The ³⁵Cl NQR spectrum of ortho-dichlorobenzene as a guest molecule in tetrakis (α-phenylethylamine)-bis(isothiocyanato)nickel(II), has been studied in the temperature range of 77 K to 250 K. At 77 K the clathrate has two resonances of equal intensity at 35.840 and 36.080 MHz, to be compared with those of pure ortho-dichlorobenzene, where there are three lines at 35.580, 35.775 and 35.824 MHz. At 230 K there occurs an irreversible phase change which results in the expulsion of the orthodichlorobenzene from the host crystal, and the NQR signals thereafter correspond to the three lines of the unclathrated guest molecule. These events were also followed and confirmed by a calorimetric study in the range 210-300 K. The phase change is thought to be due to a transformation of the host molecule, where the thiocyanato groups are in the trans configuration in the clathrate, to the cis configuration, which is known not to form a clathrate.