Conducting Coronene Cation Radical Salt Containing Magnetic Metal Ions.

Coronene is the smallest homologue of benzene and is the smallest fragment of graphene among 6-fold symmetric polycyclic aromatic hydrocarbons. In this study, we obtained the first coronene cation radical solid containing magnetic counterions by an electrochemical method. Coronene monocations in the 1:1 salt, (coronene•+)(FeBr4-), assemble in a stacking manner via π-π interactions, which lead to a rather high room-temperature conductivity of 0.6 S cm-1. The salt shows semiconducting behavior as expected from the calculated band structure, and activation energies were estimated to be 0.25 eV at T ≥ 220 K and 0.18 eV at T ≤ 220 K. The magnetic susceptibility follows the Curie-Weiss law down to about 30 K, with a Curie constant (4.47 emu K mol-1) expected for S = 5/2 spins of iron(III) ions and a high Weiss temperature (-32.2 K). Upon further cooling, the salt exhibits a susceptibility kink at 16.2 K followed by the loss of a significant fraction of the susceptibility due to long-range antiferromagnetic ordering. Theoretical calculations predicted that the indirect π-d magnetic exchange interaction through C-H···Br hydrogen bonds is equal to Jπd = -3.10 K. Although the absolute value is lower than that of the direct d-d magnetic exchange interaction between the FeBr4- anions (Jdd = -13.35 K), it is evident that the π-d interactions play a certain role in determining the magnetic behavior. Considering that an isomorphous salt, (coronene•+)(GaBr4-) involving a nonmagnetic counterpart GaBr4-, exhibits singlet-triplet magnetic behavior with a spin gap of 1.44 × 103 K, it is most likely that in (coronene)(FeBr4) the nonmagnetic π-electrons serve as mediators of the magnetic ordering of d-spins through the π-d interactions.

Bis(ethylenedithio)tetrathiafulvalene Cation Radical Salts Composed of Nonuniform Silver(I) Complex Polyanions.

Rational control of the molecular arrangement in solids has been the subject of intense research for many years. In particular, the structural control of bis(ethylenedithio)tetrathiafulvalene (ET) radical cations has attracted special interest because of the primary effect on the electronic properties of the salts. In this study, we obtained the first ET cation radical salts formed with nonuniform silver(I) complex polyanions, which involve multiple kinds of openings in the anionic layer, by an electrocrystallization method. θ-(ET)2Ag2(CN)[N(CN)2]2 (1) with a θ-type ET packing motif contains double helical chains composed of AgN(CN)2, whereas α″-(ET)2Ag2(CN)(SCN)2 (2) with an α″-type ET packing motif contains zigzag ladders composed of AgSCN. Both silver(I)-based tube-like assemblies are connected to each other by a cyano group, affording nonuniform polyanionic structures. Although both salts show semiconducting behavior, there is a distinct difference in their spin geometry, with an S = 1/2 Heisenberg antiferromagnetic square lattice in 1, which is associated with charge disproportionation or dynamical charge fluctuation in the ET layers, and an S = 1/2 Heisenberg anisotropic triangular lattice in 2, which results in spin frustration in the ET layers. The ability of the nonuniform polymeric structures in the anionic layers to act as templates for various arrangements of ET radical cations is demonstrated.

Partial Substitution of Ag(I) for Cu(I) in Quantum Spin Liquid κ-(ET)2Cu2(CN)3, Where ET Is Bis(ethylenedithio)tetrathiafulvalene.

Three mixed crystals, κ-(ET)2Ag2 xCu2(1- x)(CN)3 [ET is bis(ethylenedithio)tetrathiafulvalene; 0.24 < x < 0.71] with a κ-type packing motif of face-to-face ET dimers, were obtained by electrocrystallization. Regardless of the composition, each ET dimer fits into a hexagonal anionic opening (i.e., key-on-hole packing) similar to its parent spin liquid candidate, κ-(ET)2Cu2(CN)3. X-ray diffraction and energy dispersive spectroscopy analyses revealed that Cu and Ag atoms are statistically disordered with a fairly homogeneous distribution in a crystal. A structural variation depending on x is responsible for the change in the calculated band parameters related to intermolecular interactions, electron correlations, and frustrations. A salt with nearly equimolar amounts of Ag and Cu ( x = 0.49) is semiconductive at ambient pressure and undergoes a Mott transition upon application of hydrostatic pressure. Along with the positive pressure dependence of the transition temperature, the temperature-independent amplitude of magnetic torque at low temperatures suggests that the insulating phase is a quantum spin liquid. Further application of pressure results in the appearance of a superconducting phase. Contrary to those of the parent salts, κ-(ET)2Cu2(CN)3 and κ-(ET)2Ag2(CN)3, the transition temperature increases as the pressure increases and eventually reaches 4.5 K at 1.65 GPa.

Fullerene and endometallofullerene Kagome lattices with symmetry-forced spin frustration.

Salts of fullerene C60˙- and endometallofullerene Sc3N@Ih-C80˙- radical anions with Bu3MeP+ cations ((Bu3MeP+)3(C60˙-)3·C6H4Cl2 (1) and (Bu3MeP+)3(Sc3N@Ih-C80˙-)3·C6H4Cl2 (2)) have been obtained. The C3 symmetry of the Bu3MeP+ cation provides 2D Kagome lattices with an equilateral triangle arrangement of fullerenes in accordance with trigonal crystal symmetry P31m. The C60˙- and Sc3N@Ih-C80˙- radical anions preserve their monomeric forms in 1 and 2 with the S = 1/2 spin state down to 1.9 K. The close packing of the fullerene radical anions results in strong antiferromagnetic coupling of the spins with Weiss temperatures of -108 K for 1 and -43 K for 2. Compound 1 is a rare example of a magnetic system in which in spite of the strong magnetic coupling of spins no long-range ordering is observed down to 1.9 K. The 13C NMR spectra of the 13C enriched sample of 1 support the absence of the antiferromagnetic ordering of spins down to 1.5 K. Thus, the crystals of 1 preserve large spin frustration forced by the trigonal symmetry. Therefore, compound 1 is a promising candidate for the first observation of a quantum spin liquid (QSL) state in a fullerene-based system. Isostructural salt 2 is the first compound that contains monomeric paramagnetic Sc3N@Ih-C80˙- radical anions stable down to 1.9 K, which show strong spin frustration. These data indicate the ability of endometallofullerenes to give exotic magnetic systems such as QSLs.

Mapping molecular motions leading to charge delocalization with ultrabright electrons.

Ultrafast processes can now be studied with the combined atomic spatial resolution of diffraction methods and the temporal resolution of femtosecond optical spectroscopy by using femtosecond pulses of electrons or hard X-rays as structural probes. However, it is challenging to apply these methods to organic materials, which have weak scattering centres, thermal lability, and poor heat conduction. These characteristics mean that the source needs to be extremely bright to enable us to obtain high-quality diffraction data before cumulative heating effects from the laser excitation either degrade the sample or mask the structural dynamics. Here we show that a recently developed, ultrabright femtosecond electron source makes it possible to monitor the molecular motions in the organic salt (EDO-TTF)2PF6 as it undergoes its photo-induced insulator-to-metal phase transition. After the ultrafast laser excitation, we record time-delayed diffraction patterns that allow us to identify hundreds of Bragg reflections with which to map the structural evolution of the system. The data and supporting model calculations indicate the formation of a transient intermediate structure in the early stage of charge delocalization (less than five picoseconds), and reveal that the molecular motions driving its formation are distinct from those that, assisted by thermal relaxation, convert the system into a metallic state on the hundred-picosecond timescale. These findings establish the potential of ultrabright femtosecond electron sources for probing the primary processes governing structural dynamics with atomic resolution in labile systems relevant to chemistry and biology.

The Salts of Copper Octafluoro- and Hexadecafluorophthalocyanines Containing [CuII(F8Pc)4-]2- Dianions and [CuF16Pc]- Monoanions.

Crystalline anionic salts with copper octafluoro- and hexadecafluorophthalocyanines, (Bu4N+)2[CuII(F8Pc)4-]2-·2C6H4Cl2 (1) and (PPN+)3[CuF16Pc]33-·2C6H5CN (2), 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 1 indicate that both negative charges are mainly localized on the Pc ligand, and that the [CuII(F8Pc)4-]2- dianions are formed without reduction of CuII. The magnetic moment of 1.60 µB corresponds to the contribution of one S = 1/2 spin per dianion. The spin is localized on the CuII atom, which shows an EPR signal characteristic of CuII. Dianions are isolated in 1, providing only weak magnetic coupling of spins with a Weiss temperature of -4 K. Salt 2 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 [CuI(F16Pc)2-]- monoanions or delocalization of an extra electron on the F16Pc ligand to form [CuII(F16Pc)•3-]•- having an S = 1/2 (CuII) + 1/2 (F16Pc•3-) spin state. In fact, at 300 K, the magnetic moment of 2 of 3.25 µB per formula unit is rather close to the contribution from two [CuII(F16Pc)•3-]•- (calculated µeff is 3.46 µB). The Weiss temperature of -21.5 K indicates antiferromagnetic coupling of spins, which can be modeled by stronger intermolecular coupling between (F16Pc)•3- with J1/kB = -23.5 K and weaker intramolecular coupling between CuII and (F16Pc)•3- with J2/kB = -8.1 K. This interaction is realized in the {[CuII(F16Pc)•3-]•-}2 dimers separated by diamagnetic [CuI(F16Pc)2-]- species. In spite of the stacking arrangement of phthalocyanine macrocycles in 2, the inhomogeneous charge distribution and nonuniform distances between the macrocycles should suppress electrical conductivity.

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 (1) 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 (S = 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 CoI (S = 1) and C60•- (S = 1/2).

Pressure-Tuned Exchange Coupling of a Quantum Spin Liquid in the Molecular Triangular Lattice κ-(ET)_{2}Ag_{2}(CN)_{3}.

The effects of pressure on a quantum spin liquid are investigated in an organic Mott insulator κ-(ET)_{2}Ag_{2}(CN)_{3} with a spin-1/2 triangular lattice. The application of negative chemical pressure to κ-(ET)_{2}Cu_{2}(CN)_{3}, which is a well-known sister Mott insulator, allows for extensive tuning of antiferromagnetic exchange coupling, with J/k_{B}=175-310 K, under hydrostatic pressure. Based on ^{13}C nuclear magnetic resonance measurements under pressure, we uncover universal scaling in the static and dynamic spin susceptibilities down to low temperatures ∼0.1k_{B}T/J. The persistent fluctuations and residual specific heat coefficient are consistent with the presence of gapless low-lying excitations. Our results thus demonstrate the fundamental finite-temperature properties of a quantum spin liquid in a wide parameter range.

Conducting π Columns of Highly Symmetric Coronene, The Smallest Fragment of Graphene.

Coronene, which is the smallest D6h -symmetric polycyclic aromatic hydrocarbon, attracts particular attention as a basic component of electronic materials because it is the smallest fragment of graphene. However, carrier generation by physical methods, such as photo- or electric field-effect, has barely been studied, primarily because of the poor π-conduction pathway in pristine coronene solid. In this work we have developed unprecedented π-stacking columns of cationic coronene molecules by electrochemical hole-doping with polyoxometallate dianions. The face-to-face π-π interactions as well as the partially charged state lead to electrical conductivity at room temperature of up to 3 S cm(-1) , which is more than 10 orders of magnitude higher than that of pristine coronene solid. Additionally, the robust π-π interactions strongly suppress the in-plane rotation of the coronene molecules, which has allowed the first direct observation of the static Jahn-Teller distortion of cationic coronene molecules.

Coordination Complexes of Transition Metals (M = Mo, Fe, Rh, and Ru) with Tin(II) Phthalocyanine in Neutral, Monoanionic, and Dianionic States.

The ability of tin atoms to form stable Sn-M bonds with transition metals was used to prepare transition metal complexes with tin(II) phthalocyanine in neutral, monoanionic, and dianionic states. These complexes were obtained via the interactions of [Sn(IV)Cl2Pc(3-)](•-) or [Sn(II)Pc(3-)](•-) radical anions with {Cp*Mo(CO)2}2, {CpFe(CO)2}2, {CpMo(CO)3}2, Fe3(CO)12, {Cp*RhCl2}2, or Ph5CpRu(CO)2Cl. The neutral coordination complexes of Cp*MoBr(CO)2[Sn(II)Pc(2-)]·0.5C6H4Cl2 (1) and CpFe(CO)2[Sn(II)Pc(2-)]·2C6H4Cl2 (2) were obtained from [Sn(IV)Cl2Pc(3-)](•-). On the other hand, the coordination of transition metals to [Sn(II)Pc(3-)](•-) yielded anionic coordination complexes preserving the spin on [Sn(II)Pc(3-)](•-). However, in the case of {cryptand[2,2,2](Na(+))}{CpFe(II)(CO)2[Sn(II)Pc(4-)]}(-)·C6H4Cl2 (4), charge transfer from CpFe(I)(CO)2 to [Sn(II)Pc(3-)](•-) took place to form the diamagnetic [Sn(II)Pc(4-)](2-) dianion and {CpFe(II)(CO)2}(+). The complexes {cryptand[2,2,2](Na(+))}{Fe(CO)4[Sn(II)Pc(3-)](•-)} (5), {cryptand[2,2,2](Na(+))}{CpMo(CO)2[Sn(II)Pc(2-)Sn(II)Pc(3-)(•-)]} (6), and {cryptand[2,2,2](Na(+))}{Cp*RhCl2[Sn(II)Pc(3-)](•-)} (7) have magnetic moments of 1.75, 2.41, and 1.75 µ(B), respectively, owing to the presence of S = 1/2 spins on [Sn(II)Pc(3-)](•-) and CpMo(I)(CO)2 (for 6). In addition, the strong antiferromagnetic coupling of spins with Weiss temperatures of -35.5 -28.6 K was realized between the CpMo(I)(CO)2 and the [Sn(II)Pc(3-)](•-) units in 6 and the π-stacking {Fe(CO)4[Sn(II)Pc(3-)](•-)}2 dimers of 5, respectively. The [Sn(II)Pc(3-)](•-) radical anions substituted the chloride anions in Ph5CpRu(CO)2Cl to form the formally neutral compound {Ph5CpRu(II)(CO)2[Sn(II)Pc(3-)]} (8) in which the negative charge and spin are preserved on [Sn(II)Pc(3-)](•-). The strong antiferromagnetic coupling of spins with a magnetic exchange interaction J/k(B) = -183 K in 8 is explained by the close packing of [Sn(II)Pc(3-)](•-) in the π-stacked {Ph5CpRu(II)(CO)2[Sn(II)Pc(3-)](•-)}2 dimers.

Synthesis, structures, and properties of crystalline salts with radical anions of metal-containing and metal-free phthalocyanines.

Radical anion salts of metal-containing and metal-free phthalocyanines [MPc(3-)](·-), where M = Cu(II), Ni(II), H2, Sn(II), Pb(II), Ti(IV)O, and V(IV)O (1-10) with tetraalkylammonium cations have been obtained as single crystals by phthalocyanine reduction with sodium fluorenone ketyl. Their formation is accompanied by the Pc ligand reduction and affects the molecular structure of metal phthalocyanine radical anions as well as their optical and magnetic properties. Radical anions are characterized by the alternation of short and long C-Nimine bonds in the Pc ligand owing to the disruption of its aromaticity. Salts 1-10 show new bands at 833-1041 nm in the NIR range, whereas the Q- and Soret bands are blue-shifted by 0.13-0.25 eV (38-92 nm) and 0.04-0.07 eV (4-13 nm), respectively. Radical anions with Ni(II), Sn(II), Pb(II), and Ti(IV)O have S = 1/2 spin state, whereas [Cu(II)Pc(3-)](·-) and [V(IV)OPc(3-)](·-) containing paramagnetic Cu(II) and V(IV)O have two S = 1/2 spins per radical anion. Central metal atoms strongly affect EPR spectra of phthalocyanine radical anions. Instead of narrow EPR signals characteristic of metal-free phthalocyanine radical anions [H2Pc(3-)](·-) (linewidth of 0.08-0.24 mT), broad EPR signals are manifested (linewidth of 2-70 mT) with g-factors and linewidths that are strongly temperature-dependent. Salt 11 containing the [Na(I)Pc(2-)](-) anions as well as previously studied [Fe(I)Pc(2-)](-) and [Co(I)Pc(2-)](-) anions that are formed without reduction of the Pc ligand do not show changes in molecular structure or optical and magnetic properties characteristic of [MPc(3-)](·-) in 1-10.

Formation of {Co(dppe)}2{µ2-η(2):η(2)-η(2):η(2)-[(C60)2]} Dimers Bonded by Single C-C Bonds and Bridging η(2)-Coordinated Cobalt Atoms.

Coordination of two bridging cobalt atoms to fullerenes by the η(2) type in {Co(dppe)}2{µ2-η(2):η(2)-η(2):η(2)-[(C60)2]}·3C6H4Cl2 [1; dppe = 1,2-bis(diphenylphosphino)ethane] triggers fullerene dimerization with the formation of two intercage C-C bonds of 1.571(4) Å length. Coordination-induced fullerene dimerization opens a path to the design of fullerene structures bonded by both covalent C-C bonds and η(2)-coordination-bridged metal atoms.

Metallic and Mott insulating spin-frustrated antiferromagnetic states in ionic fullerene complexes with a two-dimensional hexagonal C60·- packing motif.

(MDABCO(+))(C60(·-))(TPC) (1), in which MDABCO(+) is N-methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene-based quasi-2D metal and contains closely packed hexagonal fullerene layers with interfullerene center-to-center distances of 10.07 Šat 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass (m*/m0 =6.7). The latter indicates a narrow-band nature, which is consistent with the calculated bandwidth of 0.10-0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200-230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ(+))(C60(·-))(TPC) (2) with a hexagonal arrangement of C60(·-) was obtained by increasing the interfullerene distance with the bulkier N-methylquinuclidinium cations (MQ(+)) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center-to-center distances in the layers (10.124, 10.155, and 10.177 Šat 250 K). Unit-cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1, 2 exhibits a nonmetallic spin-frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is -27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2, and thus a Mott-Hubbard insulating state with antiferromagnetically frustrated spins results.

Linear coordination fullerene C60 polymer [{Ni(Me3P)2}(µ-η(2),η(2)-C60)]∞ bridged by zerovalent nickel atoms.

Coordination nickel-bridged fullerene polymer [{Ni(Me3P)2}(µ-η(2),η(2)-C60)]∞ (1) has been obtained via reduction of a Ni(II)(Me3P)2Cl2 and C60 mixture. Each nickel atom is linked in the polymer with two fullerene units by η(2)-type Ni-C(C60) bonds of 2.087(8)-2.149(8) Å length. Nickel atoms are coordinated to the 6-6 bonds of C60 as well as two trimethylphosphine ligands to form a four-coordinated environment around the metal centers. Fullerene cages approach very close to each other in the polymer with a 9.693(3) Å interfullerene center-to-center distance, and two short interfullerene C-C contacts of 2.923(7) Å length are formed. Polymer chains are densely packed in a crystal with interfullerene center-to-center distances between fullerenes from neighboring polymer chains of 9.933(3) Å and multiple interfullerene C···C contacts. As a result, three-dimensional dense fullerene packing is formed in 1. According to optical and electron paramagnetic resonance spectra, fullerenes are neutral in 1 and nickel atoms have a zerovalent state with a diamagnetic d(10) electron configuration. The density functional theory calculations prove the diamagnetic state of the polymer with a singlet-triplet gap wider than 1.37 eV.

Formation of hexagonal fullerene layers from neutral and negatively charged fullerenes in {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 containing gold cations with the C3v symmetry.

Fullerene salt {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 (1) containing (Ph3P)3Au(+) cations with the C3v symmetry has been obtained as single crystals. Hexagonal corrugated fullerene layers formed in 1 alternate with the layers consisting of (Ph3P)3Au(+) and C6H4Cl2 along the c 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.

Charge-transfer solids using nucleobases: supramolecular architectures composed of cytosine and [Ni(dmit)2] assembled by multiple hydrogen bonds and heteroatomic contacts.

Protonated species of the nucleobase cytosine (C), namely the monoprotonated CH(+) and the hemiprotonated CHC(+), were used to obtain four charge-transfer complexes of [Ni(dmit)2] (dmit: 1,3-dithiole-2-thione-4,5-dithiolate). Diffusion methods afforded two semiconducting [Ni(dmit)2](-) salts; (CH)[Ni(dmit)2](CH3CN) (1) and (CHC)[Ni(dmit)2] (2). In salt 1, the [Ni(dmit)2](-) ions with a S = 1/2 spin construct a uniform one-dimensional array along the molecular long axis, and the significant intermolecular interaction along the face-to-face direction results in a spin-singlet ground state. In contrast, salt 2 exhibits the Mott insulating behavior associated with uniform 1D arrays of [Ni(dmit)2](-), which assemble a two-dimensional layer that is sandwiched between the layers of hydrogen-bonded CHC(+) ribbons. Multiple hydrogen bonds between CHC(+) and [Ni(dmit)2](-) seem to result in the absence of structural phase transition down to 0.5 K. Electrooxidation of [Ni(dmit)2](-) afforded the polymorphs of the [Ni(dmit)2](0.5-) salts, (CHC(+))[{Ni(dmit)2}(0.5-)]2 (3 and 4), which are the first mixed-valence salts of nucleobase cations with metal complex anions. Similar to 2, salt 3 contains CHC(+) ribbons that are sandwiched between the 2D [Ni(dmit)2](0.5-) layers. In the layer, the [Ni(dmit)2](0.5-) ions form dimers with a S = 1/2 spin and the narrow electronic bandwidth causes a semiconducting behavior. In salt 4, the CHC(+) units form an unprecedented corrugated 2D sheet, which is sandwiched between the 2D [Ni(dmit)2](0.5-) layers that involve ring-over-atom and spanning overlaps. In contrast to 3, salt 4 exhibits metallic behavior down to 1.8 K, associated with a wide bandwidth and a 2D Fermi surface. The ability of hydrogen-bonded CHC(+) sheets as a template for the anion radical arrangements is demonstrated.

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-As) is sandwiched between TCNQs to construct a DDA-type alternating π column flanked by another coronene (Cor-B). Whereas solid-state (2)H 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-As 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-As shows inter-column interactions with neighboring Cor-As. The solid-state (1)H 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.

Synthesis, structural and magnetic properties of ternary complexes of (Me4P+)·{[Fe(I)Pc(-2)](-)}·triptycene and (Me4P+)·{[Fe(I)Pc(-2)]-}·(N,N,N',N'-tetrabenzyl-p-phenylenediamine)0.5 with iron(I) phthalocyanine anions.

Ternary complexes of (Me4P(+))·{[Fe(I)Pc(-2)](-)}·TPC (1) and (Me4P(+))·{[Fe(I)Pc(-2)](-)}·(TBPDA)0.5 (2) containing iron(I) phthalocyanine anions, tetramethylphosphonium cations (Me4P(+)), and neutral structure-forming triptycene (TPC) or N,N,N',N'-tetrabenzyl-p-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 1 and 2, 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 1 at 280 K and 2.986(5) (100 K) and 3.011(5) Å (180 K) in 2. The {[Fe(I)Pc(-2)](-)}2 dimers are packed in the layers in 1 arranged parallel to the ac plane and in isolated chains in 2 arranged along the a axis. Extended Hückel based calculation of intermolecular overlap integrals showed stronger and weaker π-π interactions within and between phthalocyanine dimers, respectively, both in 1 and 2. EPR signals of both complexes manifest two components. An major low-field asymmetric component is attributed to the Fe(I) atoms with the d(7) configuration. An origin minor narrow signal with g-factor close to the free-electron value (g = 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 (1) and 1.76 µB (2) correspond to the contribution of about one S = ½ spin per formula unit in accordance with low-spin state of [Fe(I)Pc(-2)](-). Negative Weiss temperatures of -7.6 K (1) and -13 K (2) 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.

Mononuclear coordination complexes of fullerene C60 with zerovalent cobalt having S = 1/2 spin state: Co(η(2)-C60)(L)(C6H5CN)·(o-C6H4Cl2) (L = 1,2-bis(diphenylphosphino)ethane and 1,1'-bis(diphenylphosphino)ferrocene).

Two mononuclear coordination complexes of fullerene C60 with cobalt, Co(η(2)-C60)(dppe)(C6H5CN)·C6H4Cl2 (1) and Co(η(2)-C60)(dppf)(C6H5CN)·C6H4Cl2 (2) (dppe is 1,2-bis(diphenylphosphino)ethane and dppf is 1,1'-bis(diphenylphosphino)ferrocene) have been obtained by sodium fluorenone reduction of the Co(dppe)Cl2 or Co(dppf)Br2 and C60 mixtures. The IR and visible-NIR spectra of 1 and 2 indicate the neutral state of fullerenes. Therefore, cobalt atoms formally have the zerovalent state. Cobalt coordinates to the 6-6 bond of C60 by η(2)-type coordination with Co-C bond lengths in the 2.008(3)-2.060(3) Å range. Diphosphine and benzonitrile ligands additionally coordinate to cobalt to form a distorted square-pyramidal environment for the cobalt atoms. Complexes 1 and 2 are rare examples of fullerene coordination complexes with paramagnetic metal centers. Both complexes manifest intense asymmetric EPR signals attributed to zerovalent cobalt atoms, which can be fitted by three components with g = 2.261-2.124 (1) and g = 2.258-2.092 (2). Effective magnetic moments of 1 and 2 indicate the low-spin (S = 1/2) state of Co(0). In accordance with EPR spectra, DFT calculations show that the spin density is localized mainly on the central cobalt atoms and only slightly delocalized into C60, benzonitrile, dppe, or dppf ligands.

Experimental observation of C60 LUMO splitting in the C60(2-) dianions due to the Jahn-Teller effect. Comparison with the C60(˙-) radical anions.

New fullerene salts (TMP(+))2·(C60(2-))·(C6H4Cl2)2 (1), {DB-18-crown-6·[Na(+)]·(C6H5CN)2}2·(C60(2-))·C6H5CN·C6H4Cl2 (2), {cryptand[2,2,2]·(Na(+))}2·(C60(2-)) (3) and (PPN(+))2·(C60(2-))·(C6H4Cl2)2 (4) were obtained as single crystals. Their crystal structures were solved and their optical and magnetic properties were analyzed. The spectra of the salts in the IR and UV-visible-NIR ranges indicate the formation of C60(2-) dianions in 1-4. These salts show similar behavior in EPR measurements, explained by the diamagnetic ground state of the C60(2-) dianions and the thermal population of the excited triplet state, which is separated by an energy gap of 487-540 cm(-1). The magnetic susceptibility of 4 also increased above 130 K due to the population of the excited triplet state. The observed splitting of the C60 LUMO is attributed to the Jahn-Teller (JT) effect. We analyzed the splitting by an extended Hückel method using the single-crystal structural data for the compounds containing neutral, mono- and dianions of C60. The splitting of the initially triply degenerated C60 LUMO produces three molecular orbitals. The gap between the lowest and highest orbitals is very small in neutral C60 (128-140 cm(-1)), it increases in C60(˙-) (500-710 cm(-1)) and increases further in C60(2-) (1080-1670 cm(-1)). It was found that the splitting of the C60 LUMO is realized in different ways for the mono- and dianions. The ground and first excited state are separated in C60(˙-) by a small gap of 55-180 cm(-1) only. This gap is noticeably larger in the C60(2-) dianions and falls into the 760-1390 cm(-1) range.