The 20 K structure of p-amino-p '-nitrobiphenyl in the non-constraining environment of its beta-cyclodextrin inclusion complex

Though p-amino-p'-nitrobiphenyl (PANB) is essentially planar in its crystal line form, it takes on a twisted conformation in its 2:2 crystalline inclus ion complex with beta-cyclodextrin (beta-CD); the angles between the two ph enyl rings are 40.6(2) and 42.0(1)degrees for the two molecules respectivel y, compared with 44.1(1)degrees for biphenyl in the gas phase, thus indicat ing the absence of constraints in the beta-CD dimer cage.