A new method for electrocrystallization of AgTCNQF4 and Ag2TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in acetonitrile

Semiconducting AgTCNQF₄ (TCNQF₄ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been electrocrystallized from an acetonitrile (0.1 M Bu₄NPF₆) solution containing TCNQF₄ and Ag(MeCN) ⁺₄ . Reduction of TCNQF₄ to the TCNQF ¹⁻₄ anion, followed by reaction with Ag(MeCN) ⁺₄ forms crystalline AgTCNQF₄ on the electrode surface. Electrochemical synthesis is simplified by the reduction of TCNQF₄ prior to Ag(MeCN) ⁺₄ compared with the analogous reaction of the parent TCNQ to form AgTCNQ, where these two processes are coincident. Cyclic voltammetry and surface plasmon resonance studies reveal that the electrocrystallization process is slow on the voltammetric time scale (scan rate = 20 mV s⁻¹) for AgTCNQF₄, as it requires its solubility product to be exceeded. The solubility of AgTCNQF₄ is higher in the presence of 0.1 M Bu₄NPF₆ supporting electrolyte than in pure solvent. Cyclic voltammetry illustrates a dependence of the reduction peak potential of Ag(MeCN) ⁺₄ to metallic Ag on the electrode material with the ease of reduction following the order Au < Pt < GC < ITO. Ultraviolet-visible, Fourier transform infrared, and Raman spectra confirmed the formation of reduced TCNQF ¹⁻₄ and optical microscopy showed needle-shaped morphology for the electrocrystallized AgTCNQF₄. AgTCNQF₄ also can be formed by solid–solid transformation at a TCNQF₄-modified electrode in contact with aqueous media containing Ag⁺ ions. Chemically and electrochemically synthesized AgTCNQF₄ are spectroscopically identical. Electrocrystallization of Ag₂TCNQF₄ was also investigated; however, this was found to be thermodynamically unstable and readily decomposed to form AgTCNQF₄ and metallic Ag, as does chemically synthesized Ag₂TCNQF₄.

     

A new method for electrocrystallization of AgTCNQF4 and Ag2TCNQF4 (TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) in acetonitrile

Semiconducting AgTCNQF₄ (TCNQF₄?=?2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) has been electrocrystallized from an acetonitrile (0.1?M Bu₄NPF₆) solution containing TCNQF₄ and Ag(MeCN) ₄ ⁺ . Reduction of TCNQF₄ to the TCNQF ₄ ^1? anion, followed by reaction with Ag(MeCN) ₄ ⁺ forms crystalline AgTCNQF₄ on the electrode surface. Electrochemical synthesis is simplified by the reduction of TCNQF₄ prior to Ag(MeCN) ₄ ⁺ compared with the analogous reaction of the parent TCNQ to form AgTCNQ, where these two processes are coincident. Cyclic voltammetry and surface plasmon resonance studies reveal that the electrocrystallization process is slow on the voltammetric time scale (scan rate?=?20?mV?s^?1) for AgTCNQF₄, as it requires its solubility product to be exceeded. The solubility of AgTCNQF₄ is higher in the presence of 0.1?M Bu₄NPF₆ supporting electrolyte than in pure solvent. Cyclic voltammetry illustrates a dependence of the reduction peak potential of Ag(MeCN) ₄ ⁺ to metallic Ag on the electrode material with the ease of reduction following the order Au?<?Pt?<?GC?<?ITO. Ultraviolet-visible, Fourier transform infrared, and Raman spectra confirmed the formation of reduced TCNQF ₄ ^1? and optical microscopy showed needle-shaped morphology for the electrocrystallized AgTCNQF₄. AgTCNQF₄ also can be formed by solid?Csolid transformation at a TCNQF₄-modified electrode in contact with aqueous media containing Ag⁺ ions. Chemically and electrochemically synthesized AgTCNQF₄ are spectroscopically identical. Electrocrystallization of Ag₂TCNQF₄ was also investigated; however, this was found to be thermodynamically unstable and readily decomposed to form AgTCNQF₄ and metallic Ag, as does chemically synthesized Ag₂TCNQF₄.     

A tetranuclear organorhenium(i) complex of the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-p-quinodimethane radical anion, TCNQF4 (-)

The radical complex {(mu(4)-TCNQF4)[Re(CO)(3)(bpy)](4)}(PF(6))(3), as prepared and isolated from the reaction between TCNQF4 and [Re(CO)(3)(bpy)(MeOH)](PF(6)), was studied electrochemically and by IR vibrational spectroscopy, UV-Vis-NIR absorption spectroscopy, and by EPR at 9.5, 190 and 285 GHz. The isotropic g factor of 2.0058, the detectable g anisotropy, and the (185,187)Re EPR hyperfine coupling of 0.95 mT for four equivalent metal nuclei support predominant, but not exclusive, spin localisation at the bridging ligand. Nitrile and metal carbonyl stretching frequencies as well as the typically structured near infrared absorption band lend further support to (TCNQF4 (-))(Re(I))(4) as the most appropriate oxidation state formulation. In comparison to the non-radical complex {(mu(4)-TCNQ)[Re(CO)(3)(bpy)](4)}(PF(6))(4) an X-ray structure analysis of {(mu(4)-TCNQF4)[Re(CO)(3)(bpy)](4)}(PF(6))(3) shows a marginally more twisted (ReNCCCNRe)(C(6)X(4))(ReNCCCNRe) configuration and a different up/down arrangement of the [Re(CO)(3)(bpy)](+) groups. This first isolation, electrochemical, structural and spectroscopic characterisation of a discrete tetranuclear radical complex of a TCNQ-type ligand suggests a link between the stability of such materials and the rather small structural changes on ligand-based electron transfer.     

Chemical stability and electroconductivity of 7,7,8,8-tetracyanoquinodimethane salts containing polycation polymers

The chemical and electrical stabilities of 7,7,8,8-tetracyanoquinodimethane (TCNQ) salts composed of neutral TCNQ (TCNQ^?), anion radicals of TCNQ(TCNQ^?·), and polycation polymers were studied by measuring their electronic spectra and resistivities (ρ). The results of spectral and chemical analyses confirmed that TCNQ^?· in TCNQ salts was decomposed to α,α-dicyano-p-toluoylcyanide (DTC^?) as the final product by the intermediate formation of TCNQ^? and p-phenylenediamalononitrile (H₂TCNQ) and that H₂O played an important part in the reaction. From these results it was concluded that TCNQ salts are decomposed by two reaction processes: The resistivity of TCNQ salts increases with the decomposition of TCNQ^?·. Studies on electroconductivity of TCNQ salts assume that the change in resistivity arises from the loss of unpaired electrons which become conduction carriers and also from the disintegration of the TCNQ^? and TCNQ^?· complex which forms the conduction path.     

Reactions of hexamethyldilead with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE)

Hexamethyldilead reacts with TCNQ to give Pb(TCNQ)₂ and tetramethyllead and with TCNE to give Pb(TCNE).     

Synthesis and characterization of poly(2,3,5,6-tetrafluoro-1,4-phenylenevinylene)

Poly(2,3,5,6-tetrafluoro-1,4-phenylenevinylene) (PTFPV) was prepared for the first time by the Stille cross-coupling reaction and the resulting material was characterized through MALDI-TOF mass spectrometry, employing a novel sample preparation protocol suitable for insoluble compounds; preliminary optical and electrooptical measurements were performed.     

High pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and CuTCNQ

The high-pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) single crystals and polycrystalline CuTCNQ are presented in this paper. TCNQ shows a phase transition at 22 kbar, a pressure higher than reported earlier. CuTCNQ undergoes a first order phase transition at 30 kbar, which is characterized by the abrupt disappearance of all the Raman bands.     

Spectrophotometric determination of some antihistaminic drugs using 7,7,8,8-tetracyanoquinodimethane (TCNQ)

A simple and sensitive spectrophotometric method is suggested for analysis of 3 antihistaminic drugs, acrivastine (I), mequitazine (II), and dimethindene maleate (III). The method is based on reaction of the drugs with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in acetonitrile to form highly stable colored products that are measured at 750, 766, and 844 nm for I and II, and 480 and 618 nm for III. Beer's law is obeyed in the ranges of 5-60 microg/mL for 1, 5-50 microg/mL for II, and 10-70 microg/mL for III. The optimum assay conditions and their applicability to the determination of the cited drugs in pharmaceutical formulations are described. The method is statistically analyzed as compared with the European Pharmacopoeia (2001) method for the analysis of dimethindene maleate and reference methods for acrivastine and mequitazine drugs revealing good accuracy and precision.     

Ion-radical salt of 2-tert-butyltetrathiatetracene with 7,7,8,8-tetracyanoquinodimethane (2∶1)

Conclusions We synthesized 2-tert-butyltetrathiatetracene and its 2:1 complex with 7,7,8,8-tetra-cyanoquinodimethane, which has an ion-radical nature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 696–697, March, 1977.The authors express their gratitude to L. I. Buravov for measuring the electrical conductivity.     

Structure of two azide salts of a copper(II) macrocycle and magnetic properties of Cu(14ane)Cu(N3)4

Synthesis of azide complexes with the copper(II) macrocycle complex Cu(14ane)(2+) (where 14ane = 1,4,8,11-tetraazacyclothetradecane) has yielded two compounds. Cu(14ane)Cu(N(3))(4) contains micro(1,3)-azido bridged chains of Cu(14ane)(2+) cations and Cu(N(3))(4)(2)(-) anions. Magnetic studies reveal the presence of ferromagnetic interactions within the chains with J/k = 0.635(4) K. [Cu(14ane)N(3)]BF(4) contains [Cu(14ane)N(3)]+ cations with elongated square pyramidal geometry. The BF(4)(-) anions are weakly coordinated in the sixth coordination site of the cations.     

Copper(II) halide salts and complexes of 4-amino-2-fluoropyridine: synthesis,structure and magnetic properties

Reaction of 4-amino-2-fluoropyridine (2-F-4-AP) with copper halides produced the neutral coordination complexes: (2-F-4-AP)₂CuX₂ (X = Cl(1), Br(2)). 1 crystallizes in the orthorhombic space group Pccn in a distorted square planar geometry. Magnetic susceptibility data were fit to the uniform chain Heisenberg model resulting in C = 0.439(6)emu-K/mole-Oe and J = ?28(1) K. 2 crystallizes in the monoclinic space group C2/m and is closer to distorted tetrahedral. Intermolecular Br?Cu contacts generate a square layer. Magnetic data show very weak ferromagnetic interactions [C = 0.42(1)emu-K/mol-Oe, J = 0.71(2) K]. Similarly, reaction of 2-F-4-AP with copper halides and aqueous HX in alcohol solvents produced the salts (2-F-4-APH)₂CuX₄ (X = Cl(3), Br(4)). 3 crystallizes in the triclinic space group P-1. Crystal packing reveals short Cl?Cl contacts which generate a structural ladder. However, analysis of the magnetic data suggests that only the rails of the ladder produce a viable magnetic superexchange pathway; the uniform Heisenberg chain model provides C = 0.449(1)emu-K/mol-Oe and J = -6.9(1) K. 4 is isostructural and is also best fit by a chain model [J = ?2.7(4) K]. The brominated complex (2-F-3-Br-4-APH)₂CuBr₄·2H₂O, 5, (2-F-3-Br-4-APH = 4-amino-3-bromo-2-fluoropyridinium) was serendipitously produced as a byproduct of the synthesis of 4 and was characterized by single-crystal X-ray diffraction.     

Supramolecular architecture and magnetic properties of copper(II) and nickel(II) porphyrinogen-TCNQ electron-transfer salts

The compounds [Cu(Tz)-(MeOH)2](TCNQ)2 (1), [Ni(Tz)-(MeOH)2](TCNQ)2 (2), [Cu(Tz)2]-(TCNQ)7 (3) and [Ni(Tz)2](TCNQ)7 (4) (Tz = 2,7,12,17-tetramethyl-1,6,11,16-tetraazaporphyrinogen) were obtained by metathesis reaction of [M(Tz)](ClO4)2 with LiTCNQ and Et3NH(TCNQ)2, respectively. They were characterized by a combination of spectroscopic and physical methods. Compound 1 crystallizes in the monoclinic space group P2(1)/n with a = 8.310(2), b = 25.180(4), c = 20.727(4) A, beta = 93.58(2) degrees; Z = 4. Compound 3 crystallizes in the triclinic space group P1 with a = 11.244(1), b = 16.700(1), c = 17.321(1) A, a = 113.47(1), beta = 108.52(1), gamma = 96.12(1) degrees; Z = 2. The asymmetric unit of the compound 1 is formed by cationic [Cu(Tz)(MeOH)2]2+ and by two crystallographically non equivalent TCNQ.- anions; these anions form dimeric units by overlap of the pi clouds. The dimers form hydrogen bonds with the metal-lomacrocyclic cation through the methanol ligands. According to this structure the compound is paramagnetic and behaves as an insulator in the temperature range studied. The paramagnetism arises only from the metal-complex moieties. Compound 3 shows an unprecedented structure due to the steric requirements of the macrocycle that favors the stacking of the TCNQ groups. The structure consists of infinite stacks of TCNQ units separated by the metal-macrocyclic units; there are seven TCNQ molecules per formula unit, one of which is formally mono-anionic, while the other six bear one half of an electron per molecule. The copper is six-coordinate in a very distorted octahedral environment. The Tz ligand is located in the equatorial plane and the apical nitrogens of the nitrile groups of two TCNQ molecules complete the coordination around the copper. The compound is a semiconductor and its magnetic behavior can be explained by the sum of the Curie contribution of the metal complex and the contribution arising from the magnetic-exchange interactions of the spins located on the TCNQ units. The latter is found to be typical of one-dimensional antiferromagnetic distorted chains of S = 1/2 spins and can be fitted according to a one-dimensional Heisenberg antiferromagnetic model.     

Structural studies in main group chemistry : XIX. Organotin(IV) derivatives of tetracyanoethylene, 7,7,8,8-tetracyanoquinodimethane and 2,3,5,6-tetrachlorobenzoquinone. The isolation of stable organotin-substituted radicals

The reaction of organotin chlorides with the lithium salt of 7,7,8,8-tetracyanoquinodimethane (TCNQ) or hexaalkylditins with TCNQ yield stable organotin-substituted free radicals of the types R₃SnTCNQ^. (R = Me, n-Pr, n-Bu) and Me₂Sn(TCNQ^.)₂. The reaction of hexaphenylditin with TCNQ yields a (σ → π) charge transfer complex of stoichiometry (Ph₃SnSnPh₃)·TCNQ, whilst [Me₂SnCl(terpyridyl)⁺](TCNQ^-·) was isolated from the reaction of [Me₂SnCl(terpyridlyl)⁺][Me₂SnCl₃^-] and LiTCNQ. The oxidation of hexaalkylditins by tetracyanoethylene (TCNE) yields stable free radicals of the type R₃SnTCNE·, but treatment with 2,3,5,6-tetrachlorobenzoquinone yields either R₃SnOC₆Cl₄O·-p (R = Me) or R₃SnOC₆Cl₄OSnR₃-p (R = n-Bu, Ph). Tin-119 Mössbauer spectroscopy shows that the derivatives R₃SnTCNQ· and R₃TCNE· have trigonally-bipyramidally coordinated tin with planar [SnC₃] skeletons and bridging [TCNQ·] and [TCNE·] groups forming infinite one-dimensional chain structures. Me₃SnOC₆Cl₄O·-p was inferred to possess a similar structure but with oxy bridges forming chains with a Sn---O---Sn---O backbone. Me₂Sn(TCNQ·)₂ has a structure intermediate between tetrahedral and octahedral with a non-linear MeSnMe unit and anisobidentate chelation by two TCNQ groups. The TCNQ derivatives were of two types: (i) “green” or “brown”, indicative of delocalisation of the Ione electron over the cyanoquinone ligand, and (ii) a “blue” form in which spin-pairing of the Ione electron between adjacent organic groups takes place. Me₃SnTCNQ· may exist in both forms depending upon the mode of preparation.     

Utility of 7,7,8,8-tetracyanoquinodimethane charge transfer reagent for the spectrophotometric determination of trazodone, amineptine and amitriptyline hydrochlorides

A simple and rapid spectrophotometric method has been developed for the determination of tricyclic anti-depressant drugs such as trazodone (TZH), amineptine (APH) and amitriptyline (ATPH) hydrochlorides in pure form and in different pharmaceutical preparations. The charge transfer (CT) reaction between TZH, APH and ATPH as electron donors and TCNQ as electron acceptor was utilized for their spectrophotometric determination. The optimum experimental conditions, like time, temperature, stoichiometry, solvents, for the CT complex formation are established. The method permits the determination of TZH, APH and ATPH over a concentration range of 10-400, 10-440 and 10-300 microg ml(-1), respectively. The sensitivity (S) is found to be 0.09, 0.087 and 0.069 g cm(-2) for TZH, APH and ATPH, respectively. The SD values are found to be 0.146-0.293, 0.154-0.285 and 0.091-0.212 and RSD values are 0.142-1.92, 0.297-1.92 and 0.212-0.915 for TZH, APH and ATPH, respectively. The low values of the relative standard deviation indicate the high accuracy and precision of the method. The mean recovery values obtained together with a high correlation coefficient values, amount in the range 98-101.5, 98.7-102.9 and 93-101.9 for TZH, APH and ATPH, respectively. The method is applicable for the assay of the investigated drugs in different dosage forms and the results are in good agreement with those obtained by the official method.