Gabriele Balducci

An unusual promotion of the redox behaviour of CeO2-ZrO2 solid solutions upon sintering at high temperatures

The reduction behaviour of a high surface area CeO2-ZrO2 solid solution is compared with that of a high surface area CeO2. It is shown that, upon sintering induced by repetitive reduction/oxidation processes, the temperature of reduction of the solid solution decreases from 900 to 700 K. In contrast, the reduction at low temperatures of the CeO2 sample is strongly retarded after such treatments. The role of ZrO2 in promoting the reduction at low temperatures is discussed.

Effect of ZrO2 content on textural and structural properties of CeO2 / ZrO2 solid solutions made by citrate complexation route

Abstract Single phase homogeneous CeO 2 –ZrO 2 solid solutions with various compositions were synthesized using a citrate complexation route. Investigation of the sintering behaviour disclosed important modifications of the textural and, in particular, structural properties, which apparently create a strongly defective structure that could explain the unusual redox properties of these catalytic systems.

Synthesis and characterization of two new classes of ruthenium(III)-sulfoxide complexes with nitrogen donor ligands (L): Na[trans-RuCl4(R2SO)(L)] and mer, cis-RuCl3(R2SO)(R2SO)(L). The crystal structure of Na[trans-RuCl4(DMSO)(NH3)] · 2DMSO, Na[trans-RuCl4(DMSO)(Im)] · H2O, Me2CO (Im = imidazole) and mer, cis-RuCl3(DMSO)(DMSO)(NH3)

Abstract In this paper we report the synthesis of two new classes of chloride-sulfoxide-Ru(III) derivatives containing a nitrogen ligand (L) of general formula: Na[trans-RuCl4(R2SO)(L)] and mer, cis-RuCl3(R2SO)(R2SO)(L). Their spectroscopic characterization in the solid state (IR) and in solution (NMR, UVVis) is also described. The cyclic voltammetry of the complexes performed in aqueous solution shows in every case a monoelectronic and rather rapid Ru(III)/Ru(II) electron transfer. The observed formal potentials are much more positive than those reported for other Ru(III) complexes. The net charge, together with the, π acidic ability of DMSO, are the factors responsible for this behaviour. The crystal structures of Na[trans-RuCl4(DMSO)(NH3)] · 2DMSO (5a), Na[trans-RuCl4(DMSO)(Im)] · H2O, Me2CO 5b and mer, cis-RuCl3(DMSO)(DMSO)(NH3) (6a) have been determined by three dimensional X-ray analyses. Crystal data are: a = 9.578(2), b = 12.480(2), c = 9.594(6) A, α = 104.33(3), β = 119.04(2), γ = 80.71(3)°, triclinic, space group P 1 , Z = 2 for 5a; a = 10.790(4), b = 11.411(4), c = 7.658(4) A, α = 105.92(3), β =93.61(1), γ = 83.50(3)°, triclinic, space group P 1 , Z = 2 for 5b; a = 10.110(3), b = 9.718(3), c = 14.101(3) A, β = 108.89(3)°, monoclinic, space group P21/n, Z = 4 for 6a. Least-squares refinement based on 4897 5a, 4932 5b and 3152 6a independent reflections converged to R = 0.039, 0.031 and 0.022, respectively. In 5a and 5b, the DMSO ligand is S-bonded to Ru, with RuS bond distances (trans to N) of 2.2797(7) and 2.2956(6) A, respectively, while in 6a, one DMSO, trans to N, is S-bonded (RuS, 2.2714(6) A), and the other, trans to Cl, is O-bonded (RuO, 2.070(2) A). The RuCl bond distance, trans to O, is 2.3207(7) A. The RuCl bond distances, trans to Cl, are similar in all three compounds averaging 2.343(6) A. Relevance in the synthesis of the new derivatives comes from the known antitumor properties of isostructural Ru(III) complexes with heterocyclic nitrogen ligands. The antitumor activity of some of the new compounds are currently under investigation. Their redox potentials suggest the possibility that they might undergo an easy biological reduction in vivo.

Metal-loaded CeO2-ZrO2 solid solutions as innovative catalysts for automotive catalytic converters

The redox behaviour of a Ce0.5Zr0.5O2 solid solution is investigated by means of temperature programmed reduction (TPR) and oxygen uptake measurements. It is shown that the introduction of ZrO2 into the CeO2 framework, strongly modifies the reduction behaviour in comparison to pure CeO2. Remarkably, in contrast to the CeO2, upon repetitive reduction-oxidation processes, the temperature of reduction of the solid solution decreases from 900 to 700 K. The reduction of NO by CO over metal-loaded catalysts is investigated and the role of support Ce3+ sites in the enhancing the NO conversion is discussed.

Analogies and Differences in Palladium‐Catalyzed CO/Styrene and Ethylene/Methyl Acrylate Copolymerization Reactions

The catalytic CO/styrene and ethylene/methyl acrylate copolymerizations are compared for the first time by applying the same precatalysts. With this aim, PdII neutral, [Pd(CH3)Cl(N–N)], and monocationic, [Pd(CH3)(L)(N–N)][PF6] (L=CH3CN, DMSO), complexes with 1‐naphthyl‐ and 2‐naphthyl‐substitued α‐diimines with both an acenaphthene and a diazabutadiene skeleton as chelating nitrogen‐donor ligands (N–N) have been studied. In the case of the complexes with the 1‐naphthyl‐substituted ligands, syn and anti isomers are found both in solid state and in solution. All the monocationic complexes generate active catalysts for the CO/styrene copolymerization leading to atactic or isotactic/atactic stereoblock copolymers depending on the ligand bonded to palladium. Instead, in the case of the ethylene/methyl acrylate copolymerization only the complexes with the 1‐naphthyl‐substituted ligands generate catalysts for this reaction.

Electrochemistry of cobalt mixed Schiff base/oxime chelates☆

Abstract Diaquocobaloxime and three other chelating ligands obtained by substitution of the O ⋯ H ⋯ O bridge with (CH2)3 or BF2 groups have been examined in order to compare the effects of changes in the in-plane ligand on the relative stability of different oxidation states of the cobalt atom and on the cis-effect of the equatorial structure with those observed in the corresponding organometallic derivatives. The cis-effect of the in-plane ligand was evaluated from the electrochemistry of the CoIII/CoII electron transfer which is dependent upon the Co-solvent bond strength changes in the axial positions. The axial interaction depends mainly on the nature of the axial ligand. The introduction of either one (CH2)3 group or two BF2 groups or both leads to a displacement of the stability range of the CoII oxidation state towards more anodic redox potentials. The (CH2)3 group appears to be more effective both in the displacement of the redox potential and in teh bathochromic shift of the visible band at 450–500 nm of the CoII chelates.

The four-member square scheme in cyclic voltammetry: general solution for nernstian electron transfers

Abstract A general solution of the four-member square scheme under cyclic voltammetric conditions is presented. The diffusional problem is converted into a system of integral equations, which can be solved numerically, giving ‘individual’ currents. The heterogeneous electron transfer steps are assumed to be nernstian, while no limitations on the magnitude of the kinetic constants of the homogeneous chemical reactions are imposed.

Electrochemistry of sodium trans-bis(dimethyl sulphoxide) tetrachlororuthenate(III) and mer-trichlorotris(dimethyl sulphoxide) ruthenium(III): the first and complete electrochemical characterization of chlorodimethyl sulphoxide ruthenium(III) complexes

Abstract The results of an investigation of the electrochemical behaviour in dimethyl sulphoxide (DMSO) and aqueous solution of the two new halogen-DMSO complexes Na[ trans -RuCl 4 (DMSO) 2 ] (I) and mer -RuCl 3 (DMSO) 3 (II) are presented. Both complexes give trans -RuCl 2 (DMSO) 4 upon bulk one-electron reduction of their DMSO solutions. In DMSO solution, complex II equilibrates with a less easily reducible isomer differing in the mode of binding of one DMSO ligand. This equilibrium, together with the homogeneous chemical reactions following the heterogeneous mono-electronic reduction of II, was estimated quantitatively by means of cyclic voltammetry. Cyclic voltammetry of I in aqueous medium shows the occurrence of an H 2 O/DMSO exchange reaction following its one-electron reduction at a Pt microelectrode. The complete scheme of the reactions which characterize the bulk electrolysis behaviour of the two complexes in aqueous medium is also reported.

New Cationic and Neutral Ru(II)- and Os(II)-dmso carbonyl Compounds

The preparation and structural characterization of three cationic Ru(II)-dmso carbonyls and of four neutral mono- and dicarbonyl Os(II)-dmso derivatives is reported. The two monocarbonyl species fac-[Ru(CO)(dmso-O)3(dmso-S)2][PF6]2 (11) and cis,cis,cis-[RuCl(CO)(dmso-O)2(dmso-S)2][PF6] (12) were obtained from the neutral monocarbonyl precursor cis,trans,cis-[RuCl2(CO)(dmso-O)(dmso-S)2] (3) upon stepwise replacement of the chlorides with dmso, that binds in each case through the oxygen atom. The dicarbonyl cationic complex cis,cis,trans-[Ru(CO)2(dmso-O)2(dmso-S)Cl][PF6] (13) was instead obtained upon treatment of the neutral tricarbonyl precursor fac-[RuCl2(CO)3(dmso-O)] (8) with AgPF6 in the presence of DMSO: replacement of a Cl(-) with a dmso-O implied also the substitution of one CO ligand by another dmso (that binds through S trans to Cl). The Os(II) carbonyls trans,trans,trans-[OsCl2(CO)(dmso-O)(dmso-S)2] (17), trans,cis,cis-[OsCl2(CO)2(dmso-O)2] (18), cis,mer-[OsCl2(CO)(dmso-S)3] (19), and cis,trans,cis-[OsCl2(CO)(dmso-O)(dmso-S)2] (20) were obtained by treatment of the Os(II)-dmso precursors trans-[OsCl2(dmso-S)4] (14) and cis,fac-[OsCl2(dmso-O)(dmso-S)3] (15) with CO. Each one of them is structurally similar to an already known Ru(II) analog, even though--in agreement with the expected greater inertness of Os(II)--more forcing reaction conditions were required for their preparation. Interestingly, compound 20 could not be isolated in pure form, but only as a 1:1 cocrystallized mixture with its precursor 15. The dmso ligand is always bound through the oxygen atom when trans to CO. We are confident that the new Ru(II)- and Os(II)-dmso carbonyl species described here represent a contribution to expand the pool of complexes bearing some easily replaceable dmso ligands to be used as well-behaved precursors in inorganic synthesis.

Electrochemical investigation of dioxygen interaction with two cobalt chelates in solution and at the electrode surface

Abstract The interaction between molecular oxygen and the metal atom in two Co(II) complexes with bis(diacetylmonoxime-imino)propane-1,3 ( A ) and with the related ligand obtained from cobaloxime by substitution of both the O-H ⋯ O bridges with the -BF 2 -group ( B ) is investigated using electrochemical and spectroelectrochemical techniques. Notwithstanding the stability of the Co(II) complex B in air, the results suggest the formation of a dioxygen adduct as an unstable intermediate in the electrocatalytic reduction of molecular oxygen in the presence of either A or B . Furthermore, the oxygenation ratio at a given p O 2 appears to be quite different for the homogeneous reaction of A in the Co(II) oxidation state in bulk as compared with either the electrogenerated Co(II) (from complex A ) on the electrode surface or the Co(II) complex B .