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Massimiliano Arca

Publications and source records attributed to Massimiliano Arca.

15 recordsLinked to original sources
PubMed2006

Synthesis, reactivity and structural studies of selenide bridged carboranyl compounds.

Reaction of the lithium salt Li[1-R-1,2-closo-C(2)B(10)H(10)] with selenium under mild conditions, followed by hydrolysis gave the diselenide compound (1-Se-2-R-1,2-closo-C(2)B(10)H(10))(2) in contrast to the well-reported mercapto compounds 1-SH-2-R-1,2-closo-C(2)B(10)H(10) obtained using a similar synthetic procedure. Details for the preparation and X-ray structural characterisation of the new compounds (2-Me-1,2-closo-C(2)B(10)H(10))(2)Se, (1-Se-2-R-1,2-closo-C(2)B(10)H(10))(2) (R = Me, Ph, ) are specified. To further explore the mechanism of the dimerization reaction, the complex [Au(1-Se-2-Me-1,2-closo-C(2)B(10)H(10))(PPh(3))] was synthesized, confirming the existence of the intermediate Li[1-Se-2-R-1,2-closo-C(2)B(10)H(10)] at the early stages of the reaction before selenium oxidation. Theoretical calculations and cyclic voltammetry (CV) studies were carried out to compare the bonding nature of the sulfur and the selenium analog compounds. It was determined that diselenides have a higher tendency to reduce with respect to the disulfides and all chalcogen atoms were found to be positively charged.

Journal Article↗
PubMed2006

Synthesis and properties of gold alkene complexes. Crystal structure of [Au(bipy(oXyl))(eta(2)-CH(2)=CHPh)](PF(6)) and DFT calculations on the model cation [Au(bipy)(eta(2)-CH(2)=CH(2))](+).

Unprecedented 16-electron gold(i) olefin complexes of general formula [Au(bipy(R,R'))(eta(2)-olefin)](PF(6)) and [Au(2)(bipy(R,R'))(2)(mu-eta(2):eta(2)-diolefin)](PF(6))(2) (bipy(R,R') = 6-substituted-2,2'-bipyridine) have been prepared by reaction of dinuclear gold(III) oxo complexes [Au(2)(bipy(R,R'))(2)(mu-O)(2)](PF(6))(2) with the appropriate olefin. The X-ray crystal structures of two mononuclear complexes (olefin = styrene) show in-plane coordination of the olefin and a C[double bond, length as m-dash]C bond distance considerably lengthened with respect to the free olefin. The spectroscopic properties of the complexes are discussed and compared with those of analogous d(10) metal derivatives. Both structural and spectroscopic information indicate a substantial contribution of pi-back-donation to the Au-olefin bond in the three-coordinate species. Theoretical calculations carried out at the hybrid-DFT level on the model compound [Au(bipy)(eta(2)-CH(2)[double bond, length as m-dash]CH(2))](+) show excellent agreement with the experimental findings giving in addition an estimate of a pi-back-bonding contribution higher than that of the sigma-bonding.

Journal Article↗
PubMed2005

[M(R-dmet)2] bis(1,2-dithiolenes): a promising new class intermediate between [M(dmit)2] and [M(R,R'-timdt)2] (M = Ni, Pd, Pt).

We report the first examples of metal dithiolenes belonging to the class [M(R-dmet)(2)] [R-dmet = formally monoreduced N-substituted thiazolidine-2,4,5-trithione; R = Et, M = Ni (1), Pd (2), Pt (3)]. A comparative spectroscopic, electrochemical, and density functional theory theoretical investigation indicates that [M(R-dmet)(2)] complexes show features intermediate between those of the dithiolenes belonging to the previously reported classes [M(R,R'-timdt)(2)] and [M(dmit)(2)] (R,R'-timdt = formally monoreduced N,N'-disubstituted imidazolidine-2,4,5-trithione; dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato). UV-vis-near-IR spectroscopy and cyclic voltammetry/differential pulsed voltammetry measurements performed on 1 and 3 proved that the new dithiolenes are stable as neutral, monoanionic, and bianionic species and feature a near-IR electrochromic absorption falling at about 1000 and 1250 nm for neutral and monoanionic species, respectively.

Journal Article↗
PubMed2005

Coordination chemistry of N-aminopropyl pendant arm derivatives of mixed N/S-, and N/S/O-donor macrocycles, and construction of selective fluorimetric chemosensors for heavy metal ions.

The coordination chemistry of the N-aminopropyl pendant arm derivatives (L1c-4c) of the mixed donor macrocyclic ligands [12]aneNS2O, [12]aneNS3, [12]aneN2SO, and [15]aneNS2O2(L1a-4a) towards Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II) in aqueous solution has been investigated. The protonation and stability constants with the aforementioned metal ions were determined potentiometrically and compared, where possible, with those of the unfunctionalised macrocycles. The measured values show that Hg(II) and Cu(II) in water have the highest affinity for all ligands considered, with the N-aminopropyl pendant arm weakly coordinating the metal centres. Crystals suitable for X-ray diffraction analysis were grown for the perchlorate salt (H2L1c)(ClO4)2.dmf, and for the 1 : 1 complexes [Cd(L3a)(NO3)2](1), [Cu(L4a)dmf](ClO4)2(2), [Zn(L1c)(ClO4)]ClO4(3), [Cd(L1c)(NO3)]NO3(4), and [Hg(L2c)](ClO4)2(5). Their structures show the macrocyclic ligands adopting a folded conformation, which for the 12-membered systems can be either [2424] or [3333] depending on the nature of the metal ion. L1c-4c were also functionalised at the primary amino pendant group with different fluorogenic subunits. In particular the N-dansylamidopropyl (Lnd, n= 1-4), and the N-(9-anthracenylmethyl)aminopropyl (Lne, n= 1, 2, 4, ) pendant arm derivatives of L1a-4a were synthesised and their optical responses to the above mentioned metal ions were investigated in MeCN/H2O (4 : 1 v/v) solutions.

Crystallography, X-Ray↗
PubMed2005

DFT calculations, structural and spectroscopic studies on the products formed between IBr and N,N'-dimethylbenzoimidazole-2(3H)-thione and -2(3H)-selone.

The NBO charge distribution calculated at DFT level on the [LEX](+) species [LE=N,N'-dimethylbenzoimidazole-2(3H)-thione (3) and -2(3H)-selone (4)(Scheme 1); X=I, Br] suggests that the most likely products from the reaction 3 of 4 and with IBr are the 10-X-2 charge-transfer (CT) adduct and the 10-Se-3 "T-shaped" hypervalent adduct featuring a linear Br--Se--I system, respectively. This prediction is confirmed by the synthesis, and X-ray diffraction analysis of 3.IBr (I) and 4.I(0.72)Br(1.28)(II). In particular II, is a 10-Se-3 "T-shaped" hypervalent adduct containing an almost linear X--Se--X system [X--Se--X 179.07(3) degrees, X=I(0.36)/Br(0.64)], which is roughly perpendicular to the average plane of the benzoimidazole moiety. The FT-Raman spectra of I and II agree very well with their structural features. In particular, the complexity of the FT-Raman spectrum of II reflects the disorder in the X-ray crystal structure of this compound.

Algorithms↗
PubMed2004

Monoreduced [M(R,R'timdt)2]- dithiolenes (M = Ni, Pd, Pt; R,R'timdt = disubstituted imidazolidine-2,4,5-trithione): solid state photoconducting properties in the third optical fiber window.

Electrochemically monoreduced [M(R,R'timdt)(2)](-) dithiolenes, showing unprecedented wavelength selective photoconducting properties in the third optical fiber window (1500-1800 nm), fine-tunable through modifications in the chemical structure, allowed for the fabrication of a test photodetector with a bit rate of about 85 kbit s(-1).

Journal Article↗
PubMed2003

Coordination chemistry of a new cofacial binucleating macropolycycle derived from 1,4,7-triazacyclononane.

We have prepared and characterized a new phenol-based compartmental ligand (H(2)L) incorporating 1,4,7-triazacyclononane ([9]aneN(3)), and we have investigated its coordination behavior with Cu(II), Zn(II), Cd(II), and Pb(II). The protonation constants of the ligand and the thermodynamic stabilities of the 1:1 and 2:1 (metal/ligand) complexes with these metal ions have been investigated by means of potentiometric measurements in aqueous solutions. The mononuclear [M(L)] complexes show remarkably high stability suggesting that, along with the large number of nitrogen donors available for metal binding, deprotonated phenolic functions are also involved in binding the metal ion. The mononuclear complexes [M(L)] show a marked tendency to add a second metal ion to afford binuclear species. The formation of complexes [M(2)(H(2)L)](4+) occurs at neutral or slightly acidic pH and is generally followed by metal-assisted deprotonation of the phenolic groups to give [M(2)(HL)](3+) and [M(2)(L)](2+) in weakly basic solutions. The complexation properties of H(2)L have also been investigated in the solid state. Crystals suitable for X-ray structural analysis were obtained for the binuclear complexes [Cu(2)(L)](BF(4))(2).(1)/(2)MeCN (1), [Zn(2)(HL)](ClO(4))(3).(1)/(2)MeCN (2), and [Pb(2)(L)](ClO(4))(2).2MeCN (4). In 1 and 2, the phenolate O-donors do not bridge the two metal centers, which are, therefore, segregated each within an N(5)O-donor compartment. However, in the case of the binuclear complex [Pb(2)(L)](ClO(4))(2).2MeCN (4), the two Pb(II) centers are bridged by the phenolate oxygen atoms with each metal ion sited within an N(5)O(2)-donor compartment of L(2)(-), with a Pb.Pb distance of 3.9427(5) A.

Journal Article↗
PubMed2003

PVC membrane and coated graphite potentiometric sensors based on Et4todit for selective determination of samarium(III).

Solution studies on the binding properties of 4,5,6,7-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione (Et(4)todit) toward a number of cationic species including some lanthanide ions revealed the occurrence of a selective 1:1 complexation of the ligand with Sm(3+) ion. Consequently, Et(4)todit was used as a suitable neutral ionophore for the preparation of novel polymeric membrane (PME) and coated graphite (CGE) Sm(3+)-selective electrodes. The electrodes exhibit a Nernstian behavior for Sm(3+) ions over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M for PME and 1.0 x 10(-7)-1.0 x 10(-1) M for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 1.6 x 10(-8) M for CGE). The proposed potentiometric sensors manifest advantages of relatively fast response, and, most importantly, good selectivities relative to wide variety of other cations, including other lanthanide ions. The selectivity behavior of the proposed Sm(3+)-selective electrodes revealed a great improvement compared to the best previously reported electrode for samarium(III) ion. The potentiometric responses of the electrodes are independent of the pH of the test solution in the pH range 4.0-6.5. The electrodes were successfully applied to the recovery of Sm(3+) ion from tap water samples and also, as an indicator electrode, in potentiometric titration of samarium(III) ions.

Journal Article↗
PubMed2003

Coordination properties of new bis(1,4,7-triazacyclononane) ligands: a highly active dizinc complex in phosphate diester hydrolysis.

The synthesis and characterization of three new bis([9]aneN(3)) ligands, containing respectively 2,2'-bipyridine (L(1)), 1,10-phenanthroline (L(2)), and quinoxaline (L(3)) moieties linking the two macrocyclic units, are reported. Proton binding and Cu(II), Zn(II), Cd(II), and Pb(II) coordination with L(1)-L(3) have been studied by potentiometric titrations and, for L(1) and L(2), by spectrophotometric UV-vis measurements in aqueous solutions. All ligands can give stable mono- and dinuclear complexes. In the case of L(1), trinuclear Cu(II) complexes are also formed. The stability constants and structural features of the formed complexes are strongly affected by the different architecture and binding properties of the spacers bridging the two [9]aneN(3) units. In the case of the L(1) and L(2) mononuclear complexes, the metal is coordinated by the three donors of one [9]aneN(3) moiety; in the [ML(2)](2+) complexes, however, the phenanthroline nitrogens are also involved in metal binding. Finally, in the [ML(3)](2+) complexes both macrocyclic units, at a short distance from each other, can be involved in metal coordination, giving rise to sandwich complexes. In the binuclear complexes each metal ion is generally coordinated by one [9]aneN(3) unit. In L(1), however, the dipyridine nitrogens can also act as a potential binding site for metals. The dinuclear complexes show a marked tendency to form mono-, di-, and, in some cases, trihydroxo species in aqueous solutions. The resulting M-OH functions may behave as nucleophiles in hydrolytic reactions. The hydrolysis rate of bis(p-nitrophenyl)phosphate (BNPP) was measured in aqueous solution at 308.1 K in the presence of the L(2) and L(3) dinuclear Zn(II) complexes. Both the L(2) complexes [Zn(2)L(2)(OH)(2)](2+) and [Zn(2)L(2)(OH)(3)](+) and the L(3) complex [Zn(2)L(3)(OH)(3)](+) promote BNPP hydrolysis. The [Zn(2)L(3)(OH)(3)](+) complex is ca. 2 orders of magnitude more active than the L(2) complexes, due both to the short distance between the metal centers in [Zn(2)L(3)(OH)(3)](+), which could allow a bridging interaction of the phosphate ester, and to the simultaneous presence of single-metal bound nucleophilic Zn-OH functions. These structural features are substantially corroborated by semiempirical PM3 calculations carried out on the mono-, di-, and trihydroxo species of the L(3) dizinc complex.

Journal Article↗
PubMed2003

First example of an infinite polybromide 2D-network.

The reaction of the neutral dithiolene [Pd(Et2timdt)2] (Et2timdt = formally monoreduced diethylimidazolidine-2,4,5-trithione) with an excess of Br2 yielded few crystals of [1(Et) x 2Br](2+)(Br-)2(Br2)3 as a by-product (1(Et) = 4,5,9,10-tetrathiocino-[1,2-b:5,6-b']-1,3,6,8-tetraethyl-diimidazolyl-2,7-dithione); X-ray diffraction analysis showed that this compound represents the first example of a polybromide 2D-network templated by [1(Et) x 2Br](+2) dications, and featuring all the Br-Br distances shorter than those found in solid state bromine.

Journal Article↗
PubMed2002

Fluorometric chemosensors. Interaction of toxic heavy metal ions Pb(II), Cd(II), and Hg(II) with novel mixed-donor phenanthroline-containing macrocycles: spectrofluorometric, conductometric, and crystallographic studies.

The macrocycles L(1)-L(3) incorporating N(2)S(3)-, N(2)S(2)O-, and N(2)S(2)-donor sets, respectively, and containing the 1,10-phenanthroline unit interact in acetonitrile solution with heavy metal ions such as Pb(II), Cd(II), and Hg(II) to give 1:1 ML, 1:2 ML(2), and 2:1 M(2)L complex species, which specifically modulate the photochemical properties of the ligands. The stoichiometry of the complex species formed during spectrofluorometric titrations and their formation constants in MeCN at 25 degrees C were determined from fluorescence vs M(II)/L molar ratio data. The complexes [Pb(L(1))][ClO(4)](2).(1)/(2)H(2)O (1), [Pb(L(2))][ClO(4)](2).MeNO(2) (1a), [Pb(L(3))(2)][ClO(4)](2).2MeCN (1b), and [Cd(L(3))][NO(3)](2) (2b) were also characterized by X-ray diffraction studies. The conformation adopted by L(1)-L(3) in these species reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands trying to encapsulate the metal center within their cavity. In 1, 1a, and 2b the metal ion completes the coordination sphere by interacting with counteranion units and solvent molecules. On the contrary, the 1:2 complex 1b shows Pb(II) sandwiched between two symmetry-related molecules of L(3) reaching an overall [4N + 4S] eight-coordination.

Journal Article↗
PubMed2002

An unprecedented example of a cis-phosphonodithioato nickel(II) complex built by an extensive hydrogen bonding supramolecular network.

The P-N bond hydrolysis of the 4-methoxyphenyl-ammonium ethylamido-phosphonodithioato ligand during its complexation to NiII leads to the first example of phosphonodithioato nickel(II) complex having a cis configuration; this complex is stabilised in the solid state by an extensive and intricate network of hydrogen bondings involving the released ethylenediamine and a water molecule.

Journal Article↗
PubMed2002

Anti-thyroid drug methimazole: X-ray characterization of two novel ionic disulfides obtained from its chemical oxidation by I(2).

Interaction of methimazole (MMI, 1-methyl-imidazole-2-thione) with I2 in solvents having different polarity gives two new stable compounds containing a dication disulfide and a monocation disulfide arranged in dimers, respectively. These two species could represent effective intermediates in the reaction of MMI with an active iodine species in the thyroid gland and therefore shed more light on the mechanism of action of MMI as an antithyroid drug.

Antithyroid Agents↗
PubMed2002

4-Methoxyphenylphosphonic acid: reactivity of Lawesson's reagent.

The title compound, C(7)H(9)O(4)P, obtained as a by-product of the reaction between Lawesson's reagent, (I), and CH(3)I, can be recognized as the final product of the S/O interchange reaction at the P atom of (I). Hydrogen bonds of type P-O-H.O=P link molecules into helical chains and form ten-membered hydrogen-bonded rings with the graph-set notation R(3)(2)(10). Weaker intermolecular contacts between P-O and a phenyl H atom link the chains into a three-dimensional lattice. The parent benzenephosphonic acid [Weakley (1976). Acta Cryst. B32, 2889-2890] does not adopt an analogous structure, but its arsenic analogue [Shimada (1960). Bull. Chem. Soc. Jpn, 33, 301-304] does and can be regarded as isostructural. We rationalize these three structures in terms of their significant intermolecular interactions.

Journal Article↗