Thermally Triggered Solid‐State Single‐Crystal‐to‐Single‐Crystal Structural Transformation Accompanies Property Changes

Abstract

The 1D complex [(CuL0.5H2O)⋅H2O]n (1) (H4L = 2,2'-bipyridine-3,3',6,6'-tetracarboxylic acid) undergoes an irreversible thermally triggered single-crystal-to-single-crystal (SCSC) transformation to produce the 3D anhydrous complex [CuL0.5]n (2). This SCSC structural transformation was confirmed by single-crystal X-ray diffraction analysis, thermogravimetric (TG) analysis, powder X-ray diffraction (PXRD) patterns, variable-temperature powder X-ray diffraction (VT-PXRD) patterns, and IR spectroscopy. Structural analyses reveal that in complex 2, though the initial 1D chain is still retained as in complex 1, accompanied with the Cu-bound H2O removed and new O(carboxyl)-Cu bond forming, the coordination geometries around the Cu(II) ions vary from a distorted trigonal bipyramid to a distorted square pyramid. With the drastic structural transition, significant property changes are observed. Magnetic analyses show prominent changes from antiferromagnetism to weak ferromagnetism due to the new formed Cu1-O-C-O-Cu4 bridge. The catalytic results demonstrate that, even though both solid-state materials present high catalytic activity for the synthesis of 2-imidazolines derivatives and can be reused, the activation temperature of complex 1 is higher than that of complex 2. In addition, a possible pathway for the SCSC structural transformations is proposed.

A New Preorganized Metalloligand Linker for the Construction of Luminescent Coordination Polymers

“…The bptc ligands show an anti bridging mode by coordination of the pyridyl N atom and 6,3′-carboxylate groups with Cu­(II) ions. Moreover, the flexible coordination mode of bptc 4– ligands and Cu­(II) ions causes [[Cu­(bptc) 0.5 (H 2 O)]·H 2 O] n to undergo a thermally triggered solid-state single-crystal to single-crystal transformation to produce the 3D anhydrous complex [Cu­(bptc) 0.5 ] n . However, when H 4 bptc is combined with TM ions (Mn­(II), Cd­(II), Re­(III)) or lanthanide ions ,,, with larger ionic radii, the ligands usually adopt a syn chelating mode to coordinate the metal ions with two bipyridyl N atoms and 6,6′-carboxylate groups.…”

“…Moreover, the flexible coordination mode of bptc 4− ligands and Cu(II) ions causes [[Cu(bptc) 0.5 (H 2 O)]•H 2 O] n to undergo a thermally triggered solid-state single-crystal to single-crystal transformation to produce the 3D anhydrous complex [Cu(bptc) 0.5 ] n . 35 However, when H 4 bptc is combined with TM ions (Mn(II), 39 Cd(II), 41 Re(III) 42 ) or lanthanide ions 32,34,43,44 with larger ionic radii, the ligands usually adopt a syn chelating mode to coordinate the metal ions with two bipyridyl N atoms and 6,6′carboxylate groups. In our case, despite the presence of various competitive metal ions (La(III), Cd(II), Zn(II), and Mn(II)), like its analogues, the 1,10-phenanthroline-2,9-dicarboxamide derivatives, 37 the preorganized H 4 bptc in 1−4 adopts a syn chelating conformation and shows exclusive affinity toward linear uranyl ions with large ionic radii, leading to distinct [(UO 2 )(bptc)] 2− metalloligand motifs, which are further connected to each other and other metal ions by utilizing carboxylate groups to produce various structures.…”

“…Recently, such research interests have been extended to uranyl-based LCPs on account of their fascinating topologies and various applications. − Our group has focused on the construction of uranyl-based LCPs with characteristic UO 2 2+ -centered yellow-green emission. − Among them, in accord with to the hard–soft acid–base (HSAB) concept, several uranyl-based heterometallic LCPs were constructed by employing a series of bipyridine carboxylic acids with both soft nitrogen and hard oxygen coordination sites. − As a continuation of our study, we have chosen a multidentate bipyridyl tetracarboxylic acid, 2,2′-bipyridine-3,3′,6,6′-tetracarboxylic acid (H 4 bptc), on the basis of the following considerations. (1) The bipyridyl nitrogen atoms and carboxylate oxygen atoms may have excellent coordination activity toward various metal ions. − (2) Versatile coordination modes of bipyridyl rings and carboxylate groups show potential connectivity to build coordination polymers with novel structures. − (3) H 4 bptc contains two carboxylate groups at the 6,6′-positions of 2,2′-bipyridine; this segment resembles the structure of 1,10-phenanthroline-2,9-dicarboxamide derivatives, which has a strong affinity toward uranyl ions . Herein, by employing H 4 bptc, uranyl ions, and various metal salts, four heterometallic uranyl-based CPs, namely [[La­(UO 2 )­(bptc)­(H 2 O) 8 ]­[(UO 2 )­(Hbptc)]·6H 2 O] n ( 1 ), [Cd­(UO 2 ) 3 (bptc) 2 (H 2 O) 2 ] n ( 2 ), [Zn­(UO 2 ) 3 (bptc) 2 (H 2 O) 2 ] n ( 3 ), and [Mn­(UO 2 )­(bptc)­(H 2 O) 3 ] n ( 4 ), have been successfully synthesized under hydrothermal conditions.…”

Recent progress in strategies for preparation of metal-organic frameworks and their hybrids with different dimensions

“…Over the last few decades, much research demonstrated that SCSC conversions of MOFs could be triggered by external stimuli, including physical and chemical processes, such as temperature, pressure, gas adsorption, etc. [140][141][142][143][144][145] . Through these stimuli, the number of ligands and dimensions can be changed, such as 0D to 1D/2D and 1D to 2D/3D, leading to the synthesis of MOFs [146] .…”

Effect of Coordinated Solvent Molecules on Metal Coordination Sphere and Solvent-Induced Transformations

“…MOFs with aromatic multicarboxylate ligands could be preeminent candidates for researching single crystal to single crystal (SCSC) transformations, because a part of them possess good stability in air and/or in solvent. ,− Some aromatic multicarboxylate ligands, such as 1,4-benzenedicarboxylic acid (H 2 BDC), 1,3,5-benzenetricarboxylic acid (H 3 BTC), biphenyl-3,5,3′,5′-tetracarboxylate acid (3,5-H 4 bptc, Scheme a), biphenyl-3,4,3′,4′-tetracarboxylate acid (3,4-H 4 bptc, Scheme b), and biphenyl-2,2′,4,4′-tetracarboxylic acid (2,4-H 4 bptc, Scheme c), have been extensively studied, ,− and their MOFs’ SCSC transformations have also been studied. , While compared with these pure carboxylate ligands, our particular interest focuses on the ligand 6,6′-dinitro-2,2′,4,4′-biphenyltetracarboxylic acid (H 4 nbtc, Scheme e) because of the nitro and carboxyl doubly functionalized groups, the rotated hindrance of two phenyl rings, suitable size of the phenyl tether, and inadequate exploration in the domain of MOFs. After several examples were reported by us recently, , here as an extension study, a series of similar Mn­(II) MOFs {[Mn 2 (nbtc)­(H 2 O) 2 (S)]­·S·0.5H 2 O} n [S = DMF ( 1 ), DMA ( 2 ), NMP ( 3 ), DEF ( 4 )] (DMF = N , N ′-dimethylformamide, DMA = N , N ′-dimethylacetamide, NMP = N -methyl-2-pyrrolidinone, DEF = N , N ′-diethylformamide), exhibiting unique three-dimensional (3D) double-walled open-frameworks, have been successfully obtained.…”