Trickier than It Looks: Isomerization between Five- and Six-Coordinated Zinc in Heterometallic LiZn Molecule.

This report describes the synthesis and characterization of two heterometallic Li-Zn coordination isomers [LiZn(tbaoac)] (tbaoac = -butyl acetoacetato) that have been isolated separately by the same stoichiometric reaction run in different organic solvents. The 6-coordinated zinc isomer () was synthesized in acetone with high yield, while the 5-coordinated one () was readily obtained from ethanol. The isomer has a low solubility in organic solvents such as alkanes and haloalkanes, while its counterpart exhibits a good solubility in almost all common solvents. Two isomeric molecules feature similar centrosymmetric tetranuclear cyclic assemblies, which are different in their arrangement of tbaoac ligands. While all ligands act as μ-type in the structure of , the two tbaoac groups chelating Li appear as μ-type in , thus providing an additional coordination for Zn ions. However, the real structural transformation between these isomers was shown to be more complex than simply making or breaking a couple of Zn-O bonds. X-ray single-crystal structure analysis, powder X-ray diffraction, multinuclear NMR, DART mass spectrometry, ICP-OES analysis, and TGA have been employed for the characterization of the isomers. The combination of powder X-ray diffraction and H NMR investigation revealed that isomer can be quantitatively transformed to in ethanol, while the reverse conversion instantly takes place in acetone.