M. Laura Mercuri

Effective One-Step Gold Dissolution Using Environmentally Friendly Low-Cost Reagents

Digging for gold: Mixtures of tetraethylthiuram disulfide (Et4TDS) and I2 in acetone are capable of dissolving elemental gold and forming valuable metal complexes, in which the stoichiometry depends on the mixture composition. These mixtures can also etch the gold layer homogeneously and selectively from Si/SiO2/Ti/Au thin-layered structures under mild conditions (see figure).

New semiconductors obtained by reaction of 4-imidazoline-2-selonederivatives with TCNQ. Characterization and X-ray structure of (C9H12N4Se)2+(TCNQ)2–3

The charge transfer complexesI, II and III of three new electron donors, 1,1′-ethylenebis(3-methyl-4-imidazoline-2-selone) 1,1,1′-methylenebis(3-methyl-4-imidazoline-2-selone) 2 and 1,3-dimethyl-4-imidazoline-2-selone 3, with TCNQ have been synthesized. We report the X-ray crystal structure of II, (C9H12N4Se)(TCNQ)3 , which crystallizes in the triclinic system, space group P1, with one molecule per unit cell and a=7.563(7), b=10.371(6), c=13.575(5) A, alpha;=95.00(2), beta;=95.54(2), gamma;=109.74(2)°. The comparison with the already described crystal structure of I and a detailed spectroscopic characterization of all three complexes, allows us to show that the change of the donor yields compounds characterized by quite different charge distributions and stack types. The semiconducting properties, ranging from ∼10–2 to 6×10–4 S cm–1 , are most likely due to the TCNQ stacks, where two negative charges are distributed among three TCNQ units. At room temperature, the charge is fully delocalized along the TCNQ stack ofI, the semiconductor with the highest conductivity, whereas in II and III the charge is unevenly distributed among the TCNQ units. The donors show a strong tendency to form stable dications: in I and III they give rise to mixed-valence cations and a new dication with elimination of an Se atom is formed in II.

Tuning the oxidation state and magnetic and coordination behaviour of iron and cobalt complexes by O/S variation in mono-thio and dithio-oxamide chelating ligands

New iron and cobalt complexes coordinated with the ligands Me2pipto (N,N′-dimethyl-piperazine-3-oxo-2-thione) and Me2pipdt (N,N′-dimethyl-piperazine-2,3-dithione, S,S′), differing in one sulphur substituting the oxygen atom, have been prepared and characterized. The reaction with Me2pipto and iron salts affords the heteroleptic [FeIII(Me2pipto)2Cl2]+ or the homoleptic [FeII(Me2pipto)3]2+ cationic complexes (isolated as tetrafluoroborate salts 1 and 2) depending on the employed iron source: FeCl3 or Fe2(SO4)3 respectively. The corresponding reaction with CoCl2 as the metal source allowed us to obtain [CoII(Me2pipto)3](BF4)2 (3). By reacting FeCl3, Me2pipto and KSCN in the molar ratio 1 : 1 : 4, [FeIII(Me2pipto)(NCS)4]− is obtained and isolated as a Ph4P+ salt (4). Upon using the Me2pipdt ligand, the reaction with FeCl3 affords [FeII(Me2pipdt)3]2+ which is isolated as a tetrafluoroborate salt (5). The same cation is found in the polyiodide salt [FeII(Me2pipdt)3](I3)1.8(I)0.2 (6) obtained by reacting iron-metal powders with Me2pipdt and I2 mixtures. Through a similar reaction by using cobalt-metal powders, [CoIII(Me2pipdt)3]2(I3)2(I)4·2I2 (7) is obtained. Structural results show that in all these compounds the metal ions are in a pseudo-octahedral coordination geometry and that bond distances are consistent with the presence of iron(III) in 1 and 4 and iron(II) in 2 and cobalt(III) in 7. Magnetic susceptibility measurements show that the metals are in a high spin state in all Me2pipto complexes and a low spin state in Me2pipdt. The observed differences are relatable to the different σ-donor and π-acceptor capabilities of the ligands tuned by the S and O donor atoms. Results from DFT calculations using B3LYP and OLYP as functionals are in agreement with the observed magnetic behaviour of the complexes.