Experimental and computational studies on the synthesis of mixed-linker zeolitic imidazolate frameworks (ZIF-8)

Synthesis of mixed-linker zeolitic imidazolate frameworks (ZIF-8) has been conducted by using two types of organic linker of 2-methylimidazolate (2-MeIm) and 2-ethylimidazolate (2-EtIm) ligands. The crystal structure of mixed-linker ZIF-8 has been confirmed through Le Bail fitting of the X-ray diffraction pattern to give an average unit cell dimension of a=16.994 Å, which is relatively close to the unit cell dimension of the reported ZIF-8 material. According to the IR spectra, the formation of mixed-linker ZIF-8 is confirmed by the presence of a peak at 421 cm−1 indicating the stretching vibration of the Zn – N bond. The crystal morphology of mixed-linker ZIF-8 has been investigated from the SEM and TEM images. The crystal exhibits an almost spherical shape, which resembles a possible rhombic dodecahedron shape. Further study was conducted using a computational approach based on the density functional theory. The presence of two type ligands of either 2-EtIm and 2-MeIm does not affect the bond distance of Zn – N with an average value of 2.020 Å. The tetrahedral nature of Zn(2-EtIM/2-MeIm)>4 cluster is maintained with an N – Zn – N angle of 110.13°.