Roberto Della Pergola

Modification of the PTFE wettability by oxygen plasma treatments: influence of the operating parameters and investigation of the ageing behaviour

The effects of O2 plasma treatments on poly(tetrafluoroethylene) (PTFE) sheets are deeply investigated. The chemical modifications owing to the plasma treatment are studied by means of attenuated total reflectance Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy (XPS), while the surface topography of the plasma-treated samples is assessed by atomic force microscopy (AFM) analyses. Results are correlated with the wettability characteristics of the plasma-modified PTFE sheets, which is studied by means of contact angle (CA) and roll-off angle measurements. Finally, the ageing of the plasma-treated surfaces is investigated. The RF power input and the treatment time influence the chemical/morphological characteristics and the wettability of the plasma-treated samples. PTFE samples treated at low-power input (up to 50 W) are more hydrophilic than the untreated one. The XPS analysis reveals that OH functionalization of the outermost layers of polymeric chains decreases by increasing the RF power input, and dynamic CAs gradually increase. The AFM analysis shows a strong increase in the surface roughness as a consequence of the differential etching of the PTFE surface for samples treated at power inputs ≥100 W, with formation of globular structures. XPS analyses of the aged samples reveal a post-plasma oxidation. However, the dynamic CAs measured after 30 days are greater than those measured immediately after treatment, and for power input ≥100 W the aged plasma-treated PTFE surfaces are super-hydrophobic. This result suggests a decrease in the surface density of the exposed hydroxyl groups during ageing time, as a consequence of surface adaptation.

Chemistry of iridium carbonyl cluster. Preparation of Ir4(CO)12

Abstract Ir 4 (CO) 12 has been prepared by a two-step reductive carbonylation of IrCl 3 · 3H 2 O in ethanol or of K 2 IrCl 6 in 2-methoxyethanol at atmospheric pressure. The iridium trichloride is first transformed into [Ir(CO) 2 Cl 2 ] − , which is subsequently reduced to Ir 4 (CO) 12 . A simple method for purification of the metal carbonyl is also described.

SYNTHESIS AND CHEMICAL BEHAVIOR OF THE [CO3NI7(CO)16C2]2- AND [CO3NI7(CO)15C2]3- DICARBIDE CLUSTERS - X-RAY CRYSTAL-STRUCTURE OF [PPH4]2[CO3NI7(CO)16C2]

The synthesis and properties of the new dicarbidocarbonyl bimetallic clusters [Co3Ni7(CO)16C2]2− (I), [Co3Ni7(CO)16C2]3− (II), and [Co3Ni7(CO)15C2]3− (III), are described. Compound I, which is paramagnetic, has been synthesized in high yields by redox-condensation of Co3(CO)9CCl with [Ni9(CO)17C]2−, whereas the diamagnetic trianions II and III have been respectively obtained by reduction of I, with sodium metal in THF and sodium hydroxide in methanol. The anion I has been isolated in a crystalline state in association with several tetrasubstituted ammonium or phosphonium cations, which are characterized by elemental analysis and by a single-crystal X-ray diffraction study, of the tetraphenylphosphonium salt. The anion I has a metal frame based on a 3,4,3-C2h stack of metal atoms, which may be regarded as derived by condensation of two either octahedral or trigonal-prismatic moieties. The resulting deca-vertices metal polyhedron encapsulates a C2 fragment showing a short CC interatomic separation of 1.48 A. The three cobalt atoms cannot be distinguished from the remaining seven nickel atoms and are probably randomly distributed over the ten vertices. The M-M distances are scattered over the range 2.34–2.80 A, and each carbide carbon is encapsulated in a seven-vertices cage which may be described as a distorted capped trigonal prism. The carbonyl stereochemistry comprises six carbonyl groups terminally bonded to the atoms of the top and bottom triangular layers, and ten edge-bridging CO which span the ten inter-layer edges. The structure of this decanuclear dicarbide cluster is compared with those reported for related species and a rationalization is offered for the variations of the metal geometry and the CC interatomic separation.

The redox behaviour of the cluster anion [Fe4N(CO)12]−. Electron transfer chain catalytic substitution reactions. Crystal structure of [Fe4N(CO)11PPh3)]−

Abstract The electrochemical investigation of the redox properties of the monoanion [Fe4N(CO)12]− points out its ability to undergo sequentially two one-electron reductions. The first step leads to the quite stable dianion [Fe4N(CO)12]:2−; the EPR results indicate that in frozen solution an equilibrium exists between two different molecular geometries of such a dianion. The second electron addition produces the relatively short-lived trianion [Fe4N(CO)12]3−. In the presence of monodentate phosphines, the redox change [Fe4N(CO)12]−/2− triggers the electrocatalytic substitution of one CO group to afford the substituted monoanions [Fe4N(CO)11(PR3)]−. As a matter of fact, sub-stoichiometric amounts of Ph2CO − produce [Fe4N(CO)11(PPh3)]−, the crystal structure of which has been solved. Crystal data for [N(PPh3)2][Fe4N(CO)11(PPh3)]: triclinic, space group P 1 (No. 2), a=11.009(6), b=17.285(4), c=17.380(2) A, α=103.11(3), β=91.18(2), γ=105.26(3)°, Z=2, Dc=1.444 g cm−3, Mo Kα radiation (λ=0.71073 A), μ(Mo Kα)=10.5 cm−1, R=0.048 (Rw=0.054) for 5010 independent reflections having I > 3σ(I). Preliminary evidence is given that in the presence of bidentate phosphines one CO ligand substitution occurs at room temperature, whereas two CO groups are replaced at higher temperatures.

Iron–iridium mixed-metal carbonyl clusters. Part 2. Synthesis and chemical behaviour of the tetranuclear complexes [FeIr3(CO)12]–, [Fe2Ir2(CO)12]2–, [Fe2Ir2H(CO)12]–, and [Fe3Ir(CO)13]–. Solid-state structures of [N(PPh3)2][FeIr3(CO)12], [NEt4]2[Fe2Ir2(CO)12], and [PPh4][Fe2Ir2(CO)12-{µ3-Au(PPh3)}]

The compound [FeIr3(CO)12]– can be obtained by degradation of [FeIr4(CO)15]2– under a carbon monoxide atmosphere as well as by reduction of an equimolar mixture of [Fe(CO)5] and [Ir4(CO)12] in alcoholic NaOH under 1 atm (101 325 Pa) of carbon monoxide. The salt [N(PPh3)2][FeIr3(CO)12](1) crystallizes in the monoclinic space group P21/c with unit-cell dimensions a= 14.968(2), b= 19.892(2), c= 16.610(2)A, β= 96.10(2)°, and Z= 4. The molecular structure of the anion consists of a tetrahedron of metal atoms surrounded by twelve carbonyl groups: nine are terminally bound whereas three are bridging the edges of the FeIr2 basal face. Average bond distances are Ir–Ir 2.696, Ir–Fe 2.682, Ir–COt 1.889, Fe–COt 1.729, Ir–COb 2.154, and Fe–COb 1.887 A(b = bridging, t = terminal). The dianion [Fe2Ir2(CO)12]2–(2) was obtained by several different ways, the most selective being the condensation of [Fe2(CO)9] with [Ir(CO)4]–. The salt [NEt4]2[Fe2Ir2(CO)12](2) crystallizes in the monoclinic space group P21 with a= 9.072(5), b= 19.910(5), c= 10.094(3)A, β= 91.92(3)°, and Z= 2. The molecular structure of the dianion is based on a tetrahedral cluster of metal atoms and consists of an apical Ir(CO)3 group co-ordinated by three metal–metal bonds to a basal Fe2Ir(CO)9 fragment containing two Fe(CO)2 units and one Ir(CO)2 group linked to each other by a metal–metal bond and bridging carbonyl groups. Selected distances are: Ir–Ir 2.734(1), Fe–Fe 2.581(2), and averages Ir–Fe 2.683, Ir–COt 1.863, Fe–COt 1.722, Ir–COb 2.142, and Fe–COb 1.947 A. The salt [PPh4]2[Fe2Ir2(CO)12] reacts with [Au(PPh3)CI] to give [PPh4][Fe2Ir2(CO)12{µ3-Au(PPh3)}](3) which crystallizes in the monoclinic space group P21/c with a= 10.990(3), b= 13.693(2), c= 35.883(3)A, β= 97.39(2)°, and Z= 4. The metal framework of the anion is a trigonal bipyramid with the Au(PPh3) moiety in one of the apical positions, the other being occupied by a Fe(CO)3 group. Each edge of the equatorial triangle, formed by one iron and two iridium atoms, is spanned by a bridging carbonyl ligand, and two terminal CO groups are attached to each metal of this triangle. Selected bond distances are: Ir–Ir 2.758(1), and averages Ir–Fe 2.710, Ir–Au 2.786, Fe–Au 2.806(1), Ir–COt 1.845, Fe–COt 1.776, Ir–COb 2.113, and Fe–COb 1.996 A.

Synthesis and solid-state structure of [Pd6Ru6(CO)24]2–. Electrochemistry and 13C nuclear magnetic resonance spectra of [Fe6Pd6H(CO)24]3– and [Pd6Ru6(CO)24]2–

The cluster [Pd6Ru6(CO)24]2– was obtained in good yield from the reaction of [Ru3H(CO)11]– with [Pd(NCPh)2Cl2]. The salt [NEt4]2[Pd6Ru6(CO)24] crystallized in the triclinic space group P(no. 2) with a= 11.514(5), b= 11.602(5), c= 11.933(5)A, α= 73.01 (3), β= 78.25(3), γ= 65.26(4)°, Z= 1. Data were collected at room temperature, giving 5968 unique reflections. The structure was solved by direct methods. The final discrepancy indices were R= 0.024 and R′= 0.026 for 4129 independent reflections with I > 3σ(I). The metal skeleton consists of a trigonally distorted octahedron of palladium atoms, capped by six ruthenium atoms with twelve terminal, six edge- and six face-bridging carbonyl ligands. This ruthenium–palladium cluster adopts the same metallic polyhedron as [Fe6Pd6H(CO)24]3– but possesses two valence electrons less. The solution 13C NMR spectra of both anions are in agreement with the solid-state structures and electrochemical analysis shows that they produce labile congeners: [Pd6Ru6(CO)24]2– undergoes a one-electron oxidation with formation of the relatively stable monoanion; [Fe6Pd6H(CO)24]3– can be oxidized and reduced, to give corresponding anions with charges of 2– to 5–.

Bimetallic iron–rhodium anionic carbonyl clusters: [Fe2Rh(CO)x]–(x= 10 or 11), [FeRh4(CO)15]2–, [Fe2Rh4(CO)16]2–, and [FeRh5(CO)16]–

The synthesis and chemical behaviour of the new iron-rhodium anionic carbonyl clusters [Fe2Rh(CO)x]–(x= 10 or 11), [FeRh4(CO)15]2–, [Fe2Rh4(CO)16]2–, and [FeRh5(CO)16]– are reported. Low-temperature multinuclear n.m.r. studies (13C,13C-{103Rh}, and 103Rh) on the penta- and hexa-nuclear clusters allow their structures in solution to be unambiguously established and their fluxional behaviour has been investigated through variable-temperature measurements. None shows rearrangement of the metal polyhedron.

Synthesis and solution structure of the carbonyl cluster dianion [OsRh4(CO)9(μ2-CO)6]2−

Abstract The dianion [OsRh4(CO)15]2− has been obtained by reduction of a mixture of Rh4(CO)12 and Os3(CO)12. Variable temperature 13C NMR spectra in solution indicate that the mixed metal cluster is isostructural with [FeRh4(CO)15]2− and [RuRh4(CO)15]2−, with the Os atom located in an apical position within the trigonal bipyramidal metal skeleton. The overall ideal symmetry is Cs, with nine carbonyls terminally bound (three each on the apical metals and one each on the equatorial metals) and six bridging (the three Rheq−Rheq edges and two Os−Rheq and one Rhap−Rheq edges).

Bimetallic CoNi carbide clusters: synthesis and crystal structure of the [Co2Ni10(CO)20C]2− and [Co3Ni9(CO)20C]2− dianions

Abstract The synthesis, chemical behavior and single crystal X ray structure of two new CoNi bimetallic carbide clusters, namely [Co 2 Ni 10 (CO) 20 C] 2− and [Co 3 Ni 9 (CO) 20 C] 2− , are reported. The first complex was isolated in ca. 30% yield among the products of the reaction of Co 3 (CO) 9 CCl with [Ni 6 (CO) 12 ] 2− , while the second was obtained quantitatively by reaction with protonic acids of the previously reported [Co 3 Ni 9 (CO) 20 C] 3− . The two compounds are isostructural and show a metal frame which can be regarded as derived by distortion of a tetra-capped triangulated dodecahedron of D 2 d symmetry; the statistical (Co and Ni atoms being undistinguishable) idealized symmetry of the metal frame is only D 2 owing to progressive deformations toward a tetra-capped tetragonal antiprismatic geometry, which are probably related to the steric requirements of the interstitial carbide atom.

Characterization, redox properties and structures of the iron nitridocarbonyl clusters [Fe4N(CO)11{PPh(C5H4FeC5H5)2}]–, [Fe6N(CO)15]3– and [Fe6H(N)(CO)15]2–

The redox condensation of [Fe2(CO)8]2– with [Fe4N(CO)12]– yielded the cluster [Fe6N(CO)15]3–. Single-crystal X-ray analysis showed it to possess an octahedral metal cage, with an interstitial nitride ligand. Under the D3 idealized symmetry, all iron vertices are equivalent, being bound to one edge-bridging and two terminal carbonyls. The ion [Fe6N(CO)15]3– can be oxidized to [Fe5N(CO)14]– or protonated to the hydridic dianion [Fe6H(N)(CO)15]2–. The molecular structure of the latter was determined, and is strikingly similar to that of the parent trianion. Small deformations of the ligand shell or elongations of the Fe–Fe distances are not sufficient to determine the location of the hydride. Electrochemical experiments were consistent with the chemical findings, showing that [Fe6N(CO)15]3– undergoes three irreversible one-electron oxidation steps, ultimately generating [Fe5N(CO)14]–. A lifetime of about 15 s was evaluated for the transient radical [Fe6N(CO)15]2–. Thermal activation induces substitution of one carbonyl ligand of [Fe4N(CO)12]– by PPh(C5H4FeC5H5)2, yielding [Fe4N(CO)11{PPh(C5H4FeC5H5)2}]–, the molecular structure of which was also determined. The cluster adopts a butterfly arrangement of iron atoms, having an exposed µ4-N atom and the phosphine ligand at a wingtip position. Cyclic voltammetry showed that communication between the two ferrocenyl units of the ligand PPh(C5H4FeC5H5)2 is rather low in the free state, and is notably improved by co-ordination to the tetrairon cluster. The 15N-labelled [Fe6N(CO)15]3– and [Fe6H(N)(CO)15]2– complexes were synthesized, and the NMR chemical shifts and IR bands of the interstitial µ6-N ligands measured.