Liquid-Phase Epitaxial Growth of Highly Oriented and Multivariate Surface-Attached Metal–Organic Frameworks

Abstract

Multivariate metal−organic frameworks (MTV-MOFs) incorporating multiple chemical functionalities within single-phase crystalline materials show superior properties that arise from synergistic effects. Herein, we report an efficient and versatile method for the growth of highly oriented multivariate surface-attached MOFs (MTV-SURMOFs) by the combination of the liquid-epitaxial growth method (LPE) and the mixed-linker strategy. Twenty-six MTV-SURMOFs of the [M 2 L 2 P] type with a maximum of five different dicarboxylate linkers (L) were deposited onto suitably functionalized surfaces. Systematic studies by infrared reflection absorption (IRRA) spectroscopy and surface XRD provide evidence for the formation of highly oriented MTV-SURMOFs. Interestingly, the pK a 's of the dicarboxylate linkers play a crucial role for the orientational quality of the MTV-SURMOFs. In addition, benzene uptake experiments showed that the MTV-SURMOFs exhibit up to 2.6 times higher adsorption capacity as compared to the single-linker SURMOFs, demonstrating the synergistic effects in these surface systems.

Concentration‐Dependent Seeding as a Strategy for Fabrication of Densely Packed Surface‐Mounted Metal–Organic Frameworks (SURMOF) Layers

“…Based on recent studies of the LbL SURMOF growth mechanism, which suggest that reagent concentration might play a role in the deposition process, we wanted to systematically vary this parameter. We chose the established pillared‐layer MOF Cu 2 (F 4 bdc) 2 (dabco) (linker: F 4 bdc 2− =tetrafluorobenzene‐1,4‐dicarboxylate, pillar: dabco=1,4‐diazabicyclo‐[2.2.2]octane), because this system sensitively reacts to changes of LbL parameters . Moreover, the infrared spectrum of the F 4 bdc 2− linker exhibits shifts in the carboxylate bands that allow for a more accurate distinction of the involved species in the spectroscopic data .…”

Chiral and SHG-Active Metal–Organic Frameworks Formed in Solution and on Surfaces: Uniformity, Morphology Control, Oriented Growth, and Postassembly Functionalization

“… 43 , 45 Applications of these monolithic and homogeneous coatings include sensing, gas separation, and membrane technology. 29 , 46 − 54 (III) The orientation of crystals on surfaces is also an important structural feature (e.g., for the formation of organic resonators 55 and efficient use of channels 56 − 58 ). Methods to achieve macroscopically oriented MOFs are mainly related to carboxylate-ligand chemistry and specific structures.…”

Infrared crystallography for framework and linker orientation in metal–organic framework films

“…S12 in ESI † for XRD data) and with patterns reported in literature. 30,47 Polarization-dependent ATR spectra of CuBDC, Cu 2 (BDC) 2 -DABCO and Cu 2 (1,4-NDC) 2 DABCO with 3 and 10 layers, respectively, are given in Fig. 6.…”

“…This fact has been exploited by Terfort and co-works to differentiate between surface-attached MOF (SURMOF) lms synthesized in different crystallographic orientations. 19,30 The carboxylate bands originating from the coordination of the organic linker with the metal nodes are ideally suited to study the MOF orientation: four carboxylate bonds in their bridging conguration are oriented in a Cupaddle wheel that directs the structure of all MOFs with bimetal building units (e.g. MOFs based on M ¼ Cu, Cr, Mo, etc., compare Fig.…”

“…31 The perpendicular orientation of the carboxylate bonds to each other and also to the surface allowed Terfort and co-works to determine the out-of-plane orientation of MOF lms with different preferred orientation synthesized by LbL synthesis on gold surfaces functionalized with SAMs. 19,30 Although IRRAS is well suited to study MOF lms prepared from SAMs, the technique is restricted to oriented lms deposited on metal surfaces. Furthermore, information on the orientation of chemical bonds apart from perpendicular orientation, i.e.…”