Crystal structures and fluorescence properties of two architecture-correlated Zn(II)/Cd(II) MOFs constructed from an unprecedented tri-triazole ligand

By employing an unprecedented tri-triazole ligand, 4-amino-3,5-bis-(1H-1,2,4-triazole)-1,2,4-triazole (H2L), two Zn(II)/Cd(II) metal-organic frameworks (MOFs), [ZnL]·3H2O (1) and [CdL]·H2O (2), were successfully synthesized and characterized. In the two complexes, M(II) centers are chelated and bridged by L bridges to form a one-dimensional (1-D) 41 helical chain in 1 with high-symmetry Pbca, and a 21 helical chain in 2 with lower symmetry P21/n, respectively. The two chains are further linked by L into two structure-correlated three-dimensional (3-D) architectures. PXRD and TG analysis confirmed the phase purity and stability of 1 and 2. The solid-state fluorescence properties of the prepared MOF revealed a maximum emission at 382 nm and 393 nm (λex = 330 nm), ascribing to the intra-ligand transitions. Interestingly, an additional strong emission peak at 516 nm can be observed in 1 (below 400 °C), while the emission was silenced in 2. The additional emission band may be attributed to the subtle difference of architectural features and coordination configurations between in 1 and 2.