Distinct Chromic and Magnetic Properties of Metal–Organic Frameworks with a Redox Ligand

An electron-deficient and potentially chromic ligand has been utilized to impart redox activity, photo- and hydrochromism, and solvotomagnetism to metal–organic frameworks (MOFs). A pair of MOFs were constructed from the flexible zwitterionic viologen-tethered tetracarboxylate linker N,N′-bis­(3,5-dicarboxylatobenzyl)-4,4′-bipyridinium (L2–): [Co3(L)­(N3)4] (1) and [Mn2(L)­(N3)2(H2O)2]·3H2O (2). Both compounds show three-dimensional frameworks in which mixed azido- and carboxylato-bridged chains are connected through the electron-deficient viologen moieties. The chain in 1 is built from alternating bis­(azide) and (azide)­bis­(carboxylate) bridges, while that in 2 contains uniform (azide) (carboxylate) bridges. The MOFs shows the characteristic redox properties of the viologen moieties. The redox activity affords the MOFs with different chromic properties, owing to subtle differences in chemical environments. 1 shows reversible photochromism, which is related to the radical formation through photoinduced electron transfer from azide–carboxylate to viologen according to UV–vis, X-ray photoelectron, and electron spin resonance spectroscopy and DFT calculations. 2 is nonphotochromic for lack of appropriate pathways for electron transfer. Unexpectedly, 2 shows a novel type of solid-state hydrochromism. Upon the removal and reabsorption of water, the compound shows remarkable color change because of reversible electron transfer accompanying a reversible structural transformation. The radical mechanism is distinct from those for traditional hydrochromic inorganic and organic materials. Magnetic studies indicate ferro- and antiferromagnetic coupling in 1 and 2, respectively. What’s more, 2 shows marked magnetic response to the removal of water molecules owing to the formation of radicals. The compound illustrates a unique material exhibiting dual responses (color and magnetism) to water

Differentiable Detection of Volatile Amines with a Viologen-Derived Metal–Organic Material

The development of selective sensing materials for amine detection has received considerable attentions because amines have high toxicity and exist widely. In this article, we demonstrate for the first time that a degree of discriminative detection of alkylamines can be achieved by a metal–organic coordination material. The material is derived from Cd^II and 4,4′-bipyridinium-1,1′-bis­(phenylene-3-carboxylate), shows 1D channels lined with electron-deficient viologen chromophores, and exhibits different colors upon contact with amine vapors of different molecular sizes and types (primary, secondary, and tertiary). The vapochromism is attributable to electron transfer from the amine group to viologen. The discrimination between amines is because the analyte–receptor interactions, which either directly mediate or indirectly affect electron transfer, are influenced by the number of the N–H bonds in the amine molecule, the size of the amine molecule relative to the receptor channel and the steric hindrance for the electron donor–acceptor contacts. The material also shows reversible photo- and hydrochromism owing to stimuli-induced reversible electron transfer. The compound can be deposited in paper simply by spraying the mixture solution of the starting metal salt and the ligand. The paper can be used as portable test strips for visual and differentiable detection of amines and as erasable inkless printing medium

Differentiable Detection of Volatile Amines with a Viologen-Derived Metal–Organic Material

The development of selective sensing materials for amine detection has received considerable attentions because amines have high toxicity and exist widely. In this article, we demonstrate for the first time that a degree of discriminative detection of alkylamines can be achieved by a metal–organic coordination material. The material is derived from Cd^II and 4,4′-bipyridinium-1,1′-bis­(phenylene-3-carboxylate), shows 1D channels lined with electron-deficient viologen chromophores, and exhibits different colors upon contact with amine vapors of different molecular sizes and types (primary, secondary, and tertiary). The vapochromism is attributable to electron transfer from the amine group to viologen. The discrimination between amines is because the analyte–receptor interactions, which either directly mediate or indirectly affect electron transfer, are influenced by the number of the N–H bonds in the amine molecule, the size of the amine molecule relative to the receptor channel and the steric hindrance for the electron donor–acceptor contacts. The material also shows reversible photo- and hydrochromism owing to stimuli-induced reversible electron transfer. The compound can be deposited in paper simply by spraying the mixture solution of the starting metal salt and the ligand. The paper can be used as portable test strips for visual and differentiable detection of amines and as erasable inkless printing medium

Differentiable Detection of Volatile Amines with a Viologen-Derived Metal–Organic Material

The development of selective sensing materials for amine detection has received considerable attentions because amines have high toxicity and exist widely. In this article, we demonstrate for the first time that a degree of discriminative detection of alkylamines can be achieved by a metal–organic coordination material. The material is derived from CdII and 4,4′-bipyridinium-1,1′-bis­(phenylene-3-carboxylate), shows 1D channels lined with electron-deficient viologen chromophores, and exhibits different colors upon contact with amine vapors of different molecular sizes and types (primary, secondary, and tertiary). The vapochromism is attributable to electron transfer from the amine group to viologen. The discrimination between amines is because the analyte–receptor interactions, which either directly mediate or indirectly affect electron transfer, are influenced by the number of the N–H bonds in the amine molecule, the size of the amine molecule relative to the receptor channel and the steric hindrance for the electron donor–acceptor contacts. The material also shows reversible photo- and hydrochromism owing to stimuli-induced reversible electron transfer. The compound can be deposited in paper simply by spraying the mixture solution of the starting metal salt and the ligand. The paper can be used as portable test strips for visual and differentiable detection of amines and as erasable inkless printing medium

Magnetic and Photochromic Properties of a Manganese(II) Metal-Zwitterionic Coordination Polymer

The solvothermal reaction of Mn­(ClO₄)₂, NaN₃, and a rigid viologen-tethered tetracarboxylic acid (1,1′-bis­(3,5-dicarboxyphenyl)-4,4′-bipyridinium chloride, [H₄L]­Cl₂) led to a coordination polymer of formula [Mn₄(L)­(N₃)₆(H₂O)₂]_<i>n</i>. X-ray analysis revealed a 3D coordination structure. The Mn­(II) ions are connected by mixed azide and carboxylate bridges to give 2D layers, which are pillared by the viologen tether of the zwitterionic ligand. Magnetic analyses suggested that the compound features antiferromagnetism and field-induced metamagnetism. The compound also shows photochromic and photomagnetic properties. The long-range magnetic ordering is owed to the spin-canting structure of the Mn­(II)-azide-carboxylate layer; the photochromism involves the formation of viologen radicals via photoinduced electron transfer, and the photomagnetism is related to the interactions between the metal ion and the photogenerated radicals. The study demonstrates a strategy for the design of new multifunctional materials with photoresponsive properties

Distinct Chromic and Magnetic Properties of Metal–Organic Frameworks with a Redox Ligand

An electron-deficient and potentially chromic ligand has been utilized to impart redox activity, photo- and hydrochromism, and solvotomagnetism to metal–organic frameworks (MOFs). A pair of MOFs were constructed from the flexible zwitterionic viologen-tethered tetracarboxylate linker <i>N,N</i>′-bis­(3,5-dicarboxylatobenzyl)-4,4′-bipyridinium (L^2–): [Co₃(L)­(N₃)₄] (<b>1</b>) and [Mn₂(L)­(N₃)₂(H₂O)₂]·3H₂O (<b>2</b>). Both compounds show three-dimensional frameworks in which mixed azido- and carboxylato-bridged chains are connected through the electron-deficient viologen moieties. The chain in <b>1</b> is built from alternating bis­(azide) and (azide)­bis­(carboxylate) bridges, while that in <b>2</b> contains uniform (azide) (carboxylate) bridges. The MOFs shows the characteristic redox properties of the viologen moieties. The redox activity affords the MOFs with different chromic properties, owing to subtle differences in chemical environments. <b>1</b> shows reversible photochromism, which is related to the radical formation through photoinduced electron transfer from azide–carboxylate to viologen according to UV–vis, X-ray photoelectron, and electron spin resonance spectroscopy and DFT calculations. <b>2</b> is nonphotochromic for lack of appropriate pathways for electron transfer. Unexpectedly, <b>2</b> shows a novel type of solid-state hydrochromism. Upon the removal and reabsorption of water, the compound shows remarkable color change because of reversible electron transfer accompanying a reversible structural transformation. The radical mechanism is distinct from those for traditional hydrochromic inorganic and organic materials. Magnetic studies indicate ferro- and antiferromagnetic coupling in <b>1</b> and <b>2</b>, respectively. What’s more, <b>2</b> shows marked magnetic response to the removal of water molecules owing to the formation of radicals. The compound illustrates a unique material exhibiting dual responses (color and magnetism) to water

Magnetic and Photochromic Properties of a Manganese(II) Metal-Zwitterionic Coordination Polymer

The solvothermal reaction of Mn­(ClO₄)₂, NaN₃, and a rigid viologen-tethered tetracarboxylic acid (1,1′-bis­(3,5-dicarboxyphenyl)-4,4′-bipyridinium chloride, [H₄L]­Cl₂) led to a coordination polymer of formula [Mn₄(L)­(N₃)₆(H₂O)₂]_<i>n</i>. X-ray analysis revealed a 3D coordination structure. The Mn­(II) ions are connected by mixed azide and carboxylate bridges to give 2D layers, which are pillared by the viologen tether of the zwitterionic ligand. Magnetic analyses suggested that the compound features antiferromagnetism and field-induced metamagnetism. The compound also shows photochromic and photomagnetic properties. The long-range magnetic ordering is owed to the spin-canting structure of the Mn­(II)-azide-carboxylate layer; the photochromism involves the formation of viologen radicals via photoinduced electron transfer, and the photomagnetism is related to the interactions between the metal ion and the photogenerated radicals. The study demonstrates a strategy for the design of new multifunctional materials with photoresponsive properties

Switchable Ferro‑, Ferri‑, and Antiferromagnetic States in a Piezo- and Hydrochromic Metal–Organic Framework

The Mn­(II) metal–organic framework with a viologen-based tetracarboxylate ligand exhibits reversible optical (color) and magnetic changes concomitant with stimuli-induced electron transfer from carboxylate to viologen. Compression causes a magnetic transformation from ferro- to ferrimagnetic, while water release/reuptake switches the magnetic behavior between ferro- and antiferromagnetic

Distinct Chromic and Magnetic Properties of Metal–Organic Frameworks with a Redox Ligand

An electron-deficient and potentially chromic ligand has been utilized to impart redox activity, photo- and hydrochromism, and solvotomagnetism to metal–organic frameworks (MOFs). A pair of MOFs were constructed from the flexible zwitterionic viologen-tethered tetracarboxylate linker <i>N,N</i>′-bis­(3,5-dicarboxylatobenzyl)-4,4′-bipyridinium (L^2–): [Co₃(L)­(N₃)₄] (<b>1</b>) and [Mn₂(L)­(N₃)₂(H₂O)₂]·3H₂O (<b>2</b>). Both compounds show three-dimensional frameworks in which mixed azido- and carboxylato-bridged chains are connected through the electron-deficient viologen moieties. The chain in <b>1</b> is built from alternating bis­(azide) and (azide)­bis­(carboxylate) bridges, while that in <b>2</b> contains uniform (azide) (carboxylate) bridges. The MOFs shows the characteristic redox properties of the viologen moieties. The redox activity affords the MOFs with different chromic properties, owing to subtle differences in chemical environments. <b>1</b> shows reversible photochromism, which is related to the radical formation through photoinduced electron transfer from azide–carboxylate to viologen according to UV–vis, X-ray photoelectron, and electron spin resonance spectroscopy and DFT calculations. <b>2</b> is nonphotochromic for lack of appropriate pathways for electron transfer. Unexpectedly, <b>2</b> shows a novel type of solid-state hydrochromism. Upon the removal and reabsorption of water, the compound shows remarkable color change because of reversible electron transfer accompanying a reversible structural transformation. The radical mechanism is distinct from those for traditional hydrochromic inorganic and organic materials. Magnetic studies indicate ferro- and antiferromagnetic coupling in <b>1</b> and <b>2</b>, respectively. What’s more, <b>2</b> shows marked magnetic response to the removal of water molecules owing to the formation of radicals. The compound illustrates a unique material exhibiting dual responses (color and magnetism) to water