The NCX-NCI-HMY (X=H, Cl, Br, I, Li; M=Be, Mg; Y=H, Li, Na) trimers are investigated to find ways to enhance the iodine–hydride interaction. The interaction energy in the NCI–HMH dimer is −2.87 and −5.87 kcal mol−1 for M=Be and Mg, respectively. When the free H atom in the NCI–HMH dimer is replaced with an alkali atom, the interaction energy is enhanced greatly. When NCX is added into this dimer, the interaction energy of the iodine–hydride interaction is increased by 9–45 % and its increased percentage follows the order X=Cl<Br<H<I<Li and M=Be<Mg. The combination of the alkali substitution and the cooperativity results in a more prominent enhancing effect. The largest interaction energy is found for the NCLi–NCI–HMgLi trimer (−7.03 kcal mol−1). The influence of the I⋅⋅⋅H interaction on the X⋅⋅⋅N interaction is also studied in the trimers. Both types of interactions are analyzed with NBO, AIM, and MEP. The interaction energy in the trimer is also unveiled by a many-body analysis.