of diverse fields such as boron neutron capture therapy, boron carbide-type ceramics, as complexing agents for extraction of metal ions, in nonlinear optics, conducting polymers and more.1These neutral and related anionic carboranes show C–H acidity2and are consequently able to act as hydrogen bond donors. A handful of supramolecular complexes of carboranes exploiting such weak intermolecular interactions is known,3–9the first reported example being that of 1∶1 complexes betweeno-,m- orp-carborane and hexamethylphosphoramide,where all adopt different structures in the solid state commensurate with their differing arrangement of C–H sites.3Carboranes covalently substituted with hydrogen bond acceptor groups can self-associate in the solid state.5o-Carborane1is present as a guest molecule in inclusion or host–guest complexes with cyclodextrins,10a curved nickel macrocycle6and arene-based bowl-shaped host molecules such as calixarenes7or cyclotriveratrylene (CTV).8,9The use of arene-based hosts often results in the formation of nonclassical C–H⋯π hydrogen bonds between the polarised C–H bond of the carborane and the basic π-electrons of an aromatic ring.7,8Calix[5]arene forms1∶1, 2∶1 and 1∶2 complexes witho-carborane, all of which feature ball-and-socket [(o-carborane)∩(calix[5]arene)] assemblies showing C–H⋯π hydrogen bonding.7CTV forms 2∶1 and 1∶2 CTV∶o-carborane complexes; however, only the former displays C–H⋯π hydrogen bonding.8In the latter example, one carborane acts as a guest molecule while the other forms bifurcated C–H⋯(OMe)2hydrogen bonds to the dimethoxy moieties of the CTV to create an infinite network.9A similar hydrogen bonding interaction creates an infinite helical arrangement ofo-carboranes and CTV molecules in the complex (o-carborane)(fullerene-C70)(CTV)(1,2-dichlorobenzene).9The interaction is calculated to be energetically favoured by 5.48 kcal mol−1for the model compound (o-carborane)·(1,2-dimethoxybenzene),9approximately double the calculated stability of the carborane C–H⋯π interaction.8Given the current interest in the formation of infinite hydrogen bonded networks in the field of crystal engineering the generality of this bifurcated hydrogen bond fromo-carborane was investigated using chemically simpler hydrogen bond acceptors of the type illustrated inFig. 1. 1,2-Dimethoxybenzene (veratrole)2is essentially a substructure of cyclotriveratrylene, and is known to form a bifurcated hydrogen bond with (R)arylglycyl(R)phenylglycine,11whereas 1,10-phenanthroline3has a physically similar arrangement of hydrogen bond acceptor groups with different chemical functionality, and is also reported to act as a bifurcated hydrogen bond acceptor.12,13Both form crystalline hydrogen bonded complexes witho-carborane, the structuresof which were determined by X-ray crystallographic studies.Bifurcated interaction between an acidic C–H group ofo-carborane and an (X)2acceptor in a rigidorthoarrangement.