Temperature-dependent supramolecular isomers of a tetranuclear macrocycle and a zigzag chain based on dicopper building blocks

Two new complexes [Cu-4(2-OBPT)(2)(mu-OAc)(4)(mu-OH)(2)]center dot H2O (1) and [Cu-2(2-OBPT)(mu-OAc)(2)(mu-OH)]center dot 1.75H(2)O (2) (2-HOBPT = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol) have been synthesized and characterized by single-crystal X-ray diffraction. Complex 1 is a tetranuclear macrocycle with a centrosymmetric space group P (1) over bar, while complex 2 is a zigzag chain coordination polymer with a P2(1)/c space group. They are supramolecular isomers based on the dicopper [Cu-2(mu-OAc)(2)(mu-OH)] core and 2-OBPT ligand. Interestingly, each isomer can be afforded by control of the crystallization temperature. A mixture of complexes 1 and 2 were obtained in the range of 60-100 degrees C, while the unique 2 crystallized at 20 degrees C in a high yield of 82% and the sole 1 was afforded at 120 degrees C. Moreover, both the complexes are antiferromagnetic and the theoretical fit of the magnetic susceptibility data in the temperature range of 2-300 K gives J(1)/k(B) = -33.6(5) K, g = 2.26(1) for 1 and J(1) = -29.1(6) K, g = 2.30(1) for 2.