Identifying the Internal Network Structure of a New Copper Isonicotinate Thin‐Film Polymorph Obtained via Chemical Vapor Deposition

Abstract

tion of homogeneous films onto solid supports. [9] The presence of a surface during framework formation can strongly influence the crystallization process, even inducing the formation of unknown crystal phases. Such unique polymorphs also appear in thin films of purely organic or inorganic compounds [10] and are commonly referred to as substrate-induced polymorphs or thin-film phases. [11] Detailed knowledge of these crystal structures is essential since thin-film phases can have considerably different properties than bulk polymorphs. [12] MOF thin films and specially surface-coordinated MOFs (SURMOFs) [13,14] are known to feature unprecedented polymorphs [15,16] that are not accessible in bulk form and can strongly impact the performance of MOF-based devices. [17,18] Thin-film phases can occur when the MOF building blocks interact with surface groups, such as selfassembled monolayers, [19,15] or when the substrate is covered with a precursor layer (i.e., a metal oxide or hydroxide). [20,21] In addition, the physical state of the reagents that interact with the solid surface (i.e., in solution or the vapor phase) can be a determining factor. [22][23][24] Unfortunately, standard crystal structure solution methods are unsuitable for unknown MOF thin-film phases. In contrast to single-crystal or powder X-ray diffraction (XRD) methods, [25] the number of diffraction peaks observed in MOF thin films is The preparation of thin films is often associated with the appearance of unknown polymorphs, as both the substrate and deposition method can heavily influence crystallization processes. Here, chemical vapor deposition is used to obtain thin films of a copper-isonicotinate (Cu-INA) metal-organic framework (MOF). Starting from copper-based precursor layers (copper oxide and hydroxide), a solid-vapor conversion with vaporized isonicotinic acid in either a dry or humidified atmosphere, yields a new Cu-INA MOF polymorph. It is found that the crystalline order of the precursor layer has a strong impact on the texture of Cu-INA thin films. Furthermore, a novel methodology is introduced to determine the structure of a previously unknown thin-film phase of Cu-INA. Although only a few diffraction peaks are found via synchrotron grazing incidence X-ray diffraction (GIXRD), a triclinic unit cell can be determined, and Patterson functions can be calculated. The latter reveals the position of the copper atoms within the unit cell and the alignment of the INA linkers defining the coordination network structure. This work introduces how the combination of GIXRD data with Patterson functions can be used to identify the structure of an unknown thin-film MOF polymorph.

Vapor-Assisted Conversion of Heterobimetallic Titanium–Organic Framework Thin Films

“…These truncated octahedral particles of 1.5 μm in size are smaller than the 10 μm octahedral microcrystals first described for bulk MUV-10 . This is not surprising, as it is well known that crystal shape and size are heavily dependent on the reaction conditions and can also be influenced by the substrate. , EDX analysis also confirmed a composition close to the ideal 1:1 Ti/Ca ratio (Figure h).…”

“…49 This is not surprising, as it is well known that crystal shape and size are heavily dependent on the reaction conditions and can also be influenced by the substrate. 10,51 EDX analysis also confirmed a composition close to the ideal 1:1 Ti/Ca ratio (Figure 3h).…”

Polymorphism and orientation control of copper-dicarboxylate metal–organic framework thin films through vapour- and liquid-phase growth

“…Besides, these solvent-free methods can also yield unique MOF crystalline phases, not accessible in solution. 31,34…”

“…[24][25][26] A myriad of MOFs and coordination polymers have been synthesized under these solvent-free conditions, 26 including various Cu-carboxylate MOFs. [27][28][29][30][31] Even though MOF films oriented in the out-of-plane direction have been obtained via vapour-phase conversion, 28,32,33 in-plane oriented MOF films or heteroepitaxial growth have been just barely explored via vapour-phase syntheses. Besides, these solvent-free methods can also yield unique MOF crystalline phases, not accessible in solution.…”

“…Besides, these solvent-free methods can also yield unique MOF crystalline phases, not accessible in solution. 31,34 Here, we compare liquid-and vapour-phase conditions to grow two Cu-dicarboxylate MOFs from a precursor film of oriented Cu(OH) 2 nanobelts. We selected ligands that can afford heteroepitaxial matching conditions, namely BDC (1,4benzenedicarboxylate) and CDC (trans-1,4cyclohexanedicarboxylate).…”