Molecular Rotors of Coronene in Charge‐Transfer Solids

Ten types of neutral charge transfer (CT) complexes of coronene (electron donor; D) were obtained with various electron acceptors (A). In addition to the reported 7,7,8,8‐tetracyanoquinodimethane (TCNQ) complex of 1:1 stoichiometry with a DA‐type alternating π column, TCNQ also afforded a 3:1 complex, in which a face‐to‐face dimer of parallel coronenes ( Cor‐A s) is sandwiched between TCNQs to construct a DDA‐type alternating π column flanked by another coronene ( Cor‐B ). Whereas solid‐state ²H NMR spectra of the 1:1 TCNQ complex formed with deuterated coronene confirmed the single in‐plane 6‐fold flipping motion of the coronenes, two unsynchronized motions were confirmed for the 3:1 TCNQ complex, which is consistent with a crystallographic study. Neutral [Ni(mnt)₂] (mnt: maleonitriledithiolate) as an electron acceptor afforded a 5:2 complex with a DDA‐type alternating π column flanked by another coronene, similar to the 3:1 TCNQ complex. The fact that the Cor‐A s in the [Ni(mnt)₂] complex arrange in a non‐parallel fashion must cause the fast in‐plane rotation of Cor‐A relative to that of Cor‐B . This is in sharp contrast to the 3:1 TCNQ complex, in which the dimer of parallel Cor‐A s shows inter‐column interactions with neighboring Cor‐A s. The solid‐state ¹H NMR signal of the [Ni(mnt)₂] complex suddenly broadens at temperatures below approximately 60 K, indicating that the in‐plane rotation of the coronenes undergoes down to approximately 60 K; the rotational rate reaches the gigahertz regime at room temperature. Rotational barriers of these CT complexes, as estimated from variable‐temperature spin–lattice relaxation time (T₁) experiments, are significantly lower than that of pristine coronene. The investigated structure–property relationships indicate that the complexation not only facilitates the molecular rotation of coronenes but also provides a new solid‐state rotor system that involves unsynchronized plural rotators.     

Laser Spectroscopy and Lifetime Measurements of the S1 State of Tetracyanoquinodimethane (TCNQ) in a Cold Gas-Phase Free-Jet

The S₁ electronic state of 7,7,8,8-Tetracyanoquinodimethane (TCNQ) has been investigated by laser induced fluorescence (LIF), dispersed fluorescence (DF) spectroscopy, and lifetime measurements under jet-cooled conditions in the gas-phase. The LIF spectrum showed a weak origin band at 412.13 nm (24262 cm⁻¹) with prominent progression and combination bands involving vibrations of 327, 1098, and 2430 cm⁻¹. In addition, very strong bands appeared at ∼363.6 nm (3300 cm⁻¹ above the origin). Both the LIF and DF spectra indicate considerable geometric change in the S₁ state. The fluorescence lifetime of S₁ at zero-point level was obtained to be 220 ns. This lifetime is 40 times longer than the radiative lifetime estimated from the S₁−S₀ oscillator strength. Furthermore, the lifetimes of the vibronic bands exhibited drastic energy dependence, indicating a strong mixing with the triplet (T₁) or intramolecular charge-transfer (CT) state. This study is thought to disclose intrinsic nature of TCNQ, which has been well known as a component of organic semiconductors and a versatile p-type dopant.     

Significance of redistribution reactions detected by in situ atomic force microscopy during early stages of fast scan rate redox cycling experiments at a solid 7,7,8,8-tetracyanoquinodimethane-glassy carbon electrode-aqueous (electrolyte) interface

The reduction of solid 7,7,8,8-tetracyanoquinodimethane (TCNQ) at an electrode-TCNQ-aqueous (electrolyte) is complex, irrespective of whether the solid on the electrode surface is attached by direct adherence or formed by electrochemical deposition. In order to understand the origin of reaction pathways that accompany the [TCNQ]^0/− process, fast scan rate (0.1 V s⁻¹) redox cycling and potential step experiments on TCNQ mechanically attached to a glassy carbon electrode placed in aqueous solution containing 0.1 M electrolyte (KCl, CsCl, or Et₄NCl) have been monitored by the technique of in situ atomic force microscopy (AFM). The shapes of cycling voltammograms are consistent with the presence of a mixture of diffusion and surface processes in the initial cycles. AFM results show that, during the early stage of the redox cycling experiments, electrochemical reduction of TCNQ to sparingly soluble TCNQ⁻ is accompanied by a redistribution process. This rearrangement results in the transformation of arrays of almost amorphous solid to a lower energy microcrystalline state which has a more thin film-type appearance. When CsCl is the electrolyte, long needle-type crystals are detected by the AFM method after long periods of redox cycling. The identity of the cation in the supporting electrolyte and the solubility of the reduced salt formed by reduction of TCNQ affect the nature of the voltammetry observed during early stages of redox cycling. When the redistribution process is completed and the stable crystalline phase is formed, the voltammetry of the [TCNQ]^0/− couple is predominantly controlled by a nucleation-growth mechanism. Received: 8 March 1999 / Accepted: 12 April 1999     

Experimental investigation of excited state electron transfer reactions between some bicyclic molecules and tetracyanoquinodimethane (TCNQ)

Investigations on photoinduced electron transfer (ET) reactions between excited (ground) bicyclic electron donors 5,6,7,8-tetrahydro-2-naphthol (TH2N), 2-methoxy-5,6,7,8-tetrahydro naphthalene (2MTHN) and ground state (excited) acceptor tetracyanoquinodimethane (TCNQ) in fluid solutions of different polarity at the ambient temperature (300 K) by electronic absorption, steady state fluorescence and time-resolved spectroscopic methods in the time domain of nanosecond order have been carried out. It is suggested that in highly polar solvent acetonitrile (ACN), a loosely-structured transient geminate ion-pair complex (GIP) in the excited singlet state (S₁) is formed due to the ET encounter between the present donor TH2N or 2MTHN and TCNQ and this GIP complex rapidly dissociates into stable excited radical ions, as evidenced from steady state spectra. In polar DMF solvents, TCNQ exhibits an electronic absorption band of its anion without the presence of donor molecules. Both steady state and time-resolved data indicate that ET reactions between the present donors and acceptor TCNQ are largely impeded in the less polar solvent tetrahydrofuran (THF). In the highly polar solvent ACN, ET reactions between the donors and acceptor TCNQ have been suggested to be of adiabatic or intermediate between adiabatic and non-adiabatic types, from the observation of radical ion species in the electronic excited state. For some bicyclic donors and TCNQ acceptor systems, large negative ΔG, which is a measure of the gap between locally excited and radical ion-pair states, shows reaction occurs in highly exothermic regions. Further observations of −ΔG>λ, nuclear reorganization energy parameters and the decrement of ET rate (k_ET) with increasing exothermicity (more negative ΔG values) suggest the ET reaction for the bicyclic donor—TCNQ acceptor systems studied in the present investigation might occur in the Marcus inverted region. The possibility of building up efficient photoconducting materials with the present donor acceptor systems is suggested.     

Synthesis,Characterization and Antifungal Activity of Metal Complexes of 2-(5-((2-Chlorophenyl)Diazenyl)-2-Hydroxybenzylidene) Hydrazinecarbothioamide

Abstract

New metal complexes of Co(II), Cu(II), Ni(II), Zn(II), Mn(II), Fe(III), Ru(III), UO₂(II), and VO(II) with the Schiff base, 2-(5-((2-chlorophenyl)diazenyl)-2-hydroxy- benzylidene) hydrazine-carbothioamide (H₂L) have been prepared and characterized by elemental and thermal analyses, FT-IR, UV–Vis, mass spectra, ¹H-NMR, and ESR as well as conductivity and magnetic moments measurements. The IR spectra showed that the ligand acts as neutral tridentate, neutral bidentate or monobasic tridentate ligand. The geometries of metal complexes were either octahedral or square pyramidal. The ESR spectra of the solid copper(II) complexes indicated an axial symmetry type of a d_(x2-y2) ground state with considerably ionic or covalent environment. The effect of the presence of an azo group on the biological activity of the ligand was investigated. The ligand and its complexes are biologically inactive due to the presence of azo group.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the related elements to view the free supplemental file.     

Photophysical, electrochemical and electrochromic properties of copper-bis(4,4′-dimethyl-6,6′-diphenyl-2,2′-bipyridine) complexes

The synthesis, solution and solid state structural characterization, photophysical and electrochemical properties of two redox forms of an electrochromic copper-bis(4,4′-dimethyl-6,6′-diphenyl-2,2′-bipyridine) complex, [Cu(3)₂]ⁿ (n=+1, +2), are presented. Both complexes were characterized in the solid state by X-ray diffraction methods on single-crystals showing that both forms exist in a pseudo-tetrahedral coordination, and a comparison with other structures was made. Like most copper(I) complexes, the red [Cu(3)₂]⁺ complex shows a rather weak emission (Φ_em=2.7×10⁻⁴, dichloromethane). The lifetime of the emitting MLCT state is 34±1 ns, as observed with time resolved emission, and transient absorption (in deoxygenated dichloromethane). Typical emission and transient absorption spectra are presented. The transient absorption spectra indicate that the MLCT state absorbs stronger than the ground state, which is relatively uncommon for metal bipyridine complexes, i.e. no ground state bleaching is observed. The green [(3)₂Cu]²⁺ complex does not show any observable emission or transient absorption, which is a common feature for Cu(II) complexes of this type. The electronic absorption spectra of the chemically and electrochemically produced copper(I/II) complexes are identical. The repeated electrochemical conversion of the Cu(I) center into Cu(II) and vice versa does not cause any decomposition. This is consistent with a fully reversible Cu(I)/Cu(II) redox couple in the corresponding cyclic voltammogram, (E_1/2 (Cu(I)/Cu(II))=+0.68 V vs. SCE=+0.23 V vs. Fc/Fc⁺). These observations indicate that no large structural reorganization occurs upon electrochemical timescales (sub second), and that the different ways of generating the complexes does not effect their final structure, apart from the small differences observed in the X-ray structures of both forms. These characteristics make these complexes rather well suited for their incorporation into an electrochromic display configuration.     

Alternating π‐conjugated copolymer of dithiafulvene with 2,2′‐bipyridyl units

A π‐conjugated polymer containing a dithiafulvene unit and a bipyridyl unit was prepared by cycloaddition polymerization of aldothioketene derived from 5,5′‐diethynyl‐2,2′‐bipyridine. Ultraviolet–visible (UV–vis) absorption spectra showed that the π‐conjugation system of the polymer expanded more effectively than that of a benzene analogue of poly(dithiafulvene) obtained from 1,4‐diethynylbenzene. Cyclic voltammetry measurements indicated that the dithiafulvene–bipyridyl polymer was a weaker electron‐donor polymer than the benzene analogue. These results supported the idea that the incorporation of the electron‐accepting bipyridyl moiety into conjugated poly(dithiafulvene) induced an intramolecular charge‐transfer (CT) effect between the units. Treatment of the dithiafulvene–bipyridyl polymer with bis(2,2′‐bipyridyl)dichlororuthenium (II) [Ru(bpy)₂Cl₂] afforded a ruthenium–polymer complex. A cyclic voltammogram of the complex showed broad redox peaks, which indicated electronic interaction between the dithiafulvene and tris(bipyridyl) ruthenium complex. The dithiafulvene–bipyridyl polymer formed CT complexes with 7,7,8,8‐tetracycanoquinodimethane (TCNQ) in dimethyl sulfoxide. The UV–vis absorption indicated that the resulting CT complex contained anion radical of TCNQ and partially charge‐transferred TCNQ. The polymer showed an unusually high electrical conductivity of 3.1 × 10^?4 S/cm in its nondoped state due to the effective donor–acceptor interaction between the bipyridine unit and the dithiafulvene unit. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4083–4090, 2001     

Positive dendritic effects on the electron-donating potencies of poly(propylene imine) dendrimers

[structure: see text] Two series of poly(propylene imine), PPI, dendrimers terminated with a redox-active donor, 4-dimethylaminobenzyl (4-DMAB), including their respective nondendronized model compounds, are reported. In these two series, a positive dendritic effect was observed for the formation of charge-transfer (CT) complexes between the dendrimers and 7,7,8,8-tetracyanoquinodimethane (TCNQ). However, the nondendronized compounds did not form CT complexes with TCNQ, even though their redox potentials are similar to those of the 4-DMAB units attached to the dendrimers.     

Synthesis,spectroscopic and thermal structural investigations of the charge-transfer complexes formed in the reaction of 1-methylpiperidine with σ- and π-acceptors

The reactions of the electron donor 1-methylpiperidine (1MP) with the π-acceptors 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil = CHL) and iodine (I₂) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge-transfer (CT) complexes were recorded. The obtained results showed that the stoichiometries of the reactions are not fixed and depend on the nature of the acceptor. Based on the obtained data, the formed charge-transfer complexes were formulated as [(1MP)(TCNE)₂], [(1MP)(DDQ)]·H₂O, [(1MP)(CHL)] and [(1MP)I]I₃, while in the case of 1MP–TCNQ reaction, a short-lived CT complex is formed followed by rapid N-substitution by TCNQ forming the final reaction products 7,7,8-tricyano-8-piperidinylquinodimethane (TCPQDM). The five solids products were isolated and have been characterized by electronic spectra, infrared spectra, elemental analysis and thermal analysis.     

Encapsulation of TCNQ and the Acridinium Ion within a Bisporphyrin Cavity: Synthesis,Structure, and Photophysical and HOMO–LUMO‐Gap‐Mediated Electron‐Transfer Properties

The encapsulation of tetracyanoquinodimethane (TCNQ) and fluorescent probe acridinium ions (AcH⁺) by diethylpyrrole‐bridged bisporphyrin (H₄DEP) was used to investigate the structural and spectroscopic changes within the bisporphyrin cavity upon substrate binding. X‐ray diffraction studies of the bisporphyrin host (H₄DEP) and the encapsulated host–guest complexes (H₄DEP ? TCNQ and [H₄DEP ? AcH]ClO₄) are reported. Negative and positive shifts of the reduction and oxidation potentials, respectively, indicated that it was difficult to reduce/oxidize the encapsulated complexes. The emission intensities of bisporphyrin, upon excitation at 560 nm, were quenched by about 65 % and 95 % in H₄DEP ? TCNQ and [H₄DEP ? AcH]ClO₄, respectively, owing to photoinduced electron transfer from the excited state of the bisporphyrin to TCNQ/AcH⁺; this result was also supported by DFT calculations. Moreover, the fluorescence intensity of encapsulated AcH⁺ (excited at 340 nm) was also remarkably quenched compared to the free ions, owing to photoinduced singlet‐to‐singlet energy transfer from AcH⁺ to bisporphyrin. Thus, AcH⁺ acted as both an acceptor and a donor, depending on which part of the chromophore was excited in the host–guest complex. The electrochemically evaluated HOMO–LUMO gap was 0.71 and 1.42 eV in H₄DEP ? TCNQ and [H₄DEP ? AcH]ClO₄, respectively, whilst the gap was 2.12 eV in H₄DEP. The extremely low HOMO–LUMO gap in H₄DEP ? TCNQ led to facile electron transfer from the host to the guest, which was manifested in the lowering of the CN stretching frequency (in the solid state) in the IR spectra, a strong radical signal in the EPR spectra at 77 K, and also the presence of low‐energy bands in the UV/Vis spectra (in the solution phase). Such an efficient transfer was only possible when the donor and acceptor moieties were in close proximity to one another.     

An e.s.r. study of copper(II) complexes of N-hydroxyalkylsalicylideneimines

X-band e.s.r. spectra of copper(II) complexes of empirical formula Cu(Sal.NCH2CH2O)X (where X= H2O, py or Cl) and [Cu(Sal.NCH2CH2CH2O)]2 (Sal.N= OC6H4CHN) in solid and solution states at room temperature and at 77K are reported. In frozen solution at 77K the spectra show axial symmetry with a dx2−y2 ground state. The in-plane π-bonds show a moderate degree of covalence, while the out-of-plane π-bonds possess ionic character. The orbital populations of these complexes are 70.9, 81.3, 93.3 and 82.4% respectively, indicating a dx2−y2 ground state. This revised version was published online in June 2006 with corrections to the Cover Date.     

Luminescent organotin complexes with the ligand benzil bis(benzoylhydrazone)

Three organotin complexes have been synthesised by reaction of the ligand benzil bis(benzoylhydrazone) LH₂ with SnR₂Cl₂ or SnR₃Cl (R = Me, Bu, Ph). In all the compounds the ligand is doubly deprotonated and behaves as N₂O₂ tetradentate chelate, leading to distorted octahedral arrangements with the ligand in the equatorial plane and the organic groups in the axial positions. The complexes have been fully characterised by spectroscopic techniques including ¹³C and ¹¹⁹Sn NMR in solution and in the solid state, which confirm that the structure found in the solid state is retained in chloroform solution, and two of them by single crystal X-ray diffraction. The luminescent properties of the ligand and its complexes have also been tested as well as the effect of pH, the addition of acetone and the ionic strength over the luminescence intensity.     

稀土HEH[EHP]固体配合物的红外光谱

本文制备了La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Lu,Y等十五种稀土与2-乙基己基膦酸单(2-乙基己基)酯的固体配合物,测定了4000-100cm~(-1)的FT-IR光谱,对其主要红外光谱吸收带进行了归属。指认150cm~(-1)为Ln-O键的伸缩振动带,250cm~(-1)附近的谱带为COPO,CCPO骨架扭曲振动与Ln-O键的耦合振动带。结果表明配合物为多聚体系,PO_2与稀土离子可能为桥式配位形式。Ln-O键基本上为离子键。     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。     

Tetranuclear complexes of [Fe(CO)2(C5H5)]+ with TCNX ligands (TCNX=TCNE, TCNQ, TCNB): intramolecular electron transfer alternatives in compounds (mu4-TCNX)[MLn]4

The complexes {(mu4-TCNX)[Fe(CO)2(C5H5)]4}(BF4)4 were prepared as light-sensitive materials from [Fe(CO)2(C5H5) (THF)](BF4) and the corresponding TCNX ligands (TCNE = tetracyanoethene, TCNQ=7,7,8,8-tetracyano-p-quinodimethane, TCNB=1,2,4,5-tetracyanobenzene). Whereas the TCNE and TCNQ complexes are extremely easily reduced species with reduction potentials>+0.3 V vs ferrocenium/ferrocene, the tetranuclear complex of TCNB exhibits a significantly more negative reduction potential at about -1.0 V. Even for the complexes with strongly pi-accepting TCNE and TCNQ, the very positive reduction potentials, the unusually high nitrile stretching frequencies>2235 cm(-1), and the high-energy charge-transfer transitions indicate negligible metal-to-ligand electron transfer in the ground state, corresponding to a largely unperturbed (TCNX degrees)(FeII)4 formulation of oxidation states as caused by orthogonality between the metal-centered HOMO and the pi* LUMO of TCNX. M?ssbauer spectroscopy confirms the low-spin iron(II) state, and DFT calculations suggest coplanar TCNE and TCNQ bridging ligands in the complex tetracations. One-electron reduction to the 3+ forms of the TCNE and TCNQ complexes produces EPR spectra which confirm the predominant ligand character of the then singly occupied MO through isotropic g values slightly below 2, in addition to a negligible g anisotropy of frozen solutions at frequencies up to 285 GHz and also through an unusually well-resolved solution X band EPR spectrum of {(mu4-TCNE)[Fe(CO)2(C5H5)]4}3+ which shows the presence of four equivalent [Fe(CO)2(C5H5)]+ moieties through 57Fe and 13C(CO) hyperfine coupling in nonenriched material. DFT calculations reproduce the experimental EPR data. A survey of discrete TCNE and TCNQ complexes [(mu4-TCNX)(MLn)4] exhibits a dichotomy between the systems {(mu4-TCNX)[Fe(CO)2(C5H5)]4}4+ and {(mu4-TCNQ)[Re(CO)3(bpy)]4}4+ with their negligible metal-to-ligand electron transfer and several other compounds of TCNE or TCNQ with Mn, Ru, Os, or Cu complex fragments which display evidence for a strong such interaction, i.e., an appreciable value delta in the formulation {(mu4-TCNXdelta-)[Mx+delta/4Ln]4}. Irreversibility of the first reduction of {(mu4-TCNB)[Fe(CO)2(C5H5)]4}(BF4)4 precluded spectroelectrochemical studies; however, the high-energy CN stretching frequencies and charge transfer absorptions of that TCNB analogue also confirm the exceptional position of the complexes {(mu4-TCNX)[Fe(CO)2(C5H5)]4}(BF4)4.     

An alternative synthetic route of [3(5)](1,2,3,4,5)cyclophane,and structural properties of multibridged [3(n)]cyclophanes and their charge-transfer complexes in the solid state

To develop an improved synthetic route to [3(6)](1,2,3,4,5,6)cyclophane (CP) 2, a more practical synthetic route to [3(5)](1,2,3,4,5)CP 3 than the original one was developed, which started from [3(2)](1,3)CP 7 via [3(4)](1,2,4,5)CP 5. The fundamental structural parameters of [3(n)]CPs (n = 3-6) in the solid state were elucidated, and the observed structures were in good agreement with the most stable conformers in solution and those predicted by the theoretical calculations. In the case of [3(6)]CP 2, the most stable C(6)(h) structure was observed in the crystal structure of the 2-TCNQ-F(4) (1:1) complex, whereas the highly strained structure with a D(6)(h) symmetry was observed in the crystal structure of 2 and the 2:TCNQ:benzene (1:1:1) complex because of a severe disorder problem. [3(n)]CPs (n > 3) showed reversible redox processes, and 2 (+0.39 V vs F(c)/F(c)(+), Cl(2)CHCHCl(2)) showed the lowest first half-wave oxidation potential [E(1/2) (I)] in [3(n)]CPs. The E(1/2) (I) data support the strong donating ability of 2 and its lower homologues. This is attributed to their molecular structures where effective hyperconjugation between the benzyl hydrogens and benzene ring is possible. By taking advantage of the strong electron-donating ability of [3(n)]CPs, their CT complexes with TCNE, TCNQ, and TCNQ-F(4) were prepared, and their crystal structural properties were examined. The single-crystal conductivity data of the CT complexes indicated that the TCNQ-F(4) complexes showed higher conductivities than the corresponding TCNQ complexes mainly due to a larger charge separation. Among the [3(n)]CP-TCNQ complexes, the [3(3)](1,3,5)CP 6-TCNQ-F(4) (1:1) complex showed the highest conductivity (10(-)(4) S cm(-)(1)), and this was ascribed to the formation of an infinite column of partially overlapped acceptors with a short acceptor-acceptor distance, while the formation of such a column was not observed in the 2-TCNQ-F(4) complex. Although the conductivities of the cyclophane-CT complexes are much lower than those of the TTF related complexes, this study successfully provides the basic knowledge for understanding the CT interactions in the solid state.     

Synthesis and photophysical properties of new Ln(III) (Ln = Eu(III), Gd(III), or Tb(III)) complexes of 1-amidino-O-methylurea

Three new solid lanthanide(III) complexes, [Ln(1-AMUH)₃] · (NO₃)₃ (1-AMUH = 1-amidino-O-methylurea; Ln = Eu(III), Gd(III), or Tb(III)) were synthesised and characterised by elemental analysis, infrared spectra, magnetic moment measurement, and electron paramagnetic resonance (EPR) spectra for Gd(III) complex. The formation of lanthanide(III) complexes is confirmed by the spectroscopic studies. The photophysical properties of Gd(III), Eu(III), and Tb(III) complexes in solid state were investigated. The Tb(III) complex exhibits the strongest green emission at 543 nm and the Eu(III) complex shows a red emission at 615 nm while the Gd(III) complex shows a weak emission band at 303 nm. Under excitation with UV light, these complexes exhibited an emission characteristic of central metal ions. The powder EPR spectrum of the Gd(III) complex at 300 K exhibits a single broad band with g = 2.025. The bi-exponential nature of the decay lifetime curve is observed in the Eu(III) and Tb(III) complexes. The results reveal them to have potential as luminescent materials.     

Crystal and molecular structure of the complex radical ionic salt,N-(β-iodoethyl)pyridinium bis (7,7′,8,8′-tetracyanoquinodimethanide), (C7H9IN)+·(TCNQ)•−·(TCNQ)

A complex radical ionic salt,N-(β-iodoethyl)pyridinium bis (7,7′, 8,8′-tetracyanoquinodimethanide), (C₇H₉IN)⁺·(TCNQ)^??·(TCNQ), where TCNQ is 7,7′, 8,8′-tetracyanoquinodimethane, was synthesized and studied by X-ray structural analysis. The crystal structure of the complex consists of layers. Layers of (C₇H₉IN)⁺ cations alternate with layers of TCNQ molecules packed in stacks. Shortened intermolecular contacts occur in stacks of TCNQ and between cationic and anionic layers.     

X-ray and solution structures of Cu(II) GHK and Cu(II) DAHK complexes: influence on their redox properties

The Gly‐His‐Lys (GHK) peptide and the Asp‐Ala‐His‐Lys (DAHK) sequences are naturally occurring high‐affinity copper(II) chelators found in the blood plasma and are hence of biological interest. A structural study of the copper complexes of these peptides was conducted in the solid state and in solution by determining their X‐ray structures, and by using a large range of spectroscopies, including EPR and HYSCORE (hyperfine sub‐level correlation), X‐ray absorption and ¹H and ¹³C NMR spectroscopy. The results indicate that the structures of [Cu^II(DAHK)] in the solid state and in solution are similar and confirm the equatorial coordination sphere of NH₂, two amidyl N and one imidazole N. Additionally, a water molecule is bound apically to Cu^II as revealed by the X‐ray structure. As reported previously in the literature, [Cu^II(GHK)], which exhibits a dimeric structure in the solid state, forms a monomeric complex in solution with three nitrogen ligands: NH₂, amidyl and imidazole. The fourth equatorial site is occupied by a labile oxygen atom from a carboxylate ligand in the solid state. We probe that fourth position and study ternary complexes of [Cu^II(GHK)] with glycine or histidine. The Cu^II exchange reaction between different DAHK peptides is very slow, in contrast to [Cu^II(GHK)], in which the fast exchange was attributed to the presence of a [Cu^II(GHK)₂] complex. The redox properties of [Cu^II(GHK)] and [Cu^II(DAHK)] were investigated by cyclic voltammetry and by measuring the ascorbate oxidation in the presence of molecular oxygen. The measurements indicate that both Cu^II complexes are inert under moderate redox potentials. In contrast to [Cu^II(DAHK)], [Cu^II(GHK)] could be reduced to Cu^I around ?0.62 V (versus AgCl/Ag) with subsequent release of the Cu ion. These complete analyses of structure and redox activity of those complexes gave new insights with biological impact and can serve as models for other more complicated Cu^II–peptide interactions.     

Synthesis and physico-chemical studies on cobalt(II), nickel(II) and copper(II) complexes of benzidine diacetyloxime

The synthesis of benzidine diacetyloxime (H₂L) and its cobalt(II), nickel(II) and copper(II) complexes is described. The complexes were characterized by elemental analyses, molar conductivities, magnetic moments, i.r., u.v.–vis. spectra, t.g.a. and e.s.r. measurements. I.r. spectra show that H₂L behaves as a neutral or dinegative ligand depending on the nature of the metal salts. The molar conductances of the complexes in DMF are commensurate with their non-ionic character. The e.s.r. spectrum of the solid copper(II) complex (7) at room temperature shows broad signal, indicating spin-exchange interactions between copper(II) ions. However, in TMHF solution at 77 K, it shows an axial type ground state with mixed ionic-covalent bond character.