The supersonic beams of the (1-1) metal-ligand complexes of Al-CH3CN and Al-NH3 were produced by a laser evaporation method. Nondestructive structure selection of the complexes and the dipole moment determination were performed by using a 2-m electrostatic hexapole field. The experimentally determined permanent dipole moments are 1.2 +/- 0.1 D for Al-CH3CN and 2.7 +/- 0.2 D for Al-NH3. We find that the dipole moment of Al-NH3 becomes larger than that of neat NH3, while the formation of the Al-CH3CN complex produces a smaller dipole moment than that of neat CH3CN on the other hand. We performed the ab initio calculations to draw out plausible complex structures and to clarify the bonding character after formation of the complex, and we made comparisons with the computational results done by several groups. The Mulliken population analysis suggests the Al-->CH3CN charge flow, but on the other hand the Natural population analysis indicates very little charge flow. For the Al-NH3 complex, the polarization effect of NH3 and the N-->Al sigma donation would enhance the dipole moment strength. However, there still remains a controversial disagreement between the theoretical predictions and the experimental results. Further experimental determination using the hexapole method for various metal-ligand complexes and clusters could reveal the basic nature of interaction in the complex systems in general, and this method would complement theoretical calculations.