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

Abstract

Two new complexes [Cu₄(2-OBPT)₂(μ-OAc)₄(μ-OH)₂]·H₂O (1) and [Cu₂(2-OBPT)(μ-OAc)₂(μ-OH)]·1.75H₂O (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 groupP, while complex 2 is a zigzag chain coordination polymer with a P2₁/c space group. They are supramolecular isomers based on the dicopper [Cu₂(μ-OAc)₂(μ-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 °C, while the unique 2 crystallized at 20 °C in a high yield of 82% and the sole 1 was afforded at 120 °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 J₁/k_B = −33.6(5) K, g = 2.26(1) for 1 and J₁ = −29.1(6) K, g = 2.30(1) for 2.