Safe(r) by design guidelines for the nanotechnology industry.

Expectations for safer and sustainable chemicals and products are growing to comply with the United Nations and European strategies for sustainability. The application of Safe(r) by Design (SbD) in nanotechnology implies an iterative process where functionality, human health and safety, environmental and economic impact and cost are assessed and balanced as early as possible in the innovation process and updated at each step. The EU H2020 NanoReg2 project was the first European project to implement SbD in six companies handling and/or manufacturing nanomaterials (NMs) and nano-enabled products (NEP). The results from this experience have been used to develop these guidelines on the practical application of SbD. The SbD approach foresees the identification, estimation, and reduction of human and environmental risks as early as possible in the development of a NM or NEP, and it is based on three pillars: (i) safer NMs and NEP; (ii) safer use and end of life and (iii) safer industrial production. The presented guidelines include a set of information and tools that will help deciding at each step of the innovation process whether to continue, apply SbD measures or carry out further tests to reduce uncertainty. It does not intend to be a prescriptive protocol where all suggested steps have to be followed to achieve a SbD NM/NEP or process. Rather, the guidelines are designed to identify risks at an early state and information to be considered to identify those risks. Each company adapts the approach to its specific needs and circumstances as company decisions influence the way forward.

Study of the coordination abilities of stibine ligands to gold(I).

The reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with SbMes(n)Ph(3-n) (n = 3 (1), 2 (2), 1 (3)) produces the 1:1 adducts [AuCl(SbMes(n)Ph(3-n))] (n = 3 (4), 2 (5), 1 (6)), with a Sb-Au-Cl environment, regardless of the molar ratio used (1:1 to 1:4). Addition of the same stibines to [Au(tht)(2)]ClO(4) (molar ratio 1:1 to 1:4) results in isolation of the 1:2 adducts [Au(SbMes(n)Ph(3-n))(2)]ClO(4) (n = 3 (7), 2 (10)), containing linear Sb-Au-Sb fragments, or the 1:3 adduct [Au(SbMesPh(2))(3)]ClO(4) (11), with a quasi trigonal planar AuSb(3) core. The same 1:2 cations are produced when [Au(tht)(2)]CF(3)SO(3) is reacted with 1 or following a rearrangement process when 4 is treated with AgSbF(6), that is, [Au(SbMes(3))(2)]X (X = CF(3)SO(3) (8), SbF(6) (9)). The compounds were characterized by spectroscopic methods, and the molecular structures of 2-4, 7, 8.2CDCl(3), 9, and 11 were established by single-crystal X-ray diffraction. Theoretical calculations were carried out on model systems of type ER(3) and [Au(ER(3))(n)](+) (E = P or Sb; R = Ph or Mes; n = 2, 3, or 4) to gain insight into the bonding nature of SbR(3) ligands in homoleptic gold-stibine adducts, in comparison with phosphine-gold(I) compounds. Steric effects govern the coordination of stibines with mesityl substituents. A preference for higher coordination numbers is observed for SbPh(3) when compared with PPh(3) and experimentally observed C-Sb-C and Sb-C structural distortions of stibines upon coordination are reproduced theoretically.

Multiple evidence for gold(I)...silver(I) interactions in solution.

[AuAg3(C6F5)(CF3CO2)3(CH2PPh3)]n (2) was prepared by reaction of [Au(C6F5)(CH2PPh3)] (1) and [Ag(CF3CO2)] (1:3). The crystal structures of complexes 1 and 2 were determined by X-ray diffraction, and the latter shows a polymeric 2D arrangement built by Au...Ag, Ag...Ag, and Ag...O contacts. The metallophilic interactions observed in 2 in the solid state seem to be preserved in concentrated THF solutions, as suggested by EXAFS, pulsed-gradient spin-echo NMR, and photophysical studies, which showed that the structural motif [AuAg3(C6F5)(CF3CO2)3(CH2PPh3)] is maintained under such conditions. Time-dependent DFT calculations agree with the experimental photophysical energies and suggest a metal-to-ligand charge-transfer phosphorescence process. Ab initio calculations give an estimated interaction energy of around 60 kJ mol(-1) for each Au...Ag interaction.

Vapochromic behavior of {Ag2(Et2O)2[Au(C6F5)2]2}n with volatile organic compounds.

The vapochromic behaviors of {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1), Me2CO (2), THF (3), CH3CN (4)) were studied. {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1)) was synthesized by the reaction of [Bu4N][Au(C6F5)2] with AgOClO3 in 1:1 molar ratio in CH2Cl2/Et2O (1:2). 1 was used as starting material with THF to form {Ag2L2[Au(C6F5)2]2}n (L = THF (3)). 3 crystallizes in the monoclinic space group C2/c and consists of tetranuclear units linked together via aurophilic contacts resulting in the formation of a 1D polymer that runs parallel to the crystallographic z axis. The gold(I) atoms are linearly coordinated to two pentafluorophenyl groups and display additional Au...Ag close contacts within the tetranuclear units with distances of 2.7582(3) and 2.7709(3) A. Each silver(I) center is bonded to the two oxygen atoms of the THF molecules with a Ag-O bond distance of 2.307(3) A. TGA analysis showed that 1 loses two molecules of the coordinated solvent per molecular unit (1st one: 75-100 degrees, second one: 150-175 degrees C), whereas 2, 3, and 4 lose both volatile organic compounds (VOCs) and fluorinated ligands in a less well defined manner. Each complex loses both the fluorinated ligands and the VOCs by a temperature of about 325 degrees C to give a 1:1 gold/silver product. X-ray powder diffraction studies confirm that the reaction of vapors of VOCs with 1 in the solid state produce complete substitution of the ether molecules by the new VOC. The VOCs are replaced in the order CH3CN > Me2CO > THF > Et2O, with the ether being the easiest to replace. {Ag2(Et2O)2[Au(C6F5)2]2}n and {Ag2(THF)2[Au(C6F5)2]2} n both luminesce at room temperature and at 77 K in the solid state. Emission maxima are independent of the excitation wavelength used below about 500 nm. Emission maxima are obtained at 585 nm (ether) and 544 nm (THF) at room temperature and at 605 nm (ether) and 567 nm (THF) at 77 K.

Au(I)...Ag(I) metallophilic interactions between anionic units: theoretical studies on a AuAg4 square pyramidal arrangement.

We have studied theoretically the organometallic compound (NBu4)2[Au(3,5-C6F3Cl2)2Ag4(CF3CO2)5], whose dianionic part displays a AuAg4 square pyramidal arrangement based on closed-shell Au(I)...Ag(I) interactions between two monoanionic fragments. DFT/B3LYP, ab initio Hartree-Fock (HF), and second-order Møller Plesset perturbation theory (MP2) calculations have been carried out for simplified model systems. Model system [AuPh2]-...[Ag4(CO2H)5]- (C1) has been chosen from DFT results as an appropriate model for the study of the interactions. The four Au(I)...Ag(I) interactions and two additional C...Ag(I) interactions are observed when dispersion-type interactions are considered in the level of theory (MP2) displaying a metallophilic attraction between two anionic units. The study of model C2 (similar to C1 but with minimized C...Ag(I) interactions) permits the study of the Au(I)...Ag(I) interactions separately, which confirms the existence of stabilizing Au(I)...Ag(I) interactions around 13 kJ.mol(-1) each.

A step forward in gold-silver metallophilicity. An AuAg4 moiety with a square pyramidal arrangement.

By reaction of the Lewis base NBu4[Au(3,5-C6F3Cl2)2] and AgCF3COO in the presence of NBu4CF3COO the heterometallic compound (NBu4)2[Au(3,5-C6F3Cl22Ag4(CF3COO)5] (2) is obtained. The structure displays an unprecendented square pyramidal AuAg4 arrangement built up through four AuAg closed-shell interactions and two Au-C-Ag 3c-2e- bridges.