Experimental and theoretical studies of the interaction of silver cluster cations Ag(n)+ (n = 1-4) with ethylene

Impact of metals on (star)dust chemistry: a laboratory astrophysics approach

Laboratory experiments are essential in exploring the mechanisms involved in stardust formation. One key question is how a metal is incorporated into dust for an environment rich in elements involved in stardust formation (C, H, O, Si). To address experimentally this question we have used a radiofrequency cold plasma reactor in which cyclic organosilicon dust formation is observed. Metallic (silver) atoms were injected in the plasma during the dust nucleation phase to study their incorporation in the dust. The experiments show formation of silver nanoparticles (~15 nm) under conditions in which organosilicon dust of size 200 nm or less is grown. The presence of AgSiO bonds, revealed by infrared spectroscopy, suggests the presence of junctions between the metallic nanoparticles and the organosilicon dust. Even after annealing we could not conclude on the formation of silver silicates, emphasizing that most of silver is included in the metallic nanoparticles. The molecular analysis performed by laser mass spectrometry exhibits a complex chemistry leading to a variety of molecules including large hydrocarbons and organometallic species. In order to gain insights into the involved chemical molecular pathways, the reactivity of silver atoms/ions with acetylene was studied in a laser vaporization source. Key organometallic species, Ag n C2H m (n=1-3; m=0-2), were identified and their structures and energetic data computed using density functional theory. This allows us to propose that molecular Ag-C seeds promote the formation of Ag clusters but also catalyze hydrocarbon growth. Throughout the article, we show how the developed methodology can be used to characterize the incorporation of metal atoms both in the molecular and dust phases. The presence of silver species in the plasma was motivated by objectives finding their application in other research fields than astrochemistry. Still, the reported methodology is a demonstration laying down the ground for future studies on metals of astrophysical interest such as iron.

Are homoleptic complexes of ethylene with group 12 metals isolable in solution? A DFT study

Ethylene efficiently binds late transition metals of groups 10 and 11. In spite of their reactivity, homoleptic compounds of formula [M-(η²-C₂H₄)₃]ⁿ⁺ (with n = 0,1) have been isolated in solution and solid state and characterized spectroscopically throughout the last 50 years with metals from groups 10 and 11. X-ray diffraction studies proved that such homoleptic adducts adopt planar "wheel" structures where ethylene moieties lies flat in the same plane both in group 10 and 11. These experimental findings were also confirmed by several in-depth computational investigations carried out to understand the bond pattern of such peculiar structures. Homoleptic complexes of group 10 and 11 metals with ethylene are normally obtained in poorly coordinating solvents (like CH₂Cl₂ or light petroleum) saturated with ethylene to increase the stability of such species in solution. In the case of coinage metals, Cu(I), Ag(I) and Au(I), weakly coordinating fluorinated counter-ions (like SbF₆^-) succeeded in stabilize the ethylene adducts, but, curiously, no analogous success has been reported for Zn(II), Cd(II), and Hg(II). Isoelectronic congeners along group 12 are still elusive, however, and, to our knowledge, full experimental and theoretical characterizations are still missing. This manuscript focuses on the theoretical study of the thermodynamic stability and properties of homoleptic complexes of ethylene with metals from group 12 in comparison with those from groups 10 and 11.

Octacoordinate metal carbonyls of scandium and yttrium: theoretical calculations and experimental observation

RATIONALE

The transition metal carbonyls are among the most important complexes in coordination chemistry. The maximum coordination number in these complexes is seven. Because the cations Sc(+) and Y(+) have empty second outermost d orbital subshells, they can possibly bond eight CO ligands, forming the 18-electron d(10)s(2)p(6) noble gas configuration. The aim of this study is to determine whether the octacoordinate metal carbonyls of Sc(+) and Y(+) exist.

METHODS

The structures and bonding of M(CO)n(+) (M = Sc and Y, n = 7-9) were studied using Density Functional Theory (DFT) calculations with the functionals of B3LYP and BP86. The cationic complexes from laser ablation of Sc and Y in CO gas were analyzed by time-of-flight mass spectrometry.

RESULTS

The structures of M(CO)n(+) (M = Sc and Y, n = 7-9) and the bond dissociation energies for the last CO ligand in M(CO)n(+) (M = Sc and Y, n = 8 and 9) were obtained using DFT calculations. The products in the experiment for both metals include the series MO(CO)n(+), MO(H2O)(CO)n(+) and M(CO)n(+) (M = Sc or Y). The intensities of the MO(CO)n(+) and MO(H2O)(CO)n(+) ions change gradually with the number of CO ligands, while most M(CO)n(+) ions are very weak except for three intense ones, Sc(CO)7(+), Sc(CO)8(+) and Y(CO)8(+).

CONCLUSIONS

Comparisons between the theoretical calculations and the experimental observations indicate that eight CO ligands are chemically bonded on the central atom in the singlet state of Sc(CO)8(+) ((1)A1 state of D(4d) symmetry) and the singlet and triplet states of Y(CO)8(+) ((1)A1 state of D(4d) symmetry and (3)A(1g) state of O(h) symmetry). The (1)A1 states of both Sc(CO)8(+) and Y(CO)8(+) have the 18-electron d(10)s(2)p(6) noble gas configuration. In M(CO)9(+) (M = Sc or Y), the ninth CO is weakly adsorbed on the external shell.

Quantum Chemical Study of Atomic Structure Evolution of Cox/C60 (x ≤ 2.8) Composites

The main features of the local atomic structure of novel Cox/C60 (x<or=2.8) complex mixtures were studied using the ab initio B3LYP/6-31G* method for a set of low- and high-energy Con(C60)m (n=1, 2, m=2, 3) clusters in low and intermediate spin states. For the n = 1 isomers the spin state S=1/2 is energetically preferable, whereas the low-energy isomers of n=2 have an intermediate spin state of S=1. The eta2 (6-6 edge of C60) type of cobalt ion coordination is preferable for both the n=1 and n=2 cases. The eta2' (coordination with a 6-5 edge) and even the eta5 (C5 fragment) types can serve as low- and high-energy intermediates for the cobalt ion's migration around the C60 cage. Formation of cobalt dimers can be the final stage of evolution of Cox/C60 atomic structure approaching the equilibrium atomic geometry.