In Situ Metal-Assisted Ligand Modification Induces Mn4 Cluster to Cluster Transformation: A Crystallography, Mass Spectrometry and DFT Study.

Abstract

Dehydration of (S,S)-1,2-di(1H-benzo[d] imidazol-2-yl)ethane-1,2-diol (H 4 L) to (Z)-1,2-di(1H-benzo[d] imidazol-2-yl)ethenol) (H 3 L ) was found to be metal-assisted and occurs under solvothermal (H 2 O/CH 3 OH) leading respectively to [Mn II 4 (H 3 L) 4 Cl 2 ]Cl 2 ·5H 2 O·5CH 3 OH ( Mn 4 L 4 ) and [Mn II 4 (H 2 L ) 6 ( μ 3 -OH)]Cl·4CH 3 OH·H 2 O ( Mn 4 L 6 ). Their structures were determined from single-crystal X-Ray diffraction. Extensive ESI-MS of solutions and solids of the reaction led to a proposal consisting of an initially stepwise assembling of Mn 4 L 4 from the reactants via [MnL] and [Mn 2 L 2 ] below 80 °C, then disassembling to [MnL] and [MnL 2 ] followed by ligand modification before reassembling to Mn 4 L 6 via [MnL ], [MnL 2 ] and [Mn 2 L 3 ] with the increase of solvothermal temperature until 140 °C. Interestingly, intermediates [Mn 4 L x L 6-x ] (x = 5,4,3,2,1) were identified in the process, further suggesting an assembly-disassembly-in situ reaction-reassembly transformation mechanism. These results not only reveal that multiple phase transformations are possible even though they were not realized in the crystalline state, but also help us to better understand the complex transformation process between coordination clusters during the black box reactions.