A study of zwitterionic adducts of TCNQ (original) (raw)
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Synthetic Metals, 1993
The synthesis of novel 7z-extended TCNQ and DCNQI derivatives from the corresponding 1,4anthraquinones is described. The cyclic voltammewic data reveal that both TCNQ-type and DCNQI-type acceptors present two one-electron reduction waves to the corresponding anion-radical and dianion. These novel 2,3-fused TCNQ and DCNQI 7z-extended systems are, according to the electrochemical values, better acceptors than the previously reported 2,3-5,6-fused TCNQ and DCNQI molecules. A good linear correlation between the first reduction potential of the substituted DCNQI-type derivatives versus the HammeR's cr 3 constant has been found.
Pure and Applied Chemistry, 2000
Our efforts in the field of 'organic metals' have been focused mainly on the preparation and structural determination of D-A-D @= donor, A= acceptor ) and A-D-A molecular units in which donors and acceptors are chemically attached via bridging atoms. The strategy that directs the synthetic work aims to gain some control over architectural aspects, which are vital pre-conditions for electrical conductivity in organic materials. Thus, constructing such molecular units pre-determines the D-A molar ratio as well as the maximum degree of charge transfer. Moreover, it might also lead to the desired crystallographic arrangement, characterized by segregated stacks of both donors and acceptors, with significant overlap between adjacent units in the stack. Following this approach we have synthesized two types of molecules: one contains two donors linked to one acceptor via a -CH2-or S bridges, and the other, two acceptors linked to one donor via -CH2-bridges. Representative examples of both types show promising structural properties and partial charge transfer in their ground state. The importance of introducing heavy atoms in charge-transfer complexes has been recognized.Consequently, extensive work has been carried out on the synthesis of various TI'F derivatives, in which Se and Te atoms substitute sulfur or hydrogen atoms in the TTF framework. Recently we have synthesized new compounds in which two TIT molecules are bridged via tellurium atoms: TTF-Te-TTF and TTF-Te-Te-TTF. Their synthesis, electrochemical properties and molecular structural features are presented.
On the spectral properties of the family of complex TCNQ salts with substituted pyrazines
Synthetic Metals, 2009
ABSTRACT The group of six TCNQ salts with N-methyl derivatives of pyrazine, bearing up to four methyl groups in various pyrazine sites, was selected for the spectral studies. The influence of the spatial structure of the donors on the charge distribution on the acceptor as well as spectral features of adequate TCNQ salts were deduced. The stretching vibrations of the C=C bonds (mode nu(4)) were used for the evaluation of the charge density on the TCNQ(-) anions but the stretching vibrations of the C N bonds (mode nu(2)) indicate a diversity of the neighborhood of TCNQ species. It was shown that for the salts containing nonequivalent TCNQ anions the band nu(2) is splitted; each component of the multiplet seen in the IR and Raman spectra represents various environment of the anion. On the other hand the splitted mode nu(4) indicates an existence of TCNQ(-) anions differently charged. Thus, it was shown that the spectral methods are suitable for indicating nonequivalence of the TCNQ in their salts.
Inorganic Chemistry, 2011
Zwitterionic benzoquinone monoimines of type 1 (Scheme 1) show a remarkable delocalization of their 12 π-electron system, which forms two chemically connected but electronically separated 6π-electron subunits. 1 These potentially antiaromatic molecules have attracted much interest because of their unusual electronic structure, 2À6 their coordination chemistry, 7À15 their ability to form supramolecular arrangements, 8 and the potential applications of their metal complexes in, e.g., optical recording 10 and homogeneous catalysis. 7,9 These zwitterions can behave as noninnocent ligands in Cu 11,12 and Pd 13 chemistry and promote "metalÀmetal coupling" in Ru 14 and Mo 15 complexes. Furthermore, they have been deposited on gold and ferroelectric lithium niobate surfaces, and molecular films have been obtained which are endowed with interesting physical properties related to their strong dipolar nature. 17 Replacement of the R groups can be readily achieved by a transamination reaction, and this provides access to a range of differently functionalized zwitterions. Molecule-based materials are gaining more and more attention because of their possible applications in the fields of molecular electronics and intelligent materials. 19 In this respect, TCNE (tetracyanoethylene) and TCNQ (7,7 0 ,8,8 0 -tetracyanoquinodimethane) are important molecules, as they are both strong organic electron acceptors which can easily switch between different oxidation states. They find applications in (metal-)organic conductors 20,21 as well as magnetic materials 22 and are used as precursors to charge transfer salts. 23,24 They can undergo π/π stacking, 25À30 act as nonchelating polydentate ligands, offer a variety of coordination sites and bonding modes (σ and π coordination) to metal centers, behave as noninnocent ligands, and form oligonuclear complexes. In addition to various reactions with organic 33À41 and organometallic compounds, 42 TCNE and TCNQ can undergo insertion reactions into aromatic CÀH bonds. 43À47 We have recently described a regioselective carbonÀcarbon bond formation resulting from the reaction between the zwitterionic quinonoids 1 and TCNE or TCNQ, which leads to novel C-substituted zwitterions, (6E)-4-(butylamino)-6-(butyliminio)-3-oxo-2-(1,1,2,2-tetracyanoethyl) cyclohexa-1,4-dien-1-olate,
Dalton Transactions, 2015
The kinetically inert chromium(III) tris-(8-hydroxyquinolinate), Crq 3 , has been synthesized, crystallized from 90% methanol-water, and characterized by MALDI-TOF mass spectrometry, thermogravimetry, FTIR, NMR spectroscopy, and X-ray powder diffraction. It is formed as a methanol solvate, but the solvent can be removed by heating. Large paramagnetic shifts and spectral broadening in 1 H NMR spectra indicate electron delocalization between the metal and the ligand. DFT calculations show it is present as the meridional isomer, with the HOMO largely based on one of the metal 3d orbitals and the LUMO essentially localized on the ligands. Cyclic voltammetry (CV) in acetonitrile solutions shows four oxidation peaks and two, less intense reduction waves on the first scan. The HOMO energy determined from the first oxidation peak is fairly close to that obtained by DFT, in agreement with this being mainly metal based. Although the number of peaks decreases on subsequent CV scans, the complex shows markedly enhanced electrochemical stability compared with aluminium(III) tris-(8-hydroxyquinolinate). Solution UV/ visible absorption and solid diffuse reflectance spectra have a weak, long wavelength band, assigned to the metal based d-d transition, in addition to the normal, ligand based bands seen in metal quinolates. The energy of the lowest energy band is identical to the HOMO-LUMO separation obtained by cyclic voltammetry, in agreement with the above description. The compound is only weakly luminescent, in contrast to many other metal quinolates, due to the lowest energy transition being metal rather than ligand based. The potential of this compound as an electron transporting/hole blocking layer in optoelectronic devices is indicated. † Electronic supplementary information (ESI) available. See
Dalton Trans., 2015
The kinetically inert chromium(III) tris-(8-hydroxyquinolinate), Crq 3 , has been synthesized, crystallized from 90% methanol-water, and characterized by MALDI-TOF mass spectrometry, thermogravimetry, FTIR, NMR spectroscopy, and X-ray powder diffraction. It is formed as a methanol solvate, but solvent can be removed by heating.
Coordination Chemistry Reviews, 2014
TCNQ•radical anions (TCNQ = 7,7,8,8,-tetracyanoquinodimethane) form a wide range of semiconducting coordination polymers when coordinated to transition metals. Some such as CuTCNQ and AgTCNQ exhibit molecular switching and memory storage properties; others have intriguing magnetic properties and for example may behave as molecular magnets at low temperature. In this review, the electro-and photo-chemical synthesis and characterization of this important class of material is reviewed. In particular, the electrochemistry and the redox properties of TCNQ derivatives of coordination polymers based on Cu, Ag, Mn, Fe, Co, Ni, Zn and Cd transition metals are surveyed, with an emphasis on the mechanistic aspects of their electrochemical formation via nucleationgrowth processes. Given that TCNQ is an extremely good electron acceptor, readily forming TCNQ •and TCNQ 2-, electrochemical reduction of TCNQ in the presence of a transition metal ion provides an ideal method for synthesis of metal-TCNQ materials by electrocrystallization from organic solvents and ionic liquids or solid-solid transformation using TCNQ modified electrodes from aqueous media containing transition metal electrolytes. The significance of the reversible formal potential (E 0 f) in these studies is discussed. The coupling of electrocrystallisation on electrode surfaces and microscopic characterization of the electrodeposited materials reveals a wide range of morphologies and phases which strongly influence their properties and applications. Since TCNQ also can be photo-reduced in the presence of suitable electron donors, analogous photochemical approaches to the synthesis of TCNQ-transition metal derivatives are available. The advantages of electrochemical and photochemical methods of synthesis relative to chemical synthesis are outlined.
Structure and spectral properties of TCNQ salts with Zn(II) and Ni(II) 2,2′-bipyridine complexes
Synthetic Metals, 2014
Three new anion-radical TCNQ salts with Zn and Ni 2,2 -bipyridine complexes and appropriate solvent were synthesized as well as structurally and spectrally investigated. Two of the salts show quasi-one dimensional organization of the anions and show distinct anisotropy of the polarized reflection spectra. Both infrared and Raman spectra were extensively investigated using various spectral methods and discussed. The origin of principal absorption IR bands as well as Raman scattering lines was explained according to our quantum chemical calculations.