Photoluminescence and energy transfer studies of Dy(3+)-doped fluorophosphate glasses

Dy(3+)-doped fluorophosphate glasses with composition (in mol%) (56-x/2)P(2)O(5)+17K(2)O+(15-x/2)BaO+8Al(2)O(3) + 4AlF(3)+ xDy(2)O(3), x=0.01, 0.05, 0.1, 1.0 and 2.0, have been prepared by melt quenching technique. The luminescence spectra and lifetimes of (4)F(9/2) level of Dy(3+) ions in these glasses have been measured using the 457.9 nm line of argon ion laser as an excitation source. The free-ion calculation and Judd-Ofelt analysis have been performed. The room temperature emission spectra corresponding to (4)F(9/2)-->(6)H(J) (J=7/2, 9/2, 11/2, 13/2 and 15/2) transitions of Dy(3+) ions were measured. The fluorescence decay from (4)F(9/2) level have been measured by monitoring the intense (4)F(9/2)-->(6)H(13/2) transition. The lifetime of the decay is obtained by taking the first e-folding times of the decay curves and is found to decrease with increase in Dy(3+) ions concentration due to concentration quenching. The decay curves are found to be perfectly single exponential for samples with low Dy(3+) ion concentration. The non-exponential decay curves observed for higher concentrations are well fitted to the Inokuti-Hirayama model for S=6, which indicates that the energy transfer between the donor and acceptor is of dipole-dipole nature. The energy transfer parameter and donor to acceptor interaction increases with Dy(3+) ions concentration due to increase of energy transfer from Dy(3+) (donor) to unexcited Dy(3+) (acceptor) ions.     

New reactions of 1-alkynes catalyzed by transition metal complexes

Recently discovered catalytic reactions with ruthenium and lanthanide metal complexes have extended the scope of 1-alkynes as useful reagents. The specific formation of aryl-substituted (Z)-1,3-enzymes via the dimerization of HC(triple bond) CR(1) (R(1) = aryl) has been attained using dimeric lanthanide complexes, the catalytic activity of which appears to be unaffected by time. The dimerization of HC(triple bond) CR(2) (R(2) = t-Bu, SiMe(3)) catalyzed by Ru(cod)(cot)/PR(3) or RuH(2)(PPh(3))(3) produces a good yield of butatrienes (Z)R(2)CH=C=C=CHR(2) with a high degree of selectivity. Under certain conditions, HC(triple bond) C=SiMe(3) dimerizes to yield exclusively (Z)-M(3)Si-C(triple bond) C-CH=CH-SiMe(3). The hydration of HC(triple bond)CR(3) (R(3) = alkyl, aryl) catalyzed by RuCl(2)/PR'(3) or CpRuCl(PR"(3))(2) has realized the first example of anti-Markovnikov regioselectivity in an addition reaction of water that produces aldehydes R(3)CH(2)bond;CHO. The application of this reaction to propargylic alcohols has lead to their formal isomerization to alpha,beta-unsaturated aldehydes. In contrast, the addition of amines R(4)bond;NH(2) (R(4) = aryl) to HCtbond;CR(5) (R(5) = alkyl, aryl) conforms to Markovnikov's rule to produce ketimines R(5)bond;(C=NR(4))bond;CH(3) when catalyzed by a Ru(3)(CO)(12)/additive. Since the reaction can be performed in air without the need for any solvents, it enables the practical synthesis of aromatic ketimines, which are difficult to prepare by conventional methods. The synthesis of indoles using deactivated anilines is one practical application of this reaction. The mechanisms of some of these reactions have been analyzed in detail with the aid of theoretical calculations.     

Stability and reactivity of methane clathrate hydrates: insights from density functional theory

The sI methane clathrate hydrate consists of methane gas molecules encapsulated as dodecahedron (5(12)CH(4)) and tetrakaidecahedron (5(12)6(2)CH(4)) water cages. The characterization of the stability of these cages is crucial to an understanding of the mechanism of their formation. In the present work, we perform calculations using density functional theory to calculate interaction energies, free energies, and reactivity indices of these cages. The contributions from polarization functions to interaction energies is more than diffuse functions from Pople basis sets, though both functions from the correlation-consistent basis sets contribute significantly to interaction energies. The interaction energies and free energies show that the formation of the 5(12)CH(4) cage (from the 5(12) cage) is more favored compared to the 5(12)6(2)CH(4) cage (from the 5(12)6(2) cage). The pressure-dependent study shows a spontaneous formation of the 5(12)CH(4) cage at 273 K (P ≥ 77 bar) and the 5(12)6(2)CH(4) cage (P = 100 bar). The reactivity of the 5(12)CH(4) cage is similar to that of the 5(12) cage, but the 5(12)6(2)CH(4) cage is more reactive than the 5(12)6(2) cage.     

Microwave survey of the conformational landscape exhibited by the propeller molecule triethyl amine

Conformational studies with quantum chemical methods yielded for the most stable conformer of triethyl amine a propeller-like structure belonging to the point group C(3), which corresponds to an oblate top. The microwave spectrum of this conformer with (14)N hyperfine splitting of all rotational transitions was assigned and molecular parameters were determined. The rotational constants were found to be A = B = 2.314873978(11) GHz, the (14)N quadrupole coupling constant χ(cc) = -5.2444(07) MHz. The observed spectrum could be reproduced within experimental accuracy. The standard deviation of a global fit with 48 rotational transitions is 1.5 kHz. The propeller-like structure seems to be energetically favorable and therefore also typical for related systems like triethyl phosphine, triisopropyl amine, tri-n-propyl amine, and tri-tert-butyl amine. Furthermore, the rotational transitions of two isotopologues, (13)C(2) and (13)C(5), could be measured in natural abundance and fitted with an excellent standard deviation. The C rotational constants could be determined to be 1.32681(96) GHz and 1.32989(18) GHz for the (13)C(2) and (13)C(5) isotopologues, respectively.     

Preparation and Structures of the 2.2.2-Cryptand(1+) Salts of the [Sb(2)Se(4)](2)(-), [As(2)S(4)](2)(-), [As(10)S(3)](2)(-), and [As(4)Se(6)](2)(-) Anions

2.2.2-Cryptand(1+) salts of the [Sb(2)Se(4)](2)(-), [As(2)S(4)](2)(-), [As(10)S(3)](2)(-), and [As(4)Se(6)](2)(-) anions have been synthesized from the reduction of binary chalcogenide compounds by K in NH(3)(l) in the presence of the alkali-metal-encapsulating ligand 2.2.2-cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane), followed by recrystallization from CH(3)CN. The [Sb(2)Se(4)](2)(-) anion, which has crystallographically imposed symmetry 2, consists of two discrete edge-sharing SbSe(3) pyramids with terminal Se atoms cis to each other. The Sb-Se(t) bond distance is 2.443(1) ?, whereas the Sb-Se(b) distance is 2.615(1) ? (t = terminal; b = bridge). The Se(b)-Sb-Se(t) angles range from 104.78(4) to 105.18(5) degrees, whereas the Se(b)-Sb-Se(b) angles are 88.09(4) and 88.99(4) degrees. The (77)Se NMR data for this anion in solution are consistent with its X-ray structure (delta 337 and 124 ppm, 1:1 intensity, -30 degrees C, CH(3)CN/CD(3)CN). Similar to this [Sb(2)Se(4)](2)(-) anion, the [As(2)S(4)](2)(-) anion consists of two discrete edge-sharing AsS(3) pyramidal units. The As-S(t) bond distances are 2.136(7) and 2.120(7) ?, whereas the As-S(b) distances range from 2.306(7) to 2.325(7) ?. The S(b)-As-S(t) angles range from 106.2(3) to 108.2(3) degrees, and the S(b)-As-S(b) angles are 88.3(2) and 88.9(2) degrees. The [As(10)S(3)](2)(-) anion has an 11-atom As(10)S center composed of six five-membered edge-sharing rings. One of the three waist positions is occupied by a S atom, and the other two waist positions feature As atoms with exocyclic S atoms attached, making each As atom in the structure three-coordinate. The As-As bond distances range from 2.388(3) to 2.474(3) ?. The As-S(t) bond distances are 2.181(5) and 2.175(4) ?, and the As-S(b) bond distance is 2.284(6) ?. The [As(4)Se(6)](2)(-) anion features two AsSe(3) units joined by Se-Se bonds with the two exocyclic Se atoms trans to each other. The average As-Se(t) bond distance is 2.273(2) ?, whereas the As-Se(b) bond distances range from 2.357(3) to 2.462(2) ?. The Se(b)-As-Se(t) angles range from 101.52(8) to 105.95(9) degrees, and the Se(b)-As-Se(b) angles range from 91.82(7) to 102.97(9) degrees. The (77)Se NMR data for this anion in solution are consistent with its X-ray structure (delta 564 and 317 ppm, 3:1 intensity, 25 degrees C, DMF/CD(3)CN).     

Electronic structure of iron chlorins: characterization of bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(III)triflate and bis(l-valine methyl ester)(meso-tetraphenylchlorin)iron(II)

The synthesis and characterization of the two iron chlorin complexes [Fe(III)(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) and Fe(II)(TPC)[(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2))](2) (2) are reported. The crystal structure of complex 1 has been determined. The X-ray structure shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 2.034(4) A, and to the pyrrole trans to it N(2), 2.012(4) A, are longer than the distances to the two remaining nitrogens [N(1), 1.996(4) A, and N(3), 1.984(4) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole. The (1)H NMR isotropic shifts at 20 degrees C of the different pyrrole protons of 1 varied from -0.8 to -48.3 ppm according to bis-ligated complexes of low-spin ferric chlorins. The EPR spectrum of [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) in solution is rhombic and gives the principal g values g(1) = 2.70, g(2) = 2.33, and g(3) = 1.61 (Sigmag(2) = 15.3). These spectroscopic observations are indicative of a metal-based electron in the d(pi) orbital for the [Fe(TPC)(NH(2)CH(CO(2)CH(3))(CH(CH(3))(2)))(2)]CF(3)SO(3) (1) complex with a (d(xy))(2)(d(xz)d(yz))(3) ground state at any temperature. The X-ray structure of the ferrous complex 2 also shows that the porphyrinate rings are weakly distorted. The metal-nitrogen distances to the reduced pyrrole N(4), 1.991(5) A, and to the pyrrole trans to it N(2), 2.005(6) A, are slightly different from the distances to the two remaining nitrogens [N(1), 1.988(5) A, and N(3), 2.015(5) A], leading to a core-hole expansion of the macrocycle due to the reduced pyrrole.     

Oxidation chemistry of uranium(III) complexes of Tpa: synthesis and structural studies of oxo,hydroxo, and alkoxo complexes of uranium(IV)

The crystal structure of the complex [U(tpa)(2)]I(3), 1 (tpa = tris[(2-pyridyl)methyl]amine), has been elucidated. The complex exists as only one enantiomer in the crystal leading to the chiral space group P2(1)2(1)2(1). The coordination geometry of the metal can be described as a distorted cube. Accidental oxidation of [U(tpa)(2)]I(3) led to the isolation of the unusual mononuclear bishydroxo complex of uranium(IV) [U(tpa)(2)(OH)(2)]I(2).3CH(3)CN, 2, which was structurally characterized. The controlled reaction of [U(tpa)(2)]I(3) with water resulted in the oxidation of the metal center and led to the formation of protonated tpa and of the trinuclear U(IV) oxo complex ([U(tpa)(mu-O)I](3)(mu(3)-I))I(2), 3. The solid state and solution structures of this trimer are reported. The pathway suggested for the formation of this complex is the oxidation of the [U(tpa)(2)]I(3) complex by H(2)O to form a U(IV) hydroxo complex which then decomposes, eliminating mono-protonated tpa. The comparison with the reported reaction with water of cyclopentadienyl derivatives points to a higher reactivity toward water reduction of the bis(tpa) complex with respect to the cyclopentadienyl derivatives. The reaction of U(III) with methanol in the presence of the supporting ligand tpa leads to formation of alkoxo complexes similarly to what is found for amide or cyclopentadienyl derivatives. The monomethoxide complex [U(tpa)I(3)(OMe)], 4, has been prepared in good yield by alcoholysis of the U(III) mono(tpa) complex. The crystal structure of this complex has been determined. The reaction of [U(tpa)(2)]I(3) with 2 equiv of methanol in acetonitrile allows the isolation of the bismethoxo complex of U(IV) [U(tpa)I(2)(OMe)(2)], 5, in 35-47% yield, which has been fully characterized. To account for the oxidation of U(III) to U(IV) the suggested mechanism assumes that hydrogen is evolved in both reactions.     

Quantum chemical calculations of the redox potential of the Pu(VII)/Pu(VIII) couple

The redox potential of the Pu(VII)/Pu(VIII) couple was studied by density functional theory calculations. The spin-orbit effect was corrected at the CASSCF level. The redox potential (relative to the standard hydrogen potential) of the Pu(VII)/Pu(VIII) couple in alkaline solution was found to vary from 4.36 to 1.06 V depending on the number of Pu-O oxo bonds, coordination numbers, and coordination modes. The redox potential drops substantially as the number of Pu-O oxo bonds increases. Pu(VIII) may be synthesized in strong alkaline solution assuming that both Pu(VII) and Pu(VIII) exist in penta-oxo form, Pu (VII)O 5OH (4-) and Pu (VIII)O 5OH (3-), respectively. The Mulliken population of Pu in Pu(VII) and Pu(VIII) complexes are very similar, suggesting that the spin-orbit effect is rather small in Pu(VII) complexes and that when Pu(VII) is oxidized to Pu(VIII) the electron is stripped mainly from the ligand. Consequently, Pu(VIII) is in an unstable oxidation state and easily reduced back to Pu(VII) by the solvent water molecules. In acidic medium, the Pu(VII)/Pu(VIII) redox potential is too high to get the Pu(VIII) valence state.     

Characterization of self-assembled monolayers of porphyrins bearing multiple thiol-derivatized rigid-rod tethers

A series of multithiol-functionalized zinc porphyrins has been prepared and characterized as self-assembled monolayers (SAMs) on Au. The molecules, designated ZnPS(n) (n = 1-4), contain from one to four [(S-acetylthio)methyl]phenylethynylphenyl groups appended to the meso-position of the porphyrin; the other meso-substituents are phenyl groups. For the dithiol-functionalized molecules, both the cis- and the trans-appended structures were examined. The ZnPS(n) SAMs were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and various electrochemical methods. The studies reveal the following characteristics of the ZnPS(n) SAMs. (1) The ZnPS(n) molecules bind to the Au surface via a single thiol regardless of the number of thiol appendages that are available per molecular unit. (2) The porphyrins in the ZnPS(3) and ZnPS(4) SAMs bind to the surface in a more upright orientation than the porphyrins in the ZnPS(1), cis-ZnPS(2), and trans-ZnPS(2) SAMs. The porphyrins in the ZnPS(3) and ZnPS(4) SAMs are also more densely packed than those in the cis-ZnPS(2) and trans-ZnPS(2) SAMs. The packing density of the ZnPS(3) and ZnPS(4) SAMs is similar to that of the ZnPS(1) SAMs, despite the larger size of the molecules in the former SAMs. (3) The thermodynamics and kinetics of electron transfer are generally similar for all of the ZnPS(n) SAMs. The general similarities in the electron-transfer characteristics for all of the SAMs are attributed to the similar binding motif.     

Low-lying electronic states of the Ti2 dimer: electronic absorption spectroscopy in rare gas matrices in concert with quantum chemical calculations

Absorption spectra were measured for Ti2 in Ne and Ar matrices. The spectra give evidence for several electronic transitions in the region between 4000 and 10 000 cm(-1) and provide important information about some excited electronic states of Ti2 in proximity to the ground state. The vibrational fine structure measured for these transitions allowed to calculate the force constants and the anharmonicity of the potential energy curves of the excited states, and to estimate changes in the internuclear Ti-Ti distances relative to the electronic ground state. The quantum chemical studies confirm the previously suggested (3)Delta(g) state as the ground state of Ti2. The equilibrium bond distance is calculated to be 195.4 pm. The calculated harmonic frequency of 432 cm(-1) is in good agreement with the experimental value of 407.0 cm(-1). With the aid of the calculations it was possible to assign the experimentally observed transitions in the region between 4000 and 10 000 cm(-1) to the 1 (3)Pi(u)<--(3)Delta(g), 1 (3)Phi(u)<--(3)Delta(g), 2 (3)Pi(u)<--(3)Delta(g), 2 (3)Phi(u)<--(3)Delta(g), and (3)Delta(u)<--(3)Delta(g) excitations (in the order of increasing energy). The calculated relative energies and harmonic frequencies are in pleasing agreement with the experimentally obtained values, with deviations of less than 5% and 2%, respectively. The bond distances estimated on the basis of the experimental spectra tally satisfactorily with the predictions of our calculations.     

On the clarification of the IR stretching vibration assignment of adsorbed N2 on Rh0 and Rhdelta+ surface atoms of supported Rh crystallites

The low-temperature adsorption of N(2) on Rh/SiO(2) samples of various particle-size distributions was followed by FTIR. The addition of O(2) pulses on Rh(0) surfaces saturated with chemisorbed N(2) allowed us to reassign stretching frequencies attributed originally to N(2)-Rh(0) to N(2)-Rh(delta+). The formation of the latter oxidized Rh species is assumed to be induced by an electron withdrawal from adsorbed oxygen species on Rh surface centers neighboring those onto which N(2) species are chemisorbed. The present work, thus, enables us to delimit ranges of frequencies for which the adsorption of N(2) can be considered to occur on either Rh(0) or Rh(delta+) centers for nu(N2) lower or higher than 2243 cm(-1), respectively. The N(2)-FTIR experiments performed on the studied catalysts also suggest a lattice plane selectivity for N(2) adsorption on metallic Rh planes of different natures which, to our knowledge, has not been reported yet for Rh.     

甲基丙烯醛氧化酯化制甲基丙烯酸甲酯催化剂的制备与应用

甲基丙烯醛氧化酯化制甲基丙烯酸甲酯催化剂的制备与应用;催化剂; 甲基丙烯酸甲酯; 甲基丙烯醛; 氧化-酯化反应     

Enhanced lasing properties of dissymmetric Eu(III) complex with bidentate phosphine ligands

The luminescent and lasing properties of Eu(III) complexes were enhanced by using an dissymmetric Eu(III) complex. The photophysical properties (the emission spectral shapes, the emission lifetimes, the emission quantum yields, and the stimulated emission cross section (SEC)) were found to be dependent on the geometrical structures of Eu(III) complexes. The geometrical structures of Eu(III) complexes were determined by X-ray single crystal analyses. The symmetrical group of Eu(hfa)3(BIPHEPO) (tris(hexafluoroacetylacetonato)europium(III) 1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide)) was found to be C1, which was more dissymmetric than Eu(hfa)3(TPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry) and Eu(hfa)3(OPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry). The analytical data were supported by Judd-Ofelt analysis. The most dissymmetrical Eu(III) complex, Eu(hfa)3(BIPHEPO), showed large electron transition probability and large SEC (4.64 x 10(-20) cm2). The SEC of Eu(hfa)3(BIPHEPO) was superior to even the values of Nd-glass laser for practical use (1.6-4.5 x 10(-20) cm2). The lasing properties of Eu(III) complexes in polymer thin film were measured by photopumping of a Nd:YAG laser (355 nm). The threshold energy of lasing oscillation was found to be 0.05 mJ. The increasing rate of the lasing intensity of Eu(hfa)3(BIPHEPO) as a function of the excitation energy was much larger than that of Eu(hfa)3(TPPO)2 and Eu(hfa)3(OPPO)2. The dissymmetrical structure of Eu(hfa)3(BIPHEPO) promoted the enhancement of the lasing property.     

Titanium oxide complexes with dinitrogen. Formation and characterization of the side-on and end-on bonded titanium oxide-dinitrogen complexes in solid neon

The reactions of titanium oxide molecules with dinitrogen have been studied by matrix isolation infrared spectroscopy. The titanium monoxide molecule reacts with dinitrogen to form the TiO(N(2))(x) (x = 1-4) complexes spontaneously on annealing in solid neon. The TiO(η(1)-NN) complex is end-on bonded and was predicted to have a (3)A' ground state arising from the (3)Δ ground state of TiO. Argon doping experiments indicate that TiO(η(1)-NN) is able to form complexes with one or more argon atoms. Argon atom coordination induces a large red-shift of the N-N stretching frequency. The TiO(η(2)-N(2))(2) complex was characterized to have C(2v) symmetry, in which both the N(2) ligands are side-on bonded to the titanium metal center. The tridinitrogen complex TiO(η(1)-NN)(3) most likely has C(3v) symmetry with three end-on bonded N(2) ligands. The TiO(η(1)-NN)(4) complex was determined to have a C(4v) structure with four equivalent end-on bonded N(2) ligands. In addition, evidence is also presented for the formation of the TiO(2)(η(1)-NN)(x) (x = 1-4) complexes, which were predicted to be end-on bonded.     

A magnetic resonance imaging contrast agent capable of detecting hydrogen peroxide

The redox-active ligand N-(2-hydroxy-5-methylbenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hptp1) was prepared and complexed to manganese(II). The isolated [Mn(Hptp1)(MeCN)](2+) serves as a magnetic resonance imaging contrast agent, with an r(1) value comparable to those of other mononuclear gadolinium(III) and manganese(II) complexes. The metal and ligand are stable in aerated aqueous solutions, but the addition of H(2)O(2) causes the complex to oxidatively couple to itself through a bimolecular reaction involving the phenol groups of two Hptp1 ligands. The binuclear product is less paramagnetic per manganese(II) than its mononuclear precursor, lowering the measured r(1) per manganese(II). The manganese(II) complex with Hptp1 can thereby serve as a sensor for oxidative stress.     

Multireference theoretical investigation on selectivity of the bond fissions in photodissociation of acetyl cyanide

The selectivity of the C-CH(3) and C-CN bond fissions upon excitation of acetyl cyanide at 193 nm has been investigated at the theoretical level of multistate complete active space self-consistent field second order perturbation. The calculated results indicated that the initially excited S(3) state relaxes to S(2) via ultrafast internal conversion. The S(2) state could dissociate via two pathways. One, adiabatically dissociates to CH(3)CO(X)+CN(A). The other one internally converts to S(1) before S(1) intersystem crossing to T(1). The T(1) state subsequently dissociates to two groups of products: CH(3)(X)+OCCN(X) and CH(3)CO(X)+CN(X). The experimentally observed preference branching of CN elimination over CH(3) one and bond selectivity are the results of the competition between the adiabatic and nonadiabatic dynamics of the S(2) state.     

Photoelectron spectroscopy and density functional theory study of TiAlO(y) (-) (y=1-3) and TiAl(2)O(y) (-) (y=2-3) clusters

Small titanium-aluminum oxide clusters, TiAlO(y) (-) (y=1-3) and TiAl(2)O(y) (-) (y=2-3), were studied by using anion photoelectron spectroscopy. The adiabatic detachment energies of TiAlO(y) (-) (y=1-3) were estimated to be 1.11±0.05, 1.70±0.08, and 2.47±0.08eV based on their photoelectron spectra; those of TiAl(2)O(2) (-) and TiAl(2)O(3) (-) were estimated to be 1.17±0.08 and 2.2±0.1eV, respectively. The structures of these clusters were determined by comparison of density functional calculations with the experimental results. The structure of TiAlO(-) is nearly linear with the O atom in the middle. That of TiAlO(2) (-) is a kite-shaped structure. TiAlO(3) (-) has a kite-shaped TiAlO(2) unit with the third O atom attaching to the Ti atom. TiAl(2)O(2) (-) has two nearly degenerate Al-O-Ti-O-Al chain structures that can be considered as cis and trans forms. TiAl(2)O(3) (-) has two low-lying isomers, kite structure and book structure. The structures of these clusters indicate that the Ti atom tends to bind to more O atoms.     

Electrosynthesis of a Sc3N@I(h)-C80 methano derivative from trianionic Sc3N@I(h)-C80

The electrosynthetic method has been used for the selective synthesis of fullerene derivatives that are otherwise not accessible by other procedures. Recent attempts to electrosynthesize Sc(3)N@I(h)-C(80) derivatives using the Sc(3)N@I(h)-C(80) dianion were unsuccessful because of its low nucleophilicity. Those results prompted us to prepare the Sc(3)N@C(80) trianion, which should be more nucleophilic and reactive with electrophilic reagents. The reaction between Sc(3)N@C(80) trianions and benzal bromide (PhCHBr(2)) was successful and yielded a methano derivative, Sc(3)N@I(h)-C(80)(CHPh) (1), in which the >CHPh addend is selectively attached to a [6,6] ring junction, as characterized by MALDI-TOF mass spectrometry and NMR and UV-vis-NIR spectroscopy. The electrochemistry of 1 was studied using cyclic voltammetry, which showed that 1 exhibits the typical irreversible cathodic behavior of pristine Sc(3)N@I(h)-C(80), resembling the behavior of other methano adducts of Sc(3)N@I(h)-C(80). The successful synthesis of endohedral metallofullerene derivatives using trianionic Sc(3)N@I(h)-C(80) and dianionic Lu(3)N@I(h)-C(80), but not dianionic Sc(3)N@I(h)-C(80), prompted us to probe the causes using theoretical calculations. The Sc(3)N@I(h)-C(80) trianion has a singly occupied molecular orbital with high spin density localized on the fullerene cage, in contrast to the highest occupied molecular orbital of the Sc(3)N@I(h)-C(80) dianion, which is mainly localized on the inside cluster. The calculations provide a clear explanation for the different reactivities observed for the dianions and trianions of these endohedral fullerenes.     

Iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin

The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.     

Optical detection of phenolic compounds based on the surface plasmon resonance band of Au nanoparticles

An indirect colorimetric method is presented for detection of trace amounts of hydroquinone (1), catechol (2) and pyrogallol (3). The reduction of AuCl4(-) to Gold nanoparticles (Au-NPs) by these phenolic compounds in the presence of cetyltrimethylammonium chloride (CTAC) produced very intense surface plasmon resonance peak of Au-NPs. The plasmon absorbance of Au-NPs allows the quantitative colorimetric detection of the phenolic compounds. The calibration curves derived from the changes in absorbance at lambda = 568 nm were linear with concentration of hydroquinone, catechol and pyrogallol in the range of 7.0 x 10(-7) to 1.0 x 10(-4)M, 6.0 x 10(-6) to 2.0 x 10(-4)M and 6.0 x 10(-7) to 1.0 x 10(-4)M, respectively. The detection limits were 5.3 x 10(-7), 2.5 x 10(-6) and 3.2 x 10(-7)M for the hydroquinone, catechol and pyrogallol, respectively. The method was applied satisfactorily to the determination of phenolic compounds in water samples and pharmaceutical formulations.