Enhanced and Heteromolecular Guest Encapsulation in Non-Porous Crystals of Perfluorinated Triketonato Dinuclear Copper Complex.

Since the flexible host framework of perfluorinated mononuclear copper complex, [Cu(L1)2] (1, HL1 = 3-hydroxy-1,3-bis(pentafluorophenyl)-2-propen-1-one), with CuO4 core reversibly encapsulated several organic guest molecules through electrostatic interactions in their crystals, the corresponding dinuclear complex, [Cu2(L2)2] (2, H2L2 = 1,5-dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one), was prepared to enhance guest recognition and molecular mixture separation properties. Complex 2 comprises of Cu2O6 core and four pentafluorophenyl groups. In the crystal 2, cavities are formed on the axial sites of the metal core, that are surrounded by pentafluorophenyl groups. The crystal of 2encapsulates various guest molecules, i.e., 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 in complex 1, e.g., (2)3•(6)10 > 1•(6)2; (2)2•(7)7 > 1•7; 2•(8)3 > 1•(8)2. Naphthalene molecules, 9, was encapsulated in 2 to give 2•(9)3 but not in 1. In crystal of complex 2, heteromolecular guest encapsulation was confirmed, designated as 2•(3)2•9. TG analysis indicates that thermal stability of the guest-included crystals of 2 is higher than that of 1.