Linear CnN2 and CnP2 clusters, in the lowest energy singlet and triplet states, were studied using the B3LYP/ 6-311G** theoretical method for n = 5-10 and the B3LYP/aug-cc-pVTZ method for n = 5-8. Harmonic frequencies are also reported. Clusters with odd numbers of carbon atoms have lower lying triplet ground states, while those with even numbers of carbons are singlets. The energies of the acetylenic singlet ground states are approximately 2.5 eV below those of the lowest triplet state, while the triplet ground states tend to be more cumulenic and are preferred by 0.6-0.8 eV. A comparison of the properties of the di-heteroatom terminated clusters, on the basis of the atomic properties of nitrogen and phosphorus, is presented. Some important differences in molecular properties are highlighted.