Emanuele F. Trogu

Structural and Raman spectroscopic studies as complementary tools in elucidating the nature of the bonding in polyiodides and in donor-I2 adducts

Abstract A large number of examples of polyiodides and donor-I 2 adducts whose structures and Raman spectra are reasonably well-established, have been collected. An empirical method based on structural and Raman data, as complementary tools in elucidating the nature of the iodine moiety, is proposed to remove the arbitrariness in considering discrete/non discrete entities and to provide a unified picture of the bonding in these species. Accordingly polyiodides higher than I 3 − do not exist as discrete entities but are formed by a combination of I − and/or I 3 − with I 2 through donor–acceptor interactions. The I 3 − moiety represents a crossover, its structural and vibrational features show that it can exist as an I 3 − entity (in accordance with the existence of a covalent bond interaction describable by means of a delocalized three-center four-electron, 3c-4e, bond) or I − ·I 2 donor–acceptor adduct. The formal I 2 -adducts of donors (D) show structural and Raman features which can be explained considering three types of adducts: D·I 2 , D–I–I (covalent bond interaction describable by means of a delocalized 3c-4e bond by analogy with the I 3 − entity case) and (D–I) + ·I − , which can be considered as stages along the reaction coordinate between the separated D and I 2 and the salt [(D–I) + ]I − . The precautions to be taken in studying these species have been cited. The possibility that some of the Raman attributes in the literature need corrections has been pointed out in regard to the instability inherent in these materials since the decomposition of these species causes spurious peaks to appear in the Raman spectrum.

FT-Raman Study on Charge-Transfer Polyiodide Complexes and Comparison with Resonance Raman Results

In resonance Raman (RR) spectroscopy, the laser excitation sources have often been found to be destructive towards polyiodides if compared with the milder conditions under which the Fourier transform Raman (FT-R) technique operates. In fact, our FT-R spectra of some model polyiodides—[(CH3)4N]I5 (I5− bent), [(C2H5)4N]I7, and [(CH3)4N]I9—are significantly different from the literature RR data, give evidence of decomposition of the samples in RR, and are in agreement, respectively, with the I− · 2I2, I3− · 2I2 and (I− · 2I2) · 2I2 descriptions. In addition to the above-cited cases, the FT-R spectra of (Mn(modtc)3]Is (modtc = morpholine carbodithioato) and (moH]I5 (moH = morpholinium) are reported. The crystal structures indicate that in these two compounds the I5 anions can be properly described as I− · 2I2 and I3− · I2, respectively, and FT-R spectra agree well with this formulation. Moreover, the first FT-R spectrum of an I164– anion in [mo2ttl]2I16, ([mo2ttl]2+ = 3,5-di(N-morpholinio)-1,2,4-trithiolane), whose X-ray structure shows a sequence of two I3− … I2 … I− ·I2 (I82–) interacting anions, is reported. A close correlation of the FT-Raman peaks with the molecular species, identified by the interatomic distances, is also observed in this case. Thus, a combination of X-ray structural data and FT-R data can provide a reasonable interpretation of the nature of the acceptor iodine moiety in charge-transfer polyiodide complexes.

Synthesis, X-ray and spectroscopic characterization of obtained throught the one-step reaction of mbit·2I2 with tin metal powder (mbit = 1,1′-bis(3-methyl-4-imidazoline-2-thione)methane)

Abstract The reaction of the adduct mbit·2I2 (mbit = 1,1′-bis(3-methyl-4-imidazoline-2-thione)methane) with tin metal powder produces Sn(mbit)2I9, in mild conditions. An X-ray diffraction study on a crystal showed that the compound consists of a cation [SnI2(mbot)2]2+ having two I2 as counterions, interacting with two disordered diiodine molecules. In the cation, the metal atom lying on a symmetry centre exhibits a slightly distorted octahedral coordination with the two iodides at the apices in trans position, and with the two mbit molecules acting as bidentate chelating ligands through the sulfur atoms and forming an eight-membered ring, the tin metal atom included. The counterions I1 are slightly bent (I(2)–I(3)–I(4) 176.0(1)) and so asymmetric (I(2)–I(3) 2.841(6) I(3)−I(4) 3.016(5) A) that they can be better described as I ·I2 adducts. The presence of the two independent, centrosymmetric and disordered diiodine molecules as guests in the channel running parallel to [III] brings about I82 units of the type I2·I✓I2✓I·I2, here two triiodide ions realted by a sym centre are linked only for one third to I(5)–I(510), that is one of the two disordered guest I2 molecules (I(4)✓I(5) 3.22(I) A). Two I82 units related by a symmetry centre are held together through a non-negligible interaction (I(4)✓I(6) 3.55(1) A) involving the other disordered diiodine molecule (I(6)–I(6m)) giving rise to an octadecaioddide. Crystallographic data for C18H24N8S4I90Sn are as follows: the crystal is trigonal. M = 1783.77 space group R3, Z = 3, V = 3146(4) A ′, a = 18.100(6) A , α = 115.55(2)°, R = 0.0584 . In accordance with a description of the counterions as a sequence of the type I2·I✓I2✓I·I2. FT-Raman spectra do not show the peaks generally found in conventional triiodides, but those related to perturbed diiodine molecules.

Evaluation of thermodynamic parameters for highly correlated chemical systems: a spectrophotometric study of the 1 : 1 and 2 : 1 equilibria between I2 and 1,1′-methylenebis(3-methyl-4-imidazoline-2-thione)(mbit) and 1,1′-ethylenebis(3-methyl-4-imidazoline-2-thione)(ebit). Crystal and molecular structures of mbit·2I2 and ebit·2I2

The reactions of I2 with 1,1′-methylene- and 1,1′-ethylene-bis(3-methyl-4-imidazoline-2-thione)(mbit and ebit) have been investigated in CHCl3 solution at different temperatures by spectrophotometry. The experimental data have been processed using two different procedures of computer analysis: SUPERSPEC based on the conventional Gauss–Newton–Marquardt least-squares method; and POWELSPEC, based on Powells direct search method for the refinement of ΔH° and ΔS°. The ability of the two methods to identify the involved equilibria correctly was compared. Evidence for the stepwise formation of the 1 : 1 and 1 : 2 adducts has been obtained by the two methods for the mbit case, while POWELSPEC only was able to solve the ebit case satisfactorily. The crystal structures of the adducts mbit·2I2 and ebit·2I2 have been determined. They show that the thionic sulfur atoms co-ordinate two diiodine molecules, with S–I 2.683(2)(mbit·2I2) and 2.642(3)(ebit·2I2)A and with I–I 2.897(1) and 2.903(2)A respectively, the two S–I–I groups beings related by a two-fold axis. The structural features of the S–I–I linear group are in accordance with Fourier-transform IR and Raman spectral data and can be taken into account with a three-centre two-electron axial orbitally deficient bonding scheme.

Thiazolidine-2-thione complexes with group VI B metal-carbonyls

Abstract By u.v. irradiation of toluene solutions of [M(CO)6] and ttz the complexes [M(CO)5ttz] (where: MCr, Mo, W, and ttzthiazolidine-2-thione) were obtained, which are yellow, crystalline, diamagnetic and non-electrolytes. By means of the mass-spectra, i.r. and n.m.r. studies a full characterization of the free ligand and of that the co-ordination bond takes place through the sulphur atom of thioketonic group. A SN1-type mechanism of the photochemical reactions was pointed out by determining the quantum yields.

A Spectro- and Conductometric Study of the Reaction of Imidazoline-2-selone Derivatives with Bromine − Crystal Structure of 1,2-Bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane

The oxidative addition of Br2 to the imidazoline-2-selone derivatives 1a−c has been studied by spectrophotometric and conductometric techniques. The experimental results clearly indicate that this reaction involves the dications 2a−c, containing an Se−Se bond, as intermediates in the formation of the hypervalent 10-Se-3 selenium compounds 3a−c containing the Br−Se−Br group. The crystal structure of 1,2-bis(3-methyl-4-imidazolin-2-ylium dibromoselenanide)ethane (3c), a new stable hypervalent 10-Se-3 compound, is also reported.

Characterization of tricarbonyl-chromium(0), -molybdenum(0) and -tungsten(0) complexes with 2,2-para-cyclophane

Abstract Complexes of the type M(CO) 3 (22cy), where M = Cr, Mo, W and 22cy = 2,2-para-cyclophane were prepared and characterised. The i.r., p.m.r., mass spectrography spectra are discussed. The Mo derivative decomposes in solution giving 22cy, Mo(CO) 6 and Mo, according to a first order mechanism.

Group IIB metal and VIB metal-carbonyl thiomorpholin-3-thione derivatives

Abstract Using thiomorpholin-3-thione (ts) as ligand the complexes M(CO)5ts (where M = Cr, Mo, W), which are yellow, crystalline, non-electrolyte and diamagnetic, were obtained. Complexes of the types MX2ts2 and MX2ts (M = Zn, Cd, Hg; X = Cl, Br, I) were obtained as diamagnetic and non-electrolyte compounds. On the basis of i.r. and PMR spectra we suggest that the Cr, Mo and W-pentacarbonyl-derivatives have C4ν symmetry and are S-bonded through the thioketonic group, while all the IIB group derivatives seem to be N-bonded.

New powerful reagents based on dihalogen/N,N′-dimethylperhydrodiazepine-2,3-dithione adducts for gold dissolution: the IBr case

The synthesis, X-ray structure [monoclinic, P21/n, a = 12.1690(1), b = 7.8360(1), c = 14.4250(1) A, β = 113.808(2)°], spectroscopic and electrochemical characterization of a new powerful reagent based on the iodine monobromide adduct of the N,N′-dimethylperhydrodiazepine-2,3-dithione (Me2dazdt) ligand, able to oxidize gold metal in a one-step reaction under mild conditions, is reported. The gold metal dissolution has been performed on gold powder, wires and Au/Ti thin layers. The oxidation product has been isolated and structurally characterised as [Au(Me2dazdt)Br2]IBr2 [monoclinic, C2/c, a = 26.523(8), b = 10.191(6), c = 14.549(7) A, β = 111.57(2)°]. The metal is essentially within a square planar geometry, Me2dazdt acts as an S,S chelating ligand and two bromide ligands complete the geometry around the metal. The IBr2− counteranion is essentially linear and shows I–Br bond lengths slightly asymmetric [Br(4)–I(1) 2.742(3), Br(3)–I(1) 2.682(2) A]. A comparison with the gold removal from Si/SiO2/Au/Ti thin layers of comparable thickness to that found in microelectronic devices, by using THF solutions of IBr and I2 adducts of the Me2dazdt donor, as well as the currently used I2/I− aqueous solutions, shows that these dihalogens-adducts produce a quantitative gold removal in shorter times and leaving the underlying layer perfectly clean, and are thus highly desirable as new etching agents in the gold-based technology of semiconductor devices.

Complexes of 4,5,6,7,-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione (Et4todit) with group IIb metal halides. Crystal and molecular structure of (Cd(II)Et4toditCl2)n

Abstract The capability of Et4todit (title ligand) to coordinate through the two CS groups forced at very distant positions has been used to prepare some new ligand-bridged polymeric complexes, having stoichiometry M(II)Et4toditX2 (M(II) = Zn, Cd, Hg; X=Cl, Br). IR spectral results show that the ligand binds via thionic sulphur in all isolated compounds, and the low frequency spectrum of (CdEt4toditX2)n gives a different pattern from the rest, which all are very similar and consistent with a tetrahedral stereochemistry. The X-ray structure of (CdEt4toditCl2)n shows that the crystals are orthorhombic, space group P21212, a=14.199(4), b=15.550(4), c= 10.575(3) A, Z=4. Solution and refinement of the structure gave final residuals R=0.0461 and Rw=0.0615 using 1402 observed reflections. Coordination around the metal is trigonal-bipyramidal. Apical sites are occupied by Cl atoms (Cl(1) and Cl(2)). Both bidentate ligand and Cl(2) are bridging to form a polymeric tridimensional structure.