Assembling organic-inorganic building blocks for high-capacity electrode design

Metal-organic electrode materials have exhibited extraordinary promise for green and sustainable electrochemical energy storage devices, but usually suffer from low specific capacity, and poor cycling stability and rate capability because of limited active sites at organic functional groups. To address this issue, activating transition metals and carbon conjugate rings has become significantly effective to make transferred electrons dispersed in the whole molecule. In this work, we demonstrate that assembling inorganic-organic building blocks into "local" composite metal-organic materials could synergistically activate transition metal ions and carbon conjugate rings to operate cationic and anionic redox, respectively. Based on first-principles calculations, the composite inorganic-organic material FeF₃(4,4'-bpy) generates 8-electron transfer redox processes of Fe³⁺ + 2e^-→ Fe⁺ and 2 -C[double bond, length as m-dash]N- + 2e^-→ 2 (-C-N-)^- and 4 -C[double bond, length as m-dash]C- + 4e^-→ 4 (-C-C-)^-, achieving a high specific capacity of 796.7 mA h g^-1, maintaining structural stability, and reducing the band gap. The strongly electronegative F-ions in inorganic structure [FeF₄]^2- play an important role in making highly oxidized Fe³⁺ through forming a strong ligand field and electrochemically activating -C[double bond, length as m-dash]C-via electrostatic interaction with Li⁺. In addition, electrochemical measurements also reveal that the central metal Fe, and -C[double bond, length as m-dash]C and -C[double bond, length as m-dash]N bonds of the FeF₃(4,4'-bpy) electrode are the active sites for Li-ion storage to deliver a high reversible capacity (793.1 mA h g^-1 at 50 mA g^-1) and excellent rate capability, which are echoes of the DFT calculations. Through this design principle, we found a series of high-capacity metal organic electrode materials such as MnF₃(4,4'-bpy) (799.6 mA h g^-1) and VF₃(4,4'-bpy) (811.7 mA h g^-1).

Semiconducting crystalline inorganic-organic hybrid metal halide nanochains

One-dimensional (1D) inorganic-organic metal halide hybrids at the molecular level, which can be considered as arrays of nanochains isolated by organic components, have shown remarkable optical and electric properties. This review summarizes their reported structural types and shows how to modify their band gaps and optical and electric properties.

Topotactic desolvation and condensation reactions of 3D Zn3TiF7(H2O)2(taz)3·S (S = 3H2O or C2H5OH)

Thermodiffraction, IR, DFT calculations, and ¹H and ¹⁹F NMR characterizations of the desolvatation and reversible condensation reactions of Zn₃TiF₇(taz)₃ family.

New 2D layered structures with direct fluorine–metal bonds: MF(CH3COO) (M: Sr, Ba, Pb)

New coordination polymers with 2D network structures with fluorine directly coordinated to the metal ion were prepared both via mechanochemical synthesis and fluorolytic sol–gel synthesis.

Strong magnetic exchange and frustrated ferrimagnetic order in a weberite-type inorganic-organic hybrid fluoride

We combine powder neutron diffraction, magnetometry and ⁵⁷Fe Mössbauer spectrometry to determine the nuclear and magnetic structures of a strongly interacting weberite-type inorganic-organic hybrid fluoride, Fe₂F₅(H taz). In this structure, Fe²⁺ and Fe³⁺ cations form magnetically frustrated hexagonal tungsten bronze layers of corner-sharing octahedra. Our powder neutron diffraction data reveal that, unlike its purely inorganic fluoride weberite counterparts which adopt a centrosymmetric Imma structure, the room-temperature nuclear structure of Fe₂F₅(H taz) is best described by a non-centrosymmetric Ima2 model with refined lattice parameters a = 9.1467(2) Å, b = 9.4641(2) Å and c = 7.4829(2) Å. Magnetic susceptibility and magnetization measurements reveal that strong antiferromagnetic exchange interactions prevail in Fe₂F₅(H taz) leading to a magnetic ordering transition at T_N = 93 K. Analysis of low-temperature powder neutron diffraction data indicates that below T_N, the Fe²⁺ sublattice is ferromagnetic, with a moment of 4.1(1) µ_B per Fe²⁺ at 2 K, but that an antiferromagnetic component of 0.6(3) µ_B cants the main ferromagnetic component of Fe³⁺, which aligns antiferromagnetically to the Fe²⁺ sublattice. The zero-field and in-field Mössbauer spectra give clear evidence of an excess of high-spin Fe³⁺ species within the structure and a non-collinear magnetic structure. This article is part of the theme issue 'Mineralomimesis: natural and synthetic frameworks in science and technology'.

A magnetisation and Mössbauer study of triazole (M1−x2+Mx3+)M3+F5(Htaz)1−x(taz)x weberites (M = Fe, Co, Mn, Zn, Ga, V)

Several (M_1−x²⁺M_x³⁺)M³⁺F₅(Htaz)_1−x(taz)_x weberites, magnetically frustrated, exhibit negative magnetisations. ⁵⁷Fe Mössbauer spectrometry evidences a significant decrease of T_N for vacuum-treated samples.

New iron tetrazolate frameworks: synthesis, temperature effect, thermal behaviour, Mössbauer and magnetic studies

The exploration of the FeF3/FeF2-Hamtetraz-HF system in dimethylformamide by solvothermal synthesis evidences two isostructural 3D hybrid fluoroferrates. They are prepared from the same starting mixture at two different synthesis temperatures: 120 °C for [Hdma]·(Fe4(II)Fe(III)F8(H2O)2(amtetraz)4) () and 140 °C for [Hdma]1.5·(Fe4.5(II)Fe0.5(III)F7(H2O)(HCOO)(amtetraz)4) (). Both compounds are characterized by single crystal X-ray diffraction, X-ray thermodiffraction, TGA analysis, Mössbauer spectrometry and SQUID magnetometry. They crystallize in the monoclinic system and are built from two distinct chains connected by aminotetrazolate anions. The first chain ∞(Fe(II)FN4) is common to and and can be found in numerous fluorides. In the second chain ∞(Fe3X12) (X = F, N, O), iron cations adopt both valence states Fe(ii)/Fe(iii). The hydrolysis of DMF implies the formation of a [Hdma](+) cation and a (HCOO)(-) anion. The presence of Fe(3+) in both phases is evidenced by (57)Fe Mössbauer spectrometry. The magnetic properties are studied and two transitions from a paramagnetic regime to a long range ordered state below 30 K and 5 K are identified.