Terminal Anion Induced Zinc(II) Mononuclear Complexes trans-to-cis Isomerization Regulate Photoluminescence Properties and Its Solution Behavior

Abstract The organic ligand 1-methyl-1H-benzo[d]imidazole-2-carbaldehyde (L') was used to react with ZnX2 (X = Cl and Br) under solvothermal conditions to obtain the complex [Zn(L)2(X)2] (1, X = Cl; 2, X = Br). The ligand of L' transforms into 1-methyl-1H-benzo[d]imidazole (L). The structures analysis shows that the L' ligands of complex 1 and 2 coordinate in different way, which results different shapes in every structure. They are trans and cis isomers of Zn(II) mononuclear complexes induced by terminal anions. These also lead to the difference of weak interaction of complexes, thus affecting the mode of connection. Furthermore, the electrospray ionization mass spectrometry (ESI-MS) data show that the main molecular fragment was [Zn(L)2(X)]+ under the condition of 0 eV voltage. So those two complexes were relatively stable in CH3CN. The single crystals of complex 1 showed blue green light, but complex 2 showed very obvious blue and white light under UV lamp, this difference may be due to the ion radius of coordination halogen.