Complexation by M+ (M = Li, Be, Na, Mg, Al, K, Ca) of the highly unsaturated linear molecules NC2nX (X = N, CH; n = 0, 1, 2, 3) occurs exclusively by a coordination to the terminal N atom, yielding linear molecular cations that are here characterized using high-level, counterpoise-corrected ab initio calculations. We argue that these complexes, with a total absence of steric hindrance through nonbonding interactions, form an excellent "test set" for the purpose of investigating, in detail, the nature of the metal ion/ligand interaction. We analyze the influence of ionic, covalent, and repulsive energy contributions to the M+/ligand interaction for these species, using two different energy-decomposition schemes, and present also a complementary interpretation using the atoms-in-molecules (AIM) approach. Differences between the M+-NC2nX bond dissociation energies (BDEs) of the highly polar cyanopolyynes HC2n+1N versus the analogous nonpolar dicyanopolyynes NC2nN din-finish as the intervening carbon chain length increases, indicating that the local bond polarity of the coordinating CN group dominates over the ligand's overall polarity (or lack thereof) as an influence of M+/ ligand bond strength. The cyanopolyyne and dicyanopolyyne adducts of alkaline earth ions Be+, Mg+, and Ca+ and of All, whereas largely ionic in character, also possess significant overlying covalent tendencies. In contrast, the adducts of alkali metal ions Li+, Na+, and K+ can indeed be treated as essentially purely ionic. Among the results reported here, one striking observation (for which an underlying physical basis remains elusive) is that the M+-NC2nX series featuring an alkali metal ion exhibits a remarkably close adherence to the r(-12) dependence of the empirically assigned repulsive potential energy term in the (12, 6) Lennard-Jones potential.