Correction: Zinc(II) hydration in aqueous solution. A Raman spectroscopic investigation and an ab initio molecular orbital study.

Correction for 'Zinc(II) hydration in aqueous solution. A Raman spectroscopic investigation and an ab initio molecular orbital study' by Wolfram W. Rudolph et al., Phys. Chem. Chem. Phys., 1999, 1, 4583-4593, https://doi.org/10.1039/A904051J.

Fabrication of high quality electrochemical SERS (EC-SERS) substrates using physical vapour deposition.

Screen-printed electrodes (SPEs) are an efficient and inexpensive substrate for electrochemical surface-enhanced Raman spectroscopy (EC-SERS) studies. Traditionally, the working electrode of the SPE is modified with either a colloidal paste of metal nanoparticles or an electrodeposited metallic film. These methods can be time-consuming and often produce non-uniform nanostructured films. Physical vapour deposition (PVD) is presented in this work as an efficient and effective alternative method for the production of SERS-active SPEs. SPEs coated with silver thin films via PVD show consistent and strong EC-SERS enhancement for the detection of two probe molecules, 4-aminothiophenol (p-ATP) and 5-(pyridine-4-yl)-1,3,4-oxadiazole-2-thiol (PYOT). The EC-SERS signal intensity for p-ATP and PYOT had coefficients of variation of 8.2% and 5.5%, respectively. More generally, these substrates show promise for reliable enhancement of molecules spanning diverse analytical applications.

Spectroelectrochemical and computational studies of tetrahydrocannabinol (THC) and carboxy-tetrahydrocannabinol (THC-COOH).

Rapid and accurate detection of tetrahydrocannabinol (THC) and its main secondary metabolite carboxy-tetrahydrocannabinol (THC-COOH) is important to ensure safe roadways and workplaces, particularly in regions of the world where cannabis use is legal. In this work, we seek to demonstrate the usefulness of electrochemical SERS (EC-SERS) for the rapid detection of both THC and THC-COOH, complemented by thorough ab initio calculations for both molecules. These results indicate that application of a voltage is essential for efficient SERS detection of cannabinoids at low concentrations in bodily fluids, allowing for the eventual development of sensitive and quantitative screening tools. To the best of our knowledge, this work represents the first EC-SERS study of both THC and THC-COOH.

Electrochemical surface-enhanced Raman spectroscopy (E-SERS) of novel biodegradable ionic liquids.

Electrochemical SERS (E-SERS) was used for the first time to study the interfacial behavior of a class of pyridinium-based biodegradable ionic liquids at a silver nanoparticle (AgNP) electrode surface. An isomeric series of ionic liquids (IL) based on 3-butoxycarbonyl-1-methylpyridinium bis(trifluoromethanesulfonyl)imide were prepared, which have demonstrable biodegradability. It was found that all four of the isomeric ionic liquids studied exhibited excellent electrochemical stability as binary mixtures combined with methanol, with the absence of any specific redox processes occurring over nearly 3.0 V of applied potential. Normal Raman measurements of the neat isobutyl IL showed a signal rich in vibrational features, with strong contributions from both the anion and the bulky organic cation. E-SERS of the neat isobutyl IL was shown to exhibit excellent potential stability, with no potential-induced orientational change at the metal surface. When the ionic liquids were prepared as methanolic binary mixtures, dissociation of the IL ions was observed, and only the organic cation was shown to adsorb at the Ag/solution interface. The nature of the substituent on the ester group of the IL series was observed to have a significant effect on the orientation of the cation on the metal surface, based on the application of the metal surface selection rules combined with computational data. Notably, the isobutyl and sec-butyl isomers were observed to have an orientation wherein the pyridinium ring was oriented perpendicular to the surface, while the tert-butyl and n-butyl isomers were observed to have an orientation wherein the pyridinium ring was lying flat on the metal surface.

A Raman spectroscopic and ab initio investigation of aqueous boron speciation under alkaline hydrothermal conditions: evidence for the structure and thermodynamic stability of the diborate ion.

Raman spectra of aqueous sodium borate solutions, with and without excess NaOH, NaCl, and LiCl, have been obtained from perpendicular and parallel polarization measurements acquired using a custom-built sapphire flow cell over the temperature range 25 to 300 °C at 20 MPa. The solvent-corrected reduced isotropic spectra include a large well-defined band at 865 cm-1 which overlaps with the boric acid B(OH)3 band at 879 cm-1, and becomes increasingly intense at elevated temperatures. This band does not correspond to the spectrum of any other previously reported aqueous polyborate ions, all of which have symmetric stretching bands at frequencies below that of borate, [B(OH)4]-, at 745 cm-1. Based on the classic high-temperature potentiometric titration study by R. E. Mesmer, C. F. Baes and F. H. Sweeton, Acidity measurements at elevated temperatures. VI. Boric acid equilibriums, Inorg. Chem., 1972, 11, 537-543, the new band was postulated to arise from a diborate ion, [B2(OH)7]- or [B2O(OH)5]-. Ab initio density functional theory (DFT), together with chemical modelling studies, suggest that it is most likely [B2(OH)7]-. Thermodynamic formation quotients derived from the peak areas showed variations with ionic strength as well as charge-balance discrepancies, which suggest one or more unidentified minor equilibrium species may also be present. The most likely candidate is the divalent diborate species [B2O2(OH)4]2- which is also predicted to have a band near 865 cm-1 and is postulated to be present as a sodium ion pair. These are the first quantitative Raman spectra ever reported for borate-rich solutions under such conditions and provide the first spectroscopic evidence of a diborate species at PWR reactor coolant temperatures.

Preparation of a diphosphine with persistent phosphinyl radical character in solution: characterization, reactivity with O2, S8, Se, Te, and P4, and electronic structure calculations.

A new, easily synthesized diphosphine based on a heterocyclic 1,3,2-diazaphospholidine framework has been prepared. Due to the large, sterically encumbering Dipp groups (Dipp = 2,6-diisopropylphenyl) on the heterocyclic ring, the diphosphine undergoes homolytic cleavage of the P-P bond in solution to form two phosphinyl radicals. The diphosphine has been reacted with O(2), S(8), Se, Te, and P(4), giving products that involve insertion of elements between the P-P bond to yield the related phosphinic acid anhydride, sulfide/disulfide, selenide, telluride, and a butterfly-type perphospha-bicyclobutadiene structure with a trans,trans-geometry. All molecules have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Variable-temperature EPR spectroscopy was utilized to study the nature of the phosphinyl radical in solution. Electronic structure calculations were performed on a number of systems from the parent diphosphine [H(2)P](2) to amino-substituted [(H(2)N)(2)P](2) and cyclic amino-substituted [(H(2)C)(2)(NH)(2)P](2); then, bulky substituents (Ph or Dipp) were attached to the cyclic amino systems. Calculations on the isolated diphosphine at the B3LYP/6-31+G* level show that the homolytic cleavage of the P-P bond to form two phosphinyl radicals is favored over the diphosphine by ~11 kJ/mol. Furthermore, there is a significant amount of relaxation energy stored in the ligands (52.3 kJ/mol), providing a major driving force behind the homolytic cleavage of the central P-P bond.

Anhydrous TEMPO-H: reactions of a good hydrogen atom donor with low-valent carbon centres.

In this paper, we report a novel synthesis of anhydrous 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-H). An X-ray crystal structure and full characterization of the compound are included. Compared to hydrated TEMPO-H, its anhydrous form exhibits improved stability and a differing chemical reactivity. The reactions of anhydrous TEMPO-H with a variety of low-valent carbon centres are described. For example, anhydrous TEMPO-H was reacted with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), an unsaturated NHC. Crystals of [CHNC(6)H(2)(CH(3))(3)](2)C···HO(NC(5)H(6)(CH(3))(4)), IMes···TEMPO-H, were isolated and a crystal structure determined. The experimental structure is compared to the results of theoretical calculations on the hydrogen-bonded dimer. Anhydrous TEMPO-H was also reacted with the saturated NHC, 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr), giving the product [CH(2)Ni-Pr(2)C(6)H(3)](2)CH···O(NC(5)H(6)(CH(3))(4)). In contrast, the reaction of hydrated TEMPO-H with 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene gave small amounts of the hydrolysis product, N-(2,6-diisopropylphenyl)-N-[2-(2,6-diisopropylphenylamino)ethyl]formamide. Finally, anhydrous TEMPO-H was reacted with (triphenylphosphoranylidene)ketene to generate Ph(3)PC(H)C(=O)O(NC(5)H(6)(CH(3))(4)). A full characterization of the product, including an X-ray crystal structure, is described.

Ab initio investigation of the hydration of the tetrahedral perchlorate, perbromate, selenate, arsenate, and vanadate anions.

The geometries, energies, and vibrational frequencies of various isomers of XO(4)(m-)(H2O)n, x = Cl, Br, Se, As, V; n = 0-6, m = 1-3 are calculated at various levels up to MP2/6-31+G*. These properties are studied as a function of increasing cluster size. The experimental and theoretical vibrational spectra are compared where available.

Two-step iron(0)-mediated N-demethylation of N-methyl alkaloids.

A mild and simple two-step Fe(0)-mediated N-demethylation of a number of tertiary N-methyl alkaloids is described. The tertiary N-methylamine is first oxidized to the corresponding N-oxide, which is isolated as the hydrochloride salt. Subsequent treatment of the N-oxide hydrochloride with iron powder readily provides the N-demethylated amine. Representative substrates include a number of opiate and tropane alkaloids. Key intermediates in the synthesis of semisynthetic 14-hydroxy pharmaceutical opiates such as oxycodone and oxymorphone are also readily N-demethylated using this method.

Structure of the room-temperature ionic liquid 1-hexyl-3-methylimidazolium hydrogen sulfate: conformational isomerism.

The acidic room-temperature ionic liquid 1-hexyl-3-methylimidazolium hydrogen sulfate has recently been identified to have beneficial properties for practical applications in catalysis and electrochemistry. In the present work, the conformational isomerism of this ionic liquid is studied by means of density functional theory calculations and experiments in terms of infrared absorption and Raman scattering spectroscopy. For the hydrogen sulfate anion, the trans conformer is found to be the favored isomer in the ionic liquid. For the 1-hexyl-3-methylimidazolium cation, three different low-energy conformations were obtained, differing only in the orientation of the hexyl chain. The comparison of vibrational frequencies with IR and Raman data showed good agreement for all three conformations, indicating their presence in the ionic liquid. Beyond revealing the conformational information, the experimental spectra indicate strong interionic interactions. Vibrations of sulfuric acid could be observed, indicating possible proton transfer from the cation to the anion. This is further supported by the appearance of modes around 2000 cm(-1) in the IR spectrum, which could tentatively be assigned to C2-H stretching vibrations red-shifted as a result of strong interionic hydrogen bonds as a prerequisite of proton transfer.

Hexaaqua-gallium(III) trinitrate trihydrate.

The title compound, [Ga(H(2)O)(6)](NO(3))(3)·3H(2)O, is isostructural to other known M(III) nitrate hydrates (M = Al, Cr, Fe). The structure contains two distinct octa-hedral Ga(OH(2))(6) units (each of symmetry) which are involved in inter-molecular hydrogen bonding with the three nitrate anions and three water mol-ecules within the asymmetric unit.

Homolytic cleavage of Lawesson's reagent: N-heterocyclic carbene complexes of ArPS2 (Ar = 4-CH3O-C6H4).

Lawesson's reagent (LR) has been shown to react with the N-heterocyclic carbenes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)] to give adducts of the general form NHC·P(S)2-C6H4OCH3. Full characterizations, including X-ray crystal structures, are provided. The reaction of Woollins' reagent (WR) with IMes gave the known selanone, (IMes)Se.

RADMAP: Simple probes for rapid assessment of complex reactivity: A method and case studies on the reaction of hydrogen atoms with unsaturated organic molecules.

RADMAP, an open source program, allows for rapid analysis and visualization of the earliest stages of reactions between any molecule and a monoatomic probe (i.e., H*, H(+), H(-), Br*, or any other monoatomic species) using ab initio methods. This program creates non-planar potential energy surfaces of the initial interaction between a molecule of interest and the monoatomic probe. These surfaces can be used to both predict the site of addition as well as provide a qualitative estimate for the relative proportion of the formation of adducts; therefore, it gives insight into both the reactivity and the kinetic stability of a molecule. The program presents a way to quickly predict the number of signals anticipated in transverse field muon spin resonance spectra as well as their relative intensities.

An ab Initio Study of Facial Selectivity in the Diels-Alder Reaction.

Facial selectivities in the Diels-Alder reactions of 5-substituted 1,3-cyclopentadienes with a variety of dienophiles are predicted reliably at the ab initio HF/6-31G level. The ranges of activation energies for syn addition are large relative to those for anti addition, which are all similar to the activation energy for cyclopentadiene itself. Partitioning the activation energy into diene deformation, dienophile deformation, and diene-dienophile interaction energies shows that the major factor in determining facial selectivity is in the energy required to deform the diene into its transition state geometry. Deformation of the 5-fluoro-, 5-hydroxy-, and 5-amino-1,3-cyclopentadienes into their syn transition state geometries is predicted to require less energy than deformation of cyclopentadiene itself, which is in accord with experimental observation of syn addition with these dienes. The first definition of an ab initio steric factor is presented which correlates very well with syn activation energies. This indicates that facial selectivity with these dienes is primarily due to steric hindrance between the dienophile and the plane-nonsymmetric groups on the diene. However, we have also identified a significant lone pair-lone pair interaction with the reacting nitrogens when the dienophile is 1,2,4-triazoline-3,5-dione.

Raman and ab initio investigation of aqueous Cu(I) chloride complexes from 25 to 80 °C.

Temperature-dependent Raman studies of aqueous copper(I) chloride complexes have been carried out up to 80 °C, along with supporting ab initio calculations for the species [CuCl(n)(H2O)m](1-n), n = 0-4 and hydration numbers m = 0-6. Normalized reduced isotropic Raman spectra were obtained from perpendicular and parallel polarization measurements, with perchlorate anion, ClO4(-), as an internal standard. Although the Raman spectra were not intense, spectra could be corrected by solvent baseline subtraction, to yield quantitative reduced molar scattering coefficients for the symmetric vibrational bands at 297 ± 3 and 247 ± 3 cm(-1). The intensity variations of these bands with concentration and temperature provided strong evidence that these arise from the species [CuCl2](-) and [CuCl3](2-), respectively. The results from ab initio calculations using density functional theory predict similar relative peak positions and intensities for the totally symmetric Cu-Cl stretching bands of the species [CuCl2(H2O)6](-) and [CuCl3(H2O)6](2-), in which the water is coordinated to the chloride ions. A less intense Raman band at 350 ± 10 cm(-1) is attributed to the symmetric Cu-Cl stretching mode of hydrated species [CuCl(H2O)](0) with six waters of hydration. Temperature- and concentration-independent quantitative Raman molar scattering coefficients (S) are reported for the [CuCl2](-) and [CuCl3](2-)species.

Hydration of beryllium(II) in aqueous solutions of common inorganic salts. A combined vibrational spectroscopic and ab initio molecular orbital study.

Raman spectra of aqueous beryllium perchlorate, chloride, nitrate, and sulfate solutions have been measured over a broad concentration (0.098-4.950 mol L(-1)) range. The Raman spectroscopic data suggest that the tetra-aqua beryllium(II) ion is thermodynamically stable in perchlorate, chloride, and nitrate solutions over the concentration range measured. No inner-sphere complexes in these solutions could be detected spectroscopically except in very concentrated beryllium nitrate solutions. Beryllium sulfate solutions however, show a different picture, namely the existence of a thermodynamically stable beryllium sulfato complex most likely monodentate even at very low concentrations. At very high beryllium sulfate concentrations, a small quantity of a bidentate sulfato complex was found. With a temperature increase, the sulfato complex formation increases and this demonstrates the entropically driven sulfato complex formation. Furthermore, with increased temperature the hydrolysis increases, measured by the formation of hydrogen sulfate. Ab initio geometry optimizations and frequency calculations are reported for beryllium-water clusters with only inner sphere waters, clusters with an inner sphere and an incomplete second hydration, and clusters with a higher number of waters in the second hydration sphere. The cluster, [Be(OH2)(12)(2+)] (Be[4 + 8]) with 4 water molecules in the first sphere and 8 water molecules in the second sphere gave sufficiently realistic frequencies for BeO4 skeleton in comparison to the experimental ones. However, the cluster, [Be(OH2)(18)(2+)] (Be[6 + 12]) with 6 water molecules in the inner sphere and 12 water molecules in the outer sphere on an energy minimum gave unrealistically low BeO4 frequencies. This fact demonstrates that a six-fold coordination of Be2+ can be ruled out.

Carbon-centered strong bases in phosphonium ionic liquids.

Phosphonium ionic liquids (PhosILs), most notably tetradecyl(trihexyl)phosphonium decanoate (PhosIL-C(9)H(1)9COO), are solvents for bases such as Grignard reagents, isocyanides, Wittig reagents (phosphoranes), and N-heterocyclic carbenes (NHCs). The stability of the organometallic species in PhosIL solution is anion dependent. Small bases, such as hydroxide, react with the phosphonium ions and promote C-H exchange as suggested by deuterium-labeling studies. A method to dry and purify the ionic liquids is described and this step is important for the successful use of basic reagents in PhosIL. NHCs have been generated in PhosIL, and these persistent solutions catalyze organic transformations such as the benzoin condensation and the Kumada-Corriu cross-coupling reaction. Phosphoranes were generated in PhosIL, and their reactivity with various organic reagents was also tested. Inter-ion contacts involving tetraalkylphosphonium ions have been assessed, and the crystal structure of [(n-C(4)H(90)(4)P][CH(3)CO(2).CH(3)CO(2)H] has been determined to aid the discussion. Decomposition of organometallic compounds may also proceed through electron-transfer processes that, inter alia, may lead to decomposition of the IL, and hence the electrochemistry of some representative phosphonium and imidazolium ions has been studied. A radical derived from the electrochemical reduction of an imidazolium ion has been characterized by electron paramagnetic resonance spectroscopy.

An ab initio investigation of zinc chloro complexes.

A series of geometry, frequency, and energy calculations of chloroaquazinc(II) complexes were carried out at up to the MP2/6-31+G* level. A thorough examination of all species up to and including hexacoordinate species, and with up to six chlorides, was carried out. The structures of the complexes are compared with experimental data where available. The solution chemistry of zinc(II) in the presence of chloride is discussed, and Raman spectra of zinc perchlorate with increasing amount of chloride are presented.