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Tandem assembly-disassembly-reassembly of hierarchical Co19 coordination cluster facilitated by in-situ ligand transformation: Crystallography and ESI-MS revealed mechanism
Qiu-Jie Chen, Tian-Ying Gu, Zhao-Bo Hu, Man-Bo Zhang, Zheng Yin, and Ming-Hua Zeng*
https://doi.org/10.1016/j.cjsc.2025.100659
ABSTRACT
Odd-numbered and high-nuclearity coordination clusters are extremely rare, yet they represent an intriguing subclass lacking regular repeating building blocks and high structural symmetry for understanding self-assembled multiatomic systems. Herein, the largest cobalt and polydentate ligand based cluster featuring odd-nuclearity, namely [Co19(HL1)8(L1)12(L′)2(Ac)4]·10CH3CH2OH·6H2O (1, H2L1 = 1H-benzo[d]imidazole-2-yl)methanol, HL′ = 1H-benzo[d]imidazole), was obtained with in-situ ligand transformation from H2L1 to L′. It features a hierarchical trilayer and void-cage inside structure, consisting of central disc-shaped [Co7L10] core with two [Co6] rings on both sides. ESI-MS of crystal 1 yields a series of more than sixteen fragments, all featuring an integrated [Co19] core, suggesting stability of the polynuclear cluster in solution. During increased in-source energy from 0 to 100 eV, all MS peaks shifted to a lower m/z range, but the [Co19] core remained intact, excepting for the stepwise elimination of up to three Ac- anions or three L1 linkers. PXRD tracking of the reaction sediments showed the formation of a key precursor of [Co4L4] cubane at 3 h, and its content decreased at 6 h and vanished at 12 h, followed by the appearance of crystals 1 by generation of a clear solution at 18 h, suggesting an initial cluster assembly-disassembly process. ESI-MS spectra analysis of both reaction sediment and solution further identify the existence of other crucial higher-nuclearity reassembled fragments of [Co7L10] disk and its expansion of [Co13L12(L′)2]. A probable tandem assembly-disassembly-reassembly mechanism is put forward as [CoL2]→[Co4L4]→[Co7L10]→[Co13L12(L′)2]→[Co19L20(L′)2]. Their evolution also indicated the ingenious synergy of coexisting organic, inorganic and in-situ generated ligands, along with diverse coordination geometries of metal ions, plays a directional role in formation of odd-numbered and high-nuclearity coordination clusters. Magnetism analysis revealed antiferromagnetic coupling play dominated role in the cluster.
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