To clarify the effect of covalent surface adsorption on the geometric and electronic structure of carboranes, p-carboranethiol (pCT) was deposited on clean Au(111) surfaces under vacuum and the resulting systems were probed by scanning tunneling microscopy, scanning tunneling spectroscopy and ultraviolet photoelectron spectroscopy. The spectral features observed at different pCT coverage levels revealed the emergence of new electronic states near the surface, which were analyzed using ab initio calculations. The resulting computational and experimental data are used to explain the contributions of these states to bonding between the substrate and adsorbate, resonance with metallic substrate states and substrate-mediated intermolecular interactions.