Cyanide-bridged Coordination Polymer Research Articles

Li-ion and Na-ion insertion into size-controlled nickel hexacyanoferrate nanoparticles

The influence of particle size on the electrochemical properties of guest-ion storage materials has attracted much attention because of the extensive need for long cycle-life, high energy density, and high power batteries. The present work describes a systematic study of the effect of particle size on the guest-ion storage capabilities of a cyanide-bridged coordination polymer. A series of nickel hexacyanoferrate particles ranging from approximately 40 to 400 nm were synthesized by a co-precipitation method and were used as the cathode material for both Li-ion and Na-ion insertion/extraction experiments using organic electrolyte. A large polarization was observed for the largest particles during Li-ion cycling, indicating a heterogeneous ion concentration within the lattice. As a consequence, the available capacity of Li-ion intercalation at high rates is significantly improved by reducing the particle size. On the other hand, Na-ion intercalation shows excellent rate capability regardless of the particle size.

A series of bimetallic chain coordination polymers bearing [Ag(PPh3)2] chromophores: Synthesis, structure and luminescence

Abstract A series of three cyanide-bridged chain coordination compounds with the formulae [M(CN)2(PPh3)2Ag]n (M is Ag, Cu or Au) is presented. The compounds have been prepared by room temperature reactions of triphenylphosphane with the cyanide salts of silver(I), copper(I) and gold(I). The compounds are characterised with IR, elemental analyses, SEM-EDX and X-ray powder diffraction, and the molecular structures were elucidated by single crystal X-ray diffraction. The three compounds are best described as one-dimensional cyanide-bridged chain coordination polymers, where the tetrahedral AgI ions are coordinated by 2 triphenylphosphane ligands and 2 cyanides, forming a AgN2P2 chromophore. The linear Ag(I), Cu(I) and Au(I) centers are in two-coordinate geometry with C-bound cyanides. No aurophilic or argentophilic interactions are observed, but in the lattice only C-H…π and C-H…M hydrogen bonds are present. The solid-state luminescence properties of the three compounds are discussed and assigned, in agreement with DFT calculations, to MMLCT.

Bimetallic Cyanide-Bridged Coordination Polymers as Lithium Ion Cathode Materials: Core@Shell Nanoparticles with Enhanced Cyclability

Prussian blue analogues (PBAs) have recently been proposed as electrode materials for low-cost, long-cycle-life, and high-power batteries. However, high-capacity bimetallic examples show poor cycle stability due to surface instabilities of the reduced states. The present work demonstrates that, relative to single-component materials, higher capacity and longer cycle stability are achieved when using Prussian blue analogue core@shell particle heterostructures as the cathode material for Li-ion storage. Particle heterostructures with a size dispersion centered at 210 nm composed of a high-capacity K(0.1)Cu[Fe(CN)(6)](0.7)·3.8H(2)O (CuFe-PBA) core and lower capacity but highly stable shell of K(0.1)Ni[Fe(CN)(6)](0.7)·4.1H(2)O have been prepared and characterized. The heterostructures lead to the coexistence of both high capacity and long cycle stability because the shell protects the otherwise reactive surface of the highly reduced state of the CuFe-PBA core. Furthermore, interfacial coupling to the shell suppresses a known structural phase transition in the CuFe-PBA core, providing further evidence of synergy between the core and shell. The structure and chemical state of the heterostructure during electrochemical cycling have been monitored with ex situ X-ray diffraction and X-ray absorption experiments and compared to the behavior of the individual components.

Hydrogen-bond directed 2D cyanide-bridged coordination polymer assembled from a new pentacyanidecobalt(III) building block and a bicompartimental Schiff-base manganese(III) compound: Synthesis, structures and magnetic properties

Abstract With a new pentacyanidecobalt(III) precursor K2[Co(CN)5(CH3CN)] and a bicompartimental Schiff base manganese(III) compound, a new two-dimensional cyanide-bridged Co(III)-Mn(III) coordination polymer constructed by hydrogen-bond interactions has been successfully synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals this cationic cyanide-bridged tetranuclear complex is self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighboring complex, giving interesting 2D supramolecular structure. Investigation over magnetic susceptibility reveals the overall weak antiferromagnetic coupling between the adjacent Mn(III) ions.

Fabrication of a Cyanide-Bridged Coordination Polymer Electrode for Enhanced Electrochemical Ion Storage Ability

Host frameworks with the ability to store guest ions are very important in a wide range of applications including electrode materials for Li-ion batteries. In this report, we demonstrate that the ion storage ability of the cyanide-bridged coordination polymer (Prussian blue analogue, PBA) can be enhanced by suppressing vacancy formation. K-ions in the vacancy-suppressed PBA framework K1.72Mn[Mn(CN)6]0.93·□0.07·0.65H2O (□: a [Mn(CN)6]4– defect) were electrochemically extracted. The open circuit voltages (OCVs) during K-ion extraction exhibited two specific plateaus at 3.0 and 3.7 V vs Li/Li+. Ex situ X-ray diffraction and IR spectroscopy revealed drastic structural and electronic changes during K-ion extraction. Furthermore, after K-ion extraction, the vacancy-suppressed PBA framework was applied to the cathode material for a Li-ion battery. The charge/discharge experiments revealed that the framework can accommodate a large amount of Li-ions.

Impedance spectroscopic study on interfacial ion transfers in cyanide-bridged coordination polymer electrode with organic electrolyte

Interfacial charge transfer is a fundamental issue in both science and technology of the batteries. In this report, interfacial alkali-ion transfer between the cyanide-bridged coordination polymer (Prussian blue analogue, PBA) electrode and organic electrolytes was investigated. Electrochemical impedance spectroscopy (EIS) suggested that alkali-ion transfer at the K0.1Mn[Fe(CN)6]0.7·3.6H2O (MnFe-PBA) electrode–electrolyte interface involves two processes. One process could be interpreted as the ion transfer between the Outer Helmholtz Plane (OHP) and Inner Helmholtz Plane (IHP) including the solvation/desolvation process, the other could be interpreted as that between the IHP and electrode, including ad-ion diffusion on the electrode surface. Temperature dependence of the charge transfer resistances gave the activation energy for each process. The activation energy for Li-ion transfer between the OHP and IHP in propylene carbonate (PC) electrolyte is almost constant at the composition range of 0.1<x<0.6 in LixMnFe-PBA, which is comparable to that in ethylene carbonate (EC)-diethyl carbonate (DEC) electrolyte. In contrast, the activation energy for Li-ion transfer between the IHP and electrode depends largely on the Li-ion concentration in the PBA electrode. However, the averaged value for Li-ion transfer is higher than that for Na-ion transfer. This result indicated that Li-ion on the PBA surface diffuses with higher potential barrier than Na-ion. Furthermore, the effect of the interfacial charge transfer resistance was evaluated by the high charge/discharge rate experiments.

Electron delocalization in cyanide-bridged coordination polymer electrodes for Li-ion batteries studied by soft x-ray absorption spectroscopy

The electronic structure change during the reversible Li-ion storage reaction in a bimetallic MnFe-Prussian blue analogue (Li${}_{x}$K${}_{0.14}$Mn${}_{1.43}$[Fe(CN)${}_{6}$] $\ifmmode\cdot\else\textperiodcentered\fi{}$ 6H${}_{2}$O) was investigated by soft x-ray absorption spectroscopy. The Mn ${L}_{2,3}$-edge spectra revealed the unchanged Mn${}^{2+}$ high-spin state regardless of Li-ion concentration ($x$). On the other hand, the Fe ${L}_{2,3}$-edge spectra clearly revealed a reversible redox behavior as ${\mathrm{Fe}}^{3+}\ensuremath{\leftrightarrow}{\mathrm{Fe}}^{2+}$ states with Li-ion insertion/extraction. Experimental findings suggested strong metal-to-ligand charge transfer in conjunction with the ligand-to-metal one. The resulting charge delocalization between the Fe and CN is considered to contribute to the high reversibility of the Li-ion storage process.

A cyanide-bridged 1-D helical chain involving both four- and six-coordinate nickel(II)

A cyanide-bridged coordination polymer, {[Ni(tren)][Ni(CN)4]} n (tren = tris(2-aminoethyl)amine), has been synthesized by self-assembly of cis-[Ni(tren)]2+ and [Ni(CN)4]2− building blocks. In the molecular structure, the paramagnetic cis-[Ni(tren)]2+ cations are bridged by diamagnetic [Ni(CN)4]2− anions through two cis-cyanides to form a 1-D helical chain of {[Ni(tren)][Ni(CN)4]} n . The compound crystallizes with a centrosymmetrical space group, P21 /n, in which the helical chains are packed in alternating right- and left-handed chiralities with a helical pitch of 10.2566(3) Å (equal to the length of the b-axis), leading to the formation of a racemic compound. The crystal packing is stabilized by moderately strong hydrogen-bonding between primary amines of tren and nitrogens of terminal cyanide.

Cluster cyanide-bridged heterometallic coordination polymers: synthesis and crystal structures of compounds [{Cu2(dien)2(CN)}2{Mo4Te4(CN)12}]·14.5H2O and (H3O)3K[{Mn(H2O)2}2{Mn(H2O)2(NO3)}4{W4Te4(CN)12}2]·8H2O

The reactions of anionic molybdenum and tungsten cyanide cuboidal clusters with CuII and MnII salts afforded two new cyanide-bridged heterometallic coordination polymers with the composition [{Cu2(dien)2(CN)}2{Mo4Te4(CN)12}]⋅14.5H2O (1) and (H3O)3K[{Mn(H2O)2}2{Mn(H2O)2(NO3)}4{W4Te4(CN)12}2]·8H2O (2). The structures of these compounds were established by X-ray diffraction analysis. Compound 1 has a layered structure, in which the cuboidal cluster fragments {Mo4Te4(CN)12}6− are linked to the copper atoms of the dinuclear fragments {(H2O)(dien)Cu(μ-CN)Cu(dien)(H2O)} through the bridging CN groups. Coordination polymer 2 has a framework structure, in which the cluster fragments {W4Te4(CN)12}6− are linked to the manganese(II) aqua complexes of two types, viz., the dinuclear fragment {Mn(μ2-H2O)2Mn} and the tetranuclear cyclic fragment {(H2O)2Mn(μ2-NO3)}4, through the bridging CN groups.