Fragmentation of a One-Dimensional Zinc Coordination Polymer and Partial Reassembly Evidenced by Mass Spectrometry - zeng's paper

We report here the rare observation of a one-dimensional coordination polymer, {[Zn5(bit)4Cl6]·2(CH3CN)}n (1, Hbit = 1-methyl-2-(1H1,2,3-triazol-4-yl)-1H-benzo[d]imidazole), having one mode of binding for the polytopic ligand and three different polyhedra, tetrahedron, square-base pyramid, and octahedron, for the metal node. The formation process of 1 involves the in situ decarboxylation of Hbitc (5-(1-methyl-1H-benzo[d]imidazol-2-yl)-1H-1,2,3triazole-4-carboxylic acid) to Hbit. Apart from one bridging μ2-Cl, all the other chlorine atoms act as a terminal ligand to complete the polyhedra. While 1 is almost insoluble in most organic solvent, electrospray ionization mass spectrometry of its ultrasound-treated DMSO suspension found the two main species [Zn(bit)]+ at 0 eV and [Zn2(bit)3]+ at elevated in-source energies. Density functional theory calculation suggests a potential formation process involving the sequence: [Zn(bit)]+→ [Zn2(bit)3]+ + [Zn2(bit)2Cl]+ → [Zn3(bit)4Cl2]+. The luminescence intensity enhancement and red shift of 1 were compared with the ligand Hbit, which may be because the ligand coordinated to the metal center and increased the rigidity compared to the ligand and the interaction between the metal center and DMSO molecules. The lifetimes, 1 (1.13 ns) < Hbit (1.64 ns), and the moderate quantum yields (5.88% Hbit and 4.48% 1), indicate fluorescence.