Trimetallic Nitride Research Articles

89Y and 13C NMR Cluster and Carbon Cage Studies of an Yttrium Metallofullerene Family, Y3N@C2n (n = 40−43)

The members of a new family of yttrium trimetallic nitride-templated (TNT) endohedral metallofullerenes (EMFs), Y(3)N@C(2n) (n = 40-43), have been synthesized and purified. On the basis of experimental and computational (13)C NMR studies, we propose cage structures for Y(3)N@I(h)-C(80) (IPR allowed), Y(3)N@D(5h)-C(80) (IPR allowed), Y(3)N@C(s)-C(82) (non-IPR), Y(3)N@C(s)-C(84) (non-IPR), and Y(3)N@D(3)-C(86) (IPR allowed). A significant result is the limited number of isomers found for each carbon cage. For example, there are 24 isolated pentagon rule (IPR) and 51 568 non-IPR structures possible for the C(84) cage, but only one major isomer of Y(3)N@C(s)-C(84) was found. The current study confirms the unique role of the trimetallic nitride (M(3)N)(6+) cluster template in the Kratschmer-Huffman electric-arc process for fullerene cage size and high symmetry isomer selectivity. This study reports the first (89)Y NMR results for Y(3)N@I(h)-C(80,) Y(3)N@C(s)(51365)-C(84), and Y(3)N@D(3)(19)-C(86), which reveal a progression from isotropic to restricted (Y(3)N)(6+) cluster motional processes. Even more surprising is the sensitivity of the (89)Y NMR chemical shift parameter to subtle changes in the electronic environment at each yttrium nuclide in the (Y(3)N)(6+) cluster (more than 200 ppm for these EMFs). This (89)Y NMR study suggests that (89)Y NMR will evolve as a powerful tool for cluster motional studies of EMFs.

Facile Preparation of a New Gadofullerene-Based Magnetic Resonance Imaging Contrast Agent with High 1H Relaxivity

A new magnetic resonance imaging (MRI) contrast agent based on the trimetallic nitride templated (TNT) metallofullerene Gd(3)N@C(80) was synthesized by a facile method in high yield. The observed longitudinal and transverse relaxivities r(1) and r(2) for water hydrogens in the presence of the water-soluble gadofullerene 2 Gd(3)N@C(80)(OH)(approximately 26)(CH(2)CH(2)COOM)(approximately 16) (M = Na or H) are 207 and 282 mM(-1) s(-1) (per C(80) cage) at 2.4 T, respectively; these values are 50 times larger than those of Gd(3+) poly(aminocarboxylate) complexes, such as commercial Omniscan and Magnevist. This high (1)H relaxivity for this new hydroxylated and carboxylated gadofullerene derivative provides high signal enhancement at significantly lower Gd concentration as demonstrated by in vitro and in vivo MRI studies. Dynamic light scattering data reveal a unimodal size distribution with an average hydrodynamic radius of ca. 78 nm in pure water (pH = 7), which is significantly different from other hydroxylated or carboxylated fullerene and metallofullerene derivatives reported to date. Agarose gel infusion results indicate that the gadofullerene 2 displayed diffusion properties different from those of commercial Omniscan and those of PEG5000 modified Gd(3)N@C(80). The reactive carboxyl functionality present on this highly efficient contrast agent may also serve as a precursor for biomarker tissue-targeting purposes.

High Efficiency Organic Photovoltaic Devices Based on Derivatives of Trimetallic Nitride Endohedral Fullerenes

not Available.

Size effect of fullerene cages and encaged clusters in M3N@C2n

Based on the calculated findings that the sizes of encaged clusters determine the structures and the stability of C80-based trimetallic nitride fullerenes (TNFs), more extensive density functional theory calculations were performed on M3N@C68, M3N@C78 and M3N@C80 (M=Sc, Y and La). The calculated results demonstrated that the structures and stability undergo a transition with the increasing of the sizes of the cages and clusters. Sc3N is planar inside the three considered cages, Y3N is slightly pyramidal inside C68-6140 and C78-5 and planar inside Ih C80-7, however, La3N is pyramidal inside all the three cages. Those cages with pyramidal clusters inside deformed considerably, compared with their parent cages. In these cases, the bonding of metallic atoms toward the cages does not play an important role, and the encaged cluster tends to be located inside the cages with the largest M-M and M-C distances so that the strain energy can be released mostly. These calculations revealed the size effect of fullerene cages and encaged clusters, and can explain the position priority of M3N inside fullerene cages and the differences in yield of M3N@C2n.

Endohedral fullerenes for organic photovoltaic devices

So far, one of the fundamental limitations of organic photovoltaic (OPV) device power conversion efficiencies (PCEs) has been the low voltage output caused by a molecular orbital mismatch between the donor polymer and acceptor molecules. Here, we present a means of addressing the low voltage output by introducing novel trimetallic nitride endohedral fullerenes (TNEFs) as acceptor materials for use in photovoltaic devices. TNEFs were discovered in 1999 by Stevenson et al. ; for the first time derivatives of the TNEF acceptor, Lu(3)N@C(80), are synthesized and integrated into OPV devices. The reduced energy offset of the molecular orbitals of Lu(3)N@C(80) to the donor, poly(3-hexyl)thiophene (P3HT), reduces energy losses in the charge transfer process and increases the open circuit voltage (Voc) to 260 mV above reference devices made with [6,6]-phenyl-C(61)-butyric methyl ester (C(60)-PCBM) acceptor. PCEs >4% have been observed using P3HT as the donor material. This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset.

Metal Nitride Cluster Fullerene M3N@C80 (M=Y, Sc) Based Dyads: Synthesis, and Electrochemical, Theoretical and Photophysical Studies

The first pyrrolidine and cyclopropane derivatives of the trimetallic nitride templated (TNT) endohedral metallofullerenes I(h)-Sc(3)N@C(80) and I(h)-Y(3)N@C(80) connected to an electron-donor unit (i.e., tetrathiafulvalene, phthalocyanine or ferrocene) were successfully prepared by 1,3-dipolar cycloaddition reactions of azomethine ylides and Bingel-Hirsch-type reactions. Electrochemical studies confirmed the formation of the [6,6] regioisomers for the Y(3)N@C(80)-based dyads and the [5,6] regioisomers in the case of Sc(3)N@C(80)-based dyads. Similar to other TNT endohedral metallofullerene systems previously synthesized, irreversible reductive behavior was observed for the [6,6]-Y(3)N@C(80)-based dyads, whereas the [5,6]-Sc(3)N@C(80)-based dyads exhibited reversible reductive electrochemistry. Density functional calculations were also carried out on these dyads confirming the importance of these structures as electron transfer model systems. Furthermore, photophysical investigations on a ferrocenyl-Sc(3)N@C(80)-fulleropyrrolidine dyad demonstrated the existence of a photoinduced electron-transfer process that yields a radical ion pair with a lifetime three times longer than that obtained for the analogous C(60) dyad.

Synthesis and Characterization of a Non-IPR Fullerene Derivative: Sc3N@C68[C(COOC2H5)2

A non-IPR (isolated pentagon rule) trimetallic nitride endohedral metallofullerene derivative, a diethyl malonate adduct of Sc3N@C68, was synthesized, isolated, and characterized by mass spectrometry and NMR spectroscopy. The proposed addition site of Sc3N@C68 monoadduct was in good agreement with the experimental and calculated 13C NMR spectra, LUMO electron density study, and UV−vis spectroscopy.

Lanthanum Nitride Endohedral Fullerenes La3N@C2n (43≤n≤55): Preferential Formation of La3N@C96

While the trimetallic nitrides of Sc, Y and the lanthanides between Gd and Lu preferentially template C(80) cages, M(3)N@C(80), and while those of Ce, Pr and Nd preferentially template the C(88) cage, M(3)N@C(88), we show herein that the largest metallic nitride cluster, La(3)N, preferentially leads to the formation of La(3)N@C(96) and to a lesser extent the La(3)N@C(88). This is the first time that La(3)N is successfully encapsulated inside fullerene cages. La(3)N@C(2n) metallofullerenes were synthesized by arcing packed graphite rods in a modified Krätschmer-Huffman arc reactor, extracted from the collected soot and identified by mass spectroscopy. They were isolated and purified by high performance liquid chromatography (HPLC). Different arcing conditions were studied to maximize fullerene production, and results showed that yields have a high La(2)O(3)/C dependence. Relatively high yields were obtained when a 1:5 ratio was used. Three main fractions, La(3)N@C(88), La(3)N@C(92), and La(3)N@C(96), were characterized by UV/Vis-NIR and cyclic voltammetry. Unlike other trimetallic nitride metallofullerenes of the same carbon cage size, La(3)N@C(88) exhibits a higher HOMO-LUMO gap and irreversible reduction and oxidation steps.

Electrochemistry of Sc3N@C78 embedded in didodecyldimethylammonium bromide films in aqueous solution

The electrochemical behavior of trimetallic nitride clusterfullerene (Sc3N@C78) embedded in films of the cationic surfactant didodecyldimethylammonium bromide (DDAB) on glassy carbon (GC) electrodes in aqueous solution was investigated. Four pairs of reversible redox peaks were observed in the potential range between +0.6 and −0.9 V vs. SCE. Different to the electrochemistry of pristine Sc3N@C78 in organic solution, the first reduction is a one-electron rather than simultaneous two-electron process because of the strong binding between DDA+ and the monoanion of Sc3N@C78. The generated radial monoanion, dianion and trianion of Sc3N@C78 are stable during continuous potential cycling, while some chemical reactions take place when the third anion is further reduced in the films. The cyclic voltammograms of Sc3N@C78/DDAB films checked at different temperatures pointed to strong temperature dependence. The electrochemical processes were also measured in different electrolytes, which showed pronounced anionic dependence and no cathodic dependence on either the cation or anions present. A possible electron-transfer mechanism of a Sc3N@C78/DDAB film was presented.

Purification of Trimetallic Nitride Templated Endohedral Metallofullerenes by a Chemical Reaction of Congeners with Eutectic 9-Methylanthracene

The availability of pure samples is a major hurdle in the study of trimetallic nitride templated endohedral metallofullerenes (TNT EMFs). Current HPLC methods of purification are costly, nonrecyclable, and take considerable time. Reported herein is a solvent-free reaction of crude soot extract (empty-cage and Sc or Lu TNT EMFs) in molten 9-methylanthracene that affords almost complete conversion of empty-cage fullerenes to 9-methylanthracene adducts, while leaving TNT EMFs unreacted. After the recovered extract is washed with diethyl ether, the washed extract can then be applied to a silica gel column and subsequently flushed with toluene. To illustrate for Sc3N@C80, the sample was purified to ∼60% in a time period of 99%) in an expeditious and less costly manner.

Charged States of Sc3N@C68: An In Situ Spectroelectrochemical Study of the Radical Cation and Radical Anion of a Non-IPR Fullerene

The redox behavior of Sc 3N@C 68 is studied systematically by means of electrochemistry, in situ ESR/Vis-NIR spectroelectrochemistry, and detailed theoretical treatment. Formation of the negatively and positively charged paramagnetic species for the same trimetallic nitride endohedral fullerene is demonstrated for the first time. The electrochemical study of Sc 3N@C 68 exhibits two electrochemically irreversible but chemically reversible reduction steps and two reversible oxidation steps. A double-square reaction scheme is proposed to explain the observed redox reaction at cathodic potentials involving the reversible dimerisation of the Sc 3N@C 68 monoanion. The spin state of the radical cation and the radical anion is probed by ESR spectroscopy, indicating that in both states, the large part of the unpaired spin is delocalized on the fullerene cage. The charged states of the non-isolated pentagon rule fullerene are characterized furthermore by in situ absorption spectroscopy. The interpretation of experimental data is supported by the density functional theory (DFT) calculations of the spin distribution in the anion and cation radicals of Sc 3N@C 68 and time-dependent DFT calculations of the absorption spectra of the charged species.

Sc3N@C80‐Ferrocene Electron‐Donor/Acceptor Conjugates as Promising Materials for Photovoltaic Applications

Intriguing materials for photovoltaics: The first trimetallic nitride endohedral metallofullerene covalently connected to a donor group is efficiently synthesized in a 1,3-dipolar cycloaddition reaction. Exclusive formation of the [5,6]-regioisomer in the isolated N-methyl-2-ferrocenyl-Ih-Sc3[email protected]80-fulleropyrrolidine is confirmed by NMR spectroscopy and electrochemistry (see picture). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z800473_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

New M3N@C2n Endohedral Metallofullerene Families (M=Nd, Pr, Ce; n=40–53): Expanding the Preferential Templating of the C88 Cage and Approaching the C96 Cage

Three new families of trimetallic nitride template endohedral metallofullerenes (TNT EMFs), based on cerium, praseodymium, and neodymium clusters, were synthesized by vaporizing packed graphite rods in a conventional Krätschmer-Huffman arc reactor. Each of these families of metallofullerenes was identified and characterized by mass spectroscopy, HPLC, UV/Vis-NIR spectroscopy, and cyclic voltammetry. The mass spectra and HPLC chromatograms show that these larger metallic clusters are preferentially encapsulated by a C(88) cage. When the size of the cluster is increased, the C(96) cage is progressively favored over the predominant C(88) cage. It is also observed that the smaller cages (C(80)-C(86)) almost disappear on going from neodymium to cerium endohedral metallofullerenes. The UV/Vis-NIR spectra and cyclic voltammograms confirm the low HOMO-LUMO gap and reversible electrochemistry of these M(3)N@C(88) metallofullerenes.

The Synthesis and Characterization of Trimetallic Nitride Fullerene Nanopeapods

not Available.

Computational Study on C80 Enclosing Mixed Trimetallic Nitride Clusters of the Form GdxM3-xN (M = Sc, Sm, Lu)

Metallofullerenes of composition GdxM3-xN@C80 with 0 ≤ x ≤ 3 and M = Sc, Sm, Lu, were investigated with respect to their geometric, electronic, energetic, and magnetic properties by Density Functional Theory, using the generalized gradient approximation in combination with an on-site correlation approach. Equilibrium structures were identified for both the free GdxM3-xN (0 ≤ x ≤ 3, M = Sc, Sm, Lu) units and the composite of the trimetallic nitride core and the fullerene cage. Although the core clusters generally tend toward planarity upon encapsulation into C80, some species containing Sm atoms show a reversal of this trend. The electronic interaction between the cage and the core is characterized by the formation of a covalent region between both components. This effect proves to be strongest in those cases where no core rotation has been detected by experiment. Ferromagnetic ordering is favored by the free trimetallic nitride clusters involving Gd and Sm constituents. For GdxM3-xN@C80 (0 ≤ x ≤ 3 and M = Sc, Sm, Lu), the ferromagnetically and antiferromagnetically ordered isomers are seen to be near-degenerate. A slight preference for the former alternative is found for Sm3N@C80 while complexes containing Gd tend toward the latter.

What is stable structure about Tb 3N@C 84? IPR or IPR-violating

The geometric and electronic structures of fullerenes encapsulating trimetallic nitride cluster Tb 3N@C 84 were studied using the density functional theory. Geometric optimization showed that Tb 3N@C 84 that violates the Isolated-Pentagon Rule (IPR) with a pentalene unit formed by fused pentagon pair is the most kinetically stable isomer with the largest energy gap. Compared to IPR-violating Tb 3N@C 84 isomers, IPR-Tb 3N@C 84 is the most thermodynamically favorable endohedral compound with the lowest energy. Tb 3N@C 84 has a higher density of states (DOS) than empty C 84 molecule at the Fermi energy. This indicated that the embedment of Tb 3N unit can increase the conductance of C 84.

Selective Formation of a Symmetric Sc3N@C78 Bisadduct: Adduct Docking Controlled by an Internal Trimetallic Nitride Cluster

In this paper we report a regioselective Bingel−Hirsch reaction of Sc3N@C78 yielding a single mono- and a dominate bis-ethyl malonate derivative for the first time. The Cs-symmetric monoadduct 1 and C2v-symmetric bisadduct 2 were isolated by HPLC and characterized by MS, UV−vis, and NMR spectroscopy. The symmetric bisadduct 2 clearly demonstrate the remarkable regioselectivity control exerted by the encapsulated Sc3N cluster. We have employed a LUMO electron density surface computational approach to predict multiadduct docking sites on the ellipsoidal fullerene cage surface.

Characterization of magnetic and electronic properties of trimetallic nitride endohedral fullerenes by SQUID magnetometry and electron paramagnetic resonance

Magnetic and electronic properties of high-purity trimetallic nitride endohedral fullerenes Er3N@C80, Lu3N@C80, Sc3N@C80 diluted in a diamagnetic host were characterized by SQUID DC magnetometry and electron paramagnetic resonance (EPR) at multiple frequencies. The Er3N@C80 sample followed the Curie–Weiss law with negligible Weiss temperature of 0.16K. Based on temperature dependence and isothermal saturation magnetization the effective magnetic moment of Er3N@C80 was estimated as 10.2μB. The magnetic behavior of these fullerenes is ascribed to quenching of the orbital moment of the metal ions due to interactions between the metal centers with the nitrogen and the fullerene cage.

Preparation and Characterization of Two New Water-Soluble Endohedral Metallofullerenes as Magnetic Resonance Imaging Contrast Agents

Two new water-soluble Gd-containing endohedral metallofullerenes [ScxGd3-xN@C80OmOHn (x = 1, 2; m approximately 12; n approximately 26)] were synthesized in a simple one-step reaction and characterized by Fourier transform (FT)-IR as well as X-ray photoelectron spectroscopy (XPS). Their observed longitudinal relaxivities (R1) for water protons are 20.7 and 17.6 mM(-1) s(-1), respectively, which are significantly higher than that of the commercial magnetic resonance imaging (MRI) contrast agent (Gd-DTPA, 3.2 mM(-1) s(-1)). These results indicate these trimetallic nitride endohedral fullerenols are potential next-generation high-efficiency MRI contrast agents.

The Large Nd3N@C2n (40≤n≤49) Cluster Fullerene Family: Preferential Templating of a C88 Cage by a Trimetallic Nitride Cluster

Nd3N pushes the limits: Unlike all the other encapsulated trimetallic nitride clusters (Sc3N, Y3N, Dy3N, Gd3N, …︁), which prefer a C80 cage, the Nd3N cluster is preferentially encapsulated in a larger C88 cage (see the HPLC trace in the picture). UV/Vis/NIR spectroscopy and electrochemistry performed on the isolated Nd3[email protected]88 fraction show a very small band gap for this compound. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z703489_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.