LAUSR

N-methylbenzimidazole-2-methanol (Hmbm) and Zn(NO3)2·6H2O were reacted in acetonitrile solvothermal at 80 °C for 48 h to obtain a six-nuclear Zn(II) cluster ([ZnII6(Hmbm)2(mbm)8(NO3)4]·12H2O·2CH3CN (Zn6)). Structural analysis indicated that Zn(II) in the above Zn6 clusters showed pentacoordinates. The metal centers Zn1 and Zn2 are both in the N2O3 coordination environment, and both show a triangular bipyramid configuration. Zn3 is in a NO4 coordination environment, which is also shown as a triangular bipyramid configuration. The ion source voltage of high-resolution electrospray ionization mass spectrometry (HRESI-MS) was further adjusted to bombard the Zn6 cluster, and seven major key intermediates were identified. Furthermore, we proposed that the gradual fragmentation mechanism is Zn6 → [ZnII6(mbm)8(NO3)3]+ → [ZnII5(mbm)7(NO3)2]+ → [ZnII4(mbm)6(NO3)]+ → [ZnII3(mbm)4(NO3)]+ → [ZnII2(mbm)3]+ → [ZnII2(mbm)2(OH)(H2O)2(DMSO)]+ → [ZnII(mbm)]+. In order to understand the gradual formation of Zn6 clusters, herein, we track the changes of species in the solution in different time periods by HRESI-MS. The nine key intermediates were identified and further combined with its gradual fragmentation mechanism. We proposed the gradual assembly mechanism of [ZnII(mbm)]+ → [ZnII(mbm)(Hmbm)]+ → [ZnII2(mbm)2(NO3)]+ → [ZnII2(mbm)3]+ → [ZnII3(mbm)4(NO3)]+ → [ZnII4(mbm)5(NO3)2]+ → [ZnII4(mbm)6(NO3)]+ → [ZnII5(mbm)7(NO3)2]+ → [ZnII6(mbm)8(NO3)3]+ → Zn6. To the best of our knowledge, this is the first time that a decomposition and assembly binding strategy has been used to resolve the stepwise formation of Zn(II) clusters. Photoluminescence measurements indicate that the cluster Zn6 exhibits a strong emission peak at 300 nm and an emission shoulder at 600 nm.