A theoretical study of the complexes formed by pentazolo[1,2-a]pentazole, N-8, with neutral electron donors, hydrogen-bond donors, and anions has been carried out at the B3LYP and MP2 computational levels. In addition, the clusters formed by two, three, and four molecules of N-8 have been studied. The results show that, in general, the interaction of the central N-N bond is preferred over the formation of a HB complex with neutral molecules. A comparison of the energetic results for the N-8 complexes obtained in the present article with those for analogous complexes of C6F6 demonstrates that the N-8 complexes exhibit a stronger interaction with both neutral and anionic systems. Small cooperative effects are observed in the calculated clusters of N-8.