The flexible hostf ramework of ap erfluorinated mononuclear copper complex,[ Cu(L 1 ) 2 ]( 1,H L 1 = 3-hydroxy-1,3-bis(pentafluorophenyl)-2-propen-1-one), with aC uO 4 core reversibly encapsulateds everal organic guest molecules throughe lectrostatic interactions in its crystals. Hence, the correspondingd inuclearc omplex, [Cu 2 (L 2 ) 2 ]( 2,H 2 L 2 = 1,5-dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one), was prepared to enhanceg uest recognition and the ability to separate molecular mixtures. Complex 2 comprises a Cu 2 O 6 core and four pentafluorophenylg roups. In crystal 2, cavitiesa re formed on the axial sites of the metal core that are surroundedb yp entafluorophenylg roups.T he crystal of 2 encapsulates various guest molecules, that is, benzene (3), toluene (4), xylene (5), mesitylene (6), durene (7), and anisole (8). X-ray crystallographic and thermogravimetric (TG) studies show that three guest molecules are present in the crystal cavities. The number of guest molecules found in complex 2 was higher than that in complex 1,f or example, (2) 3 ·(6) 10 > 1·(6) 2 ,( 2) 2 ·(7) 7 > 1·7,o r2·(8) 3 > 1·(8) 2 .N aphthalene (9), was encapsulatedi n2 to give 2·(9) 3 ,b ut not in 1.I nt he crystal of complex 2,h eteromolecular guest encapsulation was confirmed, designated as 2·(3) 2 ·9.T Ga nalysis indicates that the thermals tabilityo ft he guest-included crystalso f2 is higher than that of 1. Figure 11. TG curves of guestrelease from 2·(3) 3 , 2·(9) 3 ,a nd 2·(3) 2 ·9.The scan rate was 5.0 8Cmin À1 .