Tetracyanoquinodimethane Radical Anions Research Articles

Room-Temperature Magnetic Bistability in a Salt of Organic Radical Ions.

Cocrystallization of 7,7',8,8'-tetracyanoquinodimethane radical anion (TCNQ-•) and 3-methylpyridinium-1,2,3,5-dithiadiazolyl radical cation (3-MepyDTDA+•) afforded isostructural acetonitrile (MeCN) or propionitrile (EtCN) solvates containing cofacial π dimers of homologous components. Loss of lattice solvent from the diamagnetic solvates above 366 K affords a high-temperature paramagnetic phase containing discrete TCNQ-• and weakly bound π dimers of 3-MepyDTDA+•, as evidenced by X-ray diffraction methods and magnetic susceptibility measurements. Below 268 K, a first-order phase transition occurs, leading to a low-temperature diamagnetic phase with TCNQ-• σ dimer and π dimers of 3-MepyDTDA+•. This study reveals the first example of cooperative interactions between two different organic radical ions leading to magnetic bistability, and these results are central to the future design of multicomponent functional molecular materials.

Size Controllable Metal Nanoparticles Anchored on Nitrogen Doped Carbon for Electrocatalytic Energy Conversion

AbstractMetal nanoparticles (NPs) are an important class of materials for electrocatalysis. Synthesis of metal NPs with uniform particle size below 10 nm without a capping agent is challenging due to the tendency of particle aggregation to minimize surface energy. Here we demonstrate that pyrolysis of a metal‐TCNQ (TCNQ−=tetracyanoquinodimethane radical anion) compound can produce metal NPs with controllable particle sizes anchored on nitrogen doped carbon (denoted as MetalNC). NiNC and CoNC derived from Ni‐TCNQ and Co‐TCNQ with Ni and Co particle sizes below 10 nm were successfully prepared. NiNC, with a particle size of 8.8 nm, showed excellent catalytic activity for hydrogen evolution in an alkaline medium, reaching a catalytic current density of 10 mA cm−2 at an overpotential of 230 mV. CoNC, with a particle size of 1.8 nm, exhibited the capability of producing syngas by electrocatalytic CO2 reduction over a wide potential range in an acetonitrile medium containing 0.3 M H2O. An artificial photosynthesis system based on CoNC achieved faradaic efficiencies of over 70 % for production of syngas and 22 % for formate. This work demonstrates a general strategy to synthesize size controllable metal NPs supported on carbon materials for electrocatalytic energy conversion.

Cooperation of Hydrogen-Bond and Charge-Transfer Interactions in Molecular Complexes in the Solid State

Abstract Our recent studies for the development of conducting charge-transfer complexes with well-defined assembled structures based on the cooperation of hydrogen-bond and charge-transfer interactions are described. We have designed and synthesized hydrogen-bonded charge-transfer complexes based on (1) tetrathiafulvalene derivatives having nucleobases, aminobenzo and imidazole moieties, and (2) tetracyanoquinodimethane radical anion salts with hydrogen-bond-functionalized phenalenyl and protonated oligo(imidazole) cations. The directional and site-selective hydrogen-bonds formed various supramolecular network structures, constructing segregated columns as the conduction path. Furthermore, the high polarity of hydrogen-bonds caused strong donor–acceptor or cation–anion electrostatic interactions modulating the ionicity of component molecules and the electronic structure of conduction columns. Such electronic modulation effects in addition to controlling the molecular arrangement realized the first purely organic molecular metal based on a hydrogen-bonded charge-transfer complex in the p-chloranil complex of an imidazole-functionalized tetrathiafulvalene derivative. The proton-donating/accepting ability of the hydrogen-bonding sites afforded the simultaneous proton- and charge-transfer complexes, demonstrating an important prompt for the realization of cooperative proton–electron-transfer systems.

Supramolecular Approach by Using Jahn-Teller Sites to Construct a {Mn13}-Based Coordination Polymer and Modify its Magnetic Properties

Put a spin on it: a {Mn(13)} coordination cluster has been used as a secondary building unit for the preparation of an open-framework structure for which the magnetic properties can be modified by solution adsorption of tetracyanoquinodimethane radical anions (TCNQ·(-)). The applied supramolecular approach takes advantage of kinetically labile Jahn-Teller sites and can be generalised for the construction and post-synthetic modification of multifunctional materials.

Intermolecular Hydrogen-Bond Networks and Physical Properties of BF4– and TCNQ•– Salts of Three-Fold Symmetric Tris(alkylamino)phenalenyliums

Synthesis, redox properties, and crystal structures of tris(alkylamino)phenalenyliums (TAP) having alkyl groups (n-Pr, i-Pr, t-Bu) and their charge-transfer salts with tetracyanoquinodimethane radical anion (TCNQ•–) were investigated. The electrochemical measurements revealed that TAP exhibits two irreversible reduction processes to neutral radical and anion species. The introduction of an alkylamino group caused a large negative shift of the first reduction potential and a significant decrease of the on-site Coulomb repulsion because of the electron-donating nature of amino groups and the extension of the π-electronic system. In the crystal structures of the BF4– salts, the TAP skeleton possesses a nearly 3-fold symmetric molecular plane indicating the delocalization of positive charge. The face-to-face stack of TAP formed π-dimer or columnar structures, which were connected through intermolecular N–H···F hydrogen bonds with BF4– to construct multidimensional network structures. The TCNQ•– salts prepared by the metathesis method were characterized as fully ionic salts with a 1:1 component ratio. In the crystal structures, both TAP and TCNQ•– molecules formed π-dimers, and the intermolecular hydrogen bonds between TAP and TCNQ•– constructed a two-dimensional sheet.

Mixed valence of a delocalized system: a resonance Raman study of the tetracyanoquinodimethane radical anion

AbstractThe optical absorption spectrum and resonance Raman enhancement of the lowest energy absorption band of K+7,7,8,8‐tetracyanoquinodimethane− (TCNQ) are reported and examined in the mixed valence (MV) framework. The absorption spectrum is assigned, in accordance with previous work, using Koopmans‐based calculations and the neighboring orbital model is constructed from the adiabatic orbital energies. Calculated fits of the lowest energy absorption band and the corresponding resonance Raman enhancement profiles are made using the time‐dependent theory of spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd.

Crystal structure, magnetic property and DFT analysis for a bis(tetracyanoquinodimethane)zinc(II) complex

A bis(tetracyanoquinodimethane)zinc(II) complex ( 1) was structurally characterized, in which the Zn 2+ ion occupies at an inversion centre and is bonded to two tetracyanoquinodimethane radical anions (TCNQ −), two H 2O and two DMF molecules to form almost perfectly octahedral coordination geometry. The strong H-bonding interactions are observed between H 2O molecules as well as between H 2O molecule and TCNQ − radical anion of the neighboring complex molecules, additionally, there exist π⋯π stack interactions between TCNQ − radical anions. The intermolecular H-bonding and π⋯π stack interactions lead to a supramolecular network sheet forming on the crystallographic ac-plane, and the neighboring supramolecular network sheets further extend into three-dimensional supramolecular structure via weak van der Waals forces. Symmetry-broken approach in the theoretical formwork of DFT for magnetic exchange constants analysis disclosed that the ground state of 1 is singlet state, the excited triplet state is much closed to the nonmagnetic ground state with a small energy gap of 1.25 × 10 −5 eV, and there exist AFM interaction in the TCNQ π-stacks, and these predictions are in agreement with magnetic susceptibility measurements.

Application of π-acceptors to the spectrophotometric determination of lisinopril in commercial dosage forms

Two simple, rapid and sensitive spectrophotometric methods have been proposed for the determination of lisinopril in pure form and pharmaceutical formulations. The methods are based on the charge transfer complexation reaction of the drug with 7,7,8,8,tetracyanoquinodimethane (TCNQ) and p-chloranilic acid ( pCA) in polar media. The lisinopril–TCNQ and lisinopril– pCA charge transfer complexes dissociate in acetone and methanol, respectively, and yield coloured TCNQ and pCA radical anions which are measured spectrophotometrically at 743 and 525 nm. Under optimised experimental conditions, Beer's law is obeyed in the concentration range of 2–26 and 25–300 μg ml –1 with molar absorptivity of 1.432 × 10 4 and 1.192 × 10 4 l mol –1 cm –1 for TCNQ and pCA methods, respectively. Both the methods have been applied to the determination of lisinopril in pharmaceutical dosage forms. Results of analysis are validated statistically.

Electrochemistry of Langmuir-Blodgett Films Incorporating Both a Viologen Derivative and Tetracyanoquinodimethane

A positively charged monolayer of a viologen derivative containing two long alkyl chains was prepared. Tetracyanoquinodimethane radical anions were incorporated into the Langmuir-Blodgett film during the transference process as the counterions from a subphase containing an aqueous solution of LiTCNQ. Stable monolayers were transferred onto indium tin oxide electrodes and the electrochemical properties of the films were analyzed in terms of experimental variables including the nature of the counterions, the degree of order of the films, and the number of transferred layers. These well-ordered films show very reversible electrochemical processes for the viologen, quite negative redox potentials of the viologen moieties, a ratio of 1, and no splitting of the first viologen reduction peak. The control of these properties is quite important in applications such as the catalytic reduction of a substrate. © 2002 The Electrochemical Society. All rights reserved.

Preparation and properties of tetracyanoquinodimethane radical-anion salts with azaazulenium and diazaazulenium ions

1-Aza- and 1,3-diazaazulenium ions, stable heterocyclic cations, were easily prepared. They afforded conducting salts of tetracyanoquinodimethane radical anions (TCNQ .−) by metathesis with Li +TCNQ .−. Some salts exhibit good conductivities despite 1:1 salts. The nitrile stretching frequencies of the salts obtained here are not linearly correlated with the degrees of charge transfer due to strong interactions between the nitrile groups and heteroatoms of the cations. X-ray structural analysis of 2-imino-3-thia-1-azaazulenium-TCNQ salt reveals the novel crystal structure in which a ribbon-like network is formed by short interheteroatom contacts and hydrogen bondings.

Electron spin resonance spectra and orientation of 3,4-bis(dicyanomethylene)cyclobutane-1,2-dione and tetracyanoquinodimethane radical anions in liquid crystals

The e.s.r. spectra of 3,4-bis(dicyanomethylene)cyclobutane-1,2-dione (BDCB) and tetracyanoquinodimethane (TCNQ) radical anions have been recorded in the isotropic and nematic phases of p-azoxyanisole. The variations of the 14N and 13C hyperfine splitting constants are used to evaluate the preferred orientation of the molecules in the liquid crystals. The experimental data are best accounted for by assuming for BDCB a non-axial orientation matrix, and for TCNQ a nearly axial orientation matrix with the singular direction coincident with the long axis of the molecule.