BxC1−xhost materials (0.1 < × < 0.25) and their intercalation compounds with heavy alkali metals prepared from the vapor reaction or from the reaction of cesium in ammonia solution were characterized using13C and11B NMR and EPR.13C NMR shifts and EPR dysonian lines (typical of conductors) found in intercalation compounds are qualitatively similar to those observed in their GIC analogues. Evidence are reported in favor of a breaking of the local axial symmetry due to interstitial boron atoms for highest × values and partial recover of this symmetry in the intercalation compounds.