Metastable metal imidazolates: development of targeted syntheses by combining experimental and theoretical investigations of the formation mechanisms

Abstract

In this report, we summarize our experimental and theoretical investigations in the zinc(II) imidazolate, [Zn(im) 2 ], and zinc(II) 4,5-dichloroimidazolate, [Zn(dcim) 2 ], systems that have been published previously. This comprises a study on the thermodynamic stabilities of the two densest phases with coi and zni framework structures in the [Zn(im) 2 ] system including the discovery and characterization of a new [Zn(im) 2 ·0.5py]-neb phase (py = pyridine), a study on the mechanism of formation of the [Zn(im) 2 ]-zni phase as well as a study on the discovery and characterization of a new [Zn(dcim) 2 ]-SOD phase. In addition, we present as yet unpublished work. This concerns the discovery and characterization of a new [Zn(im) 2 ·0.5mor]-neb phase (mor = morpholine) and investigations of the mechanisms of crystallization of [Zn(im) 2 ·0.5py]-neb and [Zn(im) 2 ·0.5mor]-neb as well as an evalutation of time-resolved SAXS/WAXS data recorded in-situ during the formation of [Zn(im) 2 ]-zni.

The ZIF system zinc(II) 4,5-dichoroimidazolate: theoretical and experimental investigations of the polymorphism and crystallization mechanisms

“…Concerning clusters and particles, our investigations above have added significant new details to the mechanism. However, the mechanism differs partly from that observed for the formation of dense [Zn(im) 2 ]-zni in similar dilute solution, where a particle growth by monomer addition with the particle as the monomer occurs [1,56].…”

“…Further details can be found in two recent publications [20,21]. Some previous studies on the [Zn(dcim) 2 ] system [22] had already been summarized elsewhere [1]. In addition, we present as yet unpublished work.…”

“…Zn, Co) form dense (non-porous) and open (porous) framework structures with underlying 3-dimensional tetrahedral networks (zeolitic imidazolate frameworks, ZIFs) with properties [1][2][3] that make them potentially useful for applications in many different fields ranging from separation [4] and catalysis [5] to drug delivery [6]. However, discovery of theoretically predicted and potentially existing new ZIFs still proceeds mainly on a "trial-and-error" basis [7], because synthesis-structure relationships and mechanisms of crystallization are poorly understood [1,8,9].…”

“…Since the publication of our first report in late 2014 [1], a number of remarkable papers have appeared on the prediction of hypothetical and potentially accessible structures and the mechanisms of crystallization. Going beyond earlier theoretical work based on density functional theory (DFT) to calculate relative framework stabilities at 0 K [10,11], two research groups used force field-based molecular simulation methods to investigate for the first time the influence of solvent, temperature and pressure on the stability of ZIF frameworks with different topologies.…”

Compositions and Structures of Zeolitic Imidazolate Frameworks

“…This β‐phase is considered to be a coi structure. On the other hand, under atmospheric pressure conditions, the coi structure is stable below 360 °C, and above the temperature, zni is stable; when a coi ZIF is heated, the coordination geometry of metal ions become trigonal planar followed by irreversible conversion to a zni ZIF. Other types of ZIFs (BTC ZIF‐1, DFT ZIF‐3, cag ZIF‐4) transform into thermodynamically stable zni crystals at 400 °C via intermediate amorphous ZIFs at 300 °C ,…”