Influences of water properties on the aggregation and deposition of engineered titanium dioxide nanoparticles in natural waters.

With the increasing usage of titanium dioxide nanoparticles (NPs), their release into the environment makes it important to understand their transport, fate and behaviour in natural waters. In this study, aggregation and deposition of TiO2 NPs were studied during a 3-h period by using a dynamic light scattering instrument and a UV-vis spectrophotometer, respectively. TiO2 NPs were spiked in 34 lake and 5 brackish water samples at an initial concentration of 10 mg L-1. Depending on the physicochemical properties of the natural waters, TiO2 NPs exhibited different colloidal stability. In brackish waters with high salinity, TiO2 NPs were prone to aggregate and settled rapidly. Whereas under conditions of humic and humus-poor lake waters, TiO2 NPs were suspended in water column for a longer time without remarkable change in particle size and concentration. Deposition likely occurred in nutrient-rich lakes which had high amount of nitrogen and phosphorus accompanied by high values of conductivity, alkalinity, pH and turbidity. Linear regression analysis revealed the statistically significant relationships (p ≤ 0.008) between the TiO2 NPs stability and these water properties. Our study makes a better understanding of the water properties that control the aggregation and deposition of TiO2 NPs in complex natural waters.

Homoleptic, heteroleptic and mixed-valent thallium and indium complexes of multidentate chalcogen-centred PCP-bridged ligands.

The metathetical reaction of [Li(TMEDA)][HC(PPh(2)Se)(2)] ([Li(TMEDA)]1) with TlOEt in a 1:1 molar ratio afforded a homoleptic Tl(I) complex as an adduct with LiOEt, Tl[HC(PPh(2)Se)(2)]·LiOEt (7), which undergoes selenium-proton exchange upon mild heating (60 °C) to give the mixed-valent Tl(I)/Tl(III) complex {[Tl][Tl{(Se)C(PPh(2)Se)(2)}(2)]}(∞) (8). Treatment of TlOEt with [Li(TMEDA)](2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (3b, E' = S; 3c, E' = Se) in a 2:1 molar ratio produced the binuclear Tl(i)/Tl(i) complexes Tl(2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (9b, E' = S; 9c, E' = Se), respectively. Selenium-proton exchange also occurred upon addition of [Li(TMEDA)]1 to InCl(3) to yield the heteroleptic complex (TMEDA)InCl[(Se)C(PPh(2)Se)(2)] (10a). Other examples of this class of In(III) complex, (TMEDA)InCl[(E')C(PPh(2)E)(2)] (10b, E = E' = S; 10c, E = S, E' = Se) were obtained via metathesis of InCl(3) with [Li(TMEDA)](2)[(E')C(PPh(2)E)(2)] (2b, E = E' = S; 2c, E = S, E' = Se, respectively). All new compounds have been characterized in solution by (1)H and (31)P NMR spectroscopy and the solid-state structures have been determined for 8, 9c and 10a-c by single-crystal X-ray crystallography. Complex 8 is comprised of Tl(+) ions that are weakly coordinated to octahedral [Tl{(Se)C(PPh(2)Se)(2)}(2)](-) anions to give a one-dimensional polymer. The complex 9c is comprised of two four-coordinate Tl(+) ions that are each S,S',S'',Se bonded to the hexadentate [(SPh(2)P)(2)CSeSeC(PPh(2)S)(2)](2-) ligand in which d(Se-Se) = 2.531(2) Å. The six-coordinate In(III) centres in the distorted octahedral complexes 10a-c are connected to a tridentate [(E')C(PPh(2)E)(2)](2-) dianion, a chloride ion and a neutral bidentate TMEDA ligand.

Identification of a novel η2-Se2 bonding mode in Cu(I) complexes of the dimeric selenocarbonyl dianions, [(EPh2P)2CSeSeC(PPh2E)2](2-) (E = S, Se).

A metathetical reaction between [Li(TMEDA)][(H)C(PPh2Se)2] and CuCl2 in a 2:1 molar ratio afforded the dimeric Cu(I) complex, {Cu2-η(2):η(2)-[(EPh2P)2CSeSeC(PPh2E)2]} (E = Se), via a selenium-proton exchange and an internal redox process. The analogous sulfur-containing complex (E = S) was obtained by the reactions of the dianions [(Se)C(PPh2S)2](2-) and [(SPh2P)2CSeSeC(PPh2S)2](2-) with Cu(II) and Cu(I) halides, respectively. Structural characterization of the Cu(I) complexes reveals a unique η(2)-Se2 bonding mode for the generic diselenide ligand system RSe-SeR.

Synthesis, multinuclear NMR spectra, and X-ray structures of tBu2PNP(I)tBu2 and EPR2NP(I)R2 (E = Se, Te; R = iPr, tBu).

Two synthetic routes to bifunctional P(V)/P(V) compounds of the type EPR(2)NP(I)R(2) have been developed. The reaction of Li[EP(i)Pr(2)NP(i)Pr(2)] with one molar equivalent of I(2) produces EP(i)Pr(2)NP(I)(i)Pr(2) (3a-I, E = Se; 3b-I, E = Te). Alternatively, the oxidation of Na[N(P(t)Bu(2))(2)] with I(2) in tetrahydrofuran (THF) generates the P(III)/P(V) compound (t)Bu(2)PNP(I)(t)Bu(2) (6'-I) which, on treatment with elemental selenium or tellurium in THF, yields EP(t)Bu(2)NP(I)(t)Bu(2) (3a'-I, E = Se; 3b'-I, E = Te). The acyclic compounds 3a-I, 3a'-I, 3b-I, 3b'-I, and 6'-I have been characterized in solution by multinuclear ((1)H, (31)P, (77)Se, and (125)Te) NMR spectroscopy and in the solid state by X-ray structural determinations.

Bis(µ(2)-phenyl-tellurolato)bis-(phenyl-tellurolato)tetra-µ(3)-tellurido-hexa-kis(triphenyl-phosphine)hexa-palladium(II) benzene nona-solvate.

The centrosymmetric title complex, [Pd(6)(C(6)H(5)Te)(4)Te(4)(C(18)H(15)P)(6)]·9C(6)H(6), contains two Pd(3)Te(2) cores that are joined into a cyclic hexa-nuclear complex by two bridging PhTe(-) groups. Each Pd(II) atom is coordinated by one triphenyl-phosphine ligand, one phenyl-tellurolate mol-ecule and two telluride ligands: two of the PhTe(-) ligands act as terminal ligands and two as bridging ligands. The three distinct Pd(II) atoms each show a slightly distorted PdPTe(3) square-planar coordination. The asymmetric unit also contains four and a half benzene solvent mol-ecules. Two of the benzene mol-ecules are disordered: one mol-ecule is distributed over two positions with site-occupancy factors of 0.529 (7) and 0.471 (7), while the other occupies two orientations about a centre of symmetry.

Palladium complexes containing novel cyclic selenium imides.

The first metal complexes of cyclic selenium(II) imide ligands, [PdCl2{Se,Se'-Se4(NtBu)3}] and [PdCl2{Se,Se'-Se4(NtBu)4}], which are obtained from the reaction of Se(NtBu)2 with [PdCl2(NCPh)2], contain the novel Se-N heterocycles Se4(NtBu)3 and Se4(NtBu)4.

Preparation, structure, and metallophilic interactions of dinuclear silver(I) and copper(I) complexes of selenium diimides.

The complexes [M(2){mu-N,N'-Se(NR)(2)}(2)](CF(3)SO(3))(2) (1, M = Ag, R = (t)Bu; 2, M = Ag, R = Ad; 3, M = Cu, R = (t)Bu; 4, M = Cu, R = Ad; Ad = 1-adamantyl) were prepared in good yields from the reaction of the corresponding selenium diimide with silver or copper triflate in toluene and were characterized in solution using multinuclear NMR spectroscopy. Recrystallization of 1-4 from a variety of solvents produced 1.2CH(2)Cl(2), 2(AdNH(3))(CF(3)SO(3)) (a few crystals), 3.2thf, and 4.1/2C(7)H(8), which were characterized by X-ray crystallography. All of these salts contain a metallacyclic [M(2){mu-N,N'-Se(NR)(2)}(2)](2+) [M = Ag, Cu; R = (t)Bu, Ad] cation, the frameworks of which exhibit M...M close contacts of 2.7384(9), 2.751(2), 2.556(2)-2.569(2), and 2.531(1) A, respectively. The M...M interaction was further explored by PBE/def-TZVP calculations of the dications [M(2){mu-N,N'-Se(NR)(2)}(2)](2+) (M = Ag, Cu; R = H, Me, (t)Bu, Ad). The geometry optimizations yielded metric parameters that were in good agreement with experimental values, where available. For both metals, it was observed that the M...M distance became shorter, as the organic substituent on nitrogen became bulkier. At the same time, the metallacyclic framework deviated more significantly from planarity. A survey of related dinuclear silver(I) and copper(I) complexes showed that, while there is some correlation between the bite size and the M...M distance, the latter is more dependent on the deviation from planarity of the D(2)M...MD(2) fragment. Atoms in molecules calculations clearly showed the presence of a bond critical point between the two silver or copper centers, as well as two ring critical points. Our computational results are consistent with other recent molecular orbital studies at different levels of theory and indicate the existence of d(10)-d(10) closed-shell metallophilic interactions in 1-4.

Heavy atom analogues of 1,2,3-dithiazolylium salts: preparation, structures and redox chemistry.

Synthetic routes to salts of the benzo[1,2,3]thiatellurazolylium cation [2c](+) and its selenium analogue [2b](+) are described. Access to the cation frameworks involves the intermediacy of N,N,S-trisilylated 2-aminobenzenethiol. The latter reacts smoothly with selenium and tellurium halides ECl4 (E = Se, Te) to afford the desired heterocyclic benzo cations [2b](+) and [2c](+) as their chloride salts. Anion exchange provides the corresponding GaCl4(-), OTf(-) and TeCl5(-) salts of [2c](+), all of which have been characterized by X-ray crystallography. While the gallate salts of the sulfur and selenium cations [2a](+) and [2b](+) crystallize as ion-paired cations and anions, salts of [2c](+) adopt solid-state structures that display strong association of the cations via short intermolecular Te-N' bonds. However, crystallization of [2c](+) salts in dichloroethane in the presence of GaCl3 leads to cleavage of the dimers and the formation of a Lewis acid adduct at nitrogen. Reduction of the benzo cations [2a,b](+) affords the respective radicals 2a,b, both of which have been characterized by electron paramagnetic resonance (EPR) spectroscopy. Attempts to generate the corresponding radical 2c have been unsuccessful, although a material of nominally correct elemental composition can be generated by chemical reduction. The energetics of association of [2a,b,c](+) in solution has been probed by means of density functional theory calculations using the polarized continuum model. The results suggest that the dimeric nature of the Te-centered cation is retained in solution. The strength of the interaction is, however, less than in N-alkylated tellurodiazolylium salts.

Self-association of the N-methyl benzotellurodiazolylium cation: implications for the generation of super-heavy atom radicals.

The N-methyl benzotellurodiazolylium cation self-associates in the solid state via short (2.471(3) A) 4-center TeN' intermolecular contacts; electrochemical data and the results of DFT calculations suggest that the dimers persist in solution.