Synthesis, crystal structure and coordination behaviors of two unexpected tetranuclear Zn(II) and Co(II) supramolecular boxes derived from structural variation of coumarin schiff base ligand

Two unexpected tetranuclear supramolecular boxes, [Zn4(L')4(CH3OH)2]·2CH3OH (1) and [Co4(L)2(L')2(CH3OH)2]·acetone (2), with M4(μ3-O)2(μ2-O)4 core were obtained through reacting coumarin Schiff base H2L (H2L = 4-hydroxy-3-((2-hydroxyphenyl-imino)-methyl)-2hchrome-2-one) with Zn(OAc)2·4H2O and Co(OAc)2·4H2O, respectively. Interestingly, the original ligand (H2L) has changed into a new structure (H2L') in the process of forming single crystals. The structures of 1 and 2 were characterized by X-ray single crystal diffraction. 1 and 2 are tetranuclear structures including four metal centers (Zn(II) or Co(II)), four completely deprotonated ligands (four new (L')2- in 1, two original (L)2- and two new (L')2- in 2), two coordinated methanol molecules and several crystalline solvent molecules. Significantly, due to the action of Zn(II) and Co(II), the original Schiff base H2L completely changed from coumarin skeleton to quinoline skeleton to form a new ligand (H2L') in 1, while in 2 half of the ligands H2L involved in coordination changed to H2L' configuration, the other half maintained the original structure. In 1, Zn1 ions are six-coordinate octahedral configuration and Zn2 are five-coordinate distorted square-pyramidal configuration with τ = 0.38. In 2, Co1 are six-coordinate octahedral configuration and Co2 are five-coordinate triangular bipyramidal configuration with τ = 0.66.