Anna Monaci

Heterogeneous photocatalytic oxidation of naphthalenes on zirconium and germanium phosphates

Abstract Irradiated zirconium and germanium phosphates are used as photocatalysts for the oxidation of electron-rich molecules of naphthalenes in air-saturated acetonitrile. Some of these reactions are selective: phthalic anhydride is the main reaction product (yield 70%) in the photooxidation of naphthalene. A mechanism involving the formation of radical cations via the interaction of naphthalene with irradiated zirconium phosphate and a likely scheme of reaction are proposed.

ZIRCONIUM PHOSPHATES AS PHOTOCATALYSTS

Abstract The photo-oxidation of several alkylbenzenes in mild conditions has been achieved using zirconium phosphate prepared by different methods. By irradiating solutions of 1,2-dimethylbenzene, 1,4-dimethylbenzene or 1,2,4,5-tetramethylbenzene in a polar solvent with light of λ greater then 280 nm, in the presence of zirconiun phosphate or its derived phases in a stream of air, we have observed only oxidation of the side chain. The degree of crystallinity and the chemical composition of the inorganic sensitizer, and the polarity of the solvent, influence the conversion rate of the substrate. Moreover, different oxidation products are obtained, depending on the different reaction conditions. The results of these test reactions lead to a hypothesis for their mechanism; fundamental knowledge for any further utilization of this effective photocatalytic system.

Spectroscopic and structural studies on cobalt complexes of the methyl esters of dithiocarbazic and 2-methyldithiocarbazic acids. Crystal structure of [Co{NH2NHC(S)SMe}{NH2NC(S)SMe}2]Cl·H2O

The ligand behaviour of methyl esters of dithiocarbazic acid NH2NHC(S)SMe (HL) and of 2-methyldithiocarbazic acid NH2NMeC(S)SMe (MeL) in cobalt complexes has been investigated. Complexes of CoII and CoIII have been prepared under different conditions and characterized by their electronic and i.r. spectra. HL can act as a ligand when neutral or when deprotonated (L–); MeL can be deprotonated at the terminal N only after co-ordination. The crystal structure of [Co(HL)L2] Cl·H2O has been determined by X-ray diffraction methods: crystals are monoclinic, space group P21/c, Z= 4, in a unit cell of dimensions a= 12.085(9), b= 8.903(8), c= 17.287(16)A, and β= 104.2(1)°. The structure has been solved by Patterson and Fourier methods and refined by block-diagonal least squares to R= 0.042 for 1 993 reflections. It consists of cis-octahedral [Co(HL)L2]+ cations, in which one neutral and two deprotonated molecules of methyl dithiocarbazate act as chelating ligands, chloride anions, and water molecules, held together by a network of hydrogen bonds. The bond distances in the co-ordination polyhedron are: Co–S 2.203(4), Co–N 1.993(6)A for the neutral ligand; Co–S 2.212(5) and 2.218(3), Co–N 1.977(6) and 1.980(6)A for the deprotonated ligands. The conformation of the three ligands is cis,cis, i.e. with both NHNH2 and SMe groups bent towards the CS bond.

Thermal behaviour of nickel complexes of the methyl esters of dithiocarbazic and N-substituted dithiocarbazic acids

Abstract The thermal behaviour of the high-spin complexes [NiL 3 ]X 2 (XCl, Br,I), [Ni(MeL) 3 ]Cl 2 ·3 H 2 O·0.5 EtOH, [Ni(MeL) 3 ]Y 2 (YBr, I), [Ni(BuL) 3 ]X 2 (XCl, Br, I) [Ni(MeL) 2 X 2 ] (XCl, Br, I), [Ni(Me 2 L) 2 Cl 2 ] and the low-spin complexes [Ni(LH) 2 ], [Ni(MeLH) 2 ] and [Ni(Me 2 LH) 2 ] (LNH 2 LHNH 2 NC(S)SMe; MeLNH 2 NMeC(S)SMe; MeLHNHNMeC(S)SMe; BuL=NH 2 NBu n C(S)SMe; Me 2 LNMe 2 NHC(S)SMe; MeLHNMe 2 NNC(S)SMc) have been investigation by DSC and TG and have been related to the structures of the compounds. New compounds which cannot be prepared by the usual synthetic routes have also been obtained.

Free energy relationships of ionization energies measured by ultraviolet photoelectron spectroscopy in substituted pyrroles

The ionization energies of some substituted pyrroles have been determined by u.v. photoelectron spectroscopy. Relationship between the lowest ionization potentials and the Hammett σ constants have been determined. The different influence of substituents in the α- and β-positions is discussed.

Thermal behaviour and crystal structure of dichlorobis(methyl 2-methyldithiocarbazate-N3S)cobalt(II)–methyl 2-methyldithiocarbazate (2/1), [Co{NH2NMeC(S)SMe}2Cl2]·0.5[NH2NMeC(S)SMe]

The crystal structure of [CoII(MeL)2.5Cl2](MeL = methyl 2-methyldithiocarbazate) has been determined by X-ray diffraction methods in order to define the unusual stoicheiometry of the compound. Crystals are tetragonal, space group l41/acd, Z= 16, in a unit cell of dimensions a= 12.23(1) and c= 51.02(2)A. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.068 for 615 independent observed reflections. It consists of octahedral [Co(MeL)2Cl2] units, having C2 crystallographic symmetry, where the two MeL molecules act as chelating ligands, and of free, disordered MeL molecules. The complexes are joined in layers by N–H ⋯ Cl hydrogen bonds and the MeL molecules occupy the interlayers empty space. The bond distances in the Co co-ordination polyhedron are: Co–S = 2.446(7), Co–N = 2.174(17), and Co–Cl = 2.417(6)A. The thermal behaviour [Co(MeL)2.5Cl2] has been studied by thermal gravimetric analysis (t.g.a.) and differential scanning calorimetry (d.s.c.). Evidence for the reaction 2[Co(MeL)2Cl2]·0.5MeL →[Co(MeL)3][CoCl4]+ MeL has been obtained.

Catalytic systems derived from a nickel dithiolene-like complex for the photo-oxidation of alkylaromatic compounds

Abstract The dithiolene-like [Ni[NC 6 H 5 NC(S)SCH 3 ] 2 ] either by UV irradiation in CH 3 CN or by heating at 900 °C, leads to two catalytic systems (Ni irr and Ni therm respectively) which are efficient photo-oxidizers of benzylic compounds. The irradiations of solutions of toluene, xylene, durene, benzylic alcohols and trimethyl-benzaldehyde in organic solvents, performed in an air stream in the presence of two different catalytic systems, give different products depending on the catalyst used: mono-oxygenated products in the presence of Ni irr and mono- and poly-oxygenated ones in the presence of Ni therm . The results obtained in both reactions suggest an initial electron transfer mechanism followed by a mechanism involving a radical chain process.

Ultraviolet photoelectron spectra of some methyl esters of dithiocarbazic acids and of [Ni{N(CH3)2–NC(–S)SCH3}2] and comparison with quantum-mechanical calculations

Ultraviolet photoelectron spectra of NH2–NH–C(S)SCH3, NH2–NCH3–C(S)SCH3, N(CH3)2–NH–C(S)SCH3, NHC6H5–NH–C(S)SCH3, N(C6H5)2–NH–C(S)SCH3, and [Ni{N(CH3)2–NC(–S)SCH3}2] have been recorded, and the ionisation energies related to the results of quantum-mechanical calculations. Assignments are made on the grounds of this comparison and by correlation with the parent molecules.

X-Ray and infrared structural studies on the methyl ester of dithiocarbazic acid and its N-substituted derivatives

I.r. spectral and X-ray diffraction studies were carried out on the methyl ester of dithiocarbazic acid, NH2·NH·C(:S)-SMe (I), and of its N-substituted derivatives. NMe2·NH·C(:S)SMe (II), and NH2·NMe·C(:S)SMe (III). Crystals of (I) are monoclinic, space group C2/c, Z= 8, unit cell dimensions: a= 14.018(5), b= 5.518(3), c= 14.079(4)A, β= 98.4(1)°; (II) monoclinic, space group P21/c, Z= 4, unit cell dimensions: a= 8.487(8), b= 9.920(9), c= 10.611(9)A, β= 117.1(1)°; (III), monoclinic, space group P21/c, Z= 4, unit cell dimensions: a= 7.071(5), b= 9.815(6), c= 10.142(7)A, β= 114.0(1)°. The structures were solved from diffractometer data by Patterson and Fourier methods and refined by block-diagonal least squares to R 0.028 (I). 0.036 (II), and 0.029 (III) for 1 256, 1 132, and 917 reflections. The basic units of these structures are centrosymmetric dimers formed by NH ⋯ N hvdroaen bonds in (I), and by N–H ⋯ S hydrogen bonds in (II) and (III). The component monomers are in the cis, trans-conformation, i.e. with the group–NH·NH2 bent toward C–S and the SMe towards the opposite side in (I) and in the trans, cis-conformation in (II) and (III). Change of conformation or of substituents does not significantly alter bond distances in the molecules.

Nickel complexes of the methyl esters of dithiocarbazic and N-substituted dithiocarbazic acids

The nickel complexes of the methyl esters of dithiocarbazic acid NH2NHC(=S)SMe (L), 2-methyldithiocarbazic acid NH2NMeC(=S)SMe (MeL), 2-n-butyldithiocarbazic acid, NH2NBuC(=S)SMe (BuL), 3,3-dimethyldithiocarbazic acid NMe2NHC(=S)SMe (Me2L), 3-phenyldithiocarbazic acid NHPhNHC(=S)SMe (PhL), and 3,3-diphenyldithiocarbazic acid NPh2NHC(=S)SMe (Ph2L) have been investigated. L, MeL, BuL, and Me2L can act as neutral ligands giving the high-spin complexes [NiL3]X2, [Ni(MeL)3]X2, [Ni(BuL)3]X2(X = Cl, Br, or I), and [Ni(Me2L)2Cl2]; L and Me2L can act also in deprotonated form at N(2) giving the low-spin complexes [Ni(L – H)2] and [Ni(Me2 L – H)2]. PhL and Ph2L act only in deprotonated form at N(2) giving the low-spin [Ni(PhL – H)2] and [Ni(Ph2L – H)2] respectively. MeL and BuL can be deprotonated at N(3) after co-ordination giving the low-spin complexes [Ni(MeL – H)2] and [Ni(BuL – H)2]. The complexes have been characterized by their electronic and i.r. spectra.