Metal‐Metal Coordination Chemistry: Free Clusters of Group 12 Elements with Sodium

Abstract

A systematic study of the mass spectra of particles formed in a supersonic nozzle expansion of Zn, Cd, and Hg vapors together with Na was performed. The particles discussed in this paper contain only one heavy atom and less than 12 Na ligands. Mass spectra from the neutral particles were generated by photoionization at five wavelengths (250, 260, 280, 300, and 320 nm) with a slit width corresponding to 16.5 and 3.3 nm, respectively. The abundances were corrected to relative differential ionization cross‐sections. Photoionization potentials for Nan M with 5 < n < 10 and M = Zn, Cd, Hg were measured. Below n = 6 no mixed clusters were found. The first abundance maximum occurred for all M at n = 8. A second maximum was with n = 16 or n = 18 (not covered in this paper). This selectivity can be rationalized by recent ab initio calculations by Fantucci et al. (J. Chem. Phys.; in press) and by jellium calculations, which give a closed shell at n = 8 with the occupations 1s21p62s2. Ionization potentials clearly show a level reversal to 1p‐2s‐1d in contrast to the homonuclear jellium with 1p‐1d‐2s. This is similar to previous results with KnMg (Kappes, M. et al., Chem. Phys. Lett., 1985, 119: 11). Molecular dynamics simulations with empirical potentials show that the heavy metal migrates to the center of a cube in the frozen asymptote of NagM. At finite temperatures and for larger central atoms, a square antiprismal arrangement seems to be more stable.

Metal−Metal Coordination Chemistry: Free Clusters of Group 11 Elements with Sodium

“…To obtain the neutral cluster abundances, the photoionization mass spectra recorded with monochromator slits of 5 mm (16.5-nm fwhm (full width at half-maximum)) were corrected using relative differential ionization cross sections obtained from photoionization efficiency (PIE) curves. 10 These were measured with both 5-mm and 2-mm slits (6.6-nm fwhm). Five-millimeterslit PIE measurements provided rough data for this correction, and from the 2-mm-slit measurements, ionization thresholds were extracted.…”

“…In previous work, it was shown that small sodium heteroclusters with one atom of Cd/Zn/Hg are van der Waals molecules, whereas the same heteroclusters with more than six atoms are metal-bonded clusters. 10 Such a transition could not be found for Li/Na or Na/K heteroclusters, however. 11,12 Experiments on very small CsAu clusters suggest that the ionic character is already developed in this small size range.…”

Impurity Doped Simple Metal Clusters: Optical Response

“…CLis [S]), composition dependent electron localization (e. g. Na,Cl,, x > y ) [6], as well as the molecular systematics of metal alloys [7]. Most extensively studied (apart from hetero s'-doped clusters) have been clusters containing a single halogen [8], oxygen [3] or s2 electron metal atom [1,2,7]. For these systems, the observed stability island series and ionization potential discontinuities can be rationalized to first order in terms of spherical jellium-on-jellium or jelliumon-insulator calculations [3,9].…”

“…For these systems, the observed stability island series and ionization potential discontinuities can be rationalized to first order in terms of spherical jellium-on-jellium or jelliumon-insulator calculations [3,9]. These suggest centered heteroatom geometries for the observed ,,closed shell" stability islands such as Na9X (X = halogen) [8], CsloO [3] and NasM [1,2] (M = s2 electron metal). Within this picture, heteroatoms are either electron withdrawing (e.g.…”

“…The consequence is a repositioning of jellium levels compared to the homonuclear case, with low angular momentum states experiencing largest relative stabilizations (for central potential dipscorresponding to electron donating dopants) or destabilizations (for central potential "mounds"). In extreme cases, level filling order inversions pertaina result whice has been used, for example, to rationalize 10 valence electron stability islands observed for NaaHg, NaaCd, NasZn, KsZn and KaMg [1,2,7].…”