Fullerene complexes with coordination assemblies of metalloporphyrins and metal phthalocyanines

High Temperature Accelerated Stone-Wales Transformation and the Threshold Temperature of IPR-C60 Formation

The Stone-Wales bond rotation isomerization of nonicosahedral C₆₀ (C_2v-C₆₀) into isolated-pentagon rule following icosahedral C₆₀ (I_h-C₆₀ or IPR-C₆₀) is a limiting step in the synthesis of I_h-C₆₀. However, extensive previous studies indicate that the potential energy barrier of the Stone-Wales bond rotation is between 6 and 8 eV, extremely high to allow for bond rotation at the temperatures used to produce fullerenes conventionally. This is also despite data indicating a possible fullerene road mechanism that necessitates low-temperature annealing. However, these previous investigations often have limiting factors, such as using the harmonic approximation to determine free energies at high temperatures or considering only the reverse I_h-C₆₀ to C_2v-C₆₀ transition as a basis. Indeed, when the difference in energy between I_h-C₆₀ and C_2v-C₆₀ is accounted for, this barrier is generally reduced by ∼1.5 eV. Thus, utilizing the recently developed density functional tight binding metadynamics (DFTB-MTD) interface, the effects of temperature on the bond rotation in the conversion of C_2v-C₆₀ to I_h-C₆₀ have been investigated. We found that Stone-Wales bond rotations are complex processes with both in-plane and out-of-plane transition states, and which transition path dominates depends on temperature. Our results clearly show that at temperatures of 2000 K, the free energy for a C_2v-C₆₀ to I_h-C₆₀ transition is only ∼4.21 eV and further reduces to ∼3.77 eV at 3000 K. This translates to transition times of ∼971 μs at 2000 K and ∼34 ns at 3000 K, indicating that defect healing is a fast process at temperatures typical of arc jet or laser ablation experiments. Conversely, below ∼2000 K, bond rotation becomes prohibitively slow, putting a lower threshold limit on the temperature of fullerene formation and subsequent annealing.

Solid-State Properties of Hexaazatriphenylenehexacarbonitrile HAT(CN)6 .- Radical Anions in Crystalline Salts Containing Cryptand(M+ ) and Crystal Violet Cations

Crystalline {Cryptand[2.2.2](Na⁺ )}{HAT(CN)₆ ^.- }⋅0.5C₆ H₄ Cl₂ (1), {Cryptand[2.2.2](K⁺ )}{HAT(CN)₆ ^.- } (2), (CV⁺ ){HAT(CN)₆ ^.- } (3), and (CV⁺ ){HAT(CN)₆ ^.- }⋅2C₆ H₄ Cl₂ (4) salts (where CV⁺ is the crystal violet cation) containing hexaazatriphenylenehexacarbonitrile radical anions have been obtained. The solid-state molecular structure as well as the optical and magnetic properties of HAT(CN)₆ ^.- are studied. The formation of HAT(CN)₆ ^.- in 1-4 leads to the appearance of new bands in the visible range, at 694 and 740 nm. The HAT(CN)₆ ^.- radical anions have spin state S=1/2 and are packed in one-dimensional stacks containing the {HAT(CN)₆ ^.- }₂ dimers alternated with weaker interacting pairs of HAT(CN)₆ ^.- in 1 and nearly isolated {HAT(CN)₆ ^.- }₂ dimers in 2. The {HAT(CN)₆ ^.- }₂ dimers are diamagnetic in 1 but they effectively mediate one-dimensional antiferromagnetic coupling of spins within the stacks with moderate exchange interaction of J/k_B = -80 K. The behaviour of salt 2 is described by a singlet-triplet model for the {HAT(CN)₆ ^.- }₂ dimers with an energy gap of 434(±7) K. Magnetic behaviour of both salts agree well with the data of extended Hückel calculations. Salts 3 and 4 contain isolated stacks of alternated HAT(CN)₆ ^.- and CV⁺ ions, and in this case, nearly paramagnetic behaviour is observed with Weiss temperatures of -1 and -7 K, respectively. Narrow Lorentzian EPR signals with g = 2.0033-2.0039 were found for the HAT(CN)₆ ^.- radical anions in 1 and 4 but in solution g-factor shifts to 1.9964. The electronic structure of HAT(CN)₆ ^.- is analysed based on X-ray diffraction data for 2, showing a Jahn-Teller distortion of the radical anion that reduces the symmetry from D_3h to C_s and splits the initially degenerated LUMOs.

Spectral properties of supramolecular systems based on cobalt(ii)/manganese(iii) phthalocyanine and fullero[60]pyrrolidines with PET

Photoinduced electron transfer in the metallophthalocyanine–fullerene dyads was confirmed and the main “chemical structure – spectral properties” dependences were revealed.

Dimerization of indenocorannulene radicals: imposing stability through increasing strain and curvature

One-electron reduction of bowl-shaped indenocorannulene affords a new stable dimeric dianion, as confirmed by single-crystal X-ray diffraction, NMR and UV-vis spectroscopy, and DFT calculations.

Mono-reduced Corannulene: To Couple and Not to Couple in One Crystal

One-electron reduction of corannulene, C₂₀ H₁₀ , with Li metal in diglyme resulted in crystallization of [{Li⁺ (diglyme)₂ }₄ (C₂₀ H₁₀ ^.- )₂ (C₂₀ H₁₀ -C₂₀ H₁₀ )^2- ] (1), as revealed by single-crystal X-ray diffraction. This hybrid product contains two corannulene monoanion-radicals along with a dianionic dimer, crystallized with four Li⁺ ions wrapped by diglyme molecules. The dimeric (C₂₀ H₁₀ -C₂₀ H₁₀ )^2- anion provides the first crystallographically confirmed example of spontaneous radical dimerization for C₂₀ H₁₀ ^.- . The C-C bond length between the two C₂₀ H₁₀ ^.- bowls of 1.588(5) Å is consistent with the single σ-bond character of the linker. The trans-disposition of two bowls in the centrosymmetric (C₂₀ H₁₀ -C₂₀ H₁₀ )^2- dimer is observed with the torsion angle around the central C-C bond of 180°. Comprehensive theoretical analysis of formation/decomposition processes of the dimeric dianion has been carried out in order to evaluate the nature of bonding and energetics of the C₂₀ H₁₀ ^.- coupling. It is found that such σ-bonded dimers are thermodynamically unstable due to large preparation energy and repulsive Pauli component of the bonding, but kinetically persistent due to a high energy barrier provided by the existing spin-crossing point.

Control of binding of C60 molecules to the substrate by Coulomb blockade

We report on a transition in a monolayer of C₆₀ molecules deposited on a WO₂/W(110) substrate. The transition from a static state, where the molecules are rigidly bound to the surface by a coordination bond, to a state where the molecules are loosely bound to the surface by van der Waals force and rotate continuously, has been studied using scanning tunnelling microscopy (STM). The separation between the molecules and the surface increases by 1.2 Å across the transition. The transition from the static state into the rotating state takes place at 259 K. The energy of the spinning state with respect to the lowest energy state, having a single coordinated bond, can be obtained from the statistics of the molecules switching. The binding energy of the molecule in the spinning state can be easily altered by changing the polarity of the bias voltage applied between the STM tip and the surface. The binding energy decreases by 80 meV when the bias polarity of the sample changes from positive to negative with respect to the tip. The results are consistent with the Coulomb blockade model: when electrons travel from the surface to the C₆₀ molecule, and then to the tip; charge accumulates on the molecule due to the Coulomb blockade. This increases the electrostatic interaction between the molecule's charge and a corresponding image charge generated on the metallic surface.

Porphyrinoid–Fullerene Hybrids as Candidates in Artificial Photosynthetic Schemes

Natural photosynthesis inspired the scientific community to design and synthesize molecular assemblies that possess advanced light-harvesting and electron-transfer features. In this review, we present the preparation and the photophysical investigation of novel porphyrin–fullerene hybrids acting as artificial photosynthetic systems. Porphyrinoids stand as chlorophyll analogues and have emerged as suitable photosensitizers in supramolecular electron donor–acceptor hybrids. Fullerenes (C60) are versatile electron acceptors with small reorganization energy and low reduction potentials. The novel derivatives presented herein mimic the fundamental features of the photosynthetic reaction center, namely, light harvesting, charge separation, and charge transport. To this end, a comprehensive analysis on these key processes that occur in various porphyrin–fullerene entities is illustrated in this work.

Highly stable fullerene-based porous molecular crystals with open metal sites

The synthesis of conventional porous crystals involves building a framework using reversible chemical bond formation, which can result in hydrolytic instability. In contrast, porous molecular crystals assemble using only weak intermolecular interactions, which generally do not provide the same environmental stability. Here, we report that the simple co-crystallization of a phthalocyanine derivative and a fullerene (C₆₀ or C₇₀) forms porous molecular crystals with environmental stability towards high temperature and hot aqueous base or acid. Moreover, by using diamond anvil cells and synchrotron single-crystal measurements, stability towards extreme pressure (>4 GPa) is demonstrated, with the stabilizing fullerene held between two phthalocyanines and the hold tightening at high pressure. Access to open metal centres within the porous molecular co-crystal is demonstrated by in situ crystallographic analysis of the chemisorption of pyridine, oxygen and carbon monoxide. This suggests strategies for the formation of highly stable and potentially functional porous materials using only weak van der Waals intermolecular interactions.

Metalloporphyrin Nanoparticles: Coordinating Diverse Theranostic Functions

Metalloporphyrins serve key roles in natural biological processes and also have demonstrated utility for biomedical applications. They can be encapsulated or grafted in conventional nanoparticles or can self-assemble themselves at the nanoscale. A wide range of metals can be stably chelated either before or after porphyrin nanoparticle formation, without the necessity of any additional chelator chemistry. The addition of metals can substantially alter a range of behaviors such as modulating phototherapeutic efficacy; conferring responsiveness to biological stimuli; or providing contrast for magnetic resonance, positron emission or surface enhanced Raman imaging. Chelated metals can also provide a convenient handle for bioconjugation with other molecules via axial coordination. This review provides an overview of some recent biomedical, nanoparticulate approaches involving gain-of-function metalloporphyrins and related molecules.

Molecular assembly-induced charge transfer between a mixed (phthalocyaninato)(porphyrinato) yttrium triple-decker and a fullerene

A close interface of a mixed (phthalocyaninato)(porphyrinato) yttrium triple-decker and a fullerene in cocrystals affords stronger charge transfer than each individual.

Discovery of two types of new porphyrin–C70 co-crystals: influence of intermolecular contact on the inherent resistance

Two types of supramolecular aggregates based on C₇₀ were synthesised and their inherent resistances were analysed.

Site-Directed Dimerization of Bowl-Shaped Radical Anions to Form a σ-Bonded Dibenzocorannulene Dimer

Designed site-directed dimerization of the monoanion radicals of a π-bowl in the solid state is reported. Dibenzo[a,g]corannulene (C₂₈ H₁₄ ) was selected based on the asymmetry of the charge/spin localization in the C₂₈ H₁₄^.- anion. Controlled one-electron reduction of C₂₈ H₁₄ with Cs metal in diglyme resulted in crystallization of a new dimer, [{Cs⁺ (diglyme)}₂ (C₂₈ H₁₄ -C₂₈ H₁₄ )^2- ] (1), as revealed by single crystal X-ray diffraction study performed in a broad range of temperatures. The C-C bond length between two C₂₈ H₁₄^.- bowls (1.560(8) Å) measured at -143 °C does not significantly change upon heating of the crystal to +67 °C. The single σ-bond character of the C-C linker is confirmed by calculations. The trans-disposition of two bowls in 1 is observed with the torsion angles around the central C-C bond of 172.3(5)° and 173.5(5)°. A systematic theoretical evaluation of dimerization pathways of C₂₈ H₁₄^.- radicals confirmed that the trans-isomer found in 1 is energetically favored.

Fusing a Planar Group to a π-Bowl: Electronic and Molecular Structure, Aromaticity and Solid-State Packing of Naphthocorannulene and its Anions

Molecular and electronic structure, reduction electron transfer and coordination abilities of a polycyclic aromatic hydrocarbon (PAH) having a planar naphtho-group fused to the corannulene bowl have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison of naphtho[2,3-a]corannulene (C₂₈ H₁₄ , 1) with parent corannulene (C₂₀ H₁₀ , 2) revealed the effect of framework topology change on electronic properties and aromaticity of 1. The presence of two reduction steps for 1 was predicted theoretically and confirmed experimentally. Two reversible one-electron reduction processes with the formal reduction potentials at -2.30 and -2.77 V versus Fc^+/0 were detected by cyclic voltammetry (CV) measurements, demonstrating accessibility of the corresponding mono- and dianionic states of 1. The products of the singly and doubly reduced napththocorannulene were prepared using chemical reduction with Group 1 metals and isolated as sodium and rubidium salts. Their X-ray diffraction study revealed the formation of "naked" mono- and dianions crystallized as solvent-separated ion products with one or two sodium cations as [Na⁺ (18-crown-6)(THF)₂ ][C₂₈ H₁₄^- ] and [Na⁺ (18-crown-6)(THF)₂ ]₂ [C₂₈ H₁₄^2- ] (3⋅THF and 4⋅THF, respectively). The dianion of 1 was also isolated as a contact-ion complex with two rubidium countercations, [{Rb⁺ (18-crown-6)}₂ (C₂₈ H₁₄^2- )] (5⋅THF). The structural consequences of adding one and two electrons to the carbon framework of 1 are compared for 3, 4 and 5. Changes in aromaticity and charge distribution stemming from the stepwise electron acquisition are discussed based on DFT computational study.

SnPhPc phthalocyanines with dianion Pc(2-) and radical trianion Pc˙(3-) macrocycles: syntheses, structures, and properties

The interaction of Sn(IV)Cl2Pc with an excess of NaBPh4 in the presence of fullerenes C60 and C70 provides complete dissolution of Sn(IV)Cl2Pc and the formation of blue solutions from which the crystals of [SnPhPc(2-)](+)(BPh4)(-)·C6H14 () or [SnPhPc˙(3-)]·C6H4Cl2 () were selectively isolated. According to the optical spectra, salt contains dianionic Pc(2-) macrocycles, whereas macrocycles are reduced to form the Pc˙(3-) radical trianions in . As a result, the phthalocyanine macrocycle is dianionic in , and the positive charge of Sn(IV) is compensated by the Ph(-), Pc(2-), and BPh4(-) anions in this compound. The formally neutral compound contains two anionic species of Ph(-) and Pc˙(3-) and the Sn(IV) ion as the counter cation. Phenyl substituents are linked to the Sn(IV) atoms by the Sn-C(Ph) bonds of 2.098(2) () and 2.105(2) Å () length. The dianionic Pc(2-) macrocycle significantly deviates from planarity in while Pc˙(3-) is planar in . Salt manifests only a weak impurity EPR signal. Compound manifests an intense EPR signal with g = 2.0046 and a linewidth of 0.5 mT at 298 K due to the presence of Pc˙(3-). Spins are weakly antiferromagnetically coupled in the π-stacking [SnPhPc˙(3-)]2 dimers of with a Weiss temperature of -3 K and the estimated magnetic exchange interaction J/kB = -0.23 K.

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.

On the synthesis of functionalized porphyrins and porphyrin conjugates via β-aminoporphyrins

A two-step methodology to prepare a series ofmeso-tetraarylporphyrin conjugates bearing water-soluble moieties, anchoring groups and receptor subunits.

Anionic coordination complexes of C60 and C70 with cyclopentadienyl and pentamethylcyclopentadienyl molybdenum dicarbonyl

Crystalline molybdenum η²-complexes with fullerenes C₆₀ and C₇₀ in the neutral and negatively charged form were obtained and studied.

Coordination complex of boron subphthalocyanine (BSubPc) with fluorenone pinacolate: effective π–π interaction of concave BSubPc macrocycle with fullerene C60

Dimeric coordination assembly of fluorenone pinacolate (C₂₆H₁₆O₂²⁻) with boron subphthalocyanine (BSubPc) was obtained and studied in the complex with fullerene {(BSubPc)₂(C₂₆H₁₆O₂)}·C₆₀.

Strong antiferromagnetic coupling of spins in the (MDABCO+)(C60·-) salt with 3D close packing of the C60·- radical anions (MDABCO+: N-methyldiazabicyclooctanium cation)

A new salt, (MDABCO(+))(C60(·-)) (1; MDABCO(+) = N-methyldiazabicyclooctanium cation), was obtained as single crystals. The crystal structure of 1 determined at 250 and 100 K showed 3D close packing of fullerenes with eight fullerene neighbors for each C60(·-). These neighbors are located at 10.01-10.11 Å center-to-center distances (250 K) and van der Waals interfullerene C⋅⋅⋅C contacts are formed with four fullerene neighbors arranged in the bc plane. Fullerene ordering observed below 160 K is accompanied by the appearance of one and a half independent C60(·-) and trebling of the unit cell along the b axis. Fullerenes are packed closer to each other at 100 K. As a result, fullerenes are located in the three-dimensional packing at 9.91-10.12 Å center-to-center distances and 18 short interfullerene C⋅⋅⋅C contacts are formed for each C60(·-). Although they are closed packed, fullerenes are not dimerized down to 1.9 K. Magnetic data indicate strong antiferromagnetic coupling of spins in the 70-300 K range with a Weiss temperature of Θ = -118 K. Magnetic susceptibility shows a round maximum at 46 K. Such behavior can be described well by the Heisenberg model for square two-dimensional antiferromagnetic coupling of spins with an exchange interaction of J/kB = -25.3 K. This magnetic coupling is one of the strongest observed for C60(·-) salts.