Partial Charge Transfer in the Shortest Possible Metallofullerene Peapod,La@C82⊂[11]Cycloparaphenylene

[11]Cycloparaphenylene ([11]CPP) selectively encapsulates La@C₈₂ to form the shortest possible metallofullerene–carbon nanotube (CNT) peapod, La@C₈₂?[11]CPP, in solution and in the solid state. Complexation in solution was affected by the polarity of the solvent and was 16 times stronger in the polar solvent nitrobenzene than in the nonpolar solvent 1,2‐dichlorobenzene. Electrochemical analysis revealed that the redox potentials of La@C₈₂ were negatively shifted upon complexation from free La@C₈₂. Furthermore, the shifts in the redox potentials increased with polarity of the solvent. These results are consistent with formation of a polar complex, (La@C₈₂)^δ??[11]CPP^δ+, by partial electron transfer from [11]CPP to La@C₈₂. This is the first observation of such an electronic interaction between a fullerene pea and CPP pod. Theoretical calculations also supported partial charge transfer (0.07) from [11]CPP to La@C₈₂. The structure of the complex was unambiguously determined by X‐ray crystallographic analysis, which showed the La atom inside the C₈₂ near the periphery of the [11]CPP. The dipole moment of La@C₈₂ was projected toward the CPP pea, nearly perpendicular to the CPP axis. The position of the La atom and the direction of the dipole moment in La@C₈₂?[11]CPP were significantly different from those observed in La@C₈₂?CNT, thus indicating a difference in orientation of the fullerene peas between fullerene–CPP and fullerene–CNT peapods. These results highlight the importance of pea–pea interactions in determining the orientation of the metallofullerene in metallofullerene–CNT peapods.     

Electronic Communication between two [10]cycloparaphenylenes and Bis(azafullerene) (C59N)2 Induced by Cooperative Complexation

The complex of [10]cycloparaphenylene ([10]CPP) with bis(azafullerene) (C₅₉N)₂ is investigated experimentally and computationally. Two [10]CPP rings are bound to the dimeric azafullerene giving [10]CPP?(C₅₉N)₂?[10]CPP. Photophysical and redox properties support an electronic interaction between the components especially when the second [10]CPP is bound. Unlike [10]CPP?C₆₀, in which there is negligible electronic communication between the two species, upon photoexcitation a partial charge transfer phenomenon is revealed between [10]CPP and (C₅₉N)₂ reminiscent of CPP‐encapsulated metallofullerenes. Such an alternative electron‐rich fullerene species demonstrates C₆₀‐like ground‐state properties and metallofullerene‐like excited‐state properties opening new avenues for construction of functional supramolecular architectures with organic materials.     

Harnessing Electron Transfer from the Perchlorotriphenylmethide Anion to Y@C82(C2v) to Engineer an Endometallofullerene‐Based Salt

We show that electron transfer from the perchlorotriphenylmethide anion (PTM^?) to Y@C₈₂(C_2v) is an instantaneous process, suggesting potential applications for using PTM^? to perform redox titrations of numerous endohedral metallofullerenes. The first representative of a Y@C₈₂‐based salt containing the complex cation was prepared by treating Y@C₈₂(C_2v) with the [K⁺([18]crown‐6)]PTM^? salt. The synthesis developed involves the use of the [K⁺([18]crown‐6)]PTM^? salt as a provider of both a complex cation and an electron‐donating anion that is able to reduce Y@C₈₂(C_2v). For the first time, the molar absorption coefficients for neutral and anionic forms of the pure isomer of Y@C₈₂(C_2v) were determined in organic solvents with significantly different polarities.     

Size‐ and Orientation‐Selective Encapsulation of C70 by Cycloparaphenylenes

The size‐ and orientation‐selective formation of the shortest‐possible C₇₀ peapod in solution and in the solid state by using the shortest structural unit of an “armchair” carbon nanotube (CNT), cycloparaphenylene (CPP), has been studied. [10]CPP and [11]CPP exothermically formed 1:1 complexes with C₇₀, thereby giving the resulting peapods. A van′t Hoff plot analysis revealed that the formation of these complexes in 1,2‐dichlorobenzene was mainly driven by entropy, whereas the theoretical calculations suggested that the formation of the complex in the gas phase was predominantly driven by enthalpy. C₇₀ was found to exist in two distinct orientations inside the CPP cavity, namely “lying” and “standing”, depending on the specific size of the CPP. The theoretical calculations and the X‐ray crystallographic analysis revealed that the interactions between [10]CPP and the short axis of C₇₀ in its lying orientation were isotropic and similar to those observed between [10]CPP and C₆₀. However, the interactions between [11]CPP and C₇₀ in its standing orientation were anisotropic, thereby involving the radial deformation of [11]CPP into an ellipsoidal shape. This “induced fit” maximized the van der Waals interactions with the long axis of C₇₀. Theoretical calculations revealed that the deformation occurred readily with low energy loss, thus suggesting that CPPs are highly radially elastic molecules. These results also indicate that the same type of radial deformation should occur in CNT peapods that encapsulate anisotropic fullerenes.     

Regioselective Synthesis and Characterization of Multinuclear Convex‐Bound Ruthenium‐[n]Cycloparaphenylene (n=5 and 6) Complexes

Mono‐ and multinuclear complexes of ruthenium and [n]cycloparaphenylene (CPP, n=5 and 6) were synthesized in excellent yields through ligand exchange of the cationic complex [(Cp)Ru(CH₃CN)₃](PF₆) with CPP. In the multinuclear complexes, ruthenium selectively coordinated to alternate paraphenylene units to give bis‐ and tris‐coordinated Ru complexes for [5] and [6]CPPs, respectively. Single‐crystal X‐ray analysis revealed the Ru was coordinated with η⁶‐hapticity on the convex surface of CPP.     

A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in Modular Porphyrin–[10]CPP⊃Fullerene Complexes

Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non‐covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo‐[10]CPP is the key to the synthesis of a porphyrin–[10]CPP conjugate, which binds C₆₀, C₇₀, (C₆₀)₂, and other fullerenes (K_A>10⁵ m ^?1). Fluorescence and pump–probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge‐separated states. The advantage of this approach towards electron donor–acceptor dyads is evident in the case of dumbbell‐shaped (C₆₀)₂, which gave intricate charge‐transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross‐coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.     

Investigation of Cycloparaphenylenes (CPPs) and their Noncovalent Ring-in-Ring and Fullerene-in-Ring Complexes by (Matrix-Assisted) Laser Desorption/Ionization and Density Functional Theory

[n]Cycloparaphenylenes ([n]CPPs) with n=5, 8, 10 and 12 and their noncovalent ring-in-ring and [m]fullerene-in-ring complexes with m=60, 70 and 84 have been studied by direct and matrix-assisted laser desorption ionization ((MA)LDI) and density-functional theory (DFT). LDI is introduced as a straightforward approach for the sensitive analysis of CPPs, free from unwanted decomposition and without the need of a matrix. The ring-in-ring system of [[10]CPP⊃[5]CPP]^+. was studied in positive-ion MALDI. Fragmentation and DFT indicate that the positive charge is exclusively located on the inner ring, while in [[10]CPP⊃C₆₀]^+. it is located solely on the outer nanohoop. Positive-ion MALDI is introduced as a new sensitive method for analysis of CPP⊃fullerene complexes, enabling the detection of novel complexes [[12]CPP⊃C_{60, 70 and 84}]^+. and [[10]CPP⊃C₈₄]^+.. Selective binding can be observed when mixing one fullerene with two CPPs or vice versa, reflecting ideal size requirements for efficient complex formation. Geometries, binding and fragmentation energies of CPP⊃fullerene complexes from DFT calculations explain the observed fragmentation behavior.     

In‐Depth Understanding of the Chemical Properties of Rarely Explored Carbide Cluster Metallofullerenes: A Case Study of Sc2C2@C3v(8)‐C82 that Reveals a General Rule

The chemical properties of carbide‐cluster metallofullerenes (CCMFs) remain largely unexplored, although several new members of CCMFs have been discovered recently. Herein, we report the reaction between Sc₂C₂@C_3v(8)‐C₈₂, which is viewed as a prototypical CCMF because of its high abundance, and 3‐triphenylmethyl‐5‐oxazolidinone ( 1 ) to afford the corresponding pyrrolidino derivative Sc₂C₂@C_3v(8)‐C₈₂(CH₂)₂NTrt ( 2 ; Trt=triphenylmethyl). Single‐crystal X‐ray crystallography studies of 2 revealed that the reaction takes place at a [6,6]‐bond junction, which is directly over the encapsulated C₂ unit and is far from either of the two scandium atoms. On the basis of theoretical calculations and by considering previously reports, we have found that a hexagonal carbon ring on the cage of Sc₂C₂@C_3v(8)‐C₈₂ is highly reactive toward different reagents due to the overlap of high p‐orbital axis vector (POAV) angles and large LUMO coefficients. We propose that this highly concentrated area of reactivity is generated by the encapsulation of the Sc₂C₂ cluster because this region is absent from the empty fullerene C_3v(8)‐C₈₂. Moreover, the absorption and electrochemical results confirm that derivative 2 is more stable than pristine Sc₂C₂@C_3v(8)‐C₈₂, thus illuminating its potential applications.     

Structure of the Au23−xAgx(S‐Adm)15 Nanocluster and Its Application for Photocatalytic Degradation of Organic Pollutants

Ligands play an important role in determining the atomic arrangement within the metal nanoclusters. Here, we report a new nanocluster [Au_23?xAg_x(S‐Adm)₁₅] protected by bulky adamantanethiol ligands which was obtained through a one‐pot synthesis. The total structure of [Au_23?xAg_x(S‐Adm)₁₅] comprises an Au_13?xAg_x icosahedral core, three Au₃(SR)₄ units, and one AgS₃ staple motif in contrast to the 15‐atom bipyramidal core previously seen in [Au_23?xAg_x(SR)₁₆]. UV/Vis spectroscopy indicates that the HOMO–LUMO gap of [Au_23?xAg_x(S‐Adm)₁₅] is 1.5 eV. DFT calculations reveal that [Au₁₉Ag₄(S‐Adm)₁₅] is the most stable structure among all structural possibilities. Benefitting from Ag doping, [Au_23?xAg_x(S‐Adm)₁₅] exhibits drastically improved photocatalytic activity for the degradation of rhodamine B (RhB) and phenol under visible‐light irradiation compared to Au₂₃ nanoclusters.     

Synthesis of endohedral di-and monometallofullerenes Y<Subscript>2</Subscript>@C<Subscript>84</Subscript>, Ce<Subscript>2</Subscript>@C<Subscript>78</Subscript>, and M@C<Subscript>82</Subscript> (M = Y,Ce)

Endohedral metallofullerenes Y₂@C₈₄, Ce₂@C₇₈, and M@C₈₂ (M = Y, Ce) were synthesized by the electric arc method and isolated from the soot using extraction with o-dichlorobenzene. Pure (98%) endohedral dimetallofullerenes Y₂@C₈₄ and Ce₂@C₇₈ were isolated for the first time from o-dichlorobenzene extracts using HPLC and characterized by mass spectrometry and spectrophotometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2067–2071, November, 2007.     

Bingel–Hirsch Addition on Endohedral Metallofullerenes: Kinetic Versus Thermodynamic Control

An extensive theoretical study of the Bingel–Hirsch addition of bromomalonate on scandium nitride endohedral fullerenes has been carried out. The prototypical and highly symmetrical Sc₃N@I_h‐C₈₀, with a structure that satisfies the isolated pentagon rule (IPR), and the non‐IPR Sc₃N@D₃(6140)‐C₆₈ fullerene show analogous reaction paths despite the distinct topology of the carbon networks and different rotation freedom of the internal nitride cluster. For the two metallofullerenes, our results predict that the reaction takes place under kinetic control yielding open‐cage fulleroids on [6,6] bonds, which is in good agreement with experimental data. The theoretical studies also show that predicting the reactivity of endohedral metallofullerenes is not straightforward and often an accurate analysis of the potential energy surface is required.     

Theoretical and Quantitative Structural Relationship Studies of Electrochemical Properties of the Nanostructures of Cis-Unsaturated Thiocrown Ethers and Their Supramolecular Complexes [X-UT-Y][M@C82] (M˭Ce,Gd)

The endohedral lanthanidofullerenes, an important type of organolanthanides, are stabilized by the delocalization of the negative charges on the cages of fullerenes. Since the discovery of these classes of carbon compounds and their unusual structures and properties of these molecules, many potential applications have been suggested. Unsaturated thiocrown ethers with cis-geometry are a group of crown ethers that, in light of the size of their cavities and their conformational restriction compared to a corresponding saturated system (1–9), demonstrate interesting properties for physicochemical studies. Endohedral lanthanidofullerenes M@C_x (x = 82 and M = Ce, Gd) were introduced as a new class of the spherical fullerene group with unique properties. Formation of endohedral metallofullerenes is thought to involve the transfer of electrons from the encapsulated metal atom(s) to the surrounding fullerene cage. Two of these molecules are the Ce@C₈₂ (10) and Gd@C₈₂ (11). The supramolecular complexes of 1–9 with Ce@C₈₂ (10) and Gd@C₈₂ (11) have been shown to possess a host–guest interaction for electron transfer processes, and these behaviors have previously been reported. Topological indices have been successfully used to construct effective and useful mathematical methods for finding good relationships between structural data and the various chemical and physical properties. To establish a good structural relationship between the structures of 1–9 and M@C_x that were introduced here, an index that is represented as μ_cs was utilized. This index is the ratio of summation of the number of carbon atoms (n_c ) and the number of sulfur atoms (n_s ) to the product of these two numbers for 1–9. In this study, the relationship between this index and oxidation potential ( ^oxE₁ ) of 1–9, as well as the free energy of electron transfer (ΔG_et , by the Rehm-Weller equation) between 1–9 and 10 and 11 as [X-UT-Y][Ce@C₈₂] (12) and [X-UT-Y][Gd@C₈₂] (13) complexes, is presented.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

The Unanticipated Dimerization of Ce@C2v(9)‐C82 upon Co‐crystallization with Ni(octaethylporphyrin) and Comparison with Monomeric M@C2v(9)‐C82 (M = La,Sc, and Y)

We report that Ce@C_2v(9)‐C₈₂ forms a centrosymmetric dimer when co‐crystallized with Ni(OEP) (OEP = octaethylporphyrin dianion). The crystal structure of {Ce@C_2v(9)‐C₈₂}₂?2[Ni(OEP)]?4 C₆H₆ shows that a new C?C bond with a bond length of 1.605(5) Å connects the two cages. The high spin density of the singly occupied molecular orbital (SOMO) on the cage and the pyramidalization of the cage are factors that favor dimerization. In contrast, the treatment of Ni(OEP) with M@C_2v(9)‐C₈₂ (M = La, Sc, and Y) results in crystallization of monomeric endohedral fullerenes. A systematic comparison of the X‐ray structures of M@C_2v(9)‐C₈₂ (M = Sc, Y, La, Ce, Gd, Yb, and Sm) reveals that the major metal site in each case is located at an off‐center position adjacent to a hexagonal ring along the C₂ axis of the C_2v(9)‐C₈₂ cage. DFT calculations at the M06‐2X level revealed that the positions of the metal centers in these metallofullerenes M@C_2v(9)‐C₈₂ (M = Sc, Y, and Ce), as determined by single‐crystal X‐ray structure studies, correspond to an energy minimum for each compound.     

Concise Synthesis and Facile Nanotube Assembly of a Symmetrically Multifunctionalized Cycloparaphenylene

The concise synthesis of C₃‐symmetrical [12]CPP‐hexacarboxylate has been achieved through macrocyclization by the rhodium‐catalyzed intermolecular cross‐cyclotrimerization and subsequent reductive aromatization. C₃‐Symmetrical functionalization of CPP with highly polar alkoxycarbonyl groups enabled the structurally uniform nanotube assembly in the crystalline state through multiple hydrogen‐bonding interactions giving a dimer followed by one‐dimensional stacking.     

Characterization of Tetracyanopyridine (TCNPy)‐Based Magnets: V[TCNPy]2⋅z (CH2Cl2) (Tc=111 K) and V[TCNPy]3⋅z (CH2Cl2) (Tc=90 K)

The reaction of 2,3,5,6‐tetracyanopyridine (TCNPy) with V(CO)₆ in CH₂Cl₂ forms new organic‐based magnets of V[TCNPy]_x?z (CH₂Cl₂) (x=2, 3) composition. Analysis of the IR spectra suggests that the TCNPy is reduced and coordinated to V^II sites through the nitriles. V[TCNPy]_x order as ferrimagnets with 111 and 90 K T_c values for V[TCNPy]₂ and V[TCNPy]₃, respectively. Their respective remanent magnetizations and coercive fields are 1260 and 250 emuOe mol^?1 and 9 and 6 Oe at 5 K, and they exhibit some spin‐glass behavior.     

Strain‐Induced Double Carbon–Carbon Bond Activations of Cycloparaphenylenes by a Platinum Complex: Application to the Synthesis of Cyclic Diketones

The carbon–carbon (C?C) bond activation of [n]cycloparaphenylenes ([n]CPPs) by a transition‐metal complex is herein reported. The Pt⁰ complex Pt(PPh₃)₄ regioselectively cleaves two C?C σ bonds of [5] CPP and [6]CPP to give cyclic dinuclear platinum complexes in high yields. Theoretical calculations reveal that the relief of ring strain drives the reaction. The cyclic complex was further transformed into a cyclic diketone by using a CO insertion reaction.     

The Cage and Metal Effect: Spectroscopy and Electrochemical Survey of a Series of Sm‐Containing High Metallofullerenes

A series of Sm‐containing high metallofullerenes, namely, Sm@C₈₂ (I, II, III, IV), Sm@C₈₄ (I, II, III), Sm@C₈₆, Sm@C₈₈ (I, II, III), Sm@C₉₀ (I, II, III), Sm@C₉₂ (I, II), Sm@C₉₄ (I, II, III), and Sm@C₉₆, is successfully synthesized and characterized by UV/Vis/NIR absorption spectroscopy, and cyclic and differential pulse voltammetry. Sm‐containing high metallofullerenes have a relatively larger number of isomers compared with other divalent ones. The highest boiling point of Sm among Group II metals may be responsible for this phenomenon. Comparing the spectroscopic and electrochemical behaviors of Sm‐containing metallofullerenes with those of other divalent ones, it is seen that when the size of the carbon cage enlarges, different structures form stable molecules with different metals. Furthermore, there are also some important differences in the electrochemistry properties. The cage effect on the electronic structures of high metallofullerenes is also estimated from the differences in reduction potentials between metallofullerenes and their corresponding fullerenes. It is believed that the influence of transferred electrons from the metal to the carbon cage becomes much weaker for high fullerenes. The redox property of high metallofullerene is more dependent on the carbon‐cage structure than the effect of electron transfer.     

A Complete Guide on the Influence of Metal Clusters in the Diels–Alder Regioselectivity of Ih‐C80 Endohedral Metallofullerenes

The chemical functionalization of endohedral metallofullerenes (EMFs) has aroused considerable interest due to the possibility of synthesizing new species with potential applications in materials science and medicine. Experimental and theoretical studies on the reactivity of endohedral metallofullerenes are scarce. To improve our understanding of the endohedral metallofullerene reactivity, we have systematically studied with DFT methods the Diels–Alder cycloaddition between s‐cis‐1,3‐butadiene and practically all X@I_h‐C₈₀ EMFs synthesized to date: X=Sc₃N, Lu₃N, Y₃N, La₂, Y₃, Sc₃C₂, Sc₄C₂, Sc₃CH, Sc₃NC, Sc₄O₂ and Sc₄O₃. We have studied both the thermodynamic and kinetic regioselectivity, taking into account the free rotation of the metallic cluster inside the fullerene. This systematic study has been made possible through the use of the frozen cage model (FCM), a computationally cheap approach to accurately predicting the exohedral regioselectivity of cycloaddition reactions in EMFs. Our results show that the EMFs are less reactive than the hollow I_h‐C₈₀ cage. Except for the Y₃ cluster, the additions occur predominantly at the [5,6] bond. In many cases, however, a mixture of the two possible regioisomers is predicted. In general, [6,6] addition is favored in EMFs that have a larger charge transfer from the metal cluster to the cage or a voluminous metal cluster inside. The present guide represents the first complete and exhaustive investigation of the reactivity of I_h‐C₈₀‐based EMFs.     

Synthesis,spectroscopic, thermal and biological aspects of drug‐based copper(II) complexes

A series of novel complexes of the type Cu(II)(L_n)₂(H₂O)₂]^•xH₂O [where L_n = L _1–4 , these ligands being described as: L ₁ , 2‐({4‐[6,7‐dihydrothieno[3,2‐c]pyridin‐5(4H)‐ylsulfonyl]phenylimino}methyl)phenol, x = 1; L ₂ , 2‐({4‐[6,7‐dihydrothieno[3,2‐c] pyridin‐5(4H)‐ylsulfonyl]phenylimino}methyl)‐5‐(methoxy)phenol, x = 2; L ₃ , 5‐chloro‐2‐({4‐[6,7‐dihydrothieno[3,2‐c]pyridin‐5(4H)‐ylsulfonyl]phenylimino}methyl)phenol, x = 2; and L ₄ , 5‐bromo‐4‐chloro‐2‐({4‐[6,7‐dihydrothieno[3,2‐c]pyridin‐5(4H)‐ylsulfonyl]phenylimino} methyl)phenol, x = 1] was investigated. They were characterized by elemental analysis, IR, ¹H‐NMR, ¹³C‐NMR and electronic spectra, magnetic measurements and thermal studies. The FAB‐mass spectrum of [Cu(II)( L ₁ )₂(H₂O)₂]^•H₂O was determined. A magnetic moment and reflectance spectral study revealed that an octahedral geometry could be assigned to all the prepared complexes. Ligands (L_n) and their metal complexes were screened for their in vitro antibacterial activity against Bacillus subtillis, Pseudomonas aeruginosa, Escherichia coli and Serratia marcescens bacterial strains. Kinetic parameters such as order of reaction (n), the energy of activation (E_a), the pre‐exponential factor (A), the activation entropy (ΔS^≠), the activation enthalpy (ΔH^≠) and the free energy of activation (ΔG^≠) are reported. Copyright © 2011 John Wiley & Sons, Ltd.     

Visible and near-IR spectroscopy of endohedral Gd@C82(C 2v ) and Ho@C82(C 2v ) metallofullerenes and their monoanions

Solutions of endohedral Gd@C₈₂(C _2v ) and Ho@C₈₂(C _2v ) metallofullerenes are studied by means of visible and near-IR spectroscopy upon their conversion from neutral to the anionic form via a redox reaction with the electron donor potassium perchlorotriphenylmethide K(18-crown-6)[C(C₆Cl₅)₃]. The concentrations of the studied solutions of endohedral Gd@C₈₂(C _2v ) and Ho@C₈₂(C _2v ) metallofullerenes in o-dichlorobenzene were determined from the spectroscopic data, and their molar extinction coefficients are calculated.