Nicholas R. Walker

Unexpected stability of [Cu⋅Ar]2+, [Ag⋅Ar]2+, [Au⋅Ar]2+, and their larger clusters

Experimental observations following the ionization of neutral group 11 metal/argon complexes have revealed the presence of doubly charged ions of the form [M . Ar-n](2+) for n in the range 1-6. Of particular interest are two features of the results. First, the unexpected stability of the dimer ions, [M . Ar](2+), since similar species involving a molecule rather than a rare gas atom are often unstable with respect to charge transfer. Ab initio calculations show the dimers owe their stability to a combination of a strong electrostatic interaction and the high ionization energy of argon. A second feature to the results is the high relative intensities of the [M . Ar-4](2+) and [M . Ar-6](2+) ions. Calculations show these complexes to consist of square-planar D-4h structures, with the additional two atoms in [M . Ar-6](2+) occupying axial sites, which are Jahn-Teller distorted. The calculated relative binding energies support the preferential stability of these two structures

Competitive charge transfer reactions in small [Mg(H2O)N]2+ clusters

Production of stable hydrated magnesium complexes of the general form [Mg(H2O)N]2+ (where 2⩽N⩽24) has been possible using the pick-up technique. Observations of ion intensities as a function of N together with data from collision induced dissociation processes (for ions in the range 3⩽N⩽10), indicates the existence of a closed solvation shell for N=6 to which additional water molecules are strongly bound. Collision-induced charge transfer in ions of all sizes yields solvated magnesium hydroxide ions Mg+OH(H2O)N−M−2 accompanied by the loss of a hydronium ion, H3O+, and M water molecules. For N=3, 4, and 5, the above process is seen to be in competition with charge transfer to unprotonated water, and clusters of the general form Mg(H2O)N−M+ are detected, where M now represents the total number of water molecules lost. These two separate loss channels are interpreted as being due to the presence of different structural (or transient) forms of those cluster ions where N⩽6. One structure corresponds to a highl...

Comment on “Do Cu2+NH3 and Cu2+H2O exist?: theory confirms yes!” (Chemical Physics Letters 318 (2000) 333–339)

Abstract Contrary to the theoretical results presented by El-Nahas et al. (Chem. Phys. Lett. 318 (2000) 333), we believe new experiments on [Cu·(H2O)n]2+ and [Cu·(NH3)n]2+ complexes suggest their minimum stable sizes are [Cu·(H2O)3]2+ and [Cu·(NH3)2]2+, respectively.

Cluster ion studies of Ho2+ and Ho3+ solvation in the gas phase

Abstract An attempt has been made to prepare triply charged ions of holmium in association with a range of solvent clusters. Neutral atoms of holmium are generated in the gas phase using an effusive oven and are crossed with a beam consisting of solvent/argon clusters. Collisions between the holmium atoms and the clusters lead to the formation of neutral metal–solvent complexes. Ionisation by electron impact in the source of a high resolution mass spectrometer enables measurements to be undertaken on the intensities and fragmentation patterns of the resultant ions as a function of size. Only singly and doubly charged complexes are observed when water and methanol are used as solvents. Stable triply charged complexes are formed with the solvents acetone and acetonitrile, and intensity measurements suggest the preferred coordination number in both cases is 6. Measurements following the collisional activation of the holmium/acetonitrile complexes show evidence of chemical reactivity.

An Isolated Complex of Ethyne and Gold Iodide Characterized by Broadband Rotational Spectroscopy and Ab initio Calculations

A molecular complex of C2H2 and AuI has been generated and isolated in the gas phase through laser ablation of a gold surface in the presence of an expanding sample containing small percentages of C2H2 and CF3I in a buffer gas of argon. Rotational, B0, centrifugal distortion, ΔJ and ΔJK, and nuclear quadrupole coupling constants, χaa(Au), χbb(Au) - χcc(Au), χaa(I), and χbb(I) - χcc(I), are measured for three isotopologues of C2H2···AuI through broadband rotational spectroscopy. The complex is C2v and T-shaped with C2H2 coordinating to the gold atom via donation of electrons from the π-orbitals of ethyne. On formation of the complex, the C≡C bond of ethyne extends by 0.032(4) Å relative to r(C≡C) in isolated ethyne when the respective r0 geometries are compared. The geometry of ethyne distorts such that ∠(*-C-H) (where * indicates the midpoint of the C≡C bond) is 194.7(12)° in the r0 geometry of C2H2···AuI. Ab initio calculations at the CCSD(T)(F12*)/AVTZ level are consistent with the experimentally determined geometry and further allow calculation of the dissociation energy (De) as 136 kJ mol(-1). The χaa(Au) and χaa(I) nuclear quadrupole coupling constants of AuI and also the Au-I bond length change significantly on formation of the complex consistent with the strong interaction calculated to occur between C2H2 and AuI.

H 3 P⋯AgI

The new compound H3PAgI has been synthesized in the gas phase by means of the reaction of laser-ablated silver metal with a pulse of gas consisting of a dilute mixture of ICF3 and PH3 in argon. Ground-state rotational spectra were detected and assigned for the two isotopologues H3P(107)AgI and H3P(109)AgI in their natural abundance by means of a chirped-pulse, Fourier-transform, microwave spectrometer. Both isotopologues exhibit rotational spectra of the symmetric-top type, analysis of which led to accurate values of the rotational constant B0, the quartic centrifugal distortion constants DJ and DJK, and the iodine nuclear quadrupole coupling constant χaa(I) = eQqaa. Ab initio calculations at the explicitly-correlated level of theory CCSD(T)(F12*)/aug-cc-pVDZ confirmed that the atoms PAg-I lie on the C3 axis in that order. The experimental rotational constants were interpreted to give the bond lengths r0(PAg) = 2.3488(20) Å and r0(Ag-I) = 2.5483(1) Å, in good agreement with the equilibrium lengths of 2.3387 Å and 2.5537 Å, respectively, obtained in the ab initio calculations. Measures of the strength of the interaction of PH3 and AgI (the dissociation energy De for the process H3PAgI = H3P + AgI and the intermolecular stretching force constant FPAg) are presented and are interpreted to show that the order of binding strength is H3PHI < H3PICl < H3PAgI for these metal-bonded molecules and their halogen-bonded and hydrogen-bonded analogues.

Distortions of ethyne when complexed with a cuprous or argentous halide

A new molecule C2H2···CuF has been synthesized in the gas phase by means of the reaction of laser-ablated metallic copper with a pulse of gas consisting of a dilute mixture of ethyne and sulfur hexafluoride in argon.A new molecule C2H2CuF has been synthesized in the gas phase by means of the reaction of laser-ablated metallic copper with a pulse of gas consisting of a dilute mixture of ethyne and sulfur hexafluoride in argon. The ground-state rotational spectrum was detected by two types of Fourier-transform microwave spectroscopy, namely that conducted in a microwave Fabry-Perot cavity and the chirped-pulse broadband technique. The spectroscopic constants of the six isotopologues (12)C2H2(63)Cu(19)F, (12)C2H2(65)Cu(19)F, (13)C2H2(63)Cu(19)F, (13)C2H2(65)Cu(19)F, (12)C2D2(63)Cu(19)F and (12)C2D2(65)Cu(19)F were determined and interpreted to show that the molecule has a planar, T-shaped geometry belonging to the molecular point group C2v, with CuF forming the stem of the T. Quantitative interpretation reveals that the ethyne molecule is distorted when subsumed into the complex in such manner that the C[triple bond, length as m-dash]C bond lengthens (by δr) and the two H atoms cease to be collinear with the C[triple bond, length as m-dash]C internuclear line. The H atoms move symmetrically away from the approaching Cu atom of CuF, to increase each *[triple bond, length as m-dash]C-H angle by δA = 14.65(2)°, from 180° to 194.65(2)°. Ab initio calculations at the explicitly-correlated level of theory CCSD(T)(F12*)/aug-cc-pVTZ lead to good agreement with the experimental geometry. It is shown that similar distortions δr and δA, similarly determined, for four complexes C2H2MX (M = Cu or Ag; X = F, Cl or CCH) are approximately linearly related to the energies De for the dissociation process C2H2MX = C2H2 + MX.

Gas phase complexes of H 3 N⋯CuF and H 3 N⋯CuI studied by rotational spectroscopy and

Complexes of H3NCuF and H3NCuI have been synthesised in the gas phase and characterized by microwave spectroscopy. The rotational spectra of 4 isotopologues of H3NCuF and 5 isotopologues of H3NCuI have been measured in the 6.5-18.5 GHz frequency range using a chirped-pulse Fourier transform microwave spectrometer. Each complex is generated from a gas sample containing NH3 and a halogen-containing precursor diluted in Ar. Copper is introduced by laser ablation of a solid target prior to supersonic expansion of the sample into the vacuum chamber of the microwave spectrometer. The spectrum of each complex is characteristic of a symmetric rotor and a C3v geometry in which the N, Cu and X atoms (where X is F or I) lie on the C axis. The rotational constant (B0), centrifugal distortion constants (DJ and DJK), nuclear spin-rotation (Cbb(Cu) = Ccc(Cu)) constant (for H3NCuF only) and nuclear quadrupole coupling constants (χaa(X) where (X = N, Cu, I)) are fitted to the observed transition frequencies. Structural parameters are determined from the measured rotational constants and also calculated ab initio at the CCSD(T)(F12*)/AVQZ level of theory. Force constants describing the interaction between ammonia and each metal halide are determined from DJ for each complex. Trends in the interaction strengths and geometries of BCuX (B = NH3, CO) (X = F, Cl, Br, I) are discussed.

Chemistry in Laser-Induced Plasmas: Formation of M–C≡C–Cl (M = Ag or Cu) and their Characterization by Rotational Spectroscopy

The new linear molecule Ag–C≡C–Cl has been detected and fully characterized by means of rotational spectroscopy. It was synthesized by laser ablation of a silver rod in the presence of a gaseous sample containing a low concentration of CCl4 in argon, cooled to a rotational temperature approaching ∼1–3 K through supersonic expansion, and analyzed by chirped-pulse, Fourier transform microwave spectroscopy. Six isotopologues were investigated, and for each the spectroscopic constants B0, DJ and χaa(Cl) were determined. The B0 values were interpreted to give the following bond lengths: r(Ag–C) = 2.015(14) Å and r(C–Cl) = 1.635(6) Å, with r(C≡C) = 1.2219 Å assumed from an ab initio calculation at the CCSD(T)/aug-cc-pV5Z level of theory. The Cu analogue Cu–C≡C–Cl was similarly identified and characterized.