Structure and dynamics of iron pentacarbonyl

The dynamics of CO ligand scrambling in Fe(CO)5 has been investigated by linear infrared spectroscopy in supercritical xenon solution. The activation barrier for the Berry pseudorotation in Fe(CO)5 was determined experimentally to be Ea = 2.5 ± 0.4 kcal mol–1 by quantitative analysis of the temperature-dependent spectral line shape. This compares well with the range of Ea/(kcal mol–1) = 2.0 to 2.3 calculated by various DFT methods and the value of 1.6 ± 0.3 previously obtained from 2D IR measurements by Harris et al. ( Science 2008, 319, 1820). The involvement of Fe(CO)5···Xe interactions in the ligand scrambling process was tested computationally at the BP86-D3/AE2 level and found to be negligible

Picosecond time-resolved infrared spectroscopy of rhodium and iridium azides

Picosecond time-resolved infrared spectroscopy was used to elucidate early photochemical processes in the diazido complexes M(Cp*)(N3)2(PPh3), M = Rh (1), Ir (2), using 266 nm and 400 nm excitation in THF, CH2Cl2, MeCN and toluene solutions. The time-resolved data have been interpreted with the aid of DFT calculations on vibrational spectra of the singlet ground states and triplet excited states and their rotamers. While the yields of phototransformations via N2 loss are low in both complexes, 2 cleaves a N3 ligand under 266 nm excitation. The molecular structure of 1 is also reported as determined by single crystal X-ray diffraction

Homoleptic Low-Valent Polyazides of Group 14 Elements

First examples of coordinatively unsaturated, homoleptic azido complexes of low-valent group 14 elements are reported. A simple strategy uses low-valent precursors, ionic azide transfer reagents and bulky cations to obtain salt-like compounds containing E(N3)3- of Ge(II)/Sn(II) which are fully characterised, including XRD. Remarkably, these compounds are kinetically stable at r.t. and isolable in sub-gram quantities

Tuning energetic properties through co-crystallisation - a high-pressure experimental and computational study of nitrotriazolone:4,4′-bipyridine

We report the preparation of a co-crystal formed between the energetic molecule 3-nitro-1,2,4-triazol-5-one (NTO) and 4,4′-bipyridine (BIPY), that has been structurally characterised by high-pressure single crystal and neutron powder diffraction data up to 5.93 GPa. No phase transitions or proton transfer were observed up to this pressure. At higher pressures the crystal quality degraded and the X-ray diffraction patterns showed severe twinning, with the appearance of multiple crystalline domains. Computational modelling indicates that the colour changes observed on application of pressure can be attributed to compression of the unit cell that cause heightened band dispersion and band gap narrowing that coincides with a shortening of the BIPY π⋯π stacking distance. Modelling also suggests that the application of pressure induces proton migration along an N-H⋯N intermolecular hydrogen bond. Impact-sensitivity measurements show that the co-crystal is less sensitive to initiation than NTO, whereas computational modelling suggests that the impact sensitivities of NTO and the co-crystal are broadly similar.</p

Photocatalytic reduction of CO2 to CO in aqueous solution under red-light irradiation by a Zn-porphyrin-sensitized Mn(I) catalyst

This work demonstrates photocatalytic CO2 reduction by a noble-metal-free photosensitizer-catalyst system in aqueous solution under red-light irradiation. A water-soluble Mn(I) tricarbonyl diimine complex, [MnBr(4,4′-{Et2O3PCH2}2-2,2′-bipyridyl)(CO)3] (1), has been fully characterized, including single-crystal X-ray crystallography, and shown to reduce CO2 to CO following photosensitization by tetra(N-methyl-4-pyridyl)porphyrin Zn(II) tetrachloride [Zn(TMPyP)]Cl4 (2) under 625 nm irradiation. This is the first example of 2 employed as a photosensitizer for CO2 reduction. The incorporation of −P(O)(OEt)2 groups, decoupled from the core of the catalyst by a −CH2– spacer, afforded water solubility without compromising the electronic properties of the catalyst. The photostability of the active Mn(I) catalyst over prolonged periods of irradiation with red light was confirmed by 1H and 13C{1H} NMR spectroscopy. This first report on Mn(I) species as a homogeneous photocatalyst, working in water and under red light, illustrates further future prospects of intrinsically photounstable Mn(I) complexes as solar-driven catalysts in an aqueous environment

Density functional theoretical studies of the Re-Xe bonds in Re(Cp)(CO) (PF3)Xe and Re(Cp)(CO)(2)Xe

Density functional calculations have been used to probe the electronic structures of Re(Cp)(CO)2Xe and Re(Cp)(CO)(PF3)Xe. The calculated CO stretching frequencies compare favorably with those determined experimentally. Our calculations of δXe and 3JXe-F for Re(Cp)(CO)(PF3)Xe represent the first for a well-characterized transition metal−noble gas compound and demonstrate that DFT using the BP86 and SAOP functionals reproduces these parameters to within 1% and 8% of their experimentally determined values. The calculated Re−Xe bond dissociation energies for Re(Cp)(CO)2Xe (12.3 kcal mol-1) and Re(Cp)(CO)(PF3)Xe (11.9 kcal mol-1) are also in excellent agreement with the lower limits for these energies estimated from the activation parameters for the reaction of the complexes with CO in supercritical Xe. A topological analysis of the electron density in Re(Cp)(CO)2Xe and Re(Cp)(CO)(PF3)Xe reveals positive ∇2ρ(r) at the critical points (∇2ρ(rc) = 0.1310 and 0.1396 e Å5 for Re(Cp)(CO)2Xe and Re(Cp)(CO)(PF3)Xe, respectively, indicating that the Re−Xe interaction is essentially closed-shell in both complexes. Fragment and overlap density of states analyses show that the orbital interactions in these compounds is dominated by overlap involving the Xe p orbitals and the orbitals of the Cp, CO, and/or PF3 ligands; the Re d orbitals appear to contribute little to the orbital interactions between the Re(Cp)(CO)2 and Re(Cp)(CO)(PF3), and Xe fragments

Katechismus der Schachspielkunst /

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Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

We have used fast time-resolved infrared spectroscopy to characterize a series of organometallic methane and ethane complexes in solution at room temperature: W(CO)(5)(CH(4)) and M(η(5) [Image: see text] C(5)R(5))(CO)(2)(L) [where M = Mn or Re, R = H or CH(3) (Re only); and L = CH(4) or C(2)H(6)]. In all cases, the methane complexes are found to be short-lived and significantly more reactive than the analogous n-heptane complexes. Re(Cp)(CO)(2)(CH(4)) and Re(Cp*)(CO)(2)(L) [Cp* = η(5) [Image: see text] C(5)(CH(3))(5) and L = CH(4), C(2)H(6)] were found to be in rapid equilibrium with the alkyl hydride complexes. In the presence of CO, both alkane and alkyl hydride complexes decay at the same rate. We have used picosecond time-resolved infrared spectroscopy to directly monitor the photolysis of Re(Cp*)(CO)(3) in scCH(4) and demonstrated that the initially generated Re(Cp*)(CO)(2)(CH(4)) forms an equilibrium mixture of Re(Cp*)(CO)(2)(CH(4))/Re(Cp*)(CO)(2)(CH(3))H within the first few nanoseconds (τ = 2 ns). The ratio of alkane to alkyl hydride complexes varies in the order Re(Cp)(CO)(2)(C(2)H(6)):Re(Cp)(CO)(2)(C(2)H(5))H > Re(Cp*)(CO)(2)(C(2)H(6)):Re(Cp*)(CO)(2)(C(2)H(5))H ≈ Re(Cp)(CO)(2)(CH(4)):Re(Cp)(CO)(2)(CH(3))H > Re(Cp*)(CO)(2)(CH(4)):Re(Cp*)(CO)(2)(CH(3))H. Activation parameters for the reactions of the organometallic methane and ethane complexes with CO have been measured, and the ΔH(‡) values represent lower limits for the CH(4) binding enthalpies to the metal center of W [Image: see text] CH(4) (30 kJ·mol(−1)), Mn [Image: see text] CH(4) (39 kJ·mol(−1)), and Re [Image: see text] CH(4) (51 kJ·mol(−1)) bonds in W(CO)(5)(CH(4)), Mn(Cp)(CO)(2)(CH(4)), and Re(Cp)(CO)(2)(CH(4)), respectively