The protonated lactam salts , 1, , 2, and , 3, were isolated from the non selective reaction of MoCl₅ with δ-valerolactam in dichloromethane, carried out with different molar ratios. The 1 : 2 reaction of MoCl₅ with N-methyl-2-pyrrolidone afforded the chloroiminium salt , 4, in 74% yield, together with minor amount of , 5. The products 1–5 were characterized by analytical and spectroscopic techniques, and by X-ray diffractometry in the cases of 1 and 3.