Concomitant Formation of Compositionally Distinct Coordination Polymers Based on a Triacid Linker: Solvent‐Mediated Metamorphosis

Abstract

The solvothermal reaction of the semirigid tritopic ligand 1,3,5-tris[2,6-dimethyl-4-(α-carboxy)methoxyphenyl]benzene (H 3 BTA) with Zn(NO 3 ) 2 in a DEF/EtOH/H 2 O (4:2:1 v/v/v, DEF = N,N-diethylformamide) mixture leads to the formation of three compositionally distinct coordination polymers (CPs) with different morphologies, that is, rods (Zn-R), needles (Zn-N), and blocks (Zn-B), in the same pot at different concentrations and temperatures. Two sets of compositionally distinct CPs are formed concomitantly at two different reactant concentrations, and one of them is common to the two sets. Attempts to interconvert the three CPs at different temperatures in the same solvent system revealed that the acentric crystals of Zn-N and [a]

Metal-Mediated Self-Assembly of a Twisted Biphenyl-Tetraacid Linker with Semi-rigid Core and Peripheral Flexibility: Concomitant Formation of Compositionally Distinct MOFs

“…The occurrence of this phenomenon, namely, concomitant formation of MOFs that are compositionally distinct, is rare and points to the choice of the linker in adopting two or more modes of self-assembly under identical conditions. In corroboration of previously documented results, 20 the structural flexibility by virtue of acetic acid moieties at the periphery and some degree of torsional flexibility between the aryl rings that make up the core seemingly contribute to the observed concomitant formation of MOFs in addition to the unique topologies of MOFs and the occurrence of multimetal ion clusters and 1D chains of metals ions as SBUs. In Table 3 are collected the values of the torsion angles observed between the planes of dimethoxyaryl rings (ϕ s ) and those between the aryl rings and the cetral dimethoxyaryl rings (Ψs) in all the structures of MOFs.…”

“…Given that the carboxylate functionalities exhibit variable coordination modes, our goals were to access MOFs of the flexible H 4 L linker with different metal ions, and investigate the possibility of formation of MOFs that are isomeric or compositionally distinct, as in our earlier study. 20 As evident from foregoing descriptions, we were successful in obtaining four different MOFs of the 4-connecting linker H 4 L. The four MOFs are Cd-MOF, Mn-MOF, and two concomitant Zn-MOFs with varying compositions of the linker and Zn 2+ ions. Structure determinations of the otherwise limited number of MOFs demonstrate the fact that the unique D 2d -symmetry extant to the H 4 L linker allows, in first place, access to MOFs with high solvent-accessible volumes, which vary in the range of 43−52%.…”

“…We have recently shown that increased peripheral flexibility in a trigonal triacid linker leads to concomitant formation of two different compositionally distinct MOFs, which could be isolated independently by variation of temperature. 20 This finding was also a motivation to investigate metal-assisted self-assembly of the tetraacid linker H 4 L with different metal ions. Indeed, the reaction of H 4 L with cadmium, manganese, and zinc salts led to four porous MOFs of different topologies.…”

“…17,18 The synthesis/crystallization process by which the MOFs are accessed is sensitive to different reaction parameters, and often results in the occurrence of unusual secondary building units (SBUs). 19,20 The latter in turn lead to formation of interesting and varied network structures. Consequently, formation of two or more different metal−organic frameworks from the same synthesis/crystallization pot with intriguing structure types is not rare, which indeed subverts the anticipated framework structures based on connectivity dispositions of the linker and coordination preferences of the metal ions.…”

“…Metal–organic frameworks (MOFs) are exotic porous materials that permit diverse applications such as gas storage, molecular sieving, sensing, magnetism, catalysis, bioimaging, drug delivery, etc. − Synthesis of MOFs with predefined framework structures remains still a challenge, as the reactions to access them depend on a variety of parameters, which include metal–linker ratio, pH, solvent employed, temperature, coordination number and geometry of the metal ion, nature of the counterion used, additive, etc. − It is needless to say that the structural attributes of an organic linker play a crucial role in determining the structures as well as topologies of the derived frameworks due to variable coordination modes, conformational flexibility, and presence of different secondary functional groups. , The synthesis/crystallization process by which the MOFs are accessed is sensitive to different reaction parameters, and often results in the occurrence of unusual secondary building units (SBUs). , The latter in turn lead to formation of interesting and varied network structures. Consequently, formation of two or more different metal–organic frameworks from the same synthesis/crystallization pot with intriguing structure types is not rare, which indeed subverts the anticipated framework structures based on connectivity dispositions of the linker and coordination preferences of the metal ions. − In principle, one may access coordination polymers with the same framework chemical formula, but different structures or those that differ in terms of both chemical formula as well as structural attributes. The former have been popularly termed “supramolecular isomers”, ,− while those differing in chemical formulas have been termed “structural isomers”. , The literature reveals abundant examples of solvent-, template-, counterion-, additive-, and temperature-dependent formation of isomeric coordination polymers. ,− MOFs being materials whose structures and chemical functionalities can be tuned in a bottom-up approach through the linkers modifications, the structure–property relationships help in deciphering subtle factors that are important for their functional properties.…”