After the previous discovery of MgC 3N and MgC 4H in IRC +10216, a deeper Q-band (31.0-50.3 GHz) integration on this source had revealed two additional series of harmonically related doublets that we assigned on the basis of quantum mechanical calculations to the larger radicals MgC 5N and MgC 6H. The results presented here extend and confirm previous results on magnesium-bearing molecules in IRC +10216. We derived column densities of (4.7 ± 1.3) × 10 12 for MgC 5N and (2.0 ± 0.9) × 10 13 for MgC 6H, which imply that MgC 5N/MgC 3N = 0.5 and MgC 6H/MgC 4H = 0.9. Therefore, MgC 5N and MgC 6H are present with column densities not so different from those of the immediately shorter analogs. The synthesis of these large magnesium cyanides and acetylides in IRC +10216 can be explained for their shorter counterparts by a two-step process initiated by the radiative association of Mg + with large cyanopolyynes and polyynes, which are still quite abundant in this source, followed by the dissociative recombination of the ionic complexes.
