The reaction between [Mo(HBpz 3 )(NO)I 2 ] and tetrahexylcalix[4]resorcinarene affords container molecules in which two, three or four {Mo(HBpz 3 )(NO)} units are incorporated into the rim to produce a host site. A crystal structure of the tetrametallated derivative reveals that one nitrosyl ligand forms a hydrogen bond with a CH 2 Cl 2 guest molecule included in the host site.