Organometallic hydrides as reactants in fullerene chemistry. Interaction of C60 and C70 fullerenes with HIr(CO)(PPh3)3

The iridium hydride complex HIr(CO)(PPh₃)₃ reacts with fullerenes C₆₀ and C₇₀ yielding (²-C_n)IrH(CO)(PPh₃)₂ (n = 60, 70) complexes. Their composition, configuration, and the position of the double bond coordinated with the metal atom in the fullerene moiety have been established by IR studies (comparison with deuterated analogs), and¹H and³¹P NMR spectroscopy.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1661–1665, September, 1994.The present work was financialy supported by the Russian Foundation for Basic Research (Project No. 93-09-18725) and the International Science Foundation (Project No. MNR 000).     

Lewis acid promoted preparation of isomerically pure fullerenols from fullerene peroxides C60(OOt-Bu)6 and C60(O)(OOt-Bu)6

Fullerene mixed peroxides C60(t-BuOO)6 and C60(O)(t-BuOO)6 react with Lewis acids to form various fullerenols through the partial fragmentation of t-BuOO groups. Two monohydroxyl fullerenols with the general formula C60(OH)(t-BuOO)5 and six monohydroxyl fullerenols with the general formula C60(O)(OH)(t-BuOO)5 were prepared, which are essentially the same except the location of the OH group. An additional reaction of the monohydroxyl fullerenols gave bis- and trishydroxyl fullerenols. Single-crystal X-ray structures have been obtained for the two monohydroxyl fullerenols. Other compounds are characterized by chemical correlation and their spectroscopic data. Cuprous bromide could protect the most reactive t-BuOO group from being attacked by stronger Lewis acids. The proposed mechanism mainly involves Lewis acid induced heterolysis of the peroxo O-O bond.     

From fullerene-mixed peroxide to open-cage oxafulleroid C(59)(O)(3)(OH)(2)(OO(t)()Bu)(2) embedded with furan and lactone motifs

[reaction: see text] Removal of one carbon atom from the C60 cage is achieved under mild conditions. The process involves the formation of fullerene-mixed peroxide, subsequent Lewis acid induced cleavage of O-O and C-O bonds, and thermolysis at 75 degrees C. In the proposed mechanism, the carbon atom is deleted as CO and an oxygen atom occupies the vacancy to form a furan ring. Single-crystal X-ray analysis confirmed the results.     

Singly-bonded fullerene dimers: neutral (C(60)Cl(5))(2) and cationic (C(70))(2)(2+)

C(60)Br(24) and C(70)Br(10) react with TiCl(4), splitting out bromine, and, after Br/Cl exchange, forming singly-bonded dimeric structures (C(60)Cl(5))(2) and [(C(70))(2)](Ti(3)Cl(13))(2), respectively, the latter consisting of dimeric [(C(70))(2)](2+) dications and (Ti(3)Cl(13))(-) anions.     

The reaction of fullerene C(60) with 4,6-dimethyl-1,2,3-triazine: formation of an open-cage fullerene derivative.

A thermal reaction of fullerene C(60) with 4,6-dimethyl-1,2,3-triazine (4) in o-dichlorobenzene gave azacyclohexadiene-fused fullerene derivative 5, by the reaction with intermediate azete 11, and then, after flash chromatography over SiO(2), open-cage fullerene derivative 6 having an eight-membered ring orifice on the C(60) cage. Compound 6 is assumed to be formed via addition of diradical intermediate 13 to C(60). Compound 6 underwent a further photochemical reaction with singlet oxygen with the cleavage of one of the double bonds at the rim of the orifice to afford triketone derivative 8 having a 12-membered ring orifice.     

Determination of the rate constants of addition of.P(O)(OPri)2 radicals to fullerenes C60 and C70

The rate constants of the addition of phosphoryl radicals to fullerenes C₆₀ and C₇₀ were determined by the method of competitive reactions. The phosphoryl radicals were shown to be 1.5–3 orders of magnitude more reactive than the carbon-centered radicals. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1652–1655, September, 2000.     

The Interaction of C60, C70, and C60(CN)2 radical anions with cobalt(II) tetraphenylporphyrin in solid multicomponent complexes

A method for the synthesis of the multicomponent ionic complexes: [Cr(I)(C(6)H(6))(2) (.+)][Co(II)(tpp)(fullerene)(-)].C(6)H(4)Cl(2), comprising bis(benzene)chromium (Cr(C(6)H(6))(2)), cobalt(II) tetraphenylporphyrin (Co(II)(tpp)), fullerenes (C(60), C(60)(CN)(2), and C(70)), and o-dichlorobenzene (C(6)H(4)Cl(2)) has been developed. The monoanionic state of the fullerenes has been proved by optical absorption spectra in the UV/vis/NIR and IR ranges. The crystal structures of the ionic [[Cr(I)(C(6)H(6))(2)](.+)](1.7)[[Co(II)(tpp)(C(60))](2)](1.7-). 3.3 C(6)H(4)Cl(2) and [[Cr(I)(C(6)H(6))(2)] (.+)](2)[Co(II)(tpp)[C(60)(CN)(2)]](-)[C(60)(CN)(2) (.-)]).3 C(6)H(4)Cl(2) are presented. The essentially shortened Co.C(fullerene) bond lengths of 2.28-2.32 A in these complexes indicate the formation of sigma-bonded [Co(II)(tpp)][fullerene](-) anions, which are diamagnetic. All the ionic complexes are semiconductors with room temperature conductivity of 2 x 10(-3)-4 x 10(-6) S cm(-1), and their magnetic susceptibilities show Curie-Weiss behavior. The neutral complexes of Co(II)(tpp) with C(60), C(60)(CN)(2), C(70), and Cr(0)(C(6)H(6))(2), as well as the crystal structures of [Co(II)(tpp)](C(60)).2.5 C(6)H(4)Cl(2), [Co(II)(tpp)](C(70)). 1.3 CHCl(3).0.2 C(6)H(6), and [Cr(0)(C(6)H(6))(2)][Co(II)(tpp)] are discussed. In contrast to the ionic complexes, the neutral ones have essentially longer Co.C(fullerene) bond lengths of 2.69-2.75 A.     

An insight into the aromaticity of fullerene anions: experimental evidence for diamagnetic ring currents in the five-membered rings of C(60)(6-) and C(70)(6-)

Reduction of the two "closed" [6,6] methanofullerenes, [6,6]C(61)H(2) (1) and [6,6]C(71)H(2) (5), to the corresponding hexaanions with lithium metal causes the bridgehead-bridgehead bonds to open, at least partially, and this change gives rise to diamagnetic ring currents in the resulting homoconjugated six-membered rings (6-MRs). These new ring currents shield the overlying hydrogen atoms on the methylene bridge and induce upfield shifts of 1.60 and 0.11 ppm in their (1)H NMR resonances, respectively. Analogous reduction of the already "open" [5,6]methanofullerenes, [5,6]C(61)H(2) (2) and [5,6]C(71)H(2) (3 and 4), only slightly enhances the shielding of the hydrogen atoms over the homoconjugated 6-MRs (upfield shifts of 0.13, 0.68, and 0.14 ppm, respectively) but leads to exceptionally strong diamagnetic ring currents in the homoconjugated five- membered rings (5-MRs), as evidenced by dramatic shielding of the hydrogen atoms situated over them (upfield shift of 5.01, 6.78, and 1.63 ppm, respectively). The strongest shielding is seen for the hydrogen atom sitting over the 5-MR at the pole of C(71)H(2)(6)(-) (delta = -0.255 ppm) indicating that the excess charge density is concentrated at the poles.     

Synthesis, crystal structure and photoconductivity of the first [60]fullerene complex with metal diethyldithiocarbamate: {CuII(dedtc)2}2.C60

The first molecular complex of fullerene C60 with metal dithiocarbamate, namely, {CuII(dedtc)2}2.C60(dedtc: diethyldithiocarbamate) (1) was obtained as single crystals. Butterfly-shaped CuII(dedtc)2 molecules efficiently co-crystallized with spherical fullerene molecules to form a layered structure, in which closely packed hexagonal C60 layers alternate with the layers composed of CuII(dedtc)2 dimers. The formation of the complex with C60 changes geometry and the EPR spectrum of starting CuII(dedtc)2. Magnetic susceptibility of 1 follows the Curie-Weiss law in the 300-1.9 K range with the negative Weiss constant of -2.5 K showing a weak antiferromagnetic interaction between CuII centers in the dimers. The crystals of 1 have low dark conductivity of 10(-11) S cm-1, which is consistent with a neutral ground state of the complex. Illumination of the crystals by white light increases the photocurrent by 20-50 times. The photoconductivity spectrum of 1 has a maximum at 470 nm showing that both intermolecular charge transfer between neighboring C60 molecules and photoexcitation of CuII(dedtc)2 can contribute to photogeneration of free charge carriers. The effect of a weak magnetic field with Bo<0.5 T on the photoconductivity of 1 has been found.     

Syntheses, luminescence behavior, and assembly reaction of tetraalkynylplatinate(II) complexes: crystal structures of [Pt((t)Bu(3)trpy)(Ctbd1;CC(5)H(4)N)Pt((t)Bu(3)trpy)](PF(6))(3) and [Pt(2)Ag(4)(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(8)(THF)(4)

A series of tetraalkynylplatinate(II) complexes, (NBu(4))(2)[Pt(Ctbd1;CR)(4)] (R = C(6)H(4)N-4, C(6)H(4)N-3, and C(6)H(3)N(2)-5), and the diynyl analogues, (NBu(4))(2)[Pt(Ctbd1;CCtbd1;CR)(4)] (R = C(6)H(5) and C(6)H(4)CH(3)-4), have been synthesized. These complexes displayed intense photoluminescence, which was assigned as metal-to-ligand charge transfer (MLCT) transitions. Reaction of (Bu(4)N)(2)[Pt(Ctbd1;CC(5)H(4)N-4)(4)] with 4 equiv of [Pt((t)Bu(3)trpy)(MeCN)](OTf)(2) in methanol did not yield the expected pentanuclear platinum product, [Pt(Ctbd1;CC(5)H(4)N)(4)[Pt((t)Bu(3)trpy)](4)](OTf)(6), but instead afforded a strongly luminescent 4-ethynylpyridine-bridged dinuclear complex, [Pt((t)Bu(3)trpy)(Ctbd1;CC(5)H(4)N)Pt((t)Bu(3)trpy)](PF(6))(3,) which has been structurally characterized. The emission origin is assigned as derived from states of predominantly (3)MLCT [d(pi)(Pt) --> pi((t)Bu(3)trpy)] character, probably mixed with some intraligand (3)IL [pi --> pi(Ctbd1;C)], and ligand-to-ligand charge transfer (3)LLCT [pi(Ctbd1;C) --> pi((t)()Bu(3)trpy)] character. On the other hand, reaction of (Bu(4)N)(2)[Pt(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(4)] with [Ag(MeCN)(4)][BF(4)] gave a mixed-metal aggregate, [Pt(2)Ag(4)(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(8)(THF)(4)]. The crystal structure of [Pt(2)Ag(4)(Ctbd1;CCtbd1;CC(6)H(4)CH(3)-4)(8)(THF)(4)] has also been determined. A comparison study of the spectroscopic properties of the hexanuclear platinum-silver complex with its precursor complex has been made and their spectroscopic origins were suggested.     

Formation of antiferromagnetically coupled C(60)(*)(-) and diamagnetic (C(70)(-))(2) dimers in ionic complexes of fullerenes with (MDABCO(+))(2).M(II)TPP (M = Zn, Co, Mn, and Fe) assemblies

A series of ionic multicomponent complexes comprising C60 and C70 anions and coordinating assemblies of methyldiazabicyclooctane cations with metal tetraphenylporphyrins, (MDABCO+)2.MIITPP.(C60(70)-)2.Sol. (C60, M = Zn (1); C60, M = Co (2); C60, M = Mn (3); C60, M = Fe (4); C70, M = Mn (5); and C70, M = Fe (6)) has been obtained. IR- and UV-vis-NIR spectra of 1-6 justified the formation of C60*- in 1-4 and single-bonded (C70-)2 dimers in 5 and 6. Co and Mn atoms are six-coordinated in the (MDABCO+)2.MIITPP units with relatively long M-N bonds of 2.475(2), 2.553(2), and 2.511(3) A for 2, 3, and 5, respectively. Isostructural complexes 2 and 3 contain C60*- zigzag chains separated by the (MDABCO+)2.MIITPP units, whereas in 5 the layers formed by the (C70-)2 dimers alternate with those composed of the (MDABCO+)2.MnIITPP units and noncoordinating MDABCO+ cations. Negative Weiss constants of -13 (1), -2 (3), and -2 (4) K indicate the antiferromagnetic interaction of spins, which decreases the magnetic moment of the complexes below 70-120 K. The EPR signals of 1 and 4 attributed to C60*- are split into two components at the same temperatures, which broaden and shift to higher and lower magnetic fields with the temperature decrease. Complexes 2 and 3 show single EPR signals with g-factors equal to 2.1082 and approximately 2.4 at 293 K, respectively. These values are mean between those characteristic of MIITPP and C60*-, and, consequently, the signals appear due to exchange coupling between these paramagnetic species. The antiferromagnetic ordering of C60*- spins below 70-100 K shifts g-factor values closer to those characteristic of individual MIITPP (g = 2.1907 (2) and approximately 4.9 (3) at 4 K). In contrast to 1-4, complex 5 shows paramagnetic behavior with Weiss constant close to 0.     

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二苯硒醚(TPDASe)间光诱导电子转移过程的激光光解研究

富勒烯(C60／C70)与N，N，N’，N’-四-(对甲苯基)-4，4’-二胺-1，1’-二 苯硒醚(TPDASe)间在激光光诱导条件下，发生了分子间的电子转移过程．在可见- 近红外区(600-1200nm)，观测到了TPDASe阳离子自由基、富勒烯(C60／C70)激发三 线态和阴离子自由基，在苯腈溶液中，观测瞬态谱测定了电子从TPDASe转移到富勒 烯(C60／C70)激发三线态的量子转化产率(Φet^T)和电子转移常数(Ket)．     

Preparation, Crystal Structures, and Isomerization of the Tellurium Diimide Dimers RNTe(&mgr;-NR')(2)TeNR (R = R' = (t)Bu; R = PPh(2)NSiMe(3), R' = (t)Bu, (t)Oct): X-ray Structure of the Telluradiazole Dimer [(t)Bu(2)C(6)H(2)N(2)Te](2)

The reaction of R'NHLi (R = (t)Bu, (t)Oct) with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene at -78 degrees C, followed by warming to 23 degrees C, produces the tellurium diimide dimers RNTe(&mgr;-NR')(2)TeNR (2a, R' = (t)Bu, R = NPPh(2)NSiMe(3); 2b, R' = (t)Oct, R = NPPh(2)NSiMe(3)) and Ph(2)P(NHSiMe(3))(NSiMe(3)). X-ray analyses revealed that 2a and 2b have centrosymmetric structures containing a planar four-membered Te(2)N(2) ring and short exocyclic tellurium-nitrogen bond lengths (d(Te-N) = 1.900(5) and 1.897(4) or 1.905(4) ? for 2a and 2b, respectively). The exocyclic imido substituents adopt a trans arrangement with respect to the Te(2)N(2) ring. By contrast, the reaction of 2,4,6-(t)Bu(3)C(6)H(2)NHLi with Ph(2)P(NSiMe(3))(2)Te(Cl)NPPh(2)NSiMe(3) in toluene under similar conditions produces the telluradiazole ((t)Bu(2)C(6)H(2)N(2)Te)(2) (3), which exists as a weakly associated dimer in the solid state with intramolecular Te-N distances of 2.628(4) ?. The tellurium diimide dimer (t)BuNTe(&mgr;-N(t)Bu)(2)TeN(t)Bu (2c'), prepared by the reaction of TeCl(4) with (t)BuNHLi in a 1:4 molar ratio, consists of a folded Te(2)N(2) ring with exocyclic N(t)Bu groups in a cis orientation. The (1)H, (31)P, and (125)Te NMR spectra of 2a and 2b indicate that the trans isomers slowly transform into the corresponding cis isomers in solution. Crystals of 2b are triclinic, space group P&onemacr; (No. 2), with a = 13.304(3) ?, b = 16.927(3) ?, c = 13.292(5) ?, alpha = 98.94(2), beta = 109.27(2), gamma = 69.04(2) degrees, V = 2636(1) ?(3), and Z = 4. The final R and R(w) values were 0.034 and 0.033, respectively. Crystals of 2c' are orthorhombic, space group Pnma (No. 62), with a = 9.535(3) ?, b = 14.264(3) ?, c = 16.963(4) ?, V = 2307.1(9) ?(3), and Z = 4. The final R and R(w) values were 0.040 and 0.040, respectively. Crystals of 3 are monoclinic, space group P2(1)/n (No. 14), with a = 9.117(3) ?, b = 11.481(4) ?, c = 16.550(4) ?, beta = 97.76(2) degrees, V = 1716.5(8) ?(3), and Z = 4. The final R and R(w) values were 0.031 and 0.034, respectively.     

富勒烯(C60/C70)与N,N,N',N'一四-(对甲苯基)-4,4'-二胺-1,1'-二苯硒醚(TPDASe)间光诱导电子转移过程的激光光解研究

富勒烯(C60/Z70)与N,N,N',N'-四-(对甲苯基)-4,4'-二胺-1,1'-二苯硒醚(TPDASe)间在激光光诱导条件下,发生了分子间的电子转移过程.在可见-近红外区(600～1200mm),观测到了TPDASe阳离子自由基、富勒烯(C60/C70)激发三线态和阴离子自由基,在苯腈溶液中,观测瞬态谱测定了电子从TPDASe转移到富勒烯(C60/C70)激发三线态的量子转化产率(ΦT et)和电子转移常数(Ket).     

Tris(tert-butoxy)siloxy derivatives of boron,including the boronous acid HOB[OSi(O(t)Bu)(3)](2) and the metal (siloxy)boryloxide complex Cp(2)Zr(Me)OB[OSi(O(t)Bu)(3)](2): a remarkable crystal structure with 18 independent molecules in its asymmetric unit

Silanolysis of B(O(t)Bu)(3) with 2 and 3 equiv of HOSi(O(t)Bu)(3) led to the formation of (t)BuOB[OSi(O(t)Bu)(3)](2) (1) and B[OSi(O(t)Bu)(3)](3) (2), respectively. Compounds 1 and 2 are efficient single-source molecular precursors to B/Si/O materials via thermolytic routes in nonpolar media, as demonstrated by the generation of BO(1.5).2SiO(2) (BOSi2(xg)) and BO(1.5).3SiO(2) (BOSi3(xg)) xerogels, respectively. Use of a block copolymer template provided B/Si/O materials (BOSi2(epe) and BOSi3(epe)) with a broad distribution of mesopores (by N(2) porosimetry) and smaller, more uniform particle sizes (by TEM) as compared to the nontemplated materials. Hydrolyses of 1 and 2 with excess H(2)O resulted in formation of the expected amounts of (t)BuOH and HOSi(O(t)Bu)(3); however, reaction of 1 with 1 equiv of H(2)O led to isolation of the new boronous acid HOB[OSi(O(t)Bu)(3)](2) (3). This ligand precursor is well suited for the synthesis of new metal (siloxy)boryloxide complexes via proton-transfer reactions involving the BOH group. The reaction of 3 with Cp(2)ZrMe(2) resulted in formation of Cp(2)Zr(Me)OB[OSi(O(t)Bu)(3)](2) (4) in high yield. This rare example of a transition metal boryloxide complex crystallizes in the triclinic space group Ponemacr; and exhibits a crystal structure with an unprecedented number of independent molecules in its asymmetric unit (i.e., Z' = 18 and Z = 36). This unusual crystal structure presented an opportunity to perform statistical analyses of the metric parameters for the 18 crystallographically independent molecules. Complex 4 readily converts to Cp(2)Zr[OSi(O(t)Bu)(3)](2) (5) upon thermolysis or upon dissolution in Et(2)O at room temperature.     

Radical reaction of C70Cl10 with P(OEt)3: isolation and characterization of C70[P(O)(OEt)2]nHn (n = 1, 2)

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Seven-minute synthesis of pure C(s)-C60Cl6 from [60]fullerene and iodine monochloride: first IR, Raman, and mass spectra of 99 mol % C60Cl6

Three previously reported procedures for the synthesis of pure C(s)-C60Cl6 from C60 and ICl dissolved in benzene or 1,2-dichlorobenzene were shown to actually yield complex mixtures of products that contain, at best, 54-80% C(s)-C60Cl6 based on HPLC integrated intensities. MALDI mass spectrometry was used for the first time to identify other components of the reaction mixtures. An improved synthetic procedure was developed for the synthesis of about 150 mg batches of chlorofullerenes containing 90% C(s)-C60Cl6 based on HPLC intensities. The optimum reaction time was decreased from several days to seven minutes. Small amounts of the product were purified by HPLC (toluene eluent) to 99% purity. The pure compound C(s)-C60Cl6 is stable for at least three months as a solvent-free powder at 25 degrees C. The Raman, far-IR, and MALDI mass spectra of pure C(s)-C60Cl6 are reported for the first time. The Raman and far-IR spectra, the first reported for any C60Cl(n) chlorofullerene, were used to carry out a vibrational analysis of C(s)-C60Cl6 at the DFT level of theory.     

Methanofullerene Molecular Scaffolding: Towards C60-substituted poly(triacetylenes) and expanded radialenes,preparation of a C60–C70 hybrid derivative,and a novel macrocyclization reaction

The synthesis of (E)-hex-3-ene-l, 5-diynes and 3-methylidenepenta-1, 4-diynes with pendant methano[60]-fullerene moieties as precursors to C₆₀-substituted poly(triacetylenes) (PTAs, Fig. 1) and expanded radialenes (Fig. 2) is described. The Bingel reaction of diethyl (E)-2, 3-dialkynylbut-2-ene-1, 4-diyl bis(2-bromopropane-dioates) 5 and 6 with two C₆₀ molecules (Scheme 2) afforded the monomeric, silyl-protected PTA precursors 9 and 10 which, however, could not be effectively desilylated (Scheme 4). Also formed during the synthesis of 9 and 10 , as well as during the reaction of C₆₀ with thedesilylated analogue 16 (Scheme 5 ), were the macrocyclic products 11, 12 , and 17 , respectively, resulting from double Bingel addition to one C-sphere. Rigorous analysis revealed that this novel macrocyclization reaction proceeds with complete regio- and diastereoselectivity. The second approach to a suitable PTA monomer attempted N, N′-dicyclohexylcarbodiimide(DCC)-mediated esterification of (E)-2, 3-diethynylbut-2-ene-l, 4-diol ( 18 , Scheme 6) with mono-esterified methanofullerene-dicarboxylic acid 23 ; however, this synthesis yielded only the corresponding decarboxylated methanofullerene-carboxylic ester 27 (Scheme 7). To prevent decarboxylation, a spacer was inserted between the reacting carboxylic-acid moiety and the methane C-atom in carboxymethyl ethyl 1, 2-methano[60]fullerene-61, 61-dicarboxylate ( 28 , Scheme 8), and DCC-mediated esterification with diol 18 afforded PTA monomer 32 in good yield. The formation of a suitable monomeric precursor 38 to C₆₀-substituted expanded radialenes was achieved in 5 steps starting from dihydroxyacetone (Schemes 9 and 10), with the final step consisting of the DCC-mediated esterification of 28 with 2-[1-ethynyl(prop-2-ynylidene)]propane-1, 3-diol ( 33 ). The first mixed C₆₀-C₇₀ fullerene derivative 49 , consisting of two methano[60]fullerenes attached to a methano[70]fullerene, was also prepared and fully characterized (Scheme 13). The C_s-symmetrical hybrid compound was obtained by DCC-mediated esterification of bis[2-(2-hydroxy-ethoxy)ethyl] 1, 2-methano[70]fullerene-71, 71-dicarboxylate ( 46 ) with an excess of the C₆₀-carboxylic acid 28 . The presence of two different fullerenes in the same molecule was reflected by its UV/VIS spectrum, which displayed the characteristic absorption bands of both the C₇₀ and C₆₀ mono-adducts, but at the same time indicated no electronic interaction between the different fullerene moieties. Cyclic voltammetry showed two reversible reduction steps for 49 , and comparison with the corresponding C₇₀ and C₆₀ mono-adducts 46 and 30 indicated that the three fullerenes in the composite fullerene compound behave as independent redox centers.     

Oxalate-bridged complexes of dimolybdenum and ditungsten supported by pivalate ligands: ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3). Correlation of the solid-state, molecular, and electronic structures with Raman, resonance Raman, and electronic spectral data

The compounds ((t)BuCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)C(t)Bu)(3) (M(4)OXA), where M = Mo or W, are shown by analysis of powder X-ray diffraction data to have extended lattice structures wherein oxygen atoms from the oxalate and pivalate ligands of one M(4)OXA molecule are linked to metal atoms of neighboring molecules. Raman, resonance Raman, electronic absorption (2-325 K in 2-MeTHF), and emission spectra are reported, together with corresponding spectra of the mu-O(2)(13)C(13)CO(2) isotopomers. To aid in the assignment, the Raman spectra of K(2)C(2)O(4).H(2)O and K(2)(13)C(2)O(4).H(2)O have also been recorded. The visible region of the electronic spectra is dominated by intense, fully allowed MLCT transitions, M(2) delta to oxalate pi*, which show pronounced thermochromism and extensive vibronic progressions associated with the oxalate ligand at low temperatures. With excitation into these charge-transfer bands, strong resonance enhancement is seen for Raman bands assigned to the oxalate nu(1)(a(g)) and, to a lesser extent, nu(2)(a(g)) modes. Electronic structure calculations for the model compounds (HCO(2))(3)M(2)(mu-O(2)CCO(2))M(2)(O(2)CH)(3), employing density functional theory (gradient corrected and time-dependent) with the Gaussian 98 and ADF 2000 packages, predict the planar oxalate D(2h) configuration to be favored, which maximizes M(2) delta to oxalate pi* back-bonding, and indicate low barriers (<8 kcal mol(-1)) to rotation about the oxalate C-C bonds.