The Nature of the Chemical Bond in Linear Three-Body Systems: From I3− to Mixed Chalcogen/Halogen and Trichalcogen Moieties

The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I3− and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I3− anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom

Copper(I) complexes from CuX2(X = NO3, BF4, 1 2SO4) and some heterocyclic ligands containing the thioamido group

Complexes of copper(I) CuLnX(n = 2, 3; X = NO3, BF4 1 2SO4) have been obtained by reacting the corresponding copper(II) salts with the following ligands HNCH2·CH2X·C = S (where X = NH, NMe, NEt, S, O and CH2). All the ligands bind the metal through the thioketonic sulphur, as shown by the IR spectroscopy. The copper(I) seems always to realize a trigonal planar geometry both with three molecules of ligands and with two ligands and

Copper(I) complexes of pentatomic heterocyclic selone donors.

New complexes of copper(I) with some heterocyclic pentatomic rings, X·CH2·CH2·NR·CSe, where X=CH2, NH, NMe, NEt, S and R=H, Me, Et, were prepared by reacting copper(II) chloride and bromide in MeOH. The stoichiometry of the complexes and the binding mode of the ligands have been discussed comparatively, together with those of the thione parents. It is noteworthy that the selone ligands with R=H (L) yield complexes of the type CuLnY, (n=1,2 or 3; Y=Cl or Br) like the corresponding thione ones. On the contrary, when R=Me or Et, the selonic ligands (L′) give complexes whose stoichiometries, Cu2L′Y2 and Cu3L′2Y3, differ from the thione homologues. The i.r. spectra of the complexes compared with those of the ligands support the coordinative bond via selenium atom

Investigation of the nonlinear absorption of [M(Et2timdt)2] (M = Pd, Pt) in the pico- and nanosecond timescales using the Z-scan technique

The nonlinear optical absorption of two neutral metal dithiolenes [M(Et2timdt)2] (M=Pd and Pt) has been investigated at λ = 1064 nm by the open-aperture Z-scan technique using nanosecond and picosecond pulses. For picosecond photoexcitation, both dithiolenes mainly exhibit saturable absorption. Conversely, using nanosecond pulses, a switch from saturable absorption to reverse saturable absorption has been observed depending on the central metal. Based on experimental results, energy-level structures are suggested to explain the nonlinear absorption for both temporal regimes and, in particular, the sign-reversal of nonlinear absorption