Synthesis and crystal structures of novel controlled three-dimensional organic mercury (II) supermolecule complexes based on poly N-heterocyclic carbenes

N-alkylbenzimidazole reacted with 1, 2, 4, 5-tetrakis (bromomethyl) benzene to give tetrabenzimidazolium salts H4-3Br4. The generated products were subsequently partially exchanged with KPF6 in aqueous solution, affording the benzimidazolium salt H4-3aBr(PF6)3 and H4-3bBr(PF6)3. The reaction between the two types of ligands and HgO in a 1:2 ratio in DMSO yielded new octacarbene binuclear mercury (II) encapsulated complex [Hg2(3a)2]Br2 (PF6)2·4H2O and octacarbene tetra-nuclear caged complex [Hg4(3b)2]Br4(PF6)4, which had “abnormal” structures. Single crystal structure of [Hg2(3a)2]Br2 (PF6)2·4H2O showed that there was a strong special interaction between bromide anions and benzene rings in the complex molecule, holding two new half sandwiched structures, like two hexagonal pyramids. [Hg2(3a)2]Br2 (PF6)2·4H2O is first encapsulated complex. The other complex was a novel tetranuclear mercury (II) octacarbene caged complex, which had also an unprecedented structure. Its single crystal structure showed that there was a special eight-membered ring structure, consisting of four bromide anions and four mercury ions in the complex molecule. It was a new three-dimensional sandwiched structure that looked like a Chinese bronze quadripod. Therefore, it could be seen that there was a huge difference in the three-dimensional spatial structures between the two complexes. The reason was simple that the different substituent groups on the two ligands could control in self-assembly behavior of complexes during the formation process. UV-Vis spectra and fluorescence spectra of the two typed complexes further proved special charge transfer mechanisms. The red-shift phenomenon of the complexes in ultraviolet-visible spectra is well explained by its DFT calculation. Long term thermal stability of them was verified by TGA as well.