Magnetic–Nonmagnetic Phase Transition with Interlayer Charge Disproportionation of Nb₃ Trimers in the Cluster Compound Nb₃Cl₈

We grew large single crystals of the cluster magnet Nb₃Cl₈ with a magnetic triangular lattice and investigated its magnetic properties and crystal structure. In Nb₃Cl₈, the [Nb₃]⁸⁺ cluster has a single unpaired spin, making it an <i>S</i> = 1/2 triangular lattice anti-ferromagnet. At low temperatures, Nb₃Cl₈ exhibits a magnetic–nonmagnetic phase transition driven by a charge disproportionation, in which the paramagnetic [Nb₃]⁸⁺ clusters transform into alternating layers of nonmagnetic [Nb₃]⁷⁺ and [Nb₃]⁹⁺ clusters. The observed exotic phenomenon with the strong correlation between the magnetism and structure are based on the nature of the cluster magnetism

Formation of Hexagonal Fullerene Layers from Neutral and Negatively Charged Fullerenes in {(Ph₃P)₃Au⁺}₂(C₆₀^•–)₂(C₆₀)·C₆H₄Cl₂ Containing Gold Cations with the <i>C</i>_3<i>v</i> Symmetry

Fullerene salt {(Ph₃P)₃Au⁺}₂­(C₆₀^•–)₂­(C₆₀)·​C₆H₄Cl₂ (<b>1</b>) containing (Ph₃P)₃­Au⁺ cations with the <i>C</i>_3<i>v</i> symmetry has been obtained as single crystals. Hexagonal corrugated fullerene layers formed in <b>1</b> alternate with the layers consisting of (Ph₃P)₃­Au⁺ and C₆H₄­Cl₂ along the <i>c</i> axis. According to IR spectra and peculiarities of the crystal structure, the charge on fullerenes in the layers is evaluated to be −1 for two and close to zero for one C₆₀. These fullerenes have different cationic surroundings, and positively charged gold atoms approach closer to C₆₀^•–. Charged and neutral fullerenes are closely packed within hexagonal layers with an interfullerene center-to-center distance of 10.02 Å and multiple short van der Waals C···C contacts. The distances between C₆₀^•– are essentially longer with an interfullerene center-to-center distance of 10.37 Å due to corrugation of the layers, and no van der Waals contacts are formed in this case. As a result, each C₆₀^•– has only three negatively charged fullerene neighbors with rather long interfullerene distances providing only weak antiferromagnetic interaction of spins in the fullerene layers with a Weiss temperature of −5 K

Synthesis, Structural and Magnetic Properties of Ternary Complexes of (Me₄P⁺)·{[Fe(I)Pc(−2)]⁻}·Triptycene and (Me₄P⁺)·{[Fe(I)Pc(−2)]⁻}·(<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′‑Tetrabenzyl‑<i>p</i>‑phenylenediamine)_0.5 with Iron(I) Phthalocyanine Anions

Ternary complexes of (Me₄P⁺)·{[Fe­(I)­Pc­(−2)]⁻}·TPC (<b>1</b>) and (Me₄P⁺)·{[Fe­(I)­Pc­(−2)]⁻}·(TBPDA)_0.5 (<b>2</b>) containing iron­(I) phthalocyanine anions, tetramethylphosphonium cations (Me₄P⁺), and neutral structure-forming triptycene (TPC) or <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetrabenzyl-<i>p</i>-phenylenediamine (TBPDA) molecules have been obtained as single crystals. In contrast to previously studied ionic compounds with monomeric [(Fe­(I)­Pc(−2)]⁻ anions, the anions form coordination {[Fe­(I)­Pc(−2)]⁻}₂ dimers both in <b>1</b> and <b>2</b>, in which a nitrogen atom of one phthalocyanine anion weakly coordinates to the iron­(I) atom of neighboring [Fe­(I)­Pc(−2)]⁻. The Fe···N distances in the dimers are 3.08(1) and 3.12(1) Å in <b>1</b> at 280 K and 2.986(5) (100 K) and 3.011(5) Å (180 K) in <b>2</b>. The {[Fe­(I)­Pc(−2)]⁻}₂ dimers are packed in the layers in <b>1</b> arranged parallel to the <i>ac</i> plane and in isolated chains in <b>2</b> arranged along the <i>a</i> axis. Extended Hückel based calculation of intermolecular overlap integrals showed stronger and weaker π–π interactions within and between phthalocyanine dimers, respectively, both in <b>1</b> and <b>2</b>. EPR signals of both complexes manifest two components. An major low-field asymmetric component is attributed to the Fe­(I) atoms with the d⁷ configuration. An origin minor narrow signal with <i>g</i>-factor close to the free-electron value (<i>g</i> = 2.0018–2.0035) is assigned to partial electron density transfer from the iron­(I) center to the phthalocyanine macrocycle and the formation of the [Fe­(II)­Pc(−3)]⁻ species. Effective magnetic moments of the complexes of 1.69 (<b>1</b>) and 1.76 μ_B (<b>2</b>) correspond to the contribution of about one <i>S</i> = ¹/₂ spin per formula unit in accordance with low-spin state of [Fe­(I)­Pc(−2)]⁻. Negative Weiss temperatures of −7.6 K (<b>1</b>) and −13 K (<b>2</b>) in the 30–300 K range indicate antiferromagnetic interaction of spins in the phthalocyanine dimers. The multicomponent approach was previously proposed for the anionic fullerene complex formation. It also seems very promising to design and synthesize anionic phthalocyanine complexes with one- and two-dimensional macrocycle arrangements

Molecular Design of Anionic Phthalocyanines with π–π Stacking Columnar Arrangement. Crystal Structures, Optical, and Magnetic Properties of Salts with the Iron(I) Hexadecachlorophthalocyanine Anions

Ionic compounds containing iron­(I) hexadecachlorophthalocyanine anions have been obtained for the first time as single crystals: (PPN⁺)­{[Fe­(I)­Cl₁₆Pc­(−2)]⁻} (<b>1</b>), (Ph₃MeP⁺)₂{[Fe­(I)­Cl₁₆Pc­(−2)]⁻}­(Br^–)·C₆H₄Cl₂ (<b>2</b>), and (PPN⁺)₂[Fe­(I, II)­Cl₁₆Pc­(−2)]₃⁽²⁻⁾·4C₆H₄Cl₂ (<b>3</b>), where PPN⁺ is the cation of bis­(triphenylphosphoranylidene)­ammonium and Ph₃MeP⁺ is the triphenylmethylphosphonium cation. The [Fe­(I)­Cl₁₆Pc­(−2)]⁻ anions form closely packed π–π stacking columns in <b>1</b>–<b>3</b>. Salts <b>1</b> and <b>2</b> with integer −1 charge on iron phthalocyanines have uniform and weakly dimerized columns, respectively. Salt <b>3</b> has two cations per three iron phthalocyanine molecules which are arranged in trimers within the columns. Different shift of phthalocyanines at the same interplanar distances of 3.33–3.38 Å provides essentially shorter Fe···Fe distances in <b>3</b> (3.62–3.84 Å) than those in <b>1</b> and <b>2</b> (5.07–5.45 Å). Calculations show a strong LUMO–LUMO overlapping between [Fe­(I)­Cl₁₆Pc­(−2)]⁻ in <b>1</b>–<b>3</b> with the overlap integrals of 4.1–7.6 × 10^–3. Weak signals attributed to the [Fe­(II)­Cl₁₆Pc­(−3)]⁻ species with the delocalization of electron on the phthalocyanine macrocycles are observed in the EPR spectra of <b>1</b>–<b>3</b>. The content of this admixture is less than 1% in all salts. Nevertheless, static magnetic susceptibility measurements for <b>3</b> detected significant magnetization. The effective magnetic moment is 4.05 μ_B per formula unit at 300 K. It can originate from the spins localized on the iron atoms of [Fe­(I)­Cl₁₆Pc­(−2)]⁻. The Weiss temperature of −53 K in the 60–300 K range indicates a strong antiferromagnetic interaction of spins which results in the decreases of magnetic moment of <b>3</b> with temperature below 220 K down to 2.72 μ_B at 6 K. Optical spectra of <b>1</b>–<b>3</b> show bands ascribed to [Fe­(I)­Cl₁₆Pc­(−2)]⁻ at 339–349, 538–548, 685–691, and 805–821 nm. The bands in the NIR range at 1740–1810 nm were attributed to charge transfer excitations within phthalocyanine columns associated with the unpaired electrons on the iron atoms

Spin Crossover in Anionic Cobalt-Bridged Fullerene (Bu₄N⁺){Co(Ph₃P)}₂(μ₂‑Cl^–)(μ₂‑η²,η²‑C₆₀)₂ Dimers

A spin crossover phenomena is observed in an anionic (Bu₄N⁺)­{Co­(Ph₃P)}₂(μ₂-Cl^–)­(μ₂-η²,η²-C₆₀)₂·2C₆H₁₄ (<b>1</b>) complex in which two cobalt atoms bridge two fullerene molecules to form a dimer. The dimer has a triplet ground state with two weakly coupling Co⁰ atoms (<i>S</i> = 1/2). The spin transition realized above 150 K is accompanied by a cobalt-to-fullerene charge transfer that forms a quintet excited state with a high spin Co^I (<i>S</i> = 1) and C₆₀^•– (<i>S</i> = 1/2)

Molecular Design of Anionic Phthalocyanines with π–π Stacking Columnar Arrangement. Crystal Structures, Optical, and Magnetic Properties of Salts with the Iron(I) Hexadecachlorophthalocyanine Anions

Ionic compounds containing iron­(I) hexadecachlorophthalocyanine anions have been obtained for the first time as single crystals: (PPN⁺)­{[Fe­(I)­Cl₁₆Pc­(−2)]⁻} (<b>1</b>), (Ph₃MeP⁺)₂{[Fe­(I)­Cl₁₆Pc­(−2)]⁻}­(Br^–)·C₆H₄Cl₂ (<b>2</b>), and (PPN⁺)₂[Fe­(I, II)­Cl₁₆Pc­(−2)]₃⁽²⁻⁾·4C₆H₄Cl₂ (<b>3</b>), where PPN⁺ is the cation of bis­(triphenylphosphoranylidene)­ammonium and Ph₃MeP⁺ is the triphenylmethylphosphonium cation. The [Fe­(I)­Cl₁₆Pc­(−2)]⁻ anions form closely packed π–π stacking columns in <b>1</b>–<b>3</b>. Salts <b>1</b> and <b>2</b> with integer −1 charge on iron phthalocyanines have uniform and weakly dimerized columns, respectively. Salt <b>3</b> has two cations per three iron phthalocyanine molecules which are arranged in trimers within the columns. Different shift of phthalocyanines at the same interplanar distances of 3.33–3.38 Å provides essentially shorter Fe···Fe distances in <b>3</b> (3.62–3.84 Å) than those in <b>1</b> and <b>2</b> (5.07–5.45 Å). Calculations show a strong LUMO–LUMO overlapping between [Fe­(I)­Cl₁₆Pc­(−2)]⁻ in <b>1</b>–<b>3</b> with the overlap integrals of 4.1–7.6 × 10^–3. Weak signals attributed to the [Fe­(II)­Cl₁₆Pc­(−3)]⁻ species with the delocalization of electron on the phthalocyanine macrocycles are observed in the EPR spectra of <b>1</b>–<b>3</b>. The content of this admixture is less than 1% in all salts. Nevertheless, static magnetic susceptibility measurements for <b>3</b> detected significant magnetization. The effective magnetic moment is 4.05 μ_B per formula unit at 300 K. It can originate from the spins localized on the iron atoms of [Fe­(I)­Cl₁₆Pc­(−2)]⁻. The Weiss temperature of −53 K in the 60–300 K range indicates a strong antiferromagnetic interaction of spins which results in the decreases of magnetic moment of <b>3</b> with temperature below 220 K down to 2.72 μ_B at 6 K. Optical spectra of <b>1</b>–<b>3</b> show bands ascribed to [Fe­(I)­Cl₁₆Pc­(−2)]⁻ at 339–349, 538–548, 685–691, and 805–821 nm. The bands in the NIR range at 1740–1810 nm were attributed to charge transfer excitations within phthalocyanine columns associated with the unpaired electrons on the iron atoms

Spin Crossover in Anionic Cobalt-Bridged Fullerene (Bu₄N⁺){Co(Ph₃P)}₂(μ₂‑Cl^–)(μ₂‑η²,η²‑C₆₀)₂ Dimers

A spin crossover phenomena is observed in an anionic (Bu₄N⁺)­{Co­(Ph₃P)}₂(μ₂-Cl^–)­(μ₂-η²,η²-C₆₀)₂·2C₆H₁₄ (<b>1</b>) complex in which two cobalt atoms bridge two fullerene molecules to form a dimer. The dimer has a triplet ground state with two weakly coupling Co⁰ atoms (<i>S</i> = 1/2). The spin transition realized above 150 K is accompanied by a cobalt-to-fullerene charge transfer that forms a quintet excited state with a high spin Co^I (<i>S</i> = 1) and C₆₀^•– (<i>S</i> = 1/2)

Magnetic and Optical Properties of Layered (Me₄P⁺)[M^IVO(Pc^•3–)]^•–(TPC)_0.5·C₆H₄Cl₂ Salts (M = Ti and V) Composed of π‑Stacking Dimers of Titanyl and Vanadyl Phthalocyanine Radical Anions

Two isostructural salts with radical anions of titanyl and vanadyl phthalocyanines (Me₄P⁺)­[M^IVO­(Pc^•3–)]^•–­(TPC)_0.5­·C₆H₄Cl₂ (M = Ti (<b>1</b>), V (<b>2</b>)), where TPC is triptycene, were obtained. These salts contain phthalocyanine layers composed of the {[M^IVO­(Pc^•3–)]^•–}₂ dimers with strong π–π intradimer interaction. The reduction of metal phthalocyanines was centered on the Pc macrocycles providing the appearance of new bands in the near infrared range and a blue shift of Q- and Soret bands. That results in the alternation of shorter and longer C–N_imine bonds in Pc^•3–. Only one <i>S</i> = 1/2 spin is delocalized over Pc^•3– in <b>1</b> providing a χ_M<i>T</i> value of 0.364 emu K mol^–1 at 300 K. Salt <b>1</b> showed antiferromagnetic behavior approximated by the Heisenberg model for isolated pairs of antiferromagnetically interacting spins with exchange interaction of <i>J</i>/<i>k</i>_B = −123.0 K. The χ_M<i>T</i> value for <b>2</b> is equal to 0.617 emu K mol^–1 at 300 K to show the contribution of two <i>S</i> = 1/2 spins localized on V^IV and delocalized over Pc^•3–. Magnetic behavior of <b>2</b> is described by the Heisenberg model for a four-spin system with strong intermolecular coupling between Pc^•3– in {[V^IVO­(Pc^•3–)]^•–}₂ (<i>J</i>_inter/<i>k</i>_B = −105.0 K) and weaker intramolecular coupling between the V^IV and Pc^•3– (<i>J</i>_intra/<i>k</i>_B = −15.2 K)

The Salts of Copper Octafluoro- and Hexadecafluorophthalocyanines Containing [Cu^II(F₈Pc)^4–]^2– Dianions and [CuF₁₆Pc]⁻ Monoanions

Crystalline anionic salts with copper octafluoro- and hexadecafluorophthalocyanines, (Bu₄N⁺)₂[Cu^II(F₈Pc)^4–]^2–·2C₆H₄Cl₂ (<b>1</b>) and (PPN⁺)₃[CuF₁₆Pc]₃^3–·2C₆H₅CN (<b>2</b>), where PPN⁺ is bis­(triphenylphosphoranylidene)­ammonium and Pc is phthalocyanine, have been obtained. The absence of noticeable absorption in the NIR range and DFT calculations for <b>1</b> indicate that both negative charges are mainly localized on the Pc ligand, and that the [Cu^II(F₈Pc)^4–]^2– dianions are formed without reduction of Cu^II. The magnetic moment of 1.60 μ_B corresponds to the contribution of one <i>S</i> = 1/2 spin per dianion. The spin is localized on the Cu^II atom, which shows an EPR signal characteristic of Cu^II. Dianions are isolated in <b>1</b>, providing only weak magnetic coupling of spins with a Weiss temperature of −4 K. Salt <b>2</b> contains closely packed π–π stacks built of [CuF₁₆Pc]⁻ anions of types I and II, and the interplanar distances are 3.187 and 3.275 Å. According to the DFT calculations, the [CuF₁₆Pc]⁻ anions of types I and II can have different charge distributions, with localization of an extra electron on the copper atoms to form diamagnetic [Cu^I(F₁₆Pc)^2–]⁻ monoanions or delocalization of an extra electron on the F₁₆Pc ligand to form [Cu^II(F₁₆Pc)^•3–]^•– having an <i>S</i> = 1/2 (Cu^II) + 1/2 (F₁₆Pc^•3–) spin state. In fact, at 300 K, the magnetic moment of <b>2</b> of 3.25 μ_B per formula unit is rather close to the contribution from two [Cu^II(F₁₆Pc)^•3–]^•– (calculated μ_eff is 3.46 μ_B). The Weiss temperature of −21.5 K indicates antiferromagnetic coupling of spins, which can be modeled by stronger intermolecular coupling between (F₁₆Pc)^•3– with <i>J</i>₁/<i>k</i>_B = −23.5 K and weaker intramolecular coupling between Cu^II and (F₁₆Pc)^•3– with <i>J</i>₂/<i>k</i>_B = −8.1 K. This interaction is realized in the {[Cu^II(F₁₆Pc)^•3–]^•–}₂ dimers separated by diamagnetic [Cu^I(F₁₆Pc)^2–]⁻ species. In spite of the stacking arrangement of phthalocyanine macrocycles in <b>2</b>, the inhomogeneous charge distribution and nonuniform distances between the macrocycles should suppress electrical conductivity

The Salts of Copper Octafluoro- and Hexadecafluorophthalocyanines Containing [Cu^II(F₈Pc)^4–]^2– Dianions and [CuF₁₆Pc]⁻ Monoanions

Crystalline anionic salts with copper octafluoro- and hexadecafluorophthalocyanines, (Bu₄N⁺)₂[Cu^II(F₈Pc)^4–]^2–·2C₆H₄Cl₂ (<b>1</b>) and (PPN⁺)₃[CuF₁₆Pc]₃^3–·2C₆H₅CN (<b>2</b>), where PPN⁺ is bis­(triphenylphosphoranylidene)­ammonium and Pc is phthalocyanine, have been obtained. The absence of noticeable absorption in the NIR range and DFT calculations for <b>1</b> indicate that both negative charges are mainly localized on the Pc ligand, and that the [Cu^II(F₈Pc)^4–]^2– dianions are formed without reduction of Cu^II. The magnetic moment of 1.60 μ_B corresponds to the contribution of one <i>S</i> = 1/2 spin per dianion. The spin is localized on the Cu^II atom, which shows an EPR signal characteristic of Cu^II. Dianions are isolated in <b>1</b>, providing only weak magnetic coupling of spins with a Weiss temperature of −4 K. Salt <b>2</b> contains closely packed π–π stacks built of [CuF₁₆Pc]⁻ anions of types I and II, and the interplanar distances are 3.187 and 3.275 Å. According to the DFT calculations, the [CuF₁₆Pc]⁻ anions of types I and II can have different charge distributions, with localization of an extra electron on the copper atoms to form diamagnetic [Cu^I(F₁₆Pc)^2–]⁻ monoanions or delocalization of an extra electron on the F₁₆Pc ligand to form [Cu^II(F₁₆Pc)^•3–]^•– having an <i>S</i> = 1/2 (Cu^II) + 1/2 (F₁₆Pc^•3–) spin state. In fact, at 300 K, the magnetic moment of <b>2</b> of 3.25 μ_B per formula unit is rather close to the contribution from two [Cu^II(F₁₆Pc)^•3–]^•– (calculated μ_eff is 3.46 μ_B). The Weiss temperature of −21.5 K indicates antiferromagnetic coupling of spins, which can be modeled by stronger intermolecular coupling between (F₁₆Pc)^•3– with <i>J</i>₁/<i>k</i>_B = −23.5 K and weaker intramolecular coupling between Cu^II and (F₁₆Pc)^•3– with <i>J</i>₂/<i>k</i>_B = −8.1 K. This interaction is realized in the {[Cu^II(F₁₆Pc)^•3–]^•–}₂ dimers separated by diamagnetic [Cu^I(F₁₆Pc)^2–]⁻ species. In spite of the stacking arrangement of phthalocyanine macrocycles in <b>2</b>, the inhomogeneous charge distribution and nonuniform distances between the macrocycles should suppress electrical conductivity