Related Experiment Video
Updated: Jun 29, 2026
06:53
Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
Published on: June 9, 2023
Metal-center electron affinity modulates multicolor electrochromism in 2D conjugated metal-organic frameworks
Qi Zhao1,2, Jing Yang3, Zhendong Liu4
1Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore.
Nature Communications
|June 27, 2026
Summary
Metal centers critically influence electrochromic device performance. This study reveals a metal-center electron-affinity mechanism, enhancing multicolor transitions and device speed using Zn, Ni, and Cu metal-organic frameworks.
Area of Science:
- Materials Science
- Electrochemistry
- Nanotechnology
Background:
- Two-dimensional conjugated metal-organic frameworks (MOFs) show promise for electrochromic devices.
- Current MOF electrochromics suffer from limited color palettes and unclear coloration mechanisms.
- The role of metal centers in MOF electrochromism is often overlooked, with focus primarily on ligand-centered redox processes.
Purpose of the Study:
- To investigate the critical role of metal centers in the electrochromic performance of two-dimensional conjugated MOFs.
- To elucidate a metal-center electron-affinity mechanism governing coloration.
- To identify optimal metal centers for enhanced electrochromic properties and multicolor transitions.
Main Methods:
- Employed unsupervised machine learning to screen divalent metal-catecholate (CAT) systems.
- Synthesized and characterized Zn-CAT, Ni-CAT, and Cu-CAT systems.
- Evaluated electrochromic performance, including switching speeds and cycling stability.
Main Results:
- Identified Zn, Ni, and Cu as optimal metal centers for multicolor electrochromism (green to blue to purple).
- Zn- and Ni-CAT-1 exhibited significantly faster switching speeds (4.8/5.4 s) and superior cycling stability (>20,000 cycles) compared to Cu-CAT-1 (<300 cycles).
- Demonstrated that the redox-active Cu²⁺ configuration leads to slower kinetics and degradation, unlike inert Ni²⁺ and Zn²⁺.
Conclusions:
- A metal-center electron-affinity mechanism is crucial for electrochromic performance in 2D MOFs.
- Zn and Ni centers offer superior electrochromic switching and stability over Cu.
- Findings enable the rational design of advanced multicolor electrochromic devices for applications in camouflage, displays, and wearables.
Related Concept Videos
03:02Colors and Magnetism
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.
02:58Crystal Field Theory - Octahedral Complexes
Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:42Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
02:51Metal-Ligand Bonds
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
01:23Properties of Organometallic Compounds
Organometallic compounds are compounds that contain a carbon–metal bond. Carbon belongs to an organyl group like alkyl, aryl, allyl, or benzyl groups. The metal can be from Group I or Group II of the periodic table, a transition metal, or a semimetal.
02:58Properties of Transition Metals
Transition metals are defined as those elements that have partially filled d orbitals. As shown in Figure 1, the d-block elements in groups 3–12 are transition elements. The f-block elements, also called inner transition metals (the lanthanides and actinides), also meet this criterion because the d orbital is partially occupied before the f orbitals.