Redox-active metal−organic frameworks (MOFs) have great potential for use as cathode materials in lithium-ion batteries (LIBs) with large capacities because the organic ligands can undergo multiple-electron redox processes. However, most MOFs are electrical insulators, limiting their application as electrode materials. Here, we report an electron-conductive MOF with a 2,5-dihydroxy-1,4-benzoquinone (dhbq) ligand, Fe(dhbq). This compound had an electrical conductivity of 5 × 10 −6 S cm −1 at room temperature due to d−π interactions between the Fe ion and the ligand and the permanent microporosity. Fe(dhbq) had an initial discharge capacity of 264 mA h g −1 , corresponding to the two-electron redox process of dhbq.
The coordination
polymers (CPs) with binary ligands, including
2,5-dihydroxy-1,4-benzoquinone (H2DHBQ) and 4,4′-bipyridyl
(bpy), were synthesized using
in situ
hydrolysis
of 2,5-dimethoxy-1,4-benzoquinone (DMBQ). Three kinds of CPs were
obtained depending on the metal ions. For M = Mn and Zn, a 1D zigzag
chain structure with cis conformation (
cis
-1D-M
) was obtained, whereas Co, Ni, and Cu compounds afforded a 2D net
structure with trans conformation (
trans
-2D-M
) with a 1D pore. A linear chain structure was also obtained for
M = Cu. Magnetic susceptibility (χ
M
T
) at 300 K in
cis
-1D-Mn
and
trans
-2D-Co
was evaluated
to be 4.421 and 2.950 cm
3
K mol
–1
, respectively,
indicating that both compounds are in the high-spin state. According
to the N
2
adsorption isotherms at 77 K,
trans
-2D-Ni
showed microporosity with the BET surface
area of 177 m
2
g
–1
, whereas the isomorphic
trans
-2D-Co
rarely adsorbed
N
2
at 77 K. This phenomenon was explained by the difference
of diffusion kinetics of the adsorbent molecules, which was supported
by the CO
2
adsorption isotherms at 195 K. The optical band
gaps of
cis
-1D-Mn
,
cis
-1D-Zn
,
trans
-2D-Co
, and
trans
-2D-Ni
were estimated to be 1.6, 1.8, 1.0, and 1.1 eV,
respectively, by using UV–vis–NIR spectroscopy.
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