Cory C. Pye

An implementation of the conductor-like screening model of solvation within the Amsterdam density functional package ― Part II. COSMO for real solvents

The conductor-like screening model for real solvents (COSMO-RS) has been implemented in the Amsterdam density functional program. The surface building routines now allow for finer discretization of...

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.

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

Raman spectra of aqueous Zn(II) perchlorate solutions were measured over a broad concentration (0.50–3.54 mol L-1) and temperature (25–120°C) range. The weak polarized band at 390 cm-1 and two depolarized modes at 270 and 214 cm-1 have been assigned to ν1(a1g), ν2(eg) and ν5(f2g) of the hexaaquazinc(II) ion, respectively. The infrared active mode at 365 cm-1 has been assigned to ν3(f1u). The vibrational analysis of the species [Zn(OH2)62+] was done on the basis of Oh symmetry (OH2 as point mass). The polarized mode ν1(a1g) ZnO6 has been followed over the full temperature range and band parameters (band maximum, full width of half height and band intensity) have been examined. The position of the ν1(a1g) ZnO6 mode shifts only about 4 cm-1 to lower frequencies and broadens about 32 cm-1 for a 95°C temperature increase. The Raman spectroscopic data suggest that the hexaaquazinc(II) ion is thermodynamically stable in perchlorate solution over the temperature and concentration range measured. Abinitio geometry optimizations and frequency calculations of [Zn(OH2)62+] were carried out at the Hartree–Fock and second order Moller–Plesset levels of theory, using various basis sets up to 6-31+G*. The global minimum structure of the hexaaqua Zn(II) species corresponds with symmetry Th. The unscaled vibrational frequencies of the [Zn(OH2)62+] were reported. The unscaled vibrational frequencies of the ZnO6 unit are lower than the experimental frequencies (ca. 15%), but scaling the frequencies reproduces the measured frequencies. The theoretical binding enthalpy for [Zn(OH2)62+] was calculated and accounts for ca. 64% of the experimental single ion hydration enthalpy for Zn(II). Abinitio geometry optimizations and frequency calculations are also reported for a [Zn(OH2)182+] (Zn[6+12]) cluster with 6 water molecules in the first sphere and 12 water molecules in the second sphere. The global minimum corresponds with T symmetry. Calculated frequencies of the zinc [6+12] cluster correspond well with the observed frequencies in solution. The ν1 ZnO6 (unscaled) mode occurs at 389 cm-1 in good agreement with the experimental value. The theoretical binding enthalpy for [Zn(OH2)182+] was calculated and is very close to the experimental single ion hydration enthalpy for Zn(II). The water molecules of the first sphere form strong H-bonds with water molecules in the second hydration shell because of the strong polarizing effect of the Zn(II) ion. The importance of the second hydration sphere is discussed.

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.

Indium(III) hydration in aqueous solutions of perchlorate, nitrate and sulfate. Raman and infrared spectroscopic studies and ab-initio molecular orbital calculations of indium(III)–water clusters

Raman and infrared spectra of aqueous In3+-perchlorate, -nitrate and -sulfate solutions were measured as a function of concentration and temperature. Raman spectra of In3+ perchlorate solutions reveal a strongly polarized mode of medium to strong intensity at 487 cm−1 and two broad, depolarized modes at 420 cm−1 and 306 cm−1 of much lesser intensity. These modes have been assigned to ν1(a1g), ν2(eg) and ν5(f2g) of the hexaaquaindium(III) ion, [In(OH2)63+] (Oh symmetry), respectively. The infrared active mode at 472 cm−1 has been assigned to ν3(f1u). The Raman spectra suggest that [In(OH2)63+] is stable in acidified perchlorate solutions, with no inner-sphere complex formation or hydroxo species formed over the concentration range measured. In concentrated In(NO3)3 solutions, In3+ can exist in form of both an inner-sphere complex, [In(OH2)5ONO2]2+ and an outer-sphere complex [In(OH2)63+·NO3−]. Upon dilution the inner-sphere complex dissociates and the amount of the outer-sphere complex increases. In dilute solutions the cation, [In(OH2)63+], exists together with free nitrate. In indium sulfate solutions, a stable In3+ sulfato complex could be detected using Raman spectroscopy and 115-In NMR. Sulfato complex formation is favoured with increase in temperature and thus is entropically driven. At temperatures above 100 °C a basic In3+ sulfate, In(OH)SO4 is precipitated and characterised by wet chemical analysis and X-ray diffraction. Ab initio geometry optimizations and frequency calculations of [In(OH2)n3+] clusters (n = 1–6) were carried out at the Hartree–Fock and second order Moller–Plesset levels of theory, using various basis sets up to 6-31+G*. The global minimum structure of the aqua In3+ species was reported. The unscaled vibrational frequencies of the [In(OH2)63+] cluster do not correspond well with experimental values because of the missing second hydration sphere. The theoretical binding enthalpy for [In(OH2)63+] accounts for ca. 60% of the experimental single ion hydration enthalpy for In3+. Calculations are reported for the [In(OH2)183+] cluster (In[6 + 12]) with two full hydration spheres (T symmetry), for which the calculated ν1(InO6) mode occurs at 483 cm−1 (HF/6-31G*), which is in good agreement with the experimental value at 487 cm−1, as are the other frequencies. The theoretical binding enthalpy for [In(OH2)183+] was calculated and underestimates by about 15% the experimental single ion hydration enthalpy of In3+.

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.

Zinc(II) Hydration in Aqueous Solution: A Raman Spectroscopic Investigation and An ab initio Molecular Orbital Study of Zinc(II) Water Clusters

Raman spectra of aqueous Zn(II)–perchlorate solutions were measured over broad concentration (0.50–3.54 mol-L−1) and temperature (25–120°C) ranges. The weak polarized band at 390 cm−1 and two depolarized modes at 270 and 214 cm−1 have been assigned to ν1(a1g), ν2(eg), and ν5(f2g) of the zinc–hexaaqua ion. The infrared-active mode at 365 cm−1 has been assigned to ν3(f1u). The vibrational analysis of the species [Zn(OH2)2+] was done on the basis of Oh symmetry (OH2 as point mass). The polarized mode ν1(a1g)-ZnO6 has been followed over the full temperature range and band parameters (band maximum, full width at half height, and intensity) have been examined. The position of the ν1(a1g)-ZnO6 mode shifts only about 4 cm−1 to lower frequencies and broadens by about 32 cm−1 for a 95°C temperature increase. The Raman spectroscopic data suggest that the hexaaqua–Zn(II) ion is thermodynamically stable in perchlorate solution over the temperature and concentration range measured. These findings are in contrast to ZnSO4 solutions, recently measured by one of us, where sulfate replaces a water molecule of the first hydration sphere. Ab initio geometry optimizations and frequency calculations of [Zn(OH2)2+] were carried out at the Hartree–Fock and second-order Møller–Plesset levels of theory, using various basis sets up to 6-31 + G*. The global minimum structure of the hexaaqua–Zn(II) species corresponds with symmetry Th. The unscaled vibrational frequencies of the [Zn(OH2)2+] are reported. The unscaled vibrational frequencies of the ZnO6, unit are lower than the experimental frequencies (ca. 15%), but scaling the frequencies reproduces the measured frequencies. The theoretical binding enthalpy for [Zn(OH2)2+] was calculated and accounts for ca. 66% of the experimental single-ion hydration enthalpy for Zn(II).Ab initio geometry optimizations and frequency calculations are also reported for a [Zn(OH2)218] (Zn[6 + 12]) cluster with 6 water molecules in the first sphere and 12 in the second sphere. The global minimum corresponds with T symmetry. Calculated frequencies of the zinc [6 + 12] cluster correspond well with the observed frequencies in solution. The ν1-ZnO6 (unscaled) mode occurs at 388 cm−1 almost in perfect correspondence to the experimental value. The theoretical binding enthalpy for [Zn(OH2)218] was calculated and is very close to the experimental single ion-hydration enthalpy for Zn(II). The water molecules of the first sphere form strong hydrogen bonds with water molecules in the second hydration shell because of the strong polarizing effect of the Zn(II) ion. The importance of the second hydration sphere is discussed.

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.

Lewis Base Stabilized Oxophosphonium Ions

The rich functional group chemistry of phosphorus has been exploited over the last several decades and even as of late, there have been major advances to the field. There have been regular contributions to the area of N-heterocyclic phosphenium ions A since the first reports 30 years ago. The area has seen a recent resurgence 9–23] which may be due to the popularity of the isovalent singlet carbenes and, as such, the use of phosphenium ions as ligands in transition metal chemistry has been exploited. In the context of main group chemistry, phosphenium ions have been involved in the preparation of phosphinophosphonium systems, as well in reactions with P4, [39,41–44] and other reagents.

Aqueous Solution Chemistry of Scandium(III) Studied by Raman Spectroscopy and ab initio Molecular Orbital Calculations

Aqueous solutions of Sc(ClO4)3,ScCl3, and Sc2(SO4)3 were studied by Ramanspectroscopy over a wide concentration range. In aqueous perchlorate solutionSc(III) occurs as an hexaaqua cation. The weak, polarized Raman band assignedto the ν1(a1g) ScO6 mode of the hexaaqua-Sc (III) ion has been studied as afunction of concentration and temperature. The ν1(a1g) ScO6 mode at 442 cm−1of the hexaaqua—Sc(III) shifts only 3 cm−1 to lower frequency and broadensabout 20 cm−1 for a 60°C temperature increase. The Raman spectroscopic datasuggest that the hexaaqua-Sc (III) ion is stable in perchlorate solution within theconcentration and temperature range measured. Besides the polarized componentat 442 cm−1, two weak depolarized modes at 295 and 410 cm−1 were measuredin the Raman effect. These two modes of the ScO6 unit were assigned to ν3(f2g)and ν2(eγ), respectively. The infrared active mode ν3(f1u) was measured at 460cm−1. The frequency data confirm the centrosymmetry of the Sc(III) aquacomplex, contrary to earlier Raman results. The powder spectrum of crystallineSc(ClO4) 3 · 6H2O shows the above described Raman modes as well. Thesefindings are in contrast to Sc2(SO4)3 solutions, where sulfate replaces water inthe first hydration sphere and forms thermodynamically strong sulfato complexes.In ScCl3 solutions thermodynamically weak chloro complexes could be detected.Ab initio molecular orbital calculations were performed at the HF and MP2 levelsof theory using different basis sets up to 6–31 + G(d). Gas-phase structures,binding energies, and enthalpies are reported for the Sc3+(OH2)6 and Sc3+(OH2)7cluster. The Sc—O bond length for the Sc3+(OH2)6 cluster reproduces theexperimentally determined bond length of 2.18 Å (recent EXAFS data) almost exactly.The theoretical binding energy for the hexaaqua Sc(III) ion was calculated andaccounts for ca. 54–59% of the experimental hydration enthalpy of Sc(III). Thethermodynamic stability of the Sc3+(OH2)6(OH2) cluster was compared to thatof the Sc3+(OH2)7 cluster, demonstrating that hexacoordination is inherently morestable than heptacoordination in the scandium (III) system. The calculated ν1ScO6frequency of the Sc+(OH2)6 cluster is ca. 12% lower than the experimentalfrequency. Adding an explicit second hydration sphere to give Sc3+ (OH2)18,denoted Sc[6 + 12], is shown to correct for the discrepancy. The frequencycalculation and the thermodynamic parameters for the Sc[6 + 12] cluster aregiven and the importance of the second hydration sphere is stressed. Calculatedfrequencies of the ScO6 subunit in the Sc[6 + 12] cluster agree very well withthe experimental values (for example, the calculated ν1ScO6 frequency was foundto be 447 cm−1, in excellent agreement with the above-reported experimentalvalue). The binding enthalpy for the Sc[6 + 12]cluster predicts the single ionhydration enthalpy to about 89%.