Mixed-valence Behavior Research Articles

Mixed-valence state in the dilute-impurity regime of La-substituted SmB6

Homogeneous mixed-valence (MV) behaviour is one of the most intriguing phenomena of f-electron systems. Despite extensive efforts, a fundamental aspect which remains unsettled is the experimental determination of the limiting cases for which MV emerges. Here we address this question for SmB6, a prototypical MV system characterized by two nearly-degenerate Sm2+ and Sm3+ configurations. By combining angle-resolved photoemission spectroscopy (ARPES) and x-ray absorption spectroscopy (XAS), we track the evolution of the mean Sm valence, vSm, in the SmxLa1−xB6 series. Upon substitution of Sm ions with trivalent La, we observe a linear decrease of valence fluctuations to an almost complete suppression at x = 0.2, with vSm ~ 2; surprisingly, by further reducing x, a re-entrant increase of vSm develops, approaching the value of vimp ~ 2.35 in the dilute-impurity limit. Such behaviour departs from a monotonic evolution of vSm across the whole series, as well as from the expectation of its convergence to an integer value for x → 0. Our ARPES and XAS results, complemented by a phenomenological model, demonstrate an unconventional evolution of the MV character in the SmxLa1−xB6 series, paving the way to further theoretical and experimental considerations on the concept of MV itself, and its influence on the macroscopic properties of rare-earth compounds in the dilute-to-intermediate impurity regime.

Quasiparticle multiplets and 5f electronic correlation in prototypical plutonium borides

In this paper, we investigate the electronic structures of plutonium borides (PuB x , x = 1, 2, 6, 12) to uncover the fascinating bonding behavior and orbital dependent correlations of 5f valence electrons by using the density functional theory combined with single-site dynamical mean-field method. We not only reproduce the correlated topological insulator of PuB6, but also predict the metallicity in PuB x (x = 1, 2, 12). It is found that the band structure, density of states, hybridization functions all indicate partially itinerant 5f states in PuB x (x = 1, 2, 6, 12). Especially, quasiparticle multiplets induced noteworthy valence state fluctuations implying the mixed-valence behavior of plutonium borides. Moreover, the itinerant degree of freedom for 5f electrons in PuB x (x = 1, 2, 12) is tuned by hybridization strength between 5f states and conduction bands, which is affected by atomic distance in plutonium borides. Lastly, 5f electronic correlations encoded in the electron self-energy functions demonstrate moderate 5f electronic correlations in PuB6 and orbital selective 5f electronic correlations in PuB x (x = 1, 2, 12). Consequently, the understanding of electronic structure and related crystal structure stability shall shed light on exploring novel 5f electrons states and ongoing experiment study.

Structure and magnetostriction of high Pr/Ce-content (Tb0.2Pr0.8)1–xCexFe1.93 Laves compounds

The light rare earth Pr/Ce-contained (Tb0.2Pr0.8)1–xCexFe1.93 (0 ≤ x ≤ 1.0) intermetallics were arc melted and magnetoelastic properties were investigated. The compounds of x ≥ 0.40 are found to stabilize at ambient pressure in a single Laves phase with MgCu2-type C15 structure, which is attributed to the strong Ce 4f bonding. The mixed-valence behavior, with a support of the deviation from the linear Vegard’s law for both lattice parameter a and saturation magnetization MS, is observed at room temperature. The easy magnetization direction (EMD) was determined by the analysis of XRD on both magnetically aligned samples and the (440) splitting, that is, EMD lies toward <111> axis for x ≤ 0.50 rotating to <110> for x = 0.60, accompanied with the structural distortion from rhombohedral to orthorhombic. The substitution of Ce for Tb/Pr is conductive to the reduction of magnetocrystalline anisotropy, giving rise to an improvement of the low-field magnetostriction. The excellent magnetoelastic properties can be tailored by the Ce introduction, e.g., the spontaneous magnetostriction coefficient λ111 as large as 1150 × 10−6 for x = 0.40, and the low-field induced magnetostriction achieving a high value of λa = 180 × 10−6 at 80 kA/m for x = 0.60. The excellent magnetoelastic properties and the combination in high Pr-content with low cost, suggest promising prospects in applications.

Optical, third order non-linear optical and electrochemical properties of dipolar, centrosymmetric and C2v organoimido polyoxometalate derivatives.

A family comprising seven arylimido-polyoxometalate (POM) hybrid chromophores (three of which are new), with linear dipolar, C2v and linear centrosymmetric geometries have been synthesised and studied by electronic absorption spectroscopy, electrochemistry, Z-scans (two photon absorption, TPA) and computation (DFT/TD-DFT). These reveal that POM acceptor units are an effective basis for TPA materials: the centrosymmetric bis-POM chromophores produce significant cross sections (δ up to 82 GM) from a single aryl bridge, a similar performance to larger dipolar π-systems combining carbazole or diphenylamino donors with the imido-POM acceptor. DFT/TD-DFT calculations indicate strong communication between POM and organic components is responsible for the linear and non-linear optical behaviour of these compounds, while electrochemical measurements reveal class II mixed valence behaviour resulting from an interplay of through-bond and through-space effects.

Redox Communication between Two Diarylamido/Bis(phosphine) (PNP)M Moieties Bridged by Ynediyl Linkers (M = Ni, Pd, Pt).

A series of binuclear homo- and heterobimetallic complexes of the general type (PNP)M-[linker]-M(PNP) have been prepared (M = Ni, Pd, Pt; PNP = a diarylamido/bis(phosphine) pincer ligand; -[linker]- = -C≡C-, -C≡CC≡C-, -C≡CC6H4C≡C-). Each (PNP)M site can be oxidized by one electron, and this work reports the investigation of the mixed-valence behavior in terms of the communication between the two redox sites and the degree of the delocalization in the monooxidized cation. The compounds were evaluated using cyclic voltammetry, UV-vis-NIR and EPR spectroscopy, X-ray crystallography, and DFT calculations. The complex with the longest examined linker, (PNP)Ni-C≡CC6H4C≡C-Ni(PNP) (9Ni), exhibited no discernible communication between the redox sites. The homobimetallic complexes (PNP)M-C≡CC≡C-M(PNP) (6M) displayed a lower degree of communication in comparison to the -C≡C- linker analogues (PNP)M-C≡C-M(PNP) (3M). Within each of these two subsets, the relative degree of communication and delocalization was determined to be Pd < Ni ≤ Pt. On the Robin-Day scale, compounds 6M can be assigned class I for M = Pd and class II for M = Ni, Pt. Complex 3Pd also falls into class II, while 3Ni and 3Pt may be viewed as borderline class II/III cases. It is likely that the communication in the Ni systems has the advantage of the smaller size of Ni, resulting in a greater physical proximity of the redox sites, while the 5d metal Pt possesses the greatest ability for orbital interaction with the -C≡C- linker.

Exploring the exotic f states of prototype compounds CeSb and USb

To unravel the interplay between the strong electronic correlation and itinerant-localized dual nature in typical f electron systems, we employed the density functional theory in combination with the single-site dynamical mean-field theory to systematically investigate the electronic structures of CeSb and USb. We find that the 4f states in CeSb are mostly localized with a weak quasi-particle resonance peak near the Fermi level. Conversely, the 5f electrons in USb display partially itinerant features, accompanied by mixed-valence behavior and prominent valence state fluctuations. Particularly, the 4f electronic correlations in CeSb are orbital-selective with strikingly renormalized 4f5/2 states, according to the low-energy behaviors of 4f self-energy functions. It is believed that the strong electronic correlation and fantastic bonding of f states contribute to elucidating the magnetism.

Arylamino-fluorene derivatives: Optically induced electron transfer investigation, redox-controlled modulation of absorption and fluorescence

A series of biarylaminofluorene-based systems with donor-π-donor (D-π-D) structure have been designed and synthesized in order to study the dependence on the π-conjugated bridge length of the intervalence charge-transfer transitions (IV-CT) and of the electronic coupling between the redox centers. To this purpose cyclic voltammetry, UV/Vis-NIR, fluorescence spectroscopy and computational investigations have been carried out to characterize the electronic structure of the compounds in the neutral as well as in the mono- and dication states. Additionally, a study of related D-π compounds has been performed to elucidate the effect of the interaction between two redox centers. Interestingly it was observed that the mono- and dication species exhibit intense transition bands in the NIR region, in the 10000-15000 cm−1 range, whose intensity depends on the oxidation state and thus it can be reversibly tuned by an applied potential. In a similar way, all compounds show an oxidation state dependent fluorescence which leads to electrofluorochromism. Particularly significant is the mixed valence behavior that provides these systems singular optoelectronic properties, making them excellent active components for electrochromic and electrofluorochromic applications.

Magnetostriction and Magnetic Anisotropy of (Pr0.5Nd0.5)1−xCexFe1.93 Alloys

Polycrystalline alloys of (Pr0.5Nd0.5)1−xCexFe1.93 (0 ≤ x ≤ 1.0) are arc melted and investigated for structural, magnetic, and magnetoelastic properties. The light rare earth Ce presents a mixed-valence behavior and helps form a single C15 Laves phase for the composition of x ≥ 0.40. Both the lattice parameter a and the saturation magnetization MS of the Laves phase decrease with increasing Ce content, and the dependence of a on the Ce concentration deviates the linear Vegard law. The easy direction of magnetization (EMD) at room temperature is detected toward axis by performing X-ray diffraction on magnetic-field–aligned powders. The Ce introduction into (Pr,Nd)Fe2 system can reduce the magnetocrystalline anisotropy, resulting in an enhancement of the magnetostriction at low magnetic fields. The good magnetoelastic properties, that is, a low anisotropy and a high low-field anisotropic magnetostriction λa ~ 165 ppm at 1 kOe, can be obtained for the free-heavy rare earth (Pr0.5Nd0.5)0.6Ce0.4Fe1.93 alloy, and may make it a promising candidate for applications.

Intermetallic RE6T5Al7 Phases (RE = Sc, Y, Ce-Nd, Sm, Gd-Lu; T = Ru, Ir): Diversity in their Magnetic, Magnetocaloric, and Critical Properties.

Over 20 new compounds of the RE6T5Al7 series (RE = Sc, Y, Ce-Nd, Sm, Gd-Lu; T = Ru, Ir; Yb6Ir5Ga7 type structure; superstructure of MgZn2; fully ordered Nb6.4Ir4Al7.6 type) have been synthesized. They crystallize in the hexagonal crystal system with space group P63/mcm. Their lattice parameters are in the ranges of a = 935-963 and c = 851-874 pm for the RE6Ru5Al7 and a = 913-966 and c = 825-865 pm for the RE6Ir5Al7 series. Four structures (Ho6Ru5Al7, Yb6Ru4.68(1)Al7.32(1), Sc6Ir5Al7, and Ho6Ir4.53(1)Al7.47(1)) have been refined from single-crystal data, indicating fully ordered structures for Ho6Ru5Al7 and Sc6Ir5Al7; however, T/Al mixing was observed on one crystallographic site for Ho6Ir4.53(1)Al7.47(1) and on two sites for Yb6Ru4.68(1)Al7.32(1). The Sc-, Y-, and Lu-containing compounds exhibit Pauli paramagnetism in line with a filled d band for Ru and Ir. Ce6Ru5Al7 exhibits mixed-valent behavior, while Yb6Ru5Al7 is solely trivalent. The other compounds exhibit paramagnetism and ferromagnetic phase transitions up to temperatures of TC = 83.4(1) K for Gd6Ru5Al7. In addition to the basic magnetic characterizations and studies of the electrical resistivity and heat capacity, the magnetocaloric properties of Gd6Ru5Al7, Tb6Ru5Al7, and Dy6Ru5Al7 have been investigated, revealing magnetic entropy changes of -ΔSMmax = 6.2(1), 7.7(1), and 5.4(1) J kg-1 K-1 (0 → 5 T) and relative cooling powers RCP = 242, 207, and 135 J kg-1, respectively. For a deeper insight into the second-order magnetic phase transitions, the critical behavior was investigated according to the scaling hypothesis. The critical behavior of Gd6Ru5Al7 is in accordance with the mean-field theory; the critical exponents of Tb6Ru5Al7 and Dy6Ru5Al7, however, deviate strongly from this universality class. For comparison of the structural and magnetic properties, the thus far unstudied members of the RERuAl series (RE = Sc, Y, Sm, Gd-Lu; MgZn2 type) have additionally been prepared and characterized.

Valence instability in the bulk and at the surface of the antiferromagnet SmRh2Si2

Using resonant angle-resolved photoemission spectroscopy and electron band-structure calculations, we explore the electronic structure and properties of Sm atoms at the surface and in the bulk of the antiferromagnet SmRh2Si2. We show that the Sm atoms reveal weak mixed-valent behavior both in the bulk and at the surface. Although trivalent 4f emission strongly dominates, a small divalent 4f signal near the Fermi energy can be clearly resolved for surface and bulk Sm atoms. This behavior is quite different to most other Sm-based materials which typically experience a surface valence transition to a divalent state of Sm atoms at the surface. This phenomenon is explained in analogy to the isostructural Ce compound, where strong 4f hybridization stabilizes mixed-valent ground state both in the bulk and at the surface, and which were described in the light of the single-impurity Anderson model. Implications for other RERh2Si2 (RE = rare-earth elements) compounds are discussed.

1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled β-Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes.

The dinuclear complexes {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 ([3](ClO4)2), {(μ-H2L)[Ru(pap)2]2}(ClO4)2 ([4](ClO4)2), and the asymmetric [(bpy)2Ru(μ-H2L)Ru(pap)2](ClO4)2 ([5](ClO4)2) were synthesized via the mononuclear species [Ru(H3L)(bpy)2]ClO4 ([1]ClO4) and [Ru(H3L)(pap)2]ClO4 ([2]ClO4), where H4L is the centrosymmetric 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized [1]ClO4, [2]ClO4, [3](ClO4)2, [4](ClO4)2, and [5](ClO4)2 reveals multistep oxidation and reduction processes, which were analyzed by electron paramagnetic resonance (EPR) of paramagnetic intermediates and by UV-vis-NIR spectro-electrochemistry. With support by time-dependent density functional theory (DFT) calculations the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 3(3+) versus largely bridge-centered spin in 4(3+)-a result of the presence of Ru(II)-stabilizig pap coligands. In addition to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asymmetric system 5(3+) with about equal contributions from a radical bridge formulation. In comparison to the analogues with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric H2L(2-) bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites.

Electronic structure of cage-like compound UB12 – Theory and XPS experiment

The electronic structure of cubic UB12 has been investigated by X-ray photoelectron spectroscopy (XPS) and first principles calculations employing the fully relativistic full-potential local-orbital (FPLO-9) method. The calculated densities of states (DOS) revealed unique fairly sharp five-peaks of the U 5f states with the lowest energy peak crossing the Fermi level. The calculated and experimental valence band XPS spectra are in very good accord, indicating a substantial delocalization of the U 5f electrons. On the other hand, our experimental U 4f core-level XPS spectrum exhibits both the 1-eV and 7-eV satellites, pointing to some localization effects of the U 5f electrons, which may exhibit a mixed-valence behavior. Our Fermi surfaces of UB12 calculated for ambient and such high pressure as 55GPa show only negligible differences, which can explain the earlier reported stability of the cubic crystal structure of the studied system under high pressure.

Local chemical order in Al92Ce8 metallic glass: The role of 4f-electrons

Using a combination of the synchrotron X-ray absorption spectroscopy, transmission electron microscopy, vibrating magnetometry, Faraday's method and thermal analysis, we studied Al92Ce8 alloy in the glassy, crystalline and liquid states. The cerium in the alloy demonstrates mixed valence behavior with the noticeable portion of tetravalent states. The local order and physical properties of the investigated composition are discussed in the assumption of specific chemical bonding between Al and Ce with partial involvement of 4f-electrons.

Binuclear Ruthenium Complexes of a Neutral Radical Bridging Ligand. A New “Spin” on Mixed Valency

The electronic structures of (LX)2Ru(Vd)Ru(LX)2 complexes (Vd = 1,5-diisopropyl-3-(4,6-dimethyl-2-pyrimidinyl)-6-oxoverdazyl radical; LX = acac (acetylacetonate) or hfac (hexafluoroacetylacetonate)) in multiple charge states have been investigated experimentally and computationally. The main focus was to probe the consequences of the interplay between the ruthenium ions and the redox-active verdazyl ligand for possible mixed-valent behavior. Cyclic voltammetry studies reveal one reversible reduction and one reversible oxidation process for both complexes; in addition the acac-based derivative possesses a second reversible oxidation. Analysis of a collection of experimental (X-ray structures, EPR, electronic spectra) and computational (TD-DFT (PCM)) data reveal that the ruthenium ancillary ligands (acac vs hfac) have dramatic consequences for the electronic structures of the complexes in all charge states studied. In the hfac series, the neutral complex is best regarded as a binuclear Ru(II) species bridged by a neutral radical ligand. Reduction to give the anionic complex takes place on the verdazyl ligand, whereas oxidation to the cation (a closed shell species) is shared between Vd and ruthenium. For the acac-based complexes, the neutral species is most accurately represented as a Ru(II)/Ru(III) mixed valent complex containing a bridging verdazyl anion, though some bis(Ru(II))-neutral radical character remains. The monocation complex contains a significant contribution from a "broken symmetry" singlet diradical structure, best represented as a bis-Ru(III) system with an anionic ligand, with significant spin coupling of the two Ru(III) centers via the Vd(-1) ligand (calculated J = -218 cm(-1)). The dication, a spin doublet, consists of two Ru(III) ions linked (and antiferromagnetically coupled) to the neutral radical ligand. Computed net σ- and π-back-donation, spin densities, and orbital populations are provided. Time dependent DFT is used to predict the optical spectra and assign experimental data.

ChemInform Abstract: Crystal Structure of YbCu6In6 and Mixed Valence Behavior of Yb in YbCu6‐xIn6+x (x = 0, 1, and 2) Solid Solution.

AbstractHigh quality single crystals of YbCu6In6 are prepared from the elements using excess In as a flux (alumina crucible, 1000 °C for 10 h, 850 °C for 96 h).

Solvent-dependent modulation of metal–metal electronic interactions in a dinuclear cyanoruthenate complex: a detailed electrochemical, spectroscopic and computational study

The dinuclear complex [{Ru(CN)(4)}(2)(μ-bppz)](4-) shows a strongly solvent-dependent metal-metal electronic interaction which allows the mixed-valence state to be switched from class 2 to class 3 by changing solvent from water to CH(2)Cl(2). In CH(2)Cl(2) the separation between the successive Ru(II)/Ru(III) redox couples is 350 mV and the IVCT band (from the UV/Vis/NIR spectroelectrochemistry) is characteristic of a borderline class II/III or class III mixed valence state. In water, the redox separation is only 110 mV and the much broader IVCT transition is characteristic of a class II mixed-valence state. This is consistent with the observation that raising and lowering the energy of the d(π) orbitals in CH(2)Cl(2) or water, respectively, will decrease or increase the energy gap to the LUMO of the bppz bridging ligand, which provides the delocalisation pathway via electron-transfer. IR spectroelectrochemistry could only be carried out successfully in CH(2)Cl(2) and revealed class III mixed-valence behaviour on the fast IR timescale. In contrast to this, time-resolved IR spectroscopy showed that the MLCT excited state, which is formulated as Ru(III)(bppz(˙-))Ru(II) and can therefore be considered as a mixed-valence Ru(II)/Ru(III) complex with an intermediate bridging radical anion ligand, is localised on the IR timescale with spectroscopically distinct Ru(II) and Ru(III) termini. This is because the necessary electron-transfer via the bppz ligand is more difficult because of the additional electron on bppz(˙-) which raises the orbital through which electron exchange occurs in energy. DFT calculations reproduce the electronic spectra of the complex in all three Ru(II)/Ru(II), Ru(II)/Ru(III) and Ru(III)/Ru(III) calculations in both water and CH(2)Cl(2) well as long as an explicit allowance is made for the presence of water molecules hydrogen-bonded to the cyanides in the model used. They also reproduce the excited-state IR spectra of both [Ru(CN)(4)(μ-bppz)](2-) and [{Ru(CN)(4)}(2)(μ-bppz)](4-) very well in both solvents. The reorganization of the water solvent shell indicates a possible dynamical reason for the longer life time of the triplet state in water compared to CH(2)Cl(2).

Photoswitchable Organic Mixed Valence in Dithienylcyclopentene Systems with Tertiary Amine Redox Centers

The electronic structures of the radical cations of two dithienylperfluorocyclopentene molecules with appended tertiary amine units were investigated by electrochemical and optical spectroscopic methods. The through-bond N-N distances in the photocyclized (closed) forms of the two systems are 9.3 and 17.6 Å, respectively, depending on whether the nitrogen atoms are attached directly to the two thienyl units or whether xylyl spacers are in between. In the case of the radical cation with the longer N-N distance, photocyclization of the dithienylperfluorocyclopentene core induces a changeover from class I to class II mixed valence behavior. In the case of the shorter system, the experimental data is consistent with assignment of the photocyclized form to a class III mixed valence species.

Mixed-valence behavior and strong correlation effects of metal phthalocyanines adsorbed on metals

We investigate the hierarchy of local correlation and hybridization effects in metal-organic molecules adsorbed on metals. Using x-ray magnetic circular dichroism and ligand field multiplet calculations, we demonstrate that the 3$d$ electronic ground state of monolayer metal-phthalocyanine (CoPc, FePc) on Au(111) is given by the coherent superposition of two charge states, ${d}^{n}E+{d}^{n+1}$, where $E$ represents a substrate electron antiferromagnetically coupled to the central metal ion and ${d}^{n}$ the many-body ionic orbital configuration of the unperturbed molecule. These results differ from previous models of hybrid metal-organic systems and provide a consistent description of their magnetic moments and Kondo physics in terms of spin and orbital multiplicity.

A Redox Series of Aluminum Complexes: Characterization of Four Oxidation States Including a Ligand Biradical State Stabilized via Exchange Coupling

Electrophilic activation and subsequent reduction of substrates is in general not possible because highly Lewis acidic metals lack access to multiple redox states. Herein, we demonstrate that transition metal-like redox processes and electronic structure and magnetic properties can be imparted to aluminum(III). Bis(iminopyridine) complexes containing neutral, monoanionic, and dianionic iminopyridine ligands (IP) have been characterized structurally and electronically; yellow (IP)AlCl(3) (1), deep green (IP(-))(2)AlCl (2) and (IP(-))(2)Al(CF(3)SO(3)) (3), and deep purple [(IP(2-))Al](-) (5) are presented. The mixed-valent, monoradical complex (IP(-))(IP(2-))Al is unstable toward C-C coupling, and [(IP(2-))Al](2-)(μ-IP-IP)(2-) (4) has been isolated. Variable-temperature magnetic susceptibility and EPR spectroscopy measurements indicate that the biradical character of the ligand-based triplet in 2 is stabilized by strong antiferromagnetic exchange coupling mediated by aluminum(III): J = -230 cm(-1) for Ĥ = -2J(Ŝ(L(1))·Ŝ(L(2))). Coordination geometry-dependent (IP(-))-(IP(-)) communication through aluminum(III) is observed electrochemically. The cyclic voltammogram of trigonal bipyramidal 2 displays successive ligand-based oxidation events for the two IP(1-/0) processes, at -0.86 and -1.20 V vs SCE. The 0.34 V spacing between redox couples corresponds to a conproportionation constant of K(c) = 10(5.8) for the process (IP(-))(2)AlCl + (IP)(2)AlCl → 2(IP(-))(IP)AlCl consistent with Robin and Day Class II mixed-valent behavior. Tetrahedral 5 displays localized, Class I behavior as indicated by closely spaced redox couples. Furthermore, CV's of 2 and 5 indicate that changes in the coordination environment of the aluminum center shift the potentials for the IP(1-/0) and IP(2-/1-) redox couples by up to 0.9 V.

Charge transfer and mixed-valence behavior in phtalocyanine-dimer cations

Phtalocyanine compounds deserved a considerable interest in recent times, particularly because of their possible use in the field of nanoelectronics. In particular, the charge mobility (of both electrons and holes) in phtalocyanine stacked arrangements has been recently extensively investigated. The present work focuses on the study of the hole-transfer mechanism between two phtalocyanine monomers. For an interdisk distance larger than 4.5 bohrs, the eclipsed dimer exhibits a mixed-valence behavior, with a saddle point transition state separating two equivalent minima. This behavior, however, is strongly dependent on the relative angle between the disks. In particular, the mixed-valence character of the compound is strongly enhanced for arrangements that are far from the eclipsed geometry. Moreover, for values of the angle close to π/8 and 3π/8, the ground and excited transition states have exactly the same energy, thus implying the presence of a conical intersection. These results can have deep implication in the charge transfer along phtalocyanine chains.