Multiconfigurational self-consistent field and multireference internally contracted configuration interaction studies on the excited states of weakly bonded NO2 dimer (N2O4)

In this paper, the vertical excitation energies of total of 32 states of N(2)O(4) including the lowest two singlet states and two triplet states of each of the A(g), B(3u), B(2u), B(1g), B(1u), B(2g), B(3g), and A(u) symmetries were calculated at multiconfigurational self-consistent field (MCSCF) and the multireference internally contracted configuration interaction (MRCI) levels of theory on the active space (15o,16e) with aug-cc-pVDZ basis set. The potential energy curves of the eight singlet states(1 (1)A(g), 1 (1)B(3u), 1 (1)B(2u), 1 (1)B(1g), 1 (1)B(1u), 1 (1)B(2g), 1 (1)B(3g), and 1 (1)A(u)) and eight triplet states (1 (3)A(g), 1 (3)B(3u), 1 (3)B(2u), 1 (3)B(1g), 1 (3)B(1u), 1 (3)B(2g), 1 (3)B(3g), and 1 (3)A(u)) were calculated at MCSCF and MRCI levels of theory on the active space (15o,16e) with aug-cc-pVDZ basis set along the N-N distance. The vertical excitation energies of 1 (1)B(3u), 1 (1)B(2u), and 1 (1)B(1u) states with nonzero transition moment are 4.60 eV (269.6 nm), 6.06 eV (204.6 nm), and 7.71 eV (160.8 nm), respectively, at MRCI level of theory. The photodissociation asymptotics were assigned as NO(2)(X (2)A(1))+NO(2)(X (2)A(1)) for ground state 1 (1)A(g) and the 1 (3)B(1u) state, NO(2)(X (2)A(1))+NO(2)(1 (2)A(2)) for the 1 (1)B(1g), 1 (3)B(1g), 1 (1)A(u), and 1 (3)A(u) states, NO(2)(X (2)A(1))+NO(2)(1 (2)B(1)) for the 1 (1)B(3u), 1 (3)B(3u), 1 (1)B(2g), and 1 (3)B(2g) states, and NO(2)(X (2)A(1))+NO(2)(1 (2)B(2)) for the 1 (1)B(2u), 1 (3)B(2u), 1 (1)B(3g), and 1 (3)B(3g) states.     

Hf3 cluster is triply (sigma-, pi-, and delta-) aromatic in the lowest D3h, 1A1' state

The extensive search for the global minimum structure of Hf3 at the B3LYP/LANL2DZ level of theory revealed that D3h 3A2' (1a1'(2)1a2'(2)1e'(4)2a1'(2)1e'2) and D3h 1A1' (1a1'(2)2a1'(2)1e'(4)1a2'(2)3a1'2) are the lowest triplet and singlet states, respectively, with the triplet state being the lowest one. However, at the CASSCF(10,14)/Stuttgart+2f1g level of theory these two states are degenerate, indicating that at the higher level of theory the singlet state could be in fact the global minimum structure. The triplet D3h 3A2' (1a1'21a2'(2)1e'(4)2a1'(2)1e'2) structure is doubly (sigma- and pi-) aromatic and the singlet D3h 1A1' (1a1'(2)2a1'(2)1e'(4)1a2'(2)3a1'2) structure is the first reported triply (sigma-, pi-, and delta-) aromatic system.     

Visible spectrum of titanium dioxide

The electronic spectrum in the region 17?500 cm(-1) to 18?850 cm(-1) of a cold molecular beam of TiO(2) has been investigated using laser induced fluorescence (LIF) and mass-resolved resonance enhanced multi-photoionization (REMPI) spectroscopy. Bands at 18?412 cm(-1), 18?470 cm(-1) and 18?655 cm(-1) were recorded at a resolution of 35 MHz, rotationally analyzed, and assigned as the ?(1)B(2) (0,1,2) ←X[combining tilde](1)A(1) (0,0,0), ?(1)B(2) (1,0,0) ←X[combining tilde](1)A(1) (0,0,0) and ?(1)B(2) (1,1,0) ←X[combining tilde](1)A(1) (0,0,0) transitions. The dispersed fluorescence from the ?(1)B(2) (0,1,2) and ?(1)B(2) (1,0,0) levels were combined with previous results to produce an improved set of vibrational parameters for the X[combining tilde](1)A(1) state. The optical Stark effect in the ?(1)B(2) (0,1,2) ←X[combining tilde](1)A(1) (0,0,0) and ?(1)B(2) (1,0,0) ←X[combining tilde](1)A(1) (0,0,0) bands were recorded and combined with earlier results for ?(1)B(2) (1,1,0) ←X[combining tilde](1)A(1) (0,0,0) to determine the permanent electric dipole moment for these states. The origin and harmonic vibrational constants for the ?(1)B(2) state are determined to be: T(000) = 17?593(5) cm(-1), ω(1) = 876(3) cm(-1), ω(2) = 184(1) cm(-1), and ω(3) = 316(2) cm(-1). A normal coordinate analysis was performed and Franck-Condon factors calculated.     

螯形主体分子的设计、包结性能及其在细辛挥发油 有效成分选择分离中的应用

设计了两种新的具有螯形骨架的主体分子反式-1,2-二苯基-1,2-苊二醇(1)和顺式-1,2-二(1'-萘基)-1,2-苊二醇(2),主体(1),(2)可与许多有机小分子化合物形成配位包合物。用IR和粉末XRD表征了主体分子(1)和(2)的包结物,用^1NMR测定了包结物的主客体分子摩尔比：(1)·DMF(1:2),(1)·DMSO(1:2),(1)·THF(1:2),(1)·二氧六环(1:1),(1)·吡啶(1:1),(2)·DMF(1:1)和(2)·DMSO(1:1)。单晶X射线衍射分析了包结物的晶体结构,(1)·DMF：空间群Pnaa,a=0.9377(1)nm,b=1.4351(1)nm,c=4.0463(3)nm;(1)·DMSO：空间群Pbcn,a=1.6278(1)nm,b=1.0751(1)nm,c=1.4980(1)nm;(2)·DMF：P2~1/n,a=0.9796(1)nm,b=1.2377(1)nm,c=2.2344(3)nm,β=93.02(1)°;游离主体(1)：空间群P1,a=1.0461(1)nm,b=1.1213(1)nm,c=1.5496(1)nm,α=81.74(1)°,β=75.71(1)°,γ=89.00(1)°;分析了主体分子的刚性和柔韧性对包结性能的影响。并研究了主体分子(1)选择分离细辛挥发油,将顺甲基异丁香酚从挥发油中分离出来。     

Application of equation-of-motion coupled-cluster methods to low-lying singlet and triplet electronic states of HBO and BOH

The equilibrium structures and physical properties of the X (1)sigma(+) linear electronic states, linear excited singlet and triplet electronic states of hydroboron monoxide (HBO) (A (1)sigma(-), B (1)delta, a (3)sigma(+), and b (3)delta) and boron hydroxide (BOH) (A (1)sigma(+), B (1)Pi, and b (3)Pi), and their bent counterparts (HBO a (3)A('), b (3)A("), A (1)A("), B (1)A(') and BOH X (1)A('), b (3)A('), c (3)A("), A (1)A('), B (1)A('), C (1)A(")) are investigated using excited electronic state ab initio equation-of-motion coupled-cluster (EOM-CC) methods. A new implementation of open-shell EOM-CC including iterative partial triple excitations (EOM-CC3) was tested. Coupled-cluster wave functions with single and double excitations (CCSD), single, double, and iterative partial triple excitations (CC3), and single, double, and full triple excitations (CCSDT) are employed with the correlation-consistent quadruple and quintuple zeta basis sets. The linear HBO X (1)sigma(+) state is predicted to lie 48.3 kcal mol(-1) (2.09 eV) lower in energy than the BOH X (1)sigma(+) linear stationary point at the CCSDT level of theory. The CCSDT BOH barrier to linearity is predicted to lie 3.7 kcal mol(-1) (0.16 eV). With a harmonic zero-point vibrational energy correction, the HBO X (1)sigma(+)-BOH X (1)A(') energy difference is 45.2 kcal mol(-1) (1.96 eV). The lowest triplet excited electronic state of HBO, a (3)A('), has a predicted excitation energy (T(e)) of 115 kcal mol(-1) (4.97 eV) from the HBO ground state minimum, while the lowest-bound BOH excited electronic state, b (3)A('), has a T(e) of 70.2 kcal mol(-1) (3.04 eV) with respect to BOH X (1)A('). The T(e) values predicted for the lowest singlet excited states are A (1)A(")<--X (1)sigma(+)=139 kcal mol(-1) (6.01 eV) for HBO and A (1)A(')<--X (1)A(')=102 kcal mol(-1) (4.42 eV) for BOH. Also for BOH, the triplet vertical transition energies are b (3)A(')<--X (1)A(')=71.4 kcal mol(-1) (3.10 eV) and c (3)A(")<--X (1)A(')=87.2 kcal mol(-1) (3.78 eV).     

Cyclodextrin complexation of a stilbene and the self-assembly of a simple molecular device

(E)-4-tert-Butyl-4'-oxystilbene, 1(-), is thermally stable as the (E)-1(-) isomer but may be photoisomerized to the (Z)-1(-) isomer as shown by UV-vis and (1)H NMR studies in aqueous solution. When (E)-1(-) is complexed by alphaCD two inclusion isomers (includomers) form in which alphaCD assumes either of the two possible orientations about the axis of (E)-1(-) in alphaCD.(E)-1(-) for which (1)H NMR studies yield the parameters: k(1)(298 K)= 12.3 +/- 0.6 s(-1), DeltaH(1)(++)= 94.3 +/- 4.7 kJ mol(-1), DeltaS1(++)= 92.0 +/- 5.0 J K(-1) mol(-1), and k(2)(298 K)= 10.7 +/- 0.5 s(-1), DeltaH(2)(++)= 93.1 +/- 4.7 kJ mol(-1), DeltaS2(++)= 87.3 +/- 5.0 J K(-1) mol(-1) for the minor and major includomers, respectively. The betaCD.(E)-1(-) complex either forms a single includomer or its includomers interchange at the fast exchange limit of the (1)H NMR timescale. Complexation of 1(-) by N-(6(A)-deoxy- alpha-cyclodextrin-6(A)-yl)-N'-(6(A)-deoxy- beta-cyclodextrin-6(A)-yl)urea, results in the binary complexes 2.(E)-1(-) in which both CD component annuli are occupied by (E)-1(-) and which exists exclusively in darkness and 2.(Z)-1(-) in which only one CD component is occupied by (Z)-1(-) and exists exclusively in daylight at lambda > or = 300 nm. Irradiation of solutions of the binary complexes at 300 and 355 nm results in photostationary states dominated by 2.(E)-1(-) and 2.(Z)-1(-), respectively. In the presence of 4-methylbenzoate, 4(-), 2.(Z)-1(-) forms the ternary complex 2.(Z)-1(-).4(-) where 4(-) occupies the second CD annulus. Interconversion occurs between 2.(Z)-1(-).4(-) and 2.(E)-1(-)+4(-) under the same conditions as for the binary complexes alone. Similar interactions occur in the presence of 4-methylphenolate and 4-methylphenylsulfonate. The two isomers of each of these systems represent different states of a molecular device, as do the analogous binary complexes of N,N-bis(6(A)-deoxy- beta-cyclodextrin-6(A)-yl)urea, 3, [3.(E)-1(-) and 3.(Z)-1(-), where the latter also forms a ternary complex with 4(-).     

Five new bidesmoside triterpenoid saponins from Stauntonia chinensis

Eleven triterpenoid saponins (1-11) were isolated from Stauntonia chinensis DC. (Lardizabalaceae), including five new compounds, yemuoside YM(21-25) (1-3, 6, 7) structures of which were elucidated by chemical methods and a combination of MS, 1D- and 2D- NMR experiments including DEPT, (1)H--(1)H COSY, HSQC, HMBC, TOCSY, and NOESY as 3-O-alpha-L-arabinopyranosyl-(1 --> 3)-[alpha-L-rhamnopyranosyl-(1 --> 2)-]alpha-L-arabinopyranosyl-akebonicacid-28-O-alpha-L-rhamnopyranosyl-(1 --> 4)-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (1), 3-O-beta-D-xylopyranosyl-(1 --> 3)-alpha-L-rhamnopyranosyl-(1 --> 2)-alpha-L-arabinopyranosyl-akebonic acid-28-O-alpha-L-rhamnopyranosyl-(1 --> 4)-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (2), 3-O-beta-D-glucopyranosyl-(1 --> 3)-alpha-L-arabinopyranosyl-akebonic acid-28-O-alpha-L-rhamnopyranosyl-(1 --> 4)-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (3), 3-O-alpha-L-arabinopyranosyl-(1 --> 3)-[alpha-L-rhamnopyranosyl-(1 --> 2)-]alpha-L-arabinopyranosyl-akebonic acid-28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (6), 3-O-alpha-L-arabinopyranosyl-(1 --> 3)-[alpha-L-arabinopyranosyl-(1 --> 2)-]alpha-L-arabinopyranosyl-akebonic acid-28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranosyl ester (7).     

The visible spectrum of zirconium dioxide, ZrO2

The electronic spectrum of a cold molecular beam of zirconium dioxide, ZrO(2), has been investigated using laser induced fluorescence (LIF) in the region from 17,000 cm(-1) to 18,800 cm(-1) and by mass-resolved resonance enhanced multi-photon ionization (REMPI) spectroscopy from 17,000 cm(-1)-21,000 cm(-1). The LIF and REMPI spectra are assigned to progressions in the A?(1)B(2)(ν(1), ν(2), ν(3)) ← X?(1)A(1)(0, 0, 0) transitions. Dispersed fluorescence from 13 bands was recorded and analyzed to produce harmonic vibrational parameters for the X?(1)A(1) state of ω(1) = 898(1) cm(-1), ω(2) = 287(2) cm(-1), and ω(3) = 808(3) cm(-1). The observed transition frequencies of 45 bands in the LIF and REMPI spectra produce origin and harmonic vibrational parameters for the A?(1)B(2) state of T(e) = 16,307(8) cm(-1), ω(1) = 819(3) cm(-1), ω(2) = 149(3) cm(-1), and ω(3) = 518(4) cm(-1). The spectra were modeled using a normal coordinate analysis and Franck-Condon factor predictions. The structures, harmonic vibrational frequencies, and the potential energies as a function of bending angle for the A?(1)B(2) and X?(1)A(1) states are predicted using time-dependent density functional theory, complete active space self-consistent field, and related first-principle calculations. A comparison with isovalent TiO(2) is made.     

UV-Vis, fluorescence and NMR spectroscopic investigations on inclusion properties of a designed tetrahomocalix[8]arene with fullerenes C60 and C70 in solution

The present article reports the spectroscopic investigations on non-covalent interaction of fullerenes C(60) and C(70) with a macrocyclic receptor molecule, namely, 1,3,5,7-tetrahomo-p-tert-butylcalix[8]arene (1) in toluene. Jobs method of continuous variation reveals 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds selectively C(60) compared to C(70) as obtained from binding constant (K) data of C(60)-1 (K(C60-1)) and C(70)-1 (K(C70-1)) complexes which are enumerated to be 265,000 dm(3) mol(-1) and 63,43 dm(3) mol(-1), respectively, and selectivity in binding (K(C60-1)/K(C70-1)) is estimated to be 4.18 as obtained from UV-Vis study. Steady state fluorescence studies reveal quenching of fluorescence of 1 in presence of fullerenes and the K value of the C(60)-1 and C(70)-1 complexes are estimated to be 80,760 and 68,780 dm(3) mol(-1), respectively, with selectivity in binding (K(C60-1)/K(C70-1)) ~1.18. (1)H NMR analysis provides very good support in favor of strong binding between C(60) and 1. The high value of K value for C(60)-1 complex indicates that 1 forms an inclusion complex with C(60).     

Structural characterization of four members of the electron-transfer series [PdII(L)2)2]n (L = o-Iminophenolate derivative; n = 2-, 1-, 0, 1+, 2+). ligand mixed valency in the monocation and monoanion with S = (1)/(2) ground states

The reaction of the ligand 2-(2-trifluoromethyl)anilino-4,6-di-tert-butylphenol, H(2)((1)L(IP)), and PdCl(2) (2:1) in the presence of air and excess NEt(3) in CH(2)Cl(2) produced blue-green crystals of diamagnetic [Pd(II)((1)L(ISQ))(2)] (1), where ((1)L(ISQ))(*)(-) represents the o-iminobenzosemiquinonate(1-) pi radical anion of the aromatic ((1)L(IP))(2-) dianion. The diamagnetic complex 1 was chemically oxidized with 1 equiv of Ag(BF(4)), affording red-brown crystals of paramagnetic (S = (1)/(2)) [Pd(II)((1)L(ISQ))((1)L(IBQ))](BF(4)) (2), and one-electron reduction with cobaltocene yielded paramagnetic (S = (1)/(2)) green crystals of [Cp(2)Co][Pd(II)((1)L(ISQ))((1)L(IP))] (3); ((1)L(IBQ))(0) represents the neutral, diamagnetic quinone form. Complex 1 was oxidized with 2 equiv of [NO]BF(4), affording green crystals of diamagnetic [Pd(II)((1)L(IBQ))(2)](3)(BF(4))(4){(BF(4))(2)H}(2).4CH(2)Cl(2) (5). Oxidation of [Ni(II)((1)L(ISQ))(2)] (S = 0) in CH(2)Cl(2) solution with 2 equiv of Ag(ClO(4)) generated crystals of [Ni(II)((1)L(IBQ))(2)(ClO(4))(2)].2CH(2)Cl(2) (6) with an S = 1 ground state. Complexes 1-5 constitute a five-membered complete electron-transfer series, [Pd((1)L)(2)](n) (n = 2-, 1-, 0, 1+, 2+), where only species 4, namely, diamagnetic [Pd(II)((1)L(IP))(2)](2-), has not been isolated; they are interrelated by four reversible one-electron-transfer waves in the cyclic voltammogram. Complexes 1, 2, 3, 5, and 6 have been characterized by X-ray crystallography at 100 K, which establishes that the redox processes are ligand centered. Species 2 and 3 exhibit ligand mixed valency: [Pd(II)((1)L(ISQ))((1)L(IBQ))](+) has localized ((1)L(IBQ))(0) and ((1)L(ISQ))(*)(-) ligands in the solid state, whereas in [Pd(II)((1)L(ISQ))((1)L(IP))](-) the excess electron is delocalized over both ligands in the solid-state structure of 3. Electronic and electron spin resonance spectra are reported, and the electronic structures of all members of this electron-transfer series are established.     

Contrasting singlet-triplet dynamical behavior of two vibrational levels of the acetylene S1 2(1)3(1)B2 polyad

Surface electron ejection by laser-excited metastables (SEELEM) and LIF spectra of acetylene were simultaneously recorded in the regions of the A1Au-X1Sigmag+ nominal 2(1)3(1)4(2) Ka=1<--00 and 2(1)3(1)6(2) Ka=1<--00 bands near 46,140 cm(-1). The upper states of these two bands are separated by only approximately 100 cm(-1), and the two S1 vibrational levels are known to be strongly mixed by anharmonic and Coriolis interactions. Strikingly different patterns were observed in the SEELEM spectra in the regions of the 2(1)3(1)4(2) and 2(1)3(1)6(2) vibrational levels. Because the equilibrium structure of the T3 electronic state is known to be nonplanar, excitation of nu4 (torsion) and nu6 (antisymmetric in-plane bend) are expected respectively to promote and suppress vibrational overlap between low-lying S1 and T3 vibrational levels. The nearly 50:50 mixed 2(1)3(1)4(2)-2(1)3(1)6(2) character of the S1 vibrational levels rules out this simple Franck-Condon explanation for the different appearance of the SEELEM spectra. A simple model is applied to the SEELEM/LIF spectra to explain the differences between spectral patterns in terms of a T3 doorway-mediated singlet-triplet coupling model.     

Resonant two-photon ionization spectroscopy of jet-cooled OsN: 520-418 nm

The optical transitions of supersonically cooled OsN have been investigated in the range from 19,200 to 23,900 cm(-1) using resonant two-photon ionization spectroscopy. More than 20 vibronic bands were observed, 17 of which were rotationally resolved and analyzed. The ground state is confirmed to be (2)Δ(5/2), deriving from the 1σ(2) 2σ(2) 1π(4) 1δ(3) 3σ(2) electronic configuration. The X (2)Δ(5/2) ground state rotational constant for (192)Os(14)N was found to be B(0) = 0.491921(34) cm(-1), giving r(0) = 1.62042(6) ? (1σ error limits). The observed bands were grouped into three band systems with Ω' = 7/2 and four with Ω' = 3/2, corresponding to the three (2)Φ(7/2) and four (2)Π(3/2) states expected from the 1σ(2) 2σ(2) 1π(4) 1δ(3) 3σ(1) 2π(1) and 1σ(2) 2σ(2) 1π(4) 1δ(2) 3σ(2) 2π(1) electronic configurations. In addition, two interacting upper states with Ω' = 5/2 were observed, one of which is thought to correspond to a 1σ(2) 2σ(2) 1π(3) 1δ(3) 3σ(2) 2π(1), (2)Δ(5/2) state. Spectroscopic constants are reported for all of the observed states, and comparisons to related molecules are made. The ionization energy of OsN is estimated as IE(OsN) = 8.80 ± 0.06 eV.     

Continuum and discrete pulsed cavity ring down laser absorption spectra of Br2 vapor

The absorption cross-sections at room temperature are reported for the first time, of Br2 vapor in overlapping bound-free and bound-bound transition of A(3)pi1u <-- Xsigma(g)+, X(1)pi1u <-- X(1)sigma(g)+ and B(3)pi0u <-- X(1)sigma(g)+, using cavity ring down spectroscopy (CRDS) technique. We reported here, the A(3)pi1u <-- X(1)sigma(g)+, transition is included along with the two stronger X(1)pi1u <-- X(1)sigma(g)+ and B(3)pi0u <-- X(1)sigma(g) transitions of Br2. We obtained discrete absorption cross-section in the rotational structure, the continuum absorption cross-sections, and were also able to measure the absorption cross-section in separate contribution of A(3)pi1u <-- X(1)sigma(g)+, (1)pi1u <-- X(1)sigma(g)+, and B(3)pi0u <-- X(1)sigma(g)+ transitions using CRDS method to use quantum yield of Br*((2)P(1/2)). We obtained absorption cross-section order 10(-19) cm2 and detection 10(13) molecule cm(-3) (1 mTorr) of Br2. The absorption cross-sections are increasing with increasing excitation energy in the wavelength region 510-535 nm.     

Dynamic structural change of a twisted hexaporphyrin complex by highly specific molecular recognition

The highly specific molecular recognition of a twisted hexaporphyrin complex, tris[5,5'-bis[5,10,15-tris[methoxy(ethoxy)(2)carbonylethyl]porphyrinatozinc(II)]-2,2'-bipyridine]ruthenium(II) chloride (2), is described. Complex 2 has two trisporphyrin binding sites and can bind two triamines, tris(2-aminoethyl)amine (3) (K(1) = 3.0 x 10(8) M(-1), K(2) = 3.0 x 10(7) M(-1)), 1,1,1-tris(aminomethyl)ethane (4) (K(1) = 2.0 x 10(7) M(-1), K(2) = 1.4 x 10(6) M(-1)), tris(3-aminopropyl)amine (5) (K(1) = 3.5 x 10(6) M(-1), K(2) = 6.0 x 10(6) M(-1)), and 1,3,5-tris(aminomethyl)benzene (6) (K(1) = 2.9 x 10(6) M(-1), K(2) = 1.2 x 10(6) M(-1)), strongly with its torsional motion. The 1:2 complex between 2 and the best fit triamine 3 showed the nature of the specific rigid structure in the UV-vis, fluorescence, and (1)H NMR spectra and isothermal titration calorimetry (ITC) measurements.     

Role of alkali metal cation size in the energy and rate of electron transfer to solvent-separated 1:1 [(M+)(acceptor)] (M+ = Li+, Na+, K+) ion pairs.

The effect of cation size on the rate and energy of electron transfer to [(M(+))(acceptor)] ion pairs is addressed by assigning key physicochemical properties (reactivity, relative energy, structure, and size) to an isoelectronic series of well-defined M(+)-acceptor pairs, M(+) = Li(+), Na(+), K(+). A 1e(-) acceptor anion, alpha-SiV(V)W(11)O(40)(5-) (1, a polyoxometalate of the Keggin structural class), was used in the 2e(-) oxidation of an organic electron donor, 3,3',5,5'-tetra-tert-butylbiphenyl-4,4'-diol (BPH(2)), to 3,3',5,5'-tetra-tert-butyldiphenoquinone (DPQ) in acetate-buffered 2:3 (v/v) H(2)O/t-BuOH at 60 degrees C (2 equiv of 1 are reduced by 1e(-) each to 1(red), alpha-SiV(IV)W(11)O(40)(6-)). Before an attempt was made to address the role of cation size, the mechanism and conditions necessary for kinetically well behaved electron transfer from BPH(2) to 1 were rigorously established by using GC-MS, (1)H, (7)Li, and (51)V NMR, and UV-vis spectroscopy. At constant [Li(+)] and [H(+)], the reaction rate is first order in [BPH(2)] and in [1] and zeroth order in [1(red)] and in [acetate] (base) and is independent of ionic strength, mu. The dependence of the reaction rate on [H(+)] is a function of the constant, K(a)1, for acid dissociation of BPH(2) to BPH(-) and H(+). Temperature dependence data provided activation parameters of DeltaH = 8.5 +/- 1.4 kcal mol(-1) and DeltaS = -39 +/- 5 cal mol(-1) K(-1). No evidence of preassociation between BPH(2) and 1 was observed by combined (1)H and (51)V NMR studies, while pH (pD)-dependent deuterium kinetic isotope data indicated that the O-H bond in BPH(2) remains intact during rate-limiting electron transfer from BPH(2) and 1. The formation of 1:1 ion pairs [(M(+))(SiVW(11)O(40)(5-))](4-) (M(+)1, M(+) = Li(+), Na(+), K(+)) was demonstrated, and the thermodynamic constants, K(M)(1), and rate constants, k(M)(1), associated with the formation and reactivity of each M(+)1 ion pair with BPH(2) were calculated by simultaneous nonlinear fitting of kinetic data (obtained by using all three cations) to an equation describing the rectangular hyperbolic functional dependence of k(obs) values on [M(+)]. Constants, K(M)(1)red, associated with the formation of 1:1 ion pairs between M(+) and 1(red) were obtained by using K(M)(1) values (from k(obs) data) to simultaneously fit reduction potential (E(1/2)) values (from cyclic voltammetry) of solutions of 1 containing varying concentrations of all three cations to a Nernstian equation describing the dependence of E(1/2) values on the ratio of thermodynamic constants K(M)(1) and K(M)(1)red. Formation constants, K(M)(1), and K(M)(1)red, and rate constants, k(M)(1), all increase with the size of M(+) in the order K(Li)(1) = 21 < K(Na)(1) = 54 < K(K)(1) = 65 M(-1), K(Li)(1)red = 130 < K(Na)(1)red = 570 < K(K)(1)red = 2000 M(-1), and k(Li)(1) = 0.065 < k(Na)(1) = 0.137 < k(K)(1) = 0.225 M(-1) s(-1). Changes in the chemical shifts of (7)Li NMR signals as functions of [Li(5)1] and [Li(6)1(red)] were used to establish that the complexes M(+)1 and M(+)1(red) exist as solvent-separated ion pairs. Finally, correlation between cation size and the rate and energy of electron transfer was established by consideration of K(M)(1), k(M)(1), and K(M)(1)red values along with the relative sizes of the three M(+)1 pairs (effective hydrodynamic radii, r(eff), obtained by single-potential step chronoamperometry). As M(+) increases in size, association constants, K(M)(1), become larger as smaller, more intimate solvent-separated ion pairs, M(+)1, possessing larger electron affinities (q/r), and associated with larger k(M)(1)() values, are formed. Moreover, as M(+)1 pairs are reduced to M(+)1(red) during electron transfer in the activated complexes, [BPH(2), M(+)1], contributions of ion pairing energy (proportional to -RT ln(K(M)(1)red/K(M)(1)) to the standard free energy change associated with electron transfer, DeltaG degrees (et), increase with cation size: -RT ln(K(M)(1)red/K(M)(1)) (in kcal mol(-1)) = -1.2 for Li(+), -1.5 for Na(+), and -2.3 for K(+).     

Sub-Doppler rotationally resolved spectroscopy of lower vibronic bands of benzene with Zeeman effects

Sub-Doppler high-resolution excitation spectra and the Zeeman effects of the 6(0)(1), 1(0)(1)6(0)(1), and 1(0)(2)6(0)(1) bands of the S1(1)B2u<--S(0)(1)A1g transition of benzene were measured by crossing laser beam perpendicular to a collimated molecular beam. 1593 rotational lines of the 1(0) (1)6(0) (1) band and 928 lines of the 1(0)(2)6(0)(1) band were assigned, and the molecular constants of the excited states were determined. Energy shifts were observed for the S1(1)B2u(v1=1,v6=1,J,Kl=-11) levels, and those were identified as originating from a perpendicular Coriolis interaction. Many energy shifts were observed for the S1(1)B2u(v1=2,v6=1,J,Kl) levels. The Zeeman splitting of a given J level was observed to increase with K and reach the maximum at K=J, which demonstrates that the magnetic moment lies perpendicular to the molecular plane. The Zeeman splittings of the K=J levels were observed to increase linearly with J. From the analysis, the magnetic moment is shown to be originating mostly from mixing of the S1(1)B2u and S2(1)B1u states by the J-L coupling (electronic Coriolis interaction). The number of perturbations was observed to increase as the excess energy increases, and all the perturbing levels were found to be a singlet state from the Zeeman spectra.     

Solid-state and solution-state coordination chemistry of the zinc triad with the mixed N,S donor ligand bis(2-methylpyridyl) sulfide

The binding of group 12 metal ions to bis(2-methylpyridyl) sulfide (1) was investigated by X-ray crystallography and NMR. Seven structures of the chloride and perchlorate salts of Hg(II), Cd(II), and Zn(II) with 1 are reported. Hg(1)(2)(ClO(4))(2), Cd(1)(2)(ClO(4))(2), and Zn(1)(2)(ClO(4))(2).CH(3)CN form mononuclear, six-coordinate species in the solid state with 1 binding in a tridentate coordination mode. Hg(1)(2)(ClO(4))(2) has a distorted trigonal prismatic coordination geometry while Cd(1)(2)(ClO(4))(2) and Zn(1)(2)(ClO(4))(2).CH(3)CN have distorted octahedral geometries. With chloride anions, the 1:1 metal to ligand complexes Hg(1)Cl(2), [Cd(1)Cl(2)](2), and Zn(1)Cl(2) are formed. A bidentate binding mode that lacks thioether coordination is observed for 1 in the four-coordinate, distorted tetrahedral complexes Zn(1)Cl(2) and Hg(1)Cl(2). [Cd(1)Cl(2)](2) is dimeric with a distorted octahedral coordination geometry and a tridentate 1. Hg(1)Cl(2) is comprised of pairs of loosely associated monomers and Zn(1)Cl(2) is monomeric. In addition, Hg(2)(1)Cl(4) is formed with alternating chloride and thioether bridges. The distorted square pyramidal Hg(II) centers result in a supramolecular zigzagging chain in the solid state. The solution (1)H NMR spectra of [Hg(1)(2)](2+) and [Hg(1)(NCCH(3))(x)()](2+) reveal (3)(-)(5)J((199)Hg(1)H) due to slow ligand exchange found in these thioether complexes. Implications for use of Hg(II) as a metallobioprobe are discussed.     

Frustrated beta-chloride elimination. Selective arene alkylation by alpha-chloronorbornene catalyzed by electrophilic metallocenium ion pairs

Single-site polymerization catalysts generated in situ via activation of Cp*MMe(3) (Cp* = C(5)Me(5); M = Ti, Zr), (CGC)MMe(2) (CGC = C(5)Me(4)SiMe(2)NBu(t)(); M = Ti, Zr), and Cp(2)ZrMe(2) with Ph(3)C(+)B(C(6)F(5))(4)(-) catalyze alkylation of aromatic molecules (benzene, toluene) with alpha-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C(6)H(5) (1a), C(6)H(4)CH(3) (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d(n)-norbornane-7-d(1) (aryl-d(n) = C(6)D(5) (1a-d(6)), C(6)D(4)CD(3) (1b-d(8))) are obtained via catalytic arylation of alpha-chloronorbornene in either benzene-d(6) or toluene-d(8). Isolated ion-pair complexes such as (CGC)ZrMe(toluene)(+)B(C(6)F(5))(4)(-) and Cp(2)ThMe(+)B(C(6)F(5))(4)(-) also catalyze the reaction of alpha-chloronorbornene in toluene-d(8) to give 1b-d(8) in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h(-1) (for the Cp*TiMe(3)/Ph(3)C(+)B(C(6)F(5))(4)(-)-catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by (1)H, (2)H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using (1)H-(1)H COSY, (1)H-(13)C HMBC, and (1)H-(1)H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle.     

Sensitivity of (1)J[C(1)-H(1)] magnitudes to anomeric stereochemistry in 2,3-anhydro-O-furanosides.

The magnitude of the one-bond coupling constant between C(1) and H(1) in 2,3-anhydro-O-furanosides has been shown to be sensitive to the stereochemistry at the anomeric center. A panel of 24 compounds was studied and in cases where the anomeric hydrogen is trans to the epoxide moiety, (1)J[C(1)-H(1)] = 163-168 Hz; and when this hydrogen is cis to the oxirane ring, ((1)J[C(1)-H(1)] = 171-174 Hz. In contrast, for 2,3-anhydro-S-glycosides, the size of the (1)J[C(1)-H(1)] is not sensitive to C(1) stereochemistry. Computational studies on all four methyl 2,3-anhydro-O-furanosides (5-8) demonstrated that (1)J[C(1)-H(1)] was inversely proportional to the length of the C(1)-H(1) bond. A previously reported equation, which relates C(1)-H(1) bond distance and atomic charges to (1)J[C(1)-H(1)] magnitudes, could be used to accurately predict the J values in the alpha-lyxo (5) and beta-ribo (8) isomers. In contrast, with the beta-lyxo (6) and alpha-ribo isomers (7), this equation underestimated the size of these coupling constants by 10-20 Hz.     

Optically active antifungal azoles. XI. An alternative synthetic route for 1

New routes for the synthesis of the optically active antifungal triazoles 1-[(1R,2R)-2-(2,4-difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-1-tetrazolyl)phenyl]-2-imidazolidinone (1b) and the 3-14-(1H-1,2,3-triazol-1-yl)phenyl]-2-imidazolidinone analog (1a) that possess an imidazolidine nucleus were established. The key synthetic intermediates, (2R,3R)-3-(2,2-diethoxvethyl)amino-2-(2,4-difluorophenyl)-1-(1H1,2,4-triazol-1-yl)-2-butanol (8) and (2R,3R)-2-(2,4-difiuorophenyl)-3-(2-h ydroxyethyl)amino-1-(1H-1,2,4-triazol-1-yl)-2-butanol (14), were prepared by the ring-opening reaction of the oxirane (2) with the corresponding 2-substituted ethylamines. The acetal (8) was converted to the imidazolidinones (1a, b) by condensation with the carbamates (10a, b) followed by treatment with hydrochloric acid and subsequent catalytic hydrogenation. The candidate selected for the clinical trials, 1b (TAK-456), was alternatively prepared from the hydroxyethylamino intermediate (14) via two reaction steps: condensation with the carbamate (10b) to the urea (15) and subsequent cyclization to the imidazolidinones. This newly developed synthetic route could be applied to a large scale preparation of 1b.