Sandra Lo Schiavo

Selective monitoring of parts per million levels of CO by covalently immobilized metal complexes on glass

Optical detection of parts-per-million (ppm) levels of CO by a structurally well-defined monolayer consisting of bimetallic rhodium complexes on glass substrates has been demonstrated.

Very fast CO2 response and hydrophobic properties of novel poly(ionic liquid)s

A series of polymerizable tetraalkylammonium ionic liquids based on [2-(methacryloyloxy)ethyl]dimethylheptyl ammonium cation and bis(trifluoromethylsulfonyl)imide, nonafluoro-1-butanesulfonate, dodecylbenzenesulfonate, heptadecafluorooctanesulfonate, 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanoate anions, as well as their corresponding homo- and copolymers, have been synthesized and characterized by means of 1H NMR, TG-DTA, DSC, MALDI-TOF, viscosimetry and XPS investigations. Hydrophobic and CO2 sensing properties of the poly(ionic liquid)s have been explored by dynamic contact angle and quartz crystal microbalance measurements. The CO2 sensing behavior of present polymers is very remarkable as they are featured by extremely rapid and completely reversible response without any memory-effect. Best results, in terms of sensitivity, have been obtained for [2-(methacryloyloxy)ethyl]dimethylheptyl ammonium nonafluoro-1-butanesulfonate-based homopolymer. Tensiometric data show good hydrophobic properties with θadv > 90° for all the polymers under study except the one involving 4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanoate anion (θadv = 78.3°); receding contact angles, representative of the most hydrophilic portions of the polymers surface, lie in the range 22–54° and can be further improved by choosing the proper long-chained N-alkyl groups.

A new application of ionic liquids: hydrophobic properties of tetraalkylammonium-based poly(ionic liquid)s

The potential of using poly(ionic liquid)s as a new family of hydrorepellent materials has been explored. Free-radical polymerization of a series of ionic liquids based on the polymerizable cation [2-(methacryloyloxy)ethyl]trimethylammonium and on the hydrophobic anions bis(trifluoromethylsulfonyl)imide, nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate led to the corresponding poly(ionic liquid)s that were characterized by TGA and DSC analysis, SEM, MALDI-TOF and XPS spectroscopy. Contact angle investigations show that the nature of the surface of the poly(ionic liquid)s based on the nonafluoro-1-butanesulfonate and dodecylbenzenesulfonate anions are featured by remarkable hydrophobic properties with advancing contact angles (θadv) lying in the range 113–118°, while to the polymer poly[2-(methacryloyloxy)ethyl]trimethylammonium bis(trifluoromethylsulfonyl)imide is associated poor hydrorepellent activity (θadv = 76°). The tensiometric measurements also experience receding contact angles (θrec) lying in the range 16–20° and a consequent high hysteresis suggesting that, on the outermost layers of the polymers, very high and very low-energy surface portions are present.

Polyfunctional phosphine ligands II. Iridium(I) complexes of the 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) ligand. X-ray crystal structure of [{Ir(cod)Cl}2(μ-dpnapy)]

Abstract The coordination chemistry of the polyfunctional phosphine ligand, 7-diphenylphosphino-2,4-dimethyl-1,8- naphthyridine (dpnapy) with iridium(I) complexes has been investigated. Dpnapy reacts with cis -[Ir(CO) 2 ( p - toluidine)Cl] in 1:2 and 1:1 molar ratios giving the P-monodentate containing ligand complexes trans - [Ir(CO)(dpnapy) 2 Cl] ( 1 ) and cis -[Ir(CO) 2 (dpnapy)Cl] ( 2 ), respectively. Complex 2 is unstable in solution; IR and 31 P NMR spectroscopic data show at r.t. it transforms into 1 in a short time. The reaction of dpnapy with [{Ir(cod)Cl} 2 ] (cod=cycloocta-1,5-diene) also depends on the metal to ligand ratio used. The mononuclear complex [Ir(cod)(dpnapy)Cl] ( 3 ), containing P-coordinated dpnapy, is obtained from the 1:2 dimer:ligand reaction. The 1 H and 13 C NMR spectra of 3 are temperature dependent. They show that the fluxional behaviour involves the cod ligand and is explained by the formation of a labile five-coordinate intermediate displaying a fast exchange of the non-equivalent cod protons and carbons. Treatment of 3 with AgClO 4 leads to a species, formulated on the basis of IR and analytical data, as [{Ir(cod)(dpnapy)}ClO 4 ] ( 4 ) in which dpnapy is very likely PN(8) chelated. The binuclear complex [{Ir(cod)Cl} 2 (μ-dpnapy)] ( 5 ), containing a bridging bidentate dpnapy, is obtained from the 1:1 [{Ir(cod)Cl}2]:dpnapy reaction. The bridging function of dpnapy is realized through the phosphorus and the terminal nitrogen binding sites in agreement with the NMR data and as confirmed by an X-ray analysis. Complex 5 crystallizes into the monoclinic space group P 2 1 / n with cell parameters a =17.813(4), b =12.339(3), c =18.221(5) A, β=106.73(2)° and with Z =4. The structure model, with all the non-H atoms anisotropic, was refined up to R =0.040 and R w =0.050 with the goodness-of-fit=0.91. The asymmetric unit contains one discrete molecule constitued by two independent square-planar iridium moieties, considering each ethylenic system of cycloocta-1,5-diene like a unique coordination site. No interaction exists between the two iridium metal centres.

Crystal structure of [Pd(μ3-2-propenyl)(dps)][Pd(μ3-2-propenyl)Cl2]. NMR evidence of binuclear μ3-allyl palladium(II) species with bridging dps

Abstract The reactions of di-2-pyridyl sulfide (dps) with (μ3-allyl)palladium chloride dimers gave the ionic compounds [Pd(μ3-allyl)(dps)][Pd(μ3-allyl)Cl2] (allyl=2-propenyl (1), 2-methyl-2-propenyl (2), 2-butenyl (3)). The structure of 1 has been determined by X-ray diffraction methods. Crystals are triclinic, space groupP 1 , with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) A, α= 98.82(1), β=90.46(1), γ=95.46(1)°. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 3855 observed relections to R and Rw values of 0.0269 and 0.0339, respectively. Compound 1 consists of discrete complex ion pairs, containing allyl groups coordinated to both the cationic and anionic palladium centres. In the cationic portion the dps acts as a chelate ligand and adopts an N,N inside conformation. The six-membered chelate ring shows a boat conformation. The cation and anion are connected by a short Pd2…Cl2 interaction (3.073(1) A) which determines pseudo-five-coordination for the cation. At low temperature the 1H NMR spectra in CD3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl3 they also indicate the presence of a binuclear species with bridging dps. The 1H NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl3, a lower energy process makes the π-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti π-allyl protons at high temperature.

Polyfunctional phosphine ligands. Synthesis of 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine and its co-ordination properties

The new trinucleating ligand 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) has been prepared and its co-ordination chemistry with rhodium(I) complexes investigated. Reactions with [{Rh(cod)Cl}2](cod = cycloocta-1,5-diene) lead to different products depending on the ligand to metal ratio. The P-monodentate ligand complex [Rh(cod)(dpnapy)Cl]1 is formed when a 2 : 1 ligand : dimer ratio is used. The cod region of the 1H and 13C NMR spectra of 1 is temperature dependent. The fluxional behaviour can be explained by the formation of a five-co-ordinate intermediate displaying rapid intramolecular exchange of the cod olefinic and CH2 protons. A lower activation energy process, not frozen at 215 K, is also observed. At room temperature (r.t.) the two-dimensional 1H and 31P chemical exchange spectra indicate a further slower dynamic equilibrium 1⇌2 with loss of dpnapy. The binuclear complex [{Rh(cod)Cl}2(µ-dpnapy)]2, in which dpnapy acts as bridging bidentate ligand using the phosphorus and the terminal nitrogen atoms, is the reaction product when a 1 : 1 ligand : dimer ratio is used. The 1H and 13C NMR data for complex 2 are consistent with a dimeric structure of low symmetry. Complex 2 is also involved in several dynamic processes. At r.t. the two-dimensional 1H chemical exchange spectrum shows a slow general scrambling of the cod olefinic protons and the presence of the equilibrium 2⇌1 with participation of [{Rh(cod)Cl}2]. The ligand reacts with [{Rh(CO)2Cl}2] giving as the only isolable product the metallocycle [{Rh(CO)(µ-dpnapy)Cl}2]·2CH2Cl23. The reaction proceeds through several steps involving the formation of cis-dicarbonyl intermediates as indicated by IR and NMR spectra. The structure of 3 has been determined by X-ray crystallography. It consists of two Rh(CO)Cl units, joined together by two dpnapy molecules in a head-to-tail arrangement.

Synthesis and crystal structure of the new near-linear Rh2Mo trinuclear complex [(η5-C5H5)Rh(μ-CO)-(μ-Ph2PC5H4N)Rh(CO)Mo(CO)3(η5-C5H5)]

Abstract Addition of [Mo(η5-C5H5)(CO)3]Na to a solution of the complex [η5-C5H5)Rh(μ-CO)(μ-Ph2PC5H4N)Rh(CO)Cl] (1) in THF results in the replacement of the terminal chloride by the anion [Mo(η5-C5H5)(CO)3]−, to give the near-linear trinuclear complex [(η5-C5H5)Rh(μ-CO)(μ-Ph2PC5H4N)Rh(CO)Mo(CO)3(η5-C5H5)] (3) in a good yield. The crystal structure of 3 has been determined by an X-ray diffraction study.

Self-assembly of [Bu4N][M(qdt)2] [qdt=quinoxaline-2,3-dithiolate; M=Au and Cu] in a 2D network via combination of CH⋯M and CH⋯S interactions

Abstract The compounds [Bu4N][M(qdt)2] (M=Au 1 and M=Cu 2) have been prepared and characterized by X-ray diffraction studies. Complexes 1 and 2 are isomorph and their structure consists of a two-dimensional intermolecular cation–anion network with the [Bu4N] cation acting as a four H-bonded bridging ligand.

A new supramolecular polyhedral oligomeric silsesquioxanes (POSS)–porphyrin nanohybrid: synthesis and spectroscopic characterization

An organic/inorganic nanohybrid, based on tetra-anionic mesotetrakis-(4-sulfonatophenyl)porphyrin (TPPS) and a positively charged polyhedral oligomeric silsesquioxane (POSS), has been synthesized and fully characterized. Differential scanning calorimetry and thermogravimetric analyses have allowed classification of this compound as a room temperature ionic liquid (RT-IL). The POSS bulky cation is responsible for the observed amorphous waxy solid appearance and for the high solubility in halogenated solvents. The formation of emissive nanosized porphyrin J-aggregates has been detected both in solution and on a quartz cuvette surface upon light irradiation on a dichloromethane porphyrin–POSS solution.

Synthesis and Characterization of Dirhodium(II,II)−Porphyrin-Based Multiredox Systems

Dirhodium(II,II)−porphyrin-based multiredox systems were easily prepared by combining the versatile reactivity, both axial and equatorial, of the [Rh2(form)2(O2CCF3)2(H2O)2] (form = N,N′-di-p-tolylformamidinate) complex and the well-known coordination capability of meso-substituted phenylporphyrins. In this way, redox systems featured by porphyrins axially or equatorially coordinated to the dirhodium subunits were obtained. Electrochemical and luminescence properties of the new assemblies were also investigated. Porphyrin−dirhodium(II,II) multiredox assemblies were synthesized by exploiting both the classical axial and the peculiar equatorial reactivity of the complex [Rh2(form)2(O2CCF3)2(H2O)2] (1) (form = N,N′-di-p-tolylformamidinate). The species [Rh2(form)2(PCOO)2] (2), featuring two bridged (carboxyphenyl)porphyrins in the equatorial positions, was prepared by metathetical reaction of 1 with the sodium salt of meso-5-(4-carboxyphenyl)-5,10,15-triphenylporphyrin (PCOO). Conversely, redox systems in which porphyrins are axially ligated to dirhodium were obtained by treating 1 with a variety of functionalized meso-pyridylporphyrins. Depending on the number and position of the peripheral pyridyl substituents, assemblies with different nuclearity, both in terms of metal and porphyrin subunits, were isolated. The 1:2 dirhodium/porphyrin adduct, [Rh2(form)2(O2CCF3)2(PyP)2] (3) was obtained by treatment of 1 with triphenyl(pyridyl)porphyrin (PyP). By combination of 1 with the cis-5,10-diphenyl-15,20-dipyridylporphyrin (cis-DPyP) the molecular square box, [Rh2(form)2(CF3CO2)2(cis-DPyP)]4 (4) was isolated in good yield. The reaction of 1 with 5,10,15,20-tetrakis(4-pyridyl)porphyrin (TPyP) is dependent on the experimental conditions and led to two different products: the grid polymer [{Rh2(form)2(CF3CO2)2}2(TPyP)]n (5) and the symmetric tetramer [{Rh2(form)2(CF3CO2)2}4(TPyP)] (6), respectively. All the products were characterized by conventional spectroscopic methods. Proton NMR spectroscopy resulted particularly useful for the characterization of dirhodium− phenyl(pyridyl)porphyrin aggregates. The 2,6-pyridyl proton resonances are highly affected by coordination and experience significantly upfield shifts with respect to the corresponding unbound porphyrin. Systems 2, 3, 4, and 6 underwent many redox processes in the potential window under investigation (+2; −1.4 V), each one of them can be assigned to the specific subunits of the molecular arrays. The emission studies performed on the same aggregates revealed that the porphyrin-based emission was significantly quenched by, most likely, reductive electron transfer from dirhodium subunits to the excited porphyrin chromophores. Such a process appears to be larger in the pyridylporphyrin−dirhodium systems with respect to the (carboxyphenyl)porphyrin ones.