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

Dehydration of (S,S)-1,2-bis(1H-benzo[d]imidazol-2-yl)ethane-1,2-diol (H4L) to (Z)-1,2-bis(1H-benzo[d]imidazol-2-yl)ethenol) (H3L ') was found to be metal-assisted, occurs under solvothermal conditions (H2O/CH3OH), and leads to [Mn-4(II)(H3L)(4)Cl-2]Cl-2.5 H2O.5 CH3OH (Mn4L4) and [Mn-4(II)(H2L ')(6)(mu(3)-OH)]Cl.4 CH3OH.H2O (Mn4L '(6)), respectively. Their structures were determined by single-crystal XRD. Extensive ESI-MS studies on solutions and solids of the reaction led to the proposal consisting of an initial stepwise assembly of Mn4L4 from the reactants via [MnL] and [Mn2L2] below 80 degrees C, and then disassembly to [MnL] and [MnL2] followed by ligand modification before reassembly to Mn4L '(6) via [MnL '], [MnL '(2)], and [Mn2L '(3)] with increasing solvothermal temperature up to 140 degrees C. Identification of intermediates [Mn4LxL '(6-x)] (x=5, 4, 3, 2, 1) in the process further suggested 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 to better understand the complex transformation process between coordination clusters during black-box reactions.