Francesco Isaia

On the Use of Raman Spectroscopy in the Characterization of Iodine in Charge-Transfer Complexes

FT-Raman spectra of some polyiodides and of a series of D · I2 charge-transfer complexes (where D is a molecule containing the thione or selone groups as donors), all characterized by x-ray diffraction, are reported. For the adducts with the thione compounds, which can be considered weak or medium-weak complexes, an empirical linear correlation between the frequency of the v(I-I) stretching vibrations and the d(I-I) bond distances has been found. Some polyiodides show FT-Raman spectra that are indistinguishable with respect to those displayed by the neutral complexes of weak or medium-weak strength; in such cases, the polyiodide can be regarded as a diiodine molecule, perturbed by an I n (n = 1,3,…) donor. Polyiodides of this type show Raman absorptions falling in the linear correlation.

CHARGE-TRANSFER ADDUCTS BETWEEN DONORS CONTAINING CHALCOGENS (S AND SE) AND DI-IODINE : SOLUTION STUDIES

Abstract The solution equilibria related to the 1:1 charge-transfer adduct formation between molecular iodine and several substrates containing sulfur and selenium donor atoms have been reviewed and the corresponding thermodynamic parameters ( K and Δ H °) reported for a series of thiones, selones, sulfides and selenides. A survey of the several calculation methods, based on UV–vis and in some cases 13 C-NMR spectroscopies, is also reported. Although the methods and techniques employed are very different, some correlations between the thermodynamic parameters and other experimental data, such as ν (II) Raman frequencies or UPS-binding energies, are reviewed and general conclusions drawn.

Photoinduced conductivity and nonlinear optical properties of [M(R,R′timdt)2] dithiolenes (M=Ni, Pd, Pt; R,R′timdt=monoreduced imidazolidine-2,4,5-trithione) as materials for optically driven switches and photodetectors

Abstract The unusual NIR-photoconducting properties of [M(Et,Pent-timdt)2] neutral dithiolenes (M=Ni, Pd, Pt; Et,Pent-timdt=monoreduced N-ethyl,N′-pentylimidazolidine-2,4,5-trithione) have been investigated with the aim of developing wavelength-selective air-stable photodetectors. In addition, the ps time-resolved dynamics of the absorption saturation has been studied on the Pd-complex by means of pump–probe experiments.

New perspectives in phosphonodithioate coordination chemistry. Synthesis and X-ray crystal structure of trans-bis-[O-ethyl-(4-methoxyphenyl)phosphonodithioato] nickel(II)

Abstract Attempts to optimise the synthesis of a new class of nickel(II) dithiolene complexes starting from 1,3-dialkylimidazolidine-2-thione-4,5-dione (1) and Lawessons reagent (2) have afforded a new and easy one-step synthesis of phosphonodithioate nickel(II) complexes. This consists of the direct reaction between NiCl2 and Lawessons reagent in the appropriate alcohol R′OH (R=Me, Et, i-Pr, Bu, Bz) as solvent, to give the bis-[O-alkyl/aryl-(4-methoxyphenyl)phosphonodithioato] nickel(II) complexes (5a–e) with high yields (64–91%). Among them, trans-bis-[O-ethyl-(4-methoxyphenyl)phosphonodithioato] nickel(II) (5b) was characterised by means of X-ray diffraction measurements on a single crystal. The compound crystallises in the triclinic, P 1 space group with a=6.4840(7), b=7.6032(9), c=13.055(2) A, α=99.481(9), β=99.43(1), γ=104.487(9)° and Z=1. The compound is centrosymmetric and exhibits discrete monomeric units with the ligand acting as S,S-bidentate. To explain the reactivity of Lawessons reagent, the formation of 4-methoxyphenyldithiophosphorane (6) as intermediate has been suggested. The reaction was also tested for Pd(II) and Pt(II), but in these cases the yields were not as satisfactory as for Ni(II).

Redox chemosensors: coordination chemistry towards CuII, ZnII, CdII, HgII, and PbII of 1-aza-4,10-dithia-7-oxacyclododecane ([12]aneNS2O) and its N-ferrocenylmethyl derivativeElectronic supplementary information (ESI) available: synthetic details including analytical and spectroscopic data for the isolated complexes. Ortep views of the coordination sphere around the metal centres in 1, 2 and 5. See http://www.rsc.org/suppdata/dt/b2/b210806m/

The coordination chemistry of the mixed donor 12-membered macrocyclic ligand 1-aza-4,10-dithia-7-oxacyclododecane ([12]aneNS2O) with CuII, ZnII, CdII, HgII, and PbII has been investigated both in water solution and in the solid state. The protonation constant for [12]aneNS2O and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those reported for other mixed N/S/O-donor tetradentate 12-membered macrocycles. The measured values are consistent with trends observed previously for aza macrocycles as secondary N-donors are replaced by O- and S-donors. In particular our results show that HgII in water has the highest affinity for [12]aneNS2O followed by CuII, CdII, PbII, and ZnII. For each considered metal ion, 1 ∶ 1 complexes of [12]aneNS2O have been isolated in the solid state; those of CuII, HgII, and CdII have also been characterised by X-ray crystallography. In the cases of copper(II) and cadmium(II) complexes the ligand adopts a folded [2424] conformation, whereas a more planar [3333] conformation is observed in the case of the mercury(II) complex. The macrocycle [12]aneNS2O and its structural analogue [12]aneNS3 have then been used as receptor units in the design and synthesis of the new ferrocene-containing redox-active ionophores N-ferrocenylmethyl 1-aza-4,10-dithia-7-oxacyclododecane (L1) and N-ferrocenylmethyl 1-aza-4,10,7-trithiacyclododecane (L2). Electrochemical studies carried out in MeCN in the presence of increasing amounts of CuII, ZnII, CdII, HgII, and PbII showed that the wave corresponding to the Fc/Fc+ couple of the uncomplexed ionophores L1 and L2 is gradually replaced by a new reversible wave at more positive potentials and corresponding to the Fc/Fc+ couple of the complexed ionophores. The maximum shift of the ferrocene oxidation wave was found for L1 in the presence of ZnII (230 mV) and PbII (220 mV), whereas for L2 a selective sensing response for CuII over the other guest metal cations was observed with an oxidation peak shift of 230 mV.

Colorimetric response to anions by a "robust" copper(II) complex of a [9]aneN3 pendant arm derivative: CN- and I- selective sensing.

The 1 : 1 complex [Cu(L)](BF(4))(2)·MeCN (1) of the tetradentate ligand 1-(2-quinolinylmethyl)-1,4,7-triazacyclononane (L) selectively changes its colour in the presence of CN(-) in H(2)O and MeCN (without undergoing decomplexation from the macrocyclic ligand). The same complex in MeCN assumes different colours in the presence of CN(-) or I(-).

Charge transfer complexes of benzoxazole-2(3H)-thione and benzoxazole-2(3H)-selone with diiodine: X-ray crystal structure of benzoxazole-2(3H)-thione bis(diiodine)

Abstract Solids of stoichiometry 1·I2 (C7H5I2NOS; I), 1·2I2 (C7H5I4NOS; II), 2·I2 (C7H5I2NOSe; III) and 2·2I2 (C7H5I4NOSe; IV) have been obtained by reacting respectively benzoxazole-2(3H)-thione (1) and benzoxazole-2(3H)-selone (2) with molecular diiodine in a 1:1 or 1:2 molar ratio in CH2Cl2 solution. Crystals suitable for X-ray structure determination have been obtained only for II and contain units formed by one diiodine molecule bonded almost linearly [178.44(4)°] to the thionic sulphur atom of 1 and another diiodine molecule weakly interacting with the former. The FT-Raman spectrum in the characteristics v(I-I) region shows two bands for compound II at 176 and 159 cm−1, in accordance with the presence of two differently perturbed diiodine molecules [ I (1)– I (2) = 2.769(1) A , I (3)– I (4) = 2.729(1) A ] . The FT-IR and FT-Raman spectra of compounds I, III and IV are discussed in comparison with the spectrum of II and with those reported for similar charge transfer complexes.

Ring-Opening of Lawesson’s Reagent: New Syntheses of Phosphono- and Amidophosphono-Dithioato Complexes − Structural and CP-MAS31P-NMR Characterization of [p-CH3OPh(X)PS2]2M (X = MeO,iPrNH; M = NiII, PdII, and PtII)

The opening of the P2S2 tetraatomic ring of Lawesson’s reagent (4) has proved versatile in synthesizing phosphono- and amidophosphono-dithioato mononuclear complexes [p-CH3OPh(X)PS2]2M [X = CH3O, iPrNH; M = NiII, PdII, PtII]. A one-step reaction of 4 with the appropriate metal salt in CH3OH, or in the presence of a stoichiometric amount of iPrNH2 in CHCl3, is used in the direct synthesis of the NiII and PdII complexes, but does not work in the PtII complexes. Alternatively, these syntheses can be carried out: i) by preparation and isolation of O-methyl(4-methoxyphenyl)phosphonodithioate (6) salts or isopropylamido(4-methoxyphenyl)- phosphonodithioate (7) salts by treating 4 with CH3O− in CH3OH or with iPrNH2, respectively; ii) by reaction of 6 or 7 with MCl2 or K2MCl4 [M = NiII, PdII, PtII] to give trans-bis[O-methyl(4-methoxyphenyl)phosphonodithioato]M and trans-bis[isopropylamido(4-methoxyphenyl)phosphonodithioato]M complexes. Following these routes, trans-bis[O-methyl(4-methoxyphenyl)phosphonodithioato]M [M = Ni (8a), Pd (8b), and Pt (8c)] and trans-bis[isopropylamido(4-methoxyphenyl)phosphonodithioato]M [M = Ni (9a), Pd (9b), and Pt (9c)] complexes have been synthesized and fully characterized by FAB mass, FT-IR, FT-Raman, UV/Vis, and CP-MAS 31P-NMR spectroscopy; the crystal structures of 7, 8b, 8c, and 9a are also reported.

Interaction of Methimazole with I2: X-ray Crystal Structure of the Charge Transfer Complex Methimazole−I2. Implications for the Mechanism of Action of Methimazole-Based Antithyroid Drugs

The antithyroid drug methimazole (MMI) reacts with molecular iodine to form, in a multistep process, 1-methylimidazole as final product. In this process, the charge transfer complex MMI-I 2 and the ionic disulfide [(C 4H 6N 2S-) 2] (2+) ( 1, dication MMI disulfide) have been isolated and their X-ray crystal structures solved. Dication MMI disulfide perchlorate acts effectively both in reducing I 2 to I (-) ions and in showing antioxidant properties in inactivating the enzyme lactoperoxidase compound I.

A new pyridine-based 12-membered macrocycle functionalised with different fluorescent subunits; coordination chemistry towards CuII, ZnII, CdII, HgII, and PbII

The coordination chemistry of the new pyridine-based, N2S2-donating 12-membered macrocycle 2,8-dithia-5-aza-2,6-pyridinophane (L1) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) has been investigated both in aqueous solution and in the solid state. The protonation constants for L1 and stability constants with the aforementioned metal ions have been determined potentiometrically and compared with those of ligand L2, which contains a N-aminopropyl side arm. The measured values show that Hg(II) in water has the highest affinity for both ligands followed by Cu(II), Cd(II), Pb(II), and Zn(II). For each metal ion considered, 1:1 complexes with L1 have also been isolated in the solid state, those of Cu(II) and Zn(II) having also been characterised by X-ray crystallography. In both complexes L1 adopts a folded conformation and the coordination environments around the two metal centres are very similar: four positions of a distorted octahedral coordination sphere are occupied by the donor atoms of the macrocyclic ligand, and the two mutually cis-positions unoccupied by L1 accommodate monodentate NO3- ligands. The macrocycle L1 has then been functionalised with different fluorogenic subunits. In particular, the N-dansylamidopropyl (L3), N-(9-anthracenyl)methyl (L4), and N-(8-hydroxy-2-quinolinyl)methyl (L5) pendant arm derivatives of L1 have been synthesised and their optical response to the above mentioned metal ions investigated in MeCN/H2O (4:1 v/v) solutions.