Lewis acid-base adducts of the “inorganic analog of benzene” alumazene [{2,6-(i-Pr)₂C₆H₃NAlMe}₃] (1) with acetonitrile (CH₃CN, acn) and deuteroacetonitrile (CD₃CN, d₃-acn) were synthesized, spectroscopically characterized, and their molecular structures were elucidated by the X-ray diffraction analysis as a bis-adduct 1(acn)₂ and a tris-adduct 1(d₃-acn)₃. The thermodynamics of complex formation was investigated experimentally and theoretically. Thermodynamic characteristics of process 1(acn)₃·acn (s) = 1(acn)₂ (s) + 2 acn (g) in the temperature range 294–370 K have been derived from the vapor pressure–temperature dependence measurements by the static tensimetric method. It is shown that above 435 K in the presence of 1 gaseous acn undergoes irreversible polymerization reaction. Quantum chemical computations at B3LYP/6-311G(d,p) level of theory have been performed for the 1(acn)_n and model complexes of [(HAlNH)₃] (1m), 1m(acn)_n (n = 1–3). Obtained results indicate that for the gas phase adducts upon increasing the number of acn ligands the donor-acceptor Al–N(acn) distances increase in accord with decrease of the donor-acceptor bond dissociation energies.