Showing papers by "Lester Andrews published in 2018"
TL;DR: A series of group 3 metal isocyanide complexes were prepared via the reactions of laser ablated scandium, yttrium, and lanthanum atoms with (CN)2 in an argon matrix and predicted to have doublet and singlet ground states, respectively.
Abstract: A series of group 3 metal isocyanide complexes were prepared via the reactions of laser ablated scandium, yttrium, and lanthanum atoms with (CN)2 in an argon matrix. The product structures were identified on the basis of their characteristic infrared absorptions from isotopically labeled (CN)2 samples as well as the calculated frequencies and isotopic frequency ratios. Group 3 metal atoms reacted with (CN)2 to form M(NC)2 (M = Sc, Y, La) when the samples were subjected to λ > 220 nm irradiation. Other products such as M(NC)3 and MNC were produced together with M(NC)2 through either the reactions of M(NC)2 and (CN)2 or the loss of one CN ligand from M(NC)2. CCSD(T)//B3LYP calculations reveal that ScNC possesses a 3Δ ground state, while 1Σ+ is most stable for YNC and LaNC. All of the M(NC)2 and M(NC)3 complexes were predicted to have doublet and singlet ground states, respectively. Group 3 metal cyanides are less stable than the isocyanides by at least 4 kcal/mol at the CCSD(T) level, and their C-N stretches are much weaker than the N-C stretches of the isocyanides. No absorption can be assigned to the M(CN) x complex, which would appear between 2100 and 2250 cm-1.
12 citations
TL;DR: The studies demonstrate that the isocyano nitrogen is a better π donor, so it interacts with U(VI) better than carbon and reduces the ionic nature of U(NC)n decreases as the number of isOCyano groups increases.
Abstract: Laser-ablated U atoms react with (CN)2 in excess argon and neon during codeposition at 4 K to form UNC, U(NC)2, and U(NC)4 as the major uranium-bearing products, which are identified from their matrix infrared spectra using cyanogen substituted with 13C and 15N and from quantum chemical calculations. The 12/13CN and C14/15N isotopic frequency ratios computed for the U(NC)1,2,4 molecules agree better with the observed values than those calculated for the U(CN)1,2,4 isomers. Multiplets using mixed isotopic cyanogens reveal the stoichiometries of these products, and the band positions and quantum chemical calculations confirm the isocyanide bonding arrangements, which are 14 and 51 kJ/mol more stable than the cyanide isomers for UNC and U(NC)2, respectively, and 62 kJ/mol for U(NC)4 in the isolated gas phase at the CCSD(T)/CBS level. The studies further demonstrate that the isocyano nitrogen is a better π donor, so it interacts with U(VI) better than carbon. Although the higher isocyanides are more stable th...
11 citations
TL;DR: Molecular oxygen fluorides of copper, silver and gold are synthesised, and it is shown that the oxo ligands possess radical character.
Abstract: Transition metal complexes bearing terminal oxido ligands are quite common, yet group 11 terminal oxo complexes remain elusive. Here we show that excited coinage metal atoms M (M = Au, Ag, Cu) react with OF2 to form hypofluorites FOMF and group 11 oxygen metal fluorides OMF2, OAuF and OAgF. These compounds have been characterized by IR matrix-isolation spectroscopy in conjunction with state-of-the-art quantum-chemical calculations. The oxygen fluorides are formed by photolysis of the initially prepared hypofluorites. The linear molecules OAgF and OAuF have a 3Σ − ground state with a biradical character. Two unpaired electrons are located mainly at the oxygen ligand in antibonding O−M π* orbitals. For the 2B2 ground state of the OMIIIF2 compounds only an O−M single bond arises and a significant spin-density contribution was found at the oxygen atom as well. While transition metal complexes bearing terminal oxido ligands are common, those of group 11 elements have yet to be experimentally observed. Here, Riedel and colleagues synthesise molecular oxygen fluorides of copper, silver and gold, and show that the oxo ligands possess radical character.
9 citations
TL;DR: B3LYP calculations show that aluminum chlorides form the analogous molecules and dimers, and in the search for possible new products, Al(NC)4 is calculated and found to be a stable molecule, but it was not detected here.
Abstract: Laser-ablated Al atoms react with (CN)2 in excess argon during condensation at 4 K to produce AlNC, Al(NC)2, and Al(NC)3, which were computed (B3LYP) to be 27, 16, and 28 kJ/mol lower in energy, respectively, than their cyanide counterparts. Irradiation at 220–580 nm increased absorptions for the above molecules and the very stable Al(NC)4– anion. Annealing to 30, 35, and 40 K allowed for diffusion and reaction of trapped species and produced new bands for the Al(NC)1,2,3 dimers including a rhombic ring core (C)(AlN)2(C) with C’s attached to the N’s, a (NC)2Al(II)–Al(II)(NC)2 dimer with a computed Al–Al length of 2.557 A, and the dibridged Al2(NC)6 molecule with a calculated D2h structure and rhombic ring core like Al2H6. In contrast, the Al(NC)4– anion was destroyed on annealing presumably due to neutralization by Al+. B3LYP calculations also show that aluminum chlorides form the analogous molecules and dimers. In our search for possible new products, we calculated Al(NC)4 and found it to be a stable mol...
9 citations
TL;DR: Redeker, Beckers and Riedel (RSC Adv., 2015, 5, 106568), on the basis of the detection of a very weak assigned combination band and CCSD(T) frequency calculations, reassigned the two clearly unrelated strong 550 cm-1 IR and weak 389cm-1 Raman bands to the same stable Cs+F3- ion pair species.
Abstract: Cesium fluoride evaporated from a small stainless steel Knudsen cell at 495 °C was codeposited with F2 in excess argon onto a copper wedge at 15 K and examined by focused blue argon ion laser lines scattered from the matrix sample. An 892 cm−1 Raman shifted signal was observed for F2, and stronger 461 cm−1 and weaker 389 cm−1 Raman shifted signals were observed for reaction products. All of these signals decreased in intensity upon prolonged exposure to laser light, but the 389 cm−1 signal decreased more rapidly than the 461 cm−1 signal. Temperature cycling to 40 K destroyed the 389 cm−1 signal, but the 461 cm−1 band remained intense, which was the same behavior for the very intense 550 cm−1 infrared absorption in similar experiments using a different instrument. The two strong 461 and 550 cm−1 bands related by annealing behavior were assigned to the symmetric and antisymmetric (F–F–F)− stretching modes for the trifluoride anion, respectively, in the Cs+F3− ion pair species with mutual exclusion. The weaker more vulnerable 389 cm−1 signal was attributed to an unknown, less stable (i.e. more reactive) secondary reaction product (Ault and Andrews, J. Am. Chem. Soc., 1976, 98, 1591). Nevertheless, Redeker, Beckers and Riedel (RSC Adv., 2015, 5, 106568), on the basis of the detection of a very weak assigned combination band and CCSD(T) frequency calculations, reassigned the two clearly unrelated strong 550 cm−1 IR and weak 389 cm−1 Raman bands to the same stable Cs+F3− ion pair species. We can now identify the weaker 389 cm−1 Raman band for a more photosensitive and reactive carrier as the isolated F3− anion. The required Raman blue laser photo-ionization of Cs and Rb atoms in the system and the case for this new assignment are considered in the following paper. The antisymmetric stretching frequency for this isolated anion has been assigned at 510.6 cm−1 in other IR work. We again assign with confidence the two strong and related 550 cm−1 IR and 461 cm−1 Raman bands to the same stable Cs+F3− ion pair species in solid argon.
8 citations
TL;DR: DFT and CCSD(T) calculations show the insertion complex HM-SiH3 is the most stable isomer with a near right angle H-M-Si moiety, however, silydene complexes H2M═SiH2 were calculated and identified as the moststable complexes with the lighter elements.
Abstract: The reactions of Ge, Sn, Pb, Sb, Bi, and Te atoms with silane molecules were studied using matrix-isolation Fourier transform infrared spectroscopy and density functional theoretical (DFT) calculations. All metals generate the inserted complexes HM-SiH3, which were stabilized in an argon matrix, while H2M═SiH2 and H3M≡SiH were not observed. DFT and CCSD(T) calculations show the insertion complex HM-SiH3 is the most stable isomer with a near right angle H–M–Si moiety. However, silydene complexes H2M═SiH2 (M = C, Si) were calculated and identified as the most stable complexes with the lighter elements. The bonding difference is mainly due to relativistic effects, which is that for heavier metal atoms valence s and p orbitals have a lower tendency to form hybrid orbitals.
5 citations
TL;DR: It is very interesting that both OM(η2-SO) and OM( Δ2-O2S) molecules show chiral structure, and the admixture of f orbitals into the bonding giving stronger M≡O triple bonds is explored.
Abstract: Infrared absorptions of the matrix isolated OMS, OM(η2-SO), and OM(η2-SO)(η2-O2S) (M = Ce, Th) molecules were observed following reactions of laser-ablated Ce and Th metal atoms with SO2 during condensation in excess argon and neon. Band assignments for the main vibrational modes were confirmed by appropriate 34SO2 and S18O2 isotopic shifts. B3LYP, BPW91 density functional, and CASSCF/CASPT2 calculations were performed to characterize these new reaction products and to explore the admixture of f orbitals into the bonding giving stronger M≡O triple bonds. It is very interesting that both OM(η2-SO) and OM(η2-SO)(η2-O2S) molecules show chiral structure.
4 citations
TL;DR: The insertion products of laser-ablated Pb atom reactions with ethane and mono-, di-, tri-, and tetrahalomethanes in excess argon were prepared and identified from their matrix infrared spectra on the basis of DFT computed frequencies and observed isotopic shifts.
Abstract: The insertion products of laser-ablated Pb atom reactions with ethane and mono-, di-, tri-, and tetrahalomethanes in excess argon were prepared and identified from their matrix infrared spectra on the basis of DFT computed frequencies and observed isotopic shifts. Unlike the lighter elements in group 14, the heaviest member lead exists primarily in the oxidation state 2+ using 6p orbitals in reaction products due to relativistic contraction of the 6s orbital. The C–Pb–X (X = H, F, Cl) bond is close to a right angle, indicating that Pb contributes mostly p-character to the C–Pb and Pb–X bonds. The lead reaction product with ethane is CH3CH2–Pb–H. The lower energy product in the CH2FCl reaction is CH2F–PbCl, which is photoisomerized to CH2Cl–PbF. A lead methylidene (CCl2–PbCl2) was identified only in reactions with CCl4. The relatively small energy difference between the insertion and methylidene products in the tetrachloride system allows photochemical conversion from the insertion product to the unusual 3...
3 citations
TL;DR: Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH3 and HE═WH2 molecules for E = P and As.
Abstract: Laser ablation of tungsten metal provides W atoms which react with phosphine and arsine during condensation in excess argon and neon, leading to major new infrared (IR) absorptions. Annealing, UV irradiation, and deuterium substitution experiments coupled with electronic structure calculations at the density functional theory level led to the assignment of the observed IR absorptions to the E≡WH3 and HE═WH2 molecules for E = P and As. The potential energy surfaces for hydrogen transfer from PH3 to the W were calculated at the coupled-cluster CCSD(T)/complete basis set level. Additional weak bands in the phosphide and arsenide W—H stretching region are assigned to the molecules with loss of H from W, E≡WH2. The electronic structure calculations show that the E≡WH3 molecules have a W—E triple bond, the HE═WH2 molecules have a W—E double bond, and the H2E—WH molecules have a W—E single bond. The formation of multiple E—W bonds leads to increasing stability for the isomers.