The rotational spectrum of the dimethylether (DME)-N2O complex has been studied for the normal and three N-15 isotopomers, leading to rotational, centrifugal distortion, and nuclear quadrupole coupling constants, the molecular structure, and a binding energy of 8.4 kJ mol(-1). Here, it is shown that many DME-N2O-type complexes are bound with three intermolecular bonds and that the internal rotation splitting due to the methyl groups in the rotational spectrum was fixed by complexation, implying that many weak intermolecular bonds can fix the flexible motions and maintain a rigid structure. If the model we are proposing for DME-N2O-type complexes can be applied to biomolecules, it may give something a clue to solve the biological riddle on the dynamic character of biomolecules that have conflicting properties of being rigid and binding weakly.