Organic Polar Crystals, Second Harmonic Generation, and Piezoelectric Effects from Heteroadamantanes in the Space Group R3m.

Polar crystalline materials, a subset of the non-centrosymmetric materials, are highly sought after. Their symmetry properties make them pyroelectric and also piezoelectric and capable of second-harmonic generation (SHG). For SHG and piezoelectric applications, metal oxides are commonly used. The advantages of oxides are durability and hardness - downsides are the need for high-temperature synthesis/processing and often the need to include toxic metals. Organic polar crystals, on the other hand, can avoid toxic metals and can be amenable to solution-state processing. While the vast majority of polar organic molecules crystallize in non-polar space groups, we found that both 7-chloro-1,3,5-triazaadamantane, for short Cl-TAA, and also the related Br-TAA (but not I-TAA) form polar crystals in the space group R3m, easily obtained from dichloromethane solution. Measurements confirm piezoelectric and SHG properties for Cl-TAA and Br-TAA. When the two species are crystallized together, solid solutions form, suggesting that properties of future materials can be tuned continuously.

Applications of noisy quantum computing and quantum error mitigation to "adamantaneland": a benchmarking study for quantum chemistry.

The field of quantum computing has the potential to transform quantum chemistry. The variational quantum eigensolver (VQE) algorithm has allowed quantum computing to be applied to chemical problems in the noisy intermediate-scale quantum (NISQ) era. Applications of VQE have generally focused on predicting absolute energies instead of chemical properties that are relative energy differences and that are most interesting to chemists studying a chemical problem. We address this shortcoming by constructing a molecular benchmark data set in this work containing isomers of C10H16 and carbocationic rearrangements of C10H15+, calculated at a high-level of theory. Using the data set, we compared noiseless VQE simulations to conventionally performed density functional and wavefunction theory-based methods to understand the quality of results. We also investigated the effectiveness of a quantum state tomography-based error mitigation technique in applications of VQE under noise (simulated and real). Our findings reveal that the use of quantum error mitigation is crucial in the NISQ era and advantageous to yield almost noiseless quality results.

Why Diorganyl Zinc Lewis Acidity Dramatically Increases with Narrowing C-Zn-C Bond Angle.

The Lewis acidity of a metal center is influenced not only by the electronic properties of the bonded ligands but also by the bond angles, which we suggest to be important for zinc diorganyls. Molecular orbital correlation predicts that a narrower C-Zn-C bond angle of the R2Zn fragment lowers its lowest unoccupied molecular orbital (LUMO) and increases its Lewis acidity, such that it binds added ligands more strongly. Computations on Me2Zn(bipy) (bipy = 2,2'-bipyridine) yield that, for every 10° of C-Zn-C narrowing close to tetrahedral geometry, the Zn-N distance shortens by 0.027 Å (0.048 Å per 10° for the range 180-90°) and that the LUMO of the Me2Zn fragment drops by 0.24 eV. A total of 10 dialkyl zinc complexes of bipy or 4,4'-di-tert-butyl-2,2'-bipyridine are crystallographically characterized here. Structure correlations (published and new data) confirm the link between the C-Zn-C angle and Zn-N distance. Principal component analysis provides a detailed picture of the correlated distortions. Relevance for zinc fingers/zinc enzymes is discussed.

An iridium complex with an unsupported Ir-Zn bond: di-iodido-(η5-penta-methyl-cyclo-penta-dien-yl)bis-(tri-methyl-phosphane)iridiumzinc(Ir-Zn) benzene hemisolvate.

The title compound, [IrZnI2(C10H15)(C3H9P)2]·0.5C6H6 or [Cp*(PMe3)2Ir]-[ZnI2] (Cp* = cyclo-C5Me5) was obtained and characterized as its benzene solvate [Cp*(PMe3)2Ir]-[ZnI2]·0.5C6H6. The bimetallic complex in this structure contains the Lewis-acidic fragment ZnI2 bonded to the Lewis-basic fragment Cp*(PMe3)2Ir, with an Ir-Zn bond distance of 2.452 (1) Å. The compound was obtained by reacting [Cp*(PMe3)IrI2] with 2-Ad2Zn (2-Ad = 2-adamant-yl), resulting in the reduction of the IrIII complex and formation of the IrI-ZnII adduct. The crystal studied was a twin by non-merohedry with a refined BASF parameter of 0.223 (1).

A molybdenum tris-(di-thiol-ene) complex coordinates to three bound cobalt centers in three different ways.

The synthesis and structural characterization of the mol-ecular compound (µ3-benzene-1,2-di-thiol-ato)hexa-carbonyl-bis-(µ3-1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolato)tricobaltmolybdenum, [Co3Mo(C4F6S2)2(C6H4S2)(CO)6] or Mo(tfd)2(bdt)(Co(CO)2)3 (tfd is 1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolate and bdt is benzene-1,2-di-thiol-ate), are reported. The structure of the mol-ecule contains the molybdenum tris-(di-thiol-ene) complex Mo(tfd)2(bdt) coordinated as a multidentate ligand to three cobalt dicarbonyl units. Each of the three cobalt centers is relatively close to molybdenum, with Co⋯Mo distances of 2.7224 (7), 2.8058 (7), and 2.6320 (6) Å. Additionally, each of the cobalt centers is bound via main-group donor atoms, but each one in a different way: the first cobalt atom is coordinated by two sulfur atoms from different di-thiol-enes (bdt and tfd). The second cobalt atom is coordinated by one sulfur from one tfd and two olefinic carbons from another tfd. The third cobalt is coordinated by one sulfur from bdt and two sulfurs from tfd. This is, to the best of our knowledge, the first structurally characterized example of a molybdenum (tris-)di-thiol-ene complex that coordinates to cobalt. The F atoms of two of the -CF3 groups were refined as disordered over two sets of sites with ratios of refined occupancies of 0.703 (7):0.297 (7) and 0.72 (2):0.28 (2).

A new structural model for NiFe hydrogenases: an unsaturated analogue of a classic hydrogenase model leads to more enzyme-like Ni-Fe distance and inter-planar fold.

The complex cation in the title compound, (carbonyl-1κC)(1η5-penta-methyl-cyclo-penta-dien-yl)(µ-2,3,9,10-tetra-methyl-1,4,8,11-tetra-thia-undeca-2,9-diene-1,11-diido-1κ2S,S''':2κ4S,S',S'',S''')ironnickel(Fe-Ni) hexa-fluoro-phosphate, [FeNi(C10H15)(C11H18S4)(CO)]PF6 or [Ni(L')FeCp*(CO)]PF6, is composed of the nickel complex fragment [Ni(L')] coordinated as a metalloligand (using S1 and S4) to the [FeCp*(CO)]+ fragment, where (L')2- is [S-C(Me)=C(Me)-S-(CH2)3-S-C(Me)=C(Me)-S]2- and where Cp*- is cyclo-C5(Me)5- (penta-methyl-cyclo-penta-dien-yl). The ratio of hexa-fluoro-phosphate anion per complex cation is 1:1. The structure at 150 K has ortho-rhom-bic (Pbcn) symmetry. The atoms of the complex cation are located on general positions (multiplicity = 8), whereas there are two independent hexa-fluoro-phosphate anions, each located on a twofold axis (Wyckoff position 4c; multiplicity = 4). The structure of the new dimetallic cation [Ni(L')FeCp*(CO)]+ can be described as containing a three-legged piano-stool environment for iron [Cp*Fe(CO)'S2'] and an approximately square-planar 'S4' environment for Ni. The NiS2Fe diamond-shaped substructure is notably folded at the S-S hinge: the angle between the NiS2 plane and the FeS2 plane normals is 64.85 (6)°. Largely because of this fold, the nickel-iron distance is relatively short, at 2.9195 (8) Å. The structural data for the complex cation, which contains a new unsaturated 'S4' ligand (two C=C double bonds), provide an inter-esting comparison with the known NiFe hydrogenase models containing a saturated 'S4'-ligand analogue having the same number of carbon atoms in the ligand backbone, namely with the structures of [Ni(L)FeCp(CO)]+ (as the PF6- salt, CH2Cl2 solvate) and [Ni(L)FeCp*(CO)]+ (as the PF6- salt), where (L)2- is [S-CH2-CH2-S-(CH2)3-S-CH2-CH2-S]2- and Cp- is cyclo-penta-dienyl. The saturated analogues [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ have similar Ni-Fe distances: 3.1727 (6), 3.1529 (7) Š(two independent mol-ecules in the unit cell) and 3.111 (5) Å, respectively, for the two complexes, whereas [Ni(L')FeCp*(CO)]+ described here stands out with a much shorter Ni-Fe distance [2.9196 (8) Å]. Also, [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ show inter-planar fold angles that are similar between the two: 39.56 (5), 41.99 (5) (independent mol-ecules in the unit cell) and 47.22 (9) °, respectively, whereas [Ni(L')FeCp*(CO)]+ possesses a much more pronounced fold [64.85 (6)°]. Given that larger fold angles and shorter Ni-Fe distances are considered to be structurally closer to the enzyme, unsaturation in an 'S4'-ligand of the type (S-C2-S-C3-S-C2-S)2- seems to increase structural resemblance to the enzyme for structural models of the type [Ni('S4')FeCp R (CO)]+ (Cp R = Cp or Cp*).

Coordination compounds containing bis-di-thiol-ene-chelated molybdenum(IV) and oxalate: comparison of terminal with bridging oxalate.

Two coordination compounds containing tetra-n-butyl-ammonium cations and bis-tfd-chelated molybdenum(IV) [tfd2- = S2C2(CF3)22-] and oxalate (ox2-, C2O42-) in complex anions are reported, namely bis-(tetra-n-butyl-ammonium) bis-(1,1,1,4,4,4-hexa-fluoro-but-2-ene-2,3-di-thiol-ato)oxalatomolybdate(IV)-chloro-form-oxalic acid (1/1/1), (C16H36N)2[Mo(C4F6S2)2(C2O4)]·CHCl3·C2H2O4 or (N n Bu4)2[Mo(tfd)2(ox)]·CHCl3·C2H2O4, and bis-(tetra-n-butyl-ammonium) µ-oxalato-bis-[bis-(1,1,1,4,4,4-hexa-fluoro-but-2-ene-2,3-di-thiol-ato)molybdate(IV)], (C16H36N)2[Mo2(C4F6S2)4(C2O4)] or (N n Bu4)2[(tfd)2Mo(µ-ox)Mo(tfd)2]. They contain a terminal oxalate ligand in the first compound and a bridging oxalate ligand in the second compound. Anion 12- is [Mo(tfd)2(ox)]2- and anion 22-, formally generated by adding a Mo(tfd)2 fragment onto 12-, is [(tfd)2Mo(µ-ox)Mo(tfd)2]2-. The crystalline material containing 12- is (N n Bu4)2-1·CHCl3·oxH2, while the material containing 22- is (N n Bu4)2-2. Anion 22- lies across an inversion centre. The complex anions afford a rare opportunity to compare terminal oxalate with bridging oxalate, coordinated to the same metal fragment, here (tfd)2MoIV. C-O bond-length alternation is observed for the terminal oxalate ligand in 12-: the difference between the C-O bond length involving the metal-coordinating O atom and the C-O bond length involving the uncoordinating O atom is 0.044 (12) Å. This bond-length alternation is significant but is smaller than the bond-length alternation observed for oxalic acid in the co-crystallized oxalic acid in (N n Bu4)2-1·CHCl3·oxH2, where a difference (for C=O versus C-OH) of 0.117 (14) Šwas observed. In the bridging oxalate ligand in 22-, the C-O bond lengths are equalized, within the error margin of one bond-length determination (0.006 Å). It is concluded that oxalic acid contains a localized π-system in its carb-oxy-lic acid groups, that the bridging oxalate ligand in 22- contains a delocalized π-system and that the terminal oxalate ligand in 12- contains an only partially localized π-system. In (N n Bu4)2-1·CHCl3·oxH2, the F atoms of two of the -CF3 groups in 12- are disordered over two sets of sites, as are the N and eight of the C atoms of one of the N n Bu4 cations. In (N n Bu4)2-2, the whole of the unique N n Bu4+ cation is disordered over two sets of sites. Also, in (N n Bu4)2-2, a region of disordered electron density was treated with the SQUEEZE routine in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18].

C2-isomer of [Pd(tfd)]6 [tfd is S2C2(CF3)2] as its benzene solvate: a new member of the small but growing class of homoleptic palladium(II) monodi-thio-lenes in the form of hexa-meric cubes.

The title compound, hexa-kis-[µ3-1,2-bis-(tri-fluoro-meth-yl)ethene-1,2-di-thiol-ato]-octa-hedro-hexa-palladium(II), [Pd(C4F6S2)]6, crystallizes as its benzene solvate, [Pd(tfd)]6·2.5C6H6, where tfd is the di-thiol-ene S2C2(CF3)2. The mol-ecular structure of [Pd(tfd)]6 is of the hexa-metallic cube type seen previously in three examples of hexa-meric homoleptic palladium monodi-thiol-ene structures. All structures have in common: (a) the cluster closely approximates a cube containing six PdII atoms, one at the centre of each cube face; (b) 12 S atoms occupy the mid-points of all 12 cube edges, providing for each PdII atom an approximately square-planar S4 environment; (c) each S atom is part of a di-thiol-ene mol-ecule, where the size of the di-thiol-ene ligand necessitates that only sulfur atoms on adjacent cube edges can be part of the same di-thiol-ene. This general cube-type framework has so far given rise to two isomeric types: an S6-symmetric isomer and a C2-chiral type (two isomers that are enanti-omers of each other). The structure of [Pd(tfd)]6 is of the C2-type. Out of the 12 CF3 groups, three are rotationally disordered over two positions. Further, we answer the question of whether additional, previously undiscovered, isomers could follow from the cube rules (a) through (c) above. An exhaustive analysis shows that no additional isomers are possible and that the list of isomers (one S6 isomer, two C2 enanti-omers) is complete. Each isomer type could give rise to an unlimited number of compounds if the specific di-thiol-ene used is varied.

Adamantyl metal complexes: new routes to adamantyl anions and new transmetallations.

New routes to 1- and 2-adamantyl anion equivalents are described, starting from commercially available 1- and 2-adamantylzinc bromides and employing reducing metals (Mg; Li). Adamantylmagnesium bromides (both 1-AdMgBr and 2-AdMgBr) can reliably be produced via reaction of the corresponding adamantylzinc bromides with excess magnesium metal. Reactions of adamantylzinc bromides with stoichiometic lithium biphenylide or lithium 2,2'-bipyridylide afford the new diadamantylzinc species, 1-Ad2Zn and 2-Ad2Zn, isolable free of solvent and salt impurities. Addition of 2,2'-bipyridine (bipy) leads to the crystalline adducts 1-Ad2Zn(bipy) and 2-Ad2Zn(bipy), which were structurally characterized. The resulting adamantyl anions were used in order to generate the first adamantyl complexes of mercury (1- and 2-Ad2Hg), gold (1- and 2-AdAu(PPh3), 1- and 2-AdAu(PCy3)) and bismuth (2-Ad2BiBr), of which 1- and 2-Ad2Hg, 2-AdAu(PPh3), 2-AdAu(PCy3), and 2-Ad2BiBr were isolated. These include the first structurally characterized unsupported 2-adamantyl metal complexes.

The first palladium(iv) aryldiazenido complex: relevance for C-C coupling.

Overall two-electron oxidative addition of the aryldiazonium cation para-methoxybenzenediazonium (pmbd+) to [(Tp*)PdIIMe2]- (Tp*- = hydridotris-(3,5-dimethylpyrazolyl)borate) produces the first characterized palladium(iv) aryldiazenido complex, [(Tp*)PdIVMe2(pmbd)] (pmbd- = para-methoxybenzenediazenido). Thermolysis in benzene forms a mixture of products that contains [(Tp*)PdIVMe3] and the C-C coupled product, 4,4'-dimethoxybiphenyl. The use of acetone as the thermolysis solvent changes the product distribution towards the formation of anisole. While some involvement of two-electron pathways in the decomposition cannot be ruled out, radicals, through one-electron steps, are involved in the major pathways for decomposition. The involvement of radicals is confirmed by the solvent dependent nature of the product distribution and by observing that the added N-tert-butyl-α-phenylnitrone efficiently traps aryl radicals.

A Molecular Rotor Possessing an H-M-H "Spoke" on a P-M-P "Axle": A Platinum(II) trans-Dihydride Spins Rapidly Even at 75 K.

A new class of low-barrier molecular rotors, metal trans-dihydrides, is suggested here. To test whether rapid rotation can be achieved, the known complex trans-H2Pt(P(t)Bu3)2 was experimentally studied by (2)H and (195)Pt solid-state NMR spectroscopy (powder pattern changes with temperature) and computationally modeled as a (t)Bu3P-Pt-P(t)Bu3 stator with a spinning H-Pt-H rotator. Whereas the related chloro-hydride complex, trans-H(Cl)Pt(P(t)Bu3)2, does not show rotational behavior at room temperature, the dihydride trans-H2Pt(P(t)Bu3)2 rotates fast on the NMR time scale, even at low temperatures down to at least 75 K. The highest barrier to rotation is estimated to be ∼3 kcal mol(-1), for the roughly 3 Šlong rotator in trans-H2Pt(P(t)Bu3)2.

Organization of astaxanthin within oil bodies of Haematococcus pluvialis studied with polarization-dependent harmonic generation microscopy.

Nonlinear optical microscopy was used to image the localization of astaxanthin accumulation in the green alga, Haematococcus pluvialis. Polarization-in, polarization-out (PIPO) second harmonic generation (SHG) and third harmonic generation (THG) microscopy was applied to study the crystalline organization of astaxanthin molecules in light-stressed H. pluvialis in vivo. Since astaxanthin readily forms H- and J-aggregates in aqueous solutions, PIPO THG studies of astaxanthin aggregates contained in red aplanospores were compared to PIPO THG of in vitro self-assembled H- and J-aggregates of astaxanthin. The PIPO THG data clearly showed an isotropic organization of astaxanthin in red aplanospores of H. pluvialis. This is in contrast to the highly anisotropic organization of astaxanthin in synthetic H- and J-aggregates, which showed to be uniaxial. Since carotenoids in vitro preferentially form H- and J-aggregates, but in vivo form a randomly organized structure, this implies that astaxanthin undergoes a different way of packing in biological organisms, which is either due to the unique physical environment of the alga or is controlled enzymatically.

Molecular organization of crystalline ß-carotene in carrots determined with polarization-dependent second and third harmonic generation microscopy.

Polarization-in, polarization-out (PIPO) second harmonic generation (SHG) and third harmonic generation (THG) microscopy was used to study the crystalline organization of ß-carotene molecules within individual aggregates contained in the chromoplasts of orange carrots in vivo. Multimodal PIPO SHG and PIPO THG studies of the aggregates revealed one dominant SHG and THG dipole signifying that ß-carotene molecules are oriented along a single axis. Three-dimensional visualization of the orientation of ß-carotene molecules with respect to the aggregate axis was also performed with both microscopy modalities and revealed organization of the aggregates as ribbon-like structures consisting of twists and folds. Therefore, PIPO SHG and PIPO THG microscopy provides information on the crystalline organization and the orientation of ordered biological structures in vivo where multimodal polarization dependent SHG and THG investigations are particularly advantageous as both noncentrosymmetric and centrosymmetric crystalline organizations can be probed.

The molecular second hyperpolarizability of the light-harvesting chlorophyll a/b pigment-protein complex of photosystem II.

Photosynthetic structures when imaged with nonlinear optical microscopy give rise to high third harmonic generation (THG) signal intensity due to the presence of chlorophylls and xanthophylls which have large second hyperpolarizabilitiy (γ) values. The γ value of trimers of the light-harvesting chlorophyll a/b pigment-protein complex of photosystem II (LHCII) isolated from pea (Pisum sativum) plants was investigated by the THG ratio technique at 1028 nm wavelength and found to have the value (-1600 ± 400) × 10(-41) m(2) V(-2). The large negative γ value of trimeric LHCII is due to the presence of chlorophyll a and chlorophyll b which have large negative γ values, while positive γ values of xanthophylls reduce the magnitude of the THG signal. Variation was observed between the measured γ value of LHCII and the approximated γ value of LHCII obtained by adding individual γ values of chlorophylls and xanthophylls. This difference can be attributed to the differing inter-pigment interactions of oriented chlorophylls and xanthophylls in the pigment-protein complex compared to randomly oriented non-interacting pigments in solution, as well as a differing dielectric environment of the pigments within LHCII versus the surrounding organic solvent.

Apparent anti-Woodward-Hoffmann addition to a nickel bis(dithiolene) complex: the reaction mechanism involves reduced, dimetallic intermediates.

Nickel dithiolene complexes have been proposed as electrocatalysts for alkene purification. Recent studies of the ligand-based reactions of Ni(tfd)2 (tfd = S2C2(CF3)2) and its anion [Ni(tfd)2](-) with alkenes (ethylene and 1-hexene) showed that in the absence of the anion, the reaction proceeds most rapidly to form the intraligand adduct, which decomposes by releasing a substituted dihydrodithiin. However, the presence of the anion increases the rate of formation of the stable cis-interligand adduct, and decreases the rate of dihydrodithiin formation and decomposition. In spite of both computational and experimental studies, the mechanism, especially the role of the anion, remained somewhat elusive. We are now providing a combined experimental and computational study that addresses the mechanism and explains the role of the anion. A kinetic study (global analysis) for the reaction of 1-hexene is reported, which supports the following mechanism: (1) reversible intraligand addition, (2) oxidation of the intraligand addition product prior to decomposition, and (3) interligand adduct formation catalyzed by Ni(tfd)2(-). Density functional theory (DFT) calculations were performed on the Ni(tfd)2/Ni(tfd)2(-)/ethylene system to shed light on the selectivity of adduct formation in the absence of anion and on the mechanism in which Ni(tfd)2(-) shifts the reaction from intraligand addition to interligand addition. Computational results show that in the neutral system the free energy of activation for intraligand addition is lower than that for interligand addition, in agreement with the experimental results. The computations predict that the anion enhances the rate of the cis-interligand adduct formation by forming a dimetallic complex with the neutral complex. The [(Ni(tfd)2)2](-) dimetallic complex then coordinates ethylene and isomerizes to form a Ni,S-bound ethylene complex, which then rapidly isomerizes to the stable interligand adduct but not to the intraligand adduct. Thus, the anion catalyzes the formation of the interligand adduct. Significant experimental evidence for dimetallic species derived from nickel bis(dithiolene) complexes has been found. ESI-MS data indicate the presence of a [(Ni(tfd)2)2](-) dimetallic complex as the acetonitrile adduct. A charge-neutral association complex of Ni(tfd)2 with the ethylene adduct of Ni(tfd)2 has been crystallographically characterized. Despite the small driving force for the reversible association, very major structural reorganization (square-planar → octahedral) occurs.

Measuring the molecular second hyperpolarizability in absorptive solutions by the third harmonic generation ratio technique.

Measurement of the second hyperpolarizability (γ) values of compounds can provide insight into the molecular structural requirements for enhancement of third harmonic generation (THG) signal. A convenient method for measuring the γ of compounds in solutions was developed by implementing the THG ratio method which is based on measuring the THG intensity from two interfaces using a nonlinear optical microscope while accounting for the refractive index of solutions at the fundamental and third harmonic wavelengths. We demonstrated that the difference in refractive index at both wavelengths strongly influenced the calculation of γ values when compounds have absorption near the third harmonic or fundamental wavelength. To this end, a refractometer with the wavelength tuning range from UV to near IR was constructed, and the measured refractive indices were used to extract the γ values. The γ values of carotenoids and chlorophylls found in photosynthetic pigment-protein complexes were explored. Large differences in the refractive index at third harmonic and fundamental wavelengths for chlorophylls result in γ values that are more than two orders of magnitude larger than γ values for carotenoids as well as the sign of chlorophylls'γ values is negative while carotenoids have positive γ values.

Carotenoid based bio-compatible labels for third harmonic generation microscopy.

The use of carotenoids as biologically friendly labels for third harmonic generation (THG) microscopy is demonstrated. Carotenoid containing liposomes are used to label cell structures via liposome cell fusion. The THG microscopy labels, called harmonophores, were characterized by measuring the third-order nonlinear susceptibility (χ((3))) of carotenoids: violaxanthin, neoxanthin, lutein, ß-carotene, zeaxanthin, canthaxanthin and astaxanthin. The THG ratio method was used, which is based on measuring the THG intensity from two interfaces using a nonlinear optical microscope. The second hyperpolarizability values of carotenoids were extracted from χ((3)) measurements taking into account the refractive index at fundamental and third harmonic wavelengths. The length dependence of the second hyperpolarizability of conjugated polyenes from 9 to 13 double bonds with varying oxygen functional groups was investigated. It appears that the presence of epoxides can have a higher influence than an additional conjugated double bond. Furthermore, labelling of both Drosophila Schneider 2 cells and Drosophila melanogaster larvae myocytes with ß-carotene was achieved. This study demonstrates that THG enhancement by carotenoids can be used for nontoxic in vivo labelling of subcellular structures for third harmonic generation microscopy.

Rapid, covalent addition of phosphine to dithiolene in a molybdenum tris(dithiolene). A new structural model for dimethyl sulfoxide reductase.

Triphenylphosphine (PPh(3)) rapidly and reversibly adds to the bdt ligand in the molybdenum tris(dithiolene) complex Mo(tfd)(2)(bdt) [tfd = S(2)C(2)(CF(3))(2); bdt = S(2)C(6)H(4)], turning chelating bdt into the monodentate zwitterionic ligand SC(6)H(4)SPPh(3). A second PPh(3) molecule fills the newly created open site in the crystallographically characterized product Mo(tfd)(2)(SC(6)H(4)SPPh(3))(PPh(3)), which is a structural model for dimethyl sulfoxide (DMSO) reductase. While the complex is only a precatalyst for reduction of DMSO by PPh(3) (the initially low catalytic rate increases with time), Mo(tfd)(2)(SMe(2))(2) was found to be catalytically active without an induction period.

The mechanism of alkene addition to a nickel bis(dithiolene) complex: the role of the reduced metal complex.

The binding of an alkene by Ni(tfd)(2) [tfd = S(2)C(2)(CF(3))(2)] is one of the most intriguing ligand-based reactions. In the presence of the anionic, reduced metal complex, the primary product is an interligand adduct, while in the absence of the anion, dihydrodithiins and metal complex decomposition products are preferred. New kinetic (global analysis) and computational (DFT) data explain the crucial role of the anion in suppressing decomposition and catalyzing the formation of the interligand product through a dimetallic complex that appears to catalyze alkene addition across the Ni-S bond, leading to a lower barrier for the interligand adduct.