Unconventional Pyridyl Ligand Inclusion within a Flexible Metal‐Organic Framework Bearing an N,N′‐Diethylformamide (DEF)‐Solvated Cd₅ Cluster Secondary Building Unit

Abstract

A cationic three‐dimensional (3D) metal‐organic framework (MOF) sustained by an N,N′‐diethylformamide (DEF)‐solvated zigzag‐shaped Cd5 cluster secondary building unit (SBU), [Et2NH2]2[Cd5(BTB)4(DEF)2] ⋅ 4.75DEF (1 a, H3BTB=benzene‐1,3,5‐tribenzoic acid) shows flexible framework behavior and undergoes solvate exchange with CHCl3 to yield [Et2NH2]2[Cd5(BTB)4(DEF)2] ⋅ xCHCl3 (1 b) accompanied by changes to pore sizes and shapes. Unexpectedly, the DEF solvates coordinated to the central Cd2+ could not be replaced by strongly donor pyridyl and dipyridyl ligands. Additionally, more electron‐deficient pyridyls preferentially coordinated to the flanking Cd2+ of the Cd5 SBU, as exemplified by [Et2NH2]2[Cd5(BTB)4(DEF)2(PyCHO)2] ⋅ xSol (2 a, PyCHO=4‐pyridinealdehyde) and [Et2NH2]2[Cd5(BTB)4(DEF)2(PyAc)2] ⋅ xSol (2 b, PyAc=4‐acetylpyridine). Density functional theory (DFT) calculations were used to understand these counterintuitive observations.

A Heterometallic Three-Dimensional Metal−Organic Framework Bearing an Unprecedented One-Dimensional Branched-Chain Secondary Building Unit

“…It should be noted that the MOF 1 structure reported herein is drastically different from, and as a matter of fact more complicated than, several BTB-based MOFs of Cd, such as 2D MOF of [Cd 3 (BTB) 2 (DEF) 4 ]·2(DEF) 0.5 [ 62 , 63 , 64 ], 3D MOF of [Et 2 NH 2 ] 2 [Cd 5 (BTB) 4 (DEF) 2 ]∙4.75DEF [ 65 ], and 3D MOF of [NEt 4 ] 2 [Cd 5 (BTB) 4 (H 2 O) 4 ] [ 64 ]. We are not aware of any BTB-based MOFs of Ca reported to date.…”

“…The motivation for introducing Ca 2+ into a Cd 2+ /H 3 BTB assembly originated from our quest to incorporate Ca 2+ into the linear Cd 3 -based two-dimensional (2D) MOF of [Cd 3 (BTB) 2 (DEF) 4 ]·2(DEF) 0.5 [ 62 , 63 ], as we and others have demonstrated that the heterometallic combinations of Cd/Zn, Cd/Co, and Zn/Co are readily tolerated in linear trimetallic cluster SBUs [ 26 , 66 ]. Our previous trial of the solvothermal reaction of Cd(NO 3 ) 2 ∙4H 2 O and H 3 BTB in a DEF/H 2 O/HNO 3 mixed solvent with CaSO 4 yielded a 3D anionic MOF of [Et 2 NH 2 ] 2 [Cd 5 (BTB) 4 (DEF) 2 ]∙4.75DEF featuring a zigzag-shaped Cd 5 cluster SBU [ 65 ]. The [Et 2 NH 2 ] + cations likely arose from the acid-catalyzed hydrolysis of DEF [ 67 , 68 , 69 , 70 ], and subsequently served as a template for the framework formation.…”

“…Such a complicated MOF generated via the mixed use of a Cd 2+ and Ca 2+ features the first case of a framework structure containing both Ca 2+ and BTB ligands. In addition, the structure of MOF 1 is dramatically different from, and in fact much more delicate than, all the literature examples that are exclusively from the assembly of Cd 2+ with BTB ligands [62][63][64][65].…”

“…The motivation for introducing Ca 2+ into a Cd 2+ /H 3 BTB assembly originated from our quest to incorporate Ca 2+ into the linear Cd 3 -based two-dimensional (2D) MOF of [Cd 3 (BTB) 2 (DEF) 4 ]•2(DEF) 0.5 [62,63], as we and others have demonstrated that the heterometallic combinations of Cd/Zn, Cd/Co, and Zn/Co are readily tolerated in linear trimetallic cluster SBUs [26,66] [65]. The [Et 2 NH 2 ] + cations likely arose from the acid-catalyzed hydrolysis of DEF [67][68][69][70], and subsequently served as a template for the framework formation.…”

Vacuum-Induced Guest N,N′-Diethylformamide Binding in a Metastable Cd5-Based Metal–Organic Framework

“…As a follow-up to our previous work on gas adsorption, 40 we further measured the CO 2 adsorption−desorption isotherms of two other phases: MOFs 1_4h and 1_32h with samples activated at room temperature (Figure S7). The isotherms of MOF 1_4h resemble those of MOF 1, while those of MOF 1_32h are different, although with similar gas uptake capacity.…”