Dioxygen Activation and Reduction by a Soluble Iron Phthalocyanine

Iron ions in a square-planar coordination can bind molecules at the vacant axial positions and are able to transform them in stoichiometric and catalytic reactions. Nature takes advantage of these properties by incorporating iron into porphyrin systems, which play a key role not only in the binding and transport of oxygen, but also in catalytic oxidation and reduction reactions involving cytochrome P450. Although these systems have been studied extensively, there are still unresolved questions regarding the interplay between the iron ions and the surrounding ligands. Phthalocyanines (Pc) create a similar environment for metal atoms and FePc is known for a long time. However, without axial ligands FePc aggregates leading to solids of low solubility. In this work we used a known six-coordinate iron phthalocyanine derivative with bulky substituents and removed the stabilizing axial ligands. The resulting paramagnetic, four-coordinate compound does not aggregate and dissolves well so that NMR spectroscopy can be employed for studying the molecular structure and the reactivity. Solvent molecules bind weakly to the iron centers and oxygen is reduced in the presence of H-atom donors. The stoichiometric and catalytic reactivity with oxygen was studied in more detail.

Trinuclear coordination assemblies of low-spin dicyano manganese(II) (S = 1/2) and iron(II) (S = 0) phthalocyanines with manganese(II) acetylacetonate, tris(cyclopentadienyl)gadolinium(III) and neodymium(III)

The reaction of Mn^IIPc, Fe^IIPc or Fe^IIPcCl₁₆ with KCN in the presence of cryptand[2.2.2] yielded dicyano-complexes {cryptand(K⁺)}₂{M^II(CN)₂(macrocycle^2-)}^2-·XC₆H₄Cl₂ (M = Mn and Fe, X = 1 and 2) that were used for the preparation of trinuclear assemblies of the general formula {cryptand(K⁺)}₂{M^II(CN)₂Pc·(ML)₂}^2-·nC₆H₄Cl₂ (M^II = Mn^II and Fe^II; n = 1, 4 and 5). These assemblies were formed via coordination of two manganese(II) acetylacetonate (ML = Mn^II(acac)₂, S = 5/2), tris(cyclopentadienyl)gadolinium (ML = Cp₃Gd^III, S = 7/2) or tris(cyclopentadienyl)neodymium (ML = Cp₃Nd^III, S = 3/2) units to the nitrogen atoms of bidentate cyano ligands. The N(CN)-Mn{Mn^II(acac)₂} bond is 2.129(3) Å long but the bonds are elongated to 2.43-2.49 Å for tris(cyclopentadienyl)lanthanides. {Cryptand(K⁺)}₂{Mn^II(CN)₂Pc·(Mn^II(acac)₂)₂}^2-·5C₆H₄Cl₂ (2) contains three Mn(II) ions in different spin states (S = 5/2 and 1/2). Strong antiferromagnetic coupling of spins observed between them with the exchange interaction (J) of -17.6 cm^-1 enables the formation of a high S = 9/2 spin state for {Mn^II(CN)₂Pc·(Mn^II(acac)₂)₂}^2- dianions at 2 K. The estimated exchange interaction between Mn^II (S = 1/2) and Gd^III (S = 7/2) spins in {Mn^II(CN)₂Pc·(Cp₃Gd^III)₂}^2- is only -1.1 cm^-1, and in contrast to 2, nearly independent Gd^III and Mn^II centers are formed. As a result, no transition to the high-spin state is observed in {Mn^II(CN)₂Pc·(Cp₃Gd^III)₂}^2-. The {Mn^II(CN)₂Pc·(Cp₃Nd^III)₂}^2- and{Fe^II(CN)₂Pc·(Cp₃Nd^III)₂}^2- dianions with Cp₃Nd^III show a decrease of χ_MT values in the whole studied temperature range (300-1.9 K). A similar behaviour was found previously for pristine Cp₃Nd^III and Cp₃Nd^III·L complexes (L = alkylisocyanide ligand).

A large negative magnetoresistance effect in semiconducting crystals composed of an octahedrally ligated phthalocyanine complex with high-spin manganese(iii)

A design for an octahedrally ligated phthalocyanine complex with high-spin manganese(iii) (S = 2) and Mn^III(Pc)Cl₂ (Pc = phthalocyanine) is presented. The presence of high-spin state Mn^III in the fabricated Ph₄P[Mn^III(Pc)Cl₂]₂ (Ph₄P = tetraphenylphosphonium) semiconducting molecular crystal is indicated by the Mn–Cl distance, which suggests an electronic configuration of (d_yz, d_zx)²(d_xy)¹(d_z²)¹. This was confirmed by the Curie constant (C = 5.69 emu K mol⁻¹), which was found to be significantly larger than that of the isostructural Ph₄P[Mn^III(Pc)(CN)₂]₂, where Mn^III adopts a low-spin state (S = 1). The magnetoresistance (MR) effects of Ph₄P[Mn^III(Pc)Cl₂]₂ at 26.5 K under 9 T static magnetic fields perpendicular and parallel to the c-axis were determined to be −30% and −20%, respectively, which are significantly larger values than those of Ph₄P[Mn^III(Pc)(CN)₂]₂. Furthermore, the negative MR effect is comparable to that of Ph₄P[Fe^III(Pc)(CN)₂]₂ (S = 1/2), which exhibits the largest negative MR effect reported for [M^III(Mc)L₂]-based systems (Mc = macrocyclic ligand, L = axial ligand). This suggests that the spin state of the metal ion is the key to tuning the MR effect.

A Ph4P[Mn^III(Pc)Cl2]2 molecular crystal where Mn^III adopts a high-spin state (S = 2) was designed. The large magnetoresistance effect of fabricated Ph4P[Mn^III(Pc)Cl2]2 suggests that the spin state of the metal ion is the key to tuning the MR effect.

Modern History of Organic Conductors: An Overview

This short review article provides the reader with a summary of the history of organic conductors. To retain a neutral and objective point of view regarding the history, background, novelty, and details of each research subject within this field, a thousand references have been cited with full titles and arranged in chronological order. Among the research conducted over ~70 years, topics from the last two decades are discussed in more detail than the rest. Unlike other papers in this issue, this review will help readers to understand the origin of each topic within the field of organic conductors and how they have evolved. Due to the advancements achieved over these 70 years, the field is nearing new horizons. As history is often a reflection of the future, this review is expected to show the future directions of this research field.

An electrically conducting molecular crystal composed of a magnetic iron(iii) complex (S = 1/2) with a large aromatic ligand, 1,2-naphthlalocyanine (C4h isomer): towards the development of molecular spintronics

The field of molecular spintronics has gained significant attention for the development of second-generation spintronic devices. Therefore, an electrically conducting molecular crystal, Ph₄P[Fe^III(1,2-Nc)(CN)₂]₂ (Ph₄P = tetraphenylphosphonium and 1,2-Nc = C_4h isomer of 1,2-naphthalocyanine), was fabricated as a new coordination compound with a strong π-d interaction. Furthermore, it is a mixed-valence compound with a local spin of S = 1/2 at the center of the conduction path. Crystal structure analysis revealed that Ph₄P[Fe^III(1,2-Nc)(CN)₂]₂ was isostructural to its non-magnetic analogue Ph₄P[Co^III(1,2-Nc)(CN)₂]₂ but possessed higher electrical resistivity, indicating that the strong intramolecular π-d interaction is present in the [Fe^III(1,2-Nc)(CN)₂] unit. Although the magnetic interaction between π-conduction electrons and Fe^III-d spins (π-d interaction) is crucial for the emergence of a negative magnetoresistance effect, the negative magnetoresistance effect of Ph₄P[Fe^III(1,2-Nc)(CN)₂]₂ was significantly smaller (-6% at 30 K under a static 9 T magnetic field) than those of Ph₄P[Fe^III(Pc)(CN)₂]₂ (-32%) and Ph₄P[Fe^III(tbp)(CN)₂]₂ (-13%) analogues (Pc = phthalocyanine and tbp = tetrabenzoporphyrin). This small negative magnetoresistance effect of Ph₄P[Fe^III(Pc)(CN)₂]₂ could be ascribed to the weak intermolecular antiferromagnetic interaction between its d spins. Hence, this study showed that constructing a molecular design for strengthening the intermolecular antiferromagnetic interaction is key to enhancing the negative magnetoresistance effect.

Effect of reduction on the molecular structure and optical and magnetic properties of fluorinated copper(ii) phthalocyanines

New salts based on reduced fluorinated copper(ii) phthalocyanines were obtained. The effect of reduction on the molecular structure and properties of the  [Cu^II(F_xPc)]ⁿ⁻ (x = 8 and 16) species in reduced states (n = 1 and 2) was studied.

Intermolecular interactions of tetrabenzoporphyrin- and phthalocyanine-based charge-transfer complexes

The effect of molecular modification on the intermolecular interactions in tetrabenzoporphyrin-based charge transfer complexes is reported. TPP[Fe^III(tbp)Cl₂]₂, TPP[Co^III(tbp)Cl₂]₂ and TPP[Co^III(tbp)Br₂]₂ (TPP = tetraphenylphosphonium and tbp = tetrabenzoporphyrin) were synthesized and their crystal structures were compared to those of the reported TPP[M^III(tbp)(CN)₂]₂, TPP[Fe^III(tbp)Br₂]₂ and TPP[M^III(Pc)L₂]₂ complexes (Pc = phthalocyanine; and L = CN, Cl or Br). The prepared CT complexes were isostructural to reported systems. However, their intermolecular interactions were found to depend on the combination of the macrocyclic (Mc) and axial ligands (L). In Pc-based systems, the overlap integral between HOMOs of Pc decreased with the increase in the size of the axial ligand, which indicated that the intermolecular interactions in Pc-based systems were dominated by repulsive interactions. On the other hand, in tbp-based systems, attractive and repulsive interactions competed with each other. Furthermore, charge transport properties were found to depend on the central metal ion as well as the combination of Mc and L, which suggested that minor molecular modifications to porphyrin complexes will cause drastic changes in both inter- and intramolecular interactions.

Coordination-induced metal-to-macrocycle charge transfer and effect of cations on reorientation of the CN ligand in the {SnL2Mac}2− dianions (L = CN−, OCN−, Im−; Mac = phthalo- or naphthalocyanine)

Anionic coordination {crypt(M⁺)}₂{SnL₂Mac}²⁻ complexes of tin(ii) phthalo- (Pc) and naphthalocyanines (Nc) were obtained and discussed.

An electrically conducting crystal composed of an octahedrally ligated porphyrin complex with high-spin iron(iii)

A porphyrin-based octahedrally ligated complex with high-spin iron(iii) was designed, and the resulting electrically conducting crystal TPP[Fe^III(tbp)Br₂]₂ (TPP = tetraphenylphosphonium and tbp = tetrabenzoporphyrin) was synthesised. Although TPP[Fe(tbp)Br₂]₂ was isostructural to the reported TPP[Fe(Mc)L₂]₂ systems (Mc = macrocyclic ligands such as phthalocyanine (Pc) or tbp; and L = CN, Cl, or Br), the bond lengths between Fe and ligands in the [Fe(tbp)Br₂] unit were evidently longer than those in the other units, because of the different spin states of Fe: high-spin in TPP[Fe(tbp)Br₂]₂ and low-spin in others. The magnetic anisotropy observed in the low-spin state vanished when the Fe is in the high-spin state. Based on reports for Pc-based systems, the negative magnetoresistance (MR) effect for TPP[Fe(tbp)Br₂]₂ was expected to be smaller than that for TPP[Fe(tbp)(CN)₂]₂. However, the former showed a giant negative MR effect similar to or larger than the latter, suggesting that the nature of iron is a crucial factor for the electrical properties of porphyrin-based materials.

Structural and transport properties of neutral radical crystals of CoIII(tmp)(CN)2 (tmp = 5,10,15,20-tetramethylporphyrinato) and the CN-bridged polymer [CoIII(tmp)(CN)]n

An axially ligated Co(tmp) (tmp = 5,10,15,20-tetramethylporphyrinato) anion, [Co^III(tmp)(CN)₂]^-, has been prepared and subjected to electrochemical oxidation to obtain the open shell tmp π-ligand. With acetone as the solvent, solvent-free neutral radical crystals of Co^III(tmp)(CN)₂ are obtained, whereas solvent-inclusive crystals of Co^III(tmp)(CN)₂·2CH₃CN are obtained with CH₃CN as the solvent. In both crystals, the open shell tmp ring deforms into a ruffled form, which makes the π-π interactions in the crystal weak. Thus, the electrical conductivity is low, and the crystals behave as semiconductors with a room temperature resistivity of 10⁶ Ω cm and an activation energy of about 0.3 eV. When the solvent is acetone, non-oxidized crystals of the CN-bridged polymer {[Co^III(tmp)(CN)](acetone)}_n are obtained as a byproduct. The closed shell tmp ring deforms into a ruffled form, and there π-π interactions in the crystal are negligible. The room temperature resistivity is rather high at about 10⁸ Ω cm.

Evaluation of the Giant Ferromagnetic π-d Interaction in Iron-Phthalocyanine Molecule

The interaction between itinerant π and localized d electrons in metal-phthalocyanines, namely, J_πd interaction, is considered as responsible for the giant negative magnetoresistance observed in several phthalocyanine-based conductors, among many other important physical properties. Despite the fundamental and technological importance of this on-site intramolecular interaction, its giant ferromagnetic nature has been only recently demonstrated by the experiments conducted by Murakawa et al. in the neutral radical [Fe(Pc)(CN)₂]·2CHCl₃ ( Phys. Rev. B 2015 , 92 , 054429 ). In this article, we present the theoretical evaluation of this interaction combining wave function-based electronic calculations on isolated Fe(Pc)(CN)₂ molecules and density functional theory-based periodic calculations on the crystal. Our calculations confirm the ferromagnetic nature of the π-d interaction, with a coupling constant as large as J_πd/k_B = 570 K, in excellent agreement with the experiments, and the presence of intermolecular antiferromagnetic interactions driven by the π-π overlap of neighboring phthalocyaninato molecules. The analysis of the wave function of the ground state of the Fe(Pc)(CN)₂ molecule provides the clues of the origin of this giant ferromagnetic π-d interaction.

Giant negative magnetoresistance in Ni(quinoline-8-selenoate)2

Ni(qs)₂ shows giant negative magnetoresistance as a powder sample, attributed to S = 1 magnetic properties arising from a chain structure.

A new strategy for inducing dipole moments in charge-transfer complexes: introduction of asymmetry into axially ligated iron phthalocyanines

Introduction of asymmetry into charge-transfer complexes composed of axially ligated iron phthalocyanines was achieved. In the obtained crystals of TPP[Fe^III(Pc)(CN)Cl]₂, TPP[Fe^III(Pc)(CN)Br]₂, and TPP[Fe^III(Pc)BrCl]₂ (TPP = tetraphenylphosphonium and Pc = phthalocyanine), the axial positions of the iron atoms were occupied by 50/50 ratios of the ligands CN/Cl, CN/Br, and Br/Cl, respectively. The crystal structures of the obtained CT complexes were isostructural to those composed of the symmetric analogues of the type [Fe^III(Pc)L₂] (L = CN, Cl or Br); the [Fe^III(Pc)LL'] units formed regular one-dimensional chains along the c-axis following the symmetry of the P4₂/n space group. Despite forming similar regular chains to the symmetric systems, the electrical resistivities and activation energies were enhanced in the obtained CT complexes compared to those in symmetric systems, indicating that the charge-ordered states were stabilised by the introduction of asymmetry. More specifically, the dielectric relaxation behaviour of the inhomogeneous disordered TPP[Fe^III(Pc)(CN)Cl]₂ probably suggests that a dipole moment was induced in this material.

The magnetoresistance effect in a conducting molecular crystal consisting of dicyano(phthalocyaninato)manganese(iii)

A conducting molecular crystal TPP[Mn^III(Pc)(CN)₂]₂ (Mn^III: d⁴, S = 1, TPP = tetraphenylphosphonium and Pc = phthalocyanine) was fabricated. In its crystal structure, the [Mn^III(Pc)(CN)₂] units formed a one-dimensional regular chain along the c-axis with an overlap integral value of 8.6 × 10^-3. TPP[Mn^III(Pc)(CN)₂]₂ showed a semiconducting behaviour that also has been observed for isostructural TPP[Co^III(Pc)(CN)₂]₂ (Co^III: d⁶, S = 0) and TPP[Fe^III(Pc)(CN)₂]₂ (Fe^III: d⁵, S = 1/2) whose ground states are charge-ordered states. In spite of the local magnetic moment of the Mn^III ion (S = 1) at the centre of the Pc ligand, TPP[Mn^III(Pc)(CN)₂]₂ exhibited an almost isotropic and small negative magnetoresistance (MR) effect (the MR ratio was -8.7% under 8 T at 10.7 K), contrarily to the anisotropic giant negative MR effect of TPP[Fe^III(Pc)(CN)₂]₂. The isotropy was found to be due to a (d_xz)¹(d_yz)¹ electronic configuration, and the smaller MR effect was explained by a weaker antiferromagnetic interaction between Mn^III ions than that between Fe^III ions, as suggested by a Weiss temperature Θ of -3.1 K (|J_dd|/k_B = 1.2 K).

Crystalline salts of metal phthalocyanine radical anions [M(Pc˙3−)]˙− (M = CuII, PbII, VIVO, SnIVCl2) with cryptand(Na+) cations: structure, optical and magnetic properties

Radical anion salts of metal phthalocyanines (M = Cu^II, Pb^II, V^IVO and Sn^IVCl₂) with the {cryptand(Na⁺)} cations have been obtained and studied.

Radical anion and dianion salts of titanyl macrocycles with acceptor substituents or an extended π-system

Crystalline anionic salts of titanyl macrocycles: (PPN⁺)₂{OTi^IV(PcCl₈⁴⁻)}²⁻ (1), (PPN⁺){OTi^IV(Nc˙³⁻)}˙⁻·solv (2) and (PPN⁺)₂{OTi^IV(AceTPrzPz⁴⁻)}²⁻·solv (see figure, 3) have been obtained and their optical and magnetic properties are studied.

A giant negative magnetoresistance effect in an iron tetrabenzoporphyrin complex

By measuring the electrical resistivity in TPP[Fe^III(tbp)(CN)₂]₂ (TPP = tetraphenylphosphonium and tbp = tetrabenzoporphyrin) under the application of a static magnetic field, a giant negative magnetoresistance (MR) effect with high anisotropy is observed. More specifically, the MR ratio at 13 K under a field of 9 T perpendicular to the c axis is -70%, whereas the MR ratio under a field parallel to the c axis is -40%. Furthermore, electron spin resonance (ESR) measurements indicate large anisotropy in the principal g-values of d spin (S = 1/2) in the [Fe^III(tbp)(CN)₂] unit; the g₁ value almost perpendicular to the tbp plane and the g₂ and g₃ values almost parallel to the tbp plane are 3.60, 1.24, and 0.39, respectively. It is revealed that the anisotropy in the MR effect arises from the anisotropy in the d spin, suggesting that the d spins in TPP[Fe^III(tbp)(CN)₂]₂ affect the π-conduction electron via the intramolecular π-d interaction. The anisotropy and magnitude in the giant negative MR effect for TPP[Fe^III(tbp)(CN)₂]₂ are smaller than the corresponding values for the isostructural phthalocyanine (Pc) analogue TPP[Fe^III(Pc)(CN)₂]₂. This is consistent with the fact that the intermolecular antiferromagnetic d-d interaction in TPP[Fe^III(tbp)(CN)₂]₂ (suggested by the Weiss temperature: Θ = -8.0 K) is weaker than that in TPP[Fe^III(Pc)(CN)₂]₂ (Θ = -12.3 K). This indicates that the minor modification in coordination complexes can significantly affect the MR effect via tuning the intermolecular d-d interaction as well as the intermolecular π-π overlap.

Nanocrystalline Axially Bridged Iron Phthalocyanine Polymeric Conductor: (μ-Thiocyanato)(phthalocyaninato)iron(III)

Skewered Iron(III) phthalocyanine conducting polymer can be constructed with the utilization of axial thiocyanato ligands ((μ-thiocyanato)(phthalocyaninato)iron(III)); (FeIII(Pc)(SCN)n) thereby creating additional avenues for electron transport through a linear SCN bridge, apart from the intermolecularπ-πorbital overlap between the Pc molecules. In this paper, we report on the conversion of bulkFeIII(Pc)(SCN)npolymeric organic conductor into crystalline nanostructures through horizontal vapor phase growth process. The needle-like nanostructures are deemed to provide more ordered and, thus, moreπ-πinteractive interskewerFeIII(Pc)(SCN)npolymer orientation, resulting in a twofold increase of its electrical conductivity per materials density unit.

Molecular structure, optical and magnetic properties of the {SnIVPc(3-)Cl2}•- radical anions containing negatively charged Pc ligands

Radical anion salt ( PPN +){ Sn IV Pc (3-) Cl 2}•- (1) was obtained by the reduction of tin(IV) phthalocyanine dichloride { Sn IV Pc (2-) Cl 2} with ( PPN +)( C 60•-) ( PPN + is bis(triphenylphosphoranylidene)-ammonium cation). It was shown that the reduction is centered mainly on the Pc ligand providing the appearance of a new band in the spectrum of 1 in the NIR range at 1006 nm and blue-shift of Soret and Q-bands of Sn IV Pc (2-) Cl 2. The alternation of short and long C – N imine bonds for two oppositely located isoindole units in 1 indicates possible disruption of aromaticity of the Pc ligand under reduction. Salt 1 has effective magnetic moment of 1.69 μB at 300 K corresponding to the contribution of one non-interacting S = 1/2 spin per formula unit and manifests antiferromagnetic coupling of spins with Weiss temperature of -7.3 K in the 400–30 K range. The salt shows a broad EPR signal with g = 1.9957 and linewidth of 19.3 mT at room temperature. The signal splits into two components below 120 K. Strong broadening of the EPR signal and shift of g-factors to smaller values in comparison with the EPR signal from radical anions of metal-free phthalocyanine { H 2 Pc (3-)}•- were attributed to the contribution of the { Sn III Pc (2-) Cl 2}- admixture with paramagnetic Sn III . There are π–π stacking one-dimensional chains composed of { Sn IV Pc (3-) Cl 2}•- in 1 along the a axis with weak overlapping between phenylene groups of phthalocyanine radical anions. The calculated HOMO–HOMO overlap integral is 0.0033 and the SOMO–SOMO overlap integral is only 0.0004. Metallic conductivity is not realized in 1 most probably due to weak SOMO–SOMO overlapping.

One-dimensional phthalocyanine-based conductor with S = 3/2 isotropic magnetic centers

The axially ligated phthalocyanine conductor of TPP [ Cr ( Pc )( CN )2]2 (TPP = tetraphenylphosphonium and Pc = phthalocyaninato) with d3 (S = 3/2) metal Cr III has been successfully prepared. The crystal is completely isomorphous with those of the Co and Fe analogs, and the degree of π–π interaction is almost the same in these three salts. The electrical conductivity at room temperature of the Cr system is almost the same with that of the Fe system in which S = 1/2 magnetic centers embedded in the conduction path, and the temperature dependence reveals the development of the charge disproportionation reflecting the existence of magnetic moments. Magnetic susceptibility of the Cr system shows Curie-like behavior with isotropic local moments of S = 3/2. In contrast with the Fe system, only weak antiferromagnetic interaction operates between the localized d-spins. The resistance decreases when magnetic fields are applied, but the magnetoresistance effect is not so large compared with the Fe system, indicating that the π– d interaction in the Cr system is somewhat different from that in the Fe system.

Crystal Structure of Ruthenium Phthalocyanine with Diaxial Monoatomic Ligand: Bis(Triphenylphosphine)Iminium Dichloro(Phthalocyaninato(2-))Ruthenium(III)

Axially-ligated iron phthalocyanines have been found to be good molecular conductors with giant negative magnetoresistance (GNMR) which originates from a strong intramolecularπ-dinteraction between the metal and phthalocyanine. Ab initio theoretical calculations showed that substitution of ruthenium into the phthalocyanine complex would result in a significant increase in theπ-dinteraction of the system, potentially intensifying GNMR. This paper presents the crystal preparation and X-ray structural characterization of bis(triphenylphosphine)iminium dichloro(phthalocyaninato(2-))ruthenium(III), PNP [RuIII(Pc2−)Cl2]. It is observed that [RuIII(Pc2−)Cl2] system has a symmetric planar RuPc unit with perpendicular axial ligands which results in a unidirectional and uniform solid-state arrangement, suitable forπ-dinteraction-based molecular conductors with potentially exceptional GNMR.