Nanoporous Nanorods Fabricated by Coordination Modulation and Oriented Attachment Growth

Abstract

Well-designed metal-organic hybrid porous materials-socalled porous coordination polymers (PCPs) or metalorganic frameworks (MOFs)-can be made from an assembly of organic linkers with metal ions. [1][2][3][4][5][6] This class of materials was recently recognized as an intriguing class of crystalline nanoporous materials for gas sorption, separation, and catalysis because their framework topologies and pore sizes can be designed for selective guest accommodation, and the functionality of the pore surfaces directly influences the interaction with guest molecules. Miniaturizing the size of PCP crystals to the nanometer scale [7][8][9][10] by functionalizing the crystal interfaces will provide further opportunities to integrate novel functions into the materials without changing the characteristic features of the PCP crystal itself, and will allow the correlation between the porous properties and interfacial structures of nanocrystals to be investigated. Despite the advantages of nanosized PCPs, growth processes that are most important in establishing a universal methodology for the creation of nanosized PCPs are still unclear because there is no suitable defining protocol. [7,[10][11][12][13] Understanding the crystal growth of framework materials, moreover, promises to determine the fundamental requirements of bottom-up selfassembly processes. Herein, we show that a simple but straightforward method using capping reagents that perturb the framework extension of PCPs can be applied to determine their crystal features. We describe the tetragonal framework system of PCP nanorods defined by selectively modulating the coordination interaction in the framework, which enhances the one-dimensional anisotropic fusion of the cubic nanocrystals, indicating an oriented attachment mechanism. [14,15] Moreover, the correlation between the sorption properties and crystallinity of the nanorods shows that the coordination modulation method can produce highly crystalline nanorods with high porosity comparable to that of bulk crystals synthesized by using the conventional solvothermal method.The relatively weak interactions of the coordination bonds dominate the hierarchical self-assembly process involved in constructing the sparse three-dimensional porous frameworks of PCPs with nanometer lattice constants, leading to the formation of crystals. This feature distinguishes this class of molecular-based materials from dense inorganic materials, such as metal [16] and semiconductor crystals, [17] and from conventional porous materials such as zeolites [18,19] and mesoporous silica. [20,21] Controlling the interactions between metal ions and organic linkers, so-called "coordination equilibria", is important when varying the crystal features of PCPs, such as their size, morphology, and crystallinity. Although several approaches have been developed to fabricate PCP nanoparticles, such as reversed micelles [22] and microwave-assisted methods, [23,24] the crystal-growth mechanism has rarely been discussed because it is difficult to control th...

Porous Interpenetrated Zirconium–Organic Frameworks (PIZOFs): A Chemically Versatile Family of Metal–Organic Frameworks

“…[10,12] PIZOF-1, PIZOF-2, and PIZOF-8 were obtained as single crystals with octahedral shape; PIZOF-3 to -7 were obtained as powders. The framework structure was determined from single crystals.…”

“…The modulator approach, introduced by Kitagawa and co-workers, [12] is an essential prerequisite for the synthesis of the PIZOFs. Recently, we have published that with such a modulator approach, the crystal size and the morphology of the Zr MOFs UiO-66, UiO-67, and UiO-68-NH 2 can be controlled.…”

Crystal Growth Mechanisms and Morphological Control of the Prototypical Metal–Organic Framework MOF‐5 Revealed by Atomic Force Microscopy

“…[15,25,[32][33][34] Notable success has also been achieved directly in controlling the morphology or form of nano-and micron-sized MOF crystals through the addition of modulators. [25,32,33,[35][36][37] MOF-5 [Zn 4 OA C H T U N G T R E N N U N G (bdc) 3 , bdc = 1,4-benzenedicarboxylate] is one of the archetypal permanently porous MOFs that has been synthesised [38] and is also the original member of the first family of isoreticular MOFs (IRMOF-1 to 16). [39] The crystal structure of MOF-5 consists of Zn 4 O units connected by bdc linkers to form a cubic network (space group Fm-3m) as shown in Figure 1 a.…”

Microwave‐Assisted Modular Fabrication of Nanoscale Luminescent Metal‐Organic Framework for Molecular Sensing

“…[1][2][3][4][5][6][7][8][9] Miniaturizing the size of MOF crystals to the nanometer scale offers an interesting approach to design functional nanomaterials for biological and biomedical applications, because their compositions can be systematically tuned by the judicious choice of building blocks. [15][16][17] The fabrication of nanoscale MOF materials with outstanding properties by a rapid and effective method is of great importance. [10] Nanoscale gadolinium MOF materials are used as potential multimodal contrast-enhancing agents.…”