Charge Transfer Induced Multifunctional Transitions with Sensitive Pressure Manipulation in a Metal–Organic Framework

Abstract

The metal-organic framework {[Fe(2,2'-bipyridine)(CN)4]2Co(4,4'-bipyridine)}·4H2O (Fe2Co-MOF) with single-chain magnetism undergoes an intermetallic charge transfer that converts the Fe2Co charge/spin configurations from Fe(3+)LS-Co(2+)HS-Fe(3+)LS to Fe(2+)LS-Co(3+)LS-Fe(3+)LS (LS = low spin, HS = high spin) around 220 K under ambient pressure. A series of coherent phase transitions in structure, magnetism, permittivity and ferroelectricity are found to take place accompanying with the charge transfer, making Fe2Co-MOF a unique ferroelectric single-chain magnet at low temperature. Moreover, our detailed measurements of magnetization, dielectric constant, and Raman scattering under high pressures illustrate that the charge transfer as well as the resulting multifunctional transitions can be readily induced to occur at room temperature by applying a tiny external pressure of about 0.5 kbar. The present study thus provides a pressure well-controllable multifunctional material with potential applications in a broad temperature region across room temperature.

Light‐Induced Bidirectional Metal‐to‐Metal Charge Transfer in a Linear Fe2Co Complex

“…Noticeably, there was an observable dielectric relaxation process in the measured frequency range, that is, the peak temperature ( T ) varied from 256 K at 0.5 kHz to 266 K at 1 000 kHz. The origin of the dielectric anomalies may be associated with the electron transfer between the Fe–Co centers, which causes changes in the local polarizability that contribute to the dielectric constant ,…”

Ferroelectricity in Metal–Organic Frameworks: Characterization and Mechanisms

“…The polarity of the low‐temperature phase has been confirmed through pyroelectric current measurements. The Curie temperature of 220 K has been reported, and a polarization hysteresis loop obtained was obtained through the PUND method at 10 K . We note that water effects can be excluded as the loop was measured at cryogenic temperatures, at which polarization owing to the motion of water molecules can be ruled out.…”

“…Atomic scheme: Fe, orange; Co, purple; C, gray; N, blue. Reprinted with permission from ref . Copyright (2015) American Chemical Society.…”

Ligand-to-Ligand Charge Transfer within Metal–Organic Frameworks Based on Manganese Coordination Polymers with Tetrathiafulvalene-Bicarboxylate and Bipyridine Ligands

“…6 One example of a metal-to-metal charge-transfer (MMCT) MOF is an Fe-and Co-included system with a 4,4′-bipyridine pillar and a cyanide bridge. 7 In the development of functional CT MOF materials, research on ligand-to-ligand charge-transfer (LLCT) MOFs is still less advanced. This might be because several factors must be controlled at the same time.…”