Evidence for Core Oxygen Dynamics and Exchange in Metal Oxide Nanocrystals from In Situ ¹⁷O MAS NMR

Long-term stability of the properties of nanocrystals (NCs) is of paramount importance for any applicative development. However, these are jeopardized by chemical and structural alterations of the NCs induced by the environment and the working conditions. Among the species that alter the NCs properties, water molecules are of tremendous importance. We used ¹⁷O solid-state NMR spectroscopy to follow this process and the dynamics of O atoms in metal oxide NCs. Using ZnO as reference material, different chemical environments for the O atoms are characterized and a dynamic exchange process between the NCs and the O atoms from water is evidenced. The exchange does not involve only surface atoms but also ones located deeper inside the ZnO core of the NCs. Finally, a postsynthesis process based on watering/drying cycles is proposed that may greatly improve the long-term stability of metal oxide NCs

CH Bond Activation of Methane by a Transient η²‑Cyclopropene/Metallabicyclobutane Complex of Niobium

This study challenges the problem of the activation of a CH bond of methane by soluble transition metal complexes. High pressure solution NMR, isotopic labeling studies, and kinetic analyses of the degenerate exchange of methane in the methyl complex [Tp^Me2NbCH₃(<i>c</i>-C₃H₅)­(MeCCMe)] (<b>1</b>) are reported. Stoichiometric methane activation by the mesitylene complex [Tp^Me2Nb­(CH₂-3,5-C₆H₃Me₂)­(<i>c</i>-C₃H₅) (MeCCMe)] (<b>2</b>) giving <b>1</b> is also realized. Evidence is provided that these reactions proceed via an intramolecular abstraction of a β-H of the cyclopropyl group to form either methane or mesitylene from <b>1</b> or <b>2</b>, respectively, yielding the transient unsaturated η²-cyclopropene/metallabicyclobutane intermediate [Tp^Me2Nb­(η²-<i>c</i>-C₃H₄) (MeCCMe)] <b>A</b>. This is followed by its mechanistic reverse 1,3-CH bond addition of methane yielding the product

Interaction between a Bisphosphonate, Tiludronate, and Biomimetic Nanocrystalline Apatites

Bisphosphonates (BPs) are well established as successful antiresorptive agents for the prevention and treatment of bone diseases such as osteoporosis and Paget’s disease. The aim of this work was to clarify the reaction mechanisms between a BP molecule, tiludronate, and the nanocrystalline apatite surface. The adsorption of tiludronate on well-characterized synthetic biomimetic nanocrystalline apatites with homogeneous but different compositions and surface characteristics was investigated to determine the effect of the nanocrystalline apatite substrate on the adsorption behavior. The results show that the adsorption of tiludronate on nanocrystalline biomimetic apatite surfaces varies over a large range. The most immature apatitic samples exhibited the highest affinity and the greatest amount adsorbed at saturation. Maturation of the nanocrystals induces a decrease of these values. The amount of phosphate ion released per adsorbed BP molecule varied, depending on the nanocrystalline substrate considered. The adsorption mechanism, although associated with a release of phosphate ions, cannot be considered as a simple ion exchange process involving one or two phosphate ions on the surface. A two-step process is proposed consisting of a surface binding of BP groups to calcium ions associated with a proton release inducing the protonation of surface orthophosphate ions and their eventual solubilization

Heteroleptic Silver(I) Complexes Prepared from Phenanthroline and Bis-phosphine Ligands

The heteroleptic coordination scenario of silver­(I) with various phenanthroline ligands (NN) and different bis-phosphine (PP) derivatives has been investigated. In addition to the X-ray crystal structural characterization of the resulting mixed ligand Ag­(I) complexes, detailed NMR studies have been performed to disclose the behavior of the prepared silver­(I) complexes in solution. The results obtained with silver­(I) have been also systematically related to the one obtained for copper­(I) with the same combination of PP and NN ligands. Starting from an equimolar mixture of AgBF₄, bis­[(2-diphenylphosphino)­phenyl] ether (POP), and 1,10-phenanthroline (phen), the mononuclear complex [Ag­(POP)­(phen)]⁺ has been obtained as the tetrafluoroborate salt. By following the same experimental procedure starting from bis­(diphenylphosphino)­methane (dppm) or 1,3-bis­(diphenylphosphino)­propane (dppp) as the PP ligand, dinuclear complexes with two bridging PP ligands, i.e., [Ag₂(NN)₂(μ-dppm)₂]²⁺ and [Ag₂(NN)₂(μ-dppp)₂]²⁺ with NN = phen or Bphen (bathophenanthroline), have been isolated as the tetrafluoroborate salts. Surprisingly, by using an equimolar ratio of AgBF₄, phen or Bphen, and 1,2-bis­(diphenyl-phosphino)­ethane (dppe), the corresponding monobridged diphosphine dinuclear complexes [Ag₂(NN)₂(μ-dppe)]²⁺ have been obtained as the tetrafluoroborate salts. These compounds have been also prepared in excellent yield by using a more appropriate 2:1:2 (phen:dppe:Ag) stoichiometry. These results prompted us to also perform the reactions with dppm and dppp using a 1:2:2 (PP:NN:Ag) stoichiometry. Under these conditions, [Ag₂(NN)₂(μ-dppm)]­(BF₄)₂ (NN = phen or Bphen) and [Ag₂(NN)₂(μ-dppp)]­(BF₄)₂ (NN = phen or Bphen) have been obtained upon crystallization. When compared to their copper­(I) analogues, the complexation scenario becomes more complex with silver­(I) as the system tolerates also coordinatively frustrated metal ligand assemblies, i.e., with a trigonal coordination geometry. Depending on the stoichiometry or on the nature of the PP partner, silver­(I) shows an adaptive capability leading to various complexes with different coordination geometries and composition. However, as in the case of copper­(I), their solution behavior is highly dependent on the relative thermodynamic stability of the various possible complexes. In most of the cases, a single Ag­(I) complex is observed in solution and the NMR data are in a perfect agreement with their solid state structures. The dppp-containing complexes are the only notable exception; both [Ag₂(NN)₂(μ-dppp)₂]­(BF₄)₂ and [Ag₂(NN)₂(μ-dppp)]­(BF₄)₂ are stable in the solid state but a dynamic mixture is observed as soon as these compounds are dissolved. Finally, whereas both dppe and dppp are chelating ligands for copper­(I), it is not the case anymore with silver­(I) for which a destabilization of species with chelating dppe and dppp ligands is clearly suggested by our results

Heteroleptic Silver(I) Complexes Prepared from Phenanthroline and Bis-phosphine Ligands

The heteroleptic coordination scenario of silver­(I) with various phenanthroline ligands (NN) and different bis-phosphine (PP) derivatives has been investigated. In addition to the X-ray crystal structural characterization of the resulting mixed ligand Ag­(I) complexes, detailed NMR studies have been performed to disclose the behavior of the prepared silver­(I) complexes in solution. The results obtained with silver­(I) have been also systematically related to the one obtained for copper­(I) with the same combination of PP and NN ligands. Starting from an equimolar mixture of AgBF₄, bis­[(2-diphenylphosphino)­phenyl] ether (POP), and 1,10-phenanthroline (phen), the mononuclear complex [Ag­(POP)­(phen)]⁺ has been obtained as the tetrafluoroborate salt. By following the same experimental procedure starting from bis­(diphenylphosphino)­methane (dppm) or 1,3-bis­(diphenylphosphino)­propane (dppp) as the PP ligand, dinuclear complexes with two bridging PP ligands, i.e., [Ag₂(NN)₂(μ-dppm)₂]²⁺ and [Ag₂(NN)₂(μ-dppp)₂]²⁺ with NN = phen or Bphen (bathophenanthroline), have been isolated as the tetrafluoroborate salts. Surprisingly, by using an equimolar ratio of AgBF₄, phen or Bphen, and 1,2-bis­(diphenyl-phosphino)­ethane (dppe), the corresponding monobridged diphosphine dinuclear complexes [Ag₂(NN)₂(μ-dppe)]²⁺ have been obtained as the tetrafluoroborate salts. These compounds have been also prepared in excellent yield by using a more appropriate 2:1:2 (phen:dppe:Ag) stoichiometry. These results prompted us to also perform the reactions with dppm and dppp using a 1:2:2 (PP:NN:Ag) stoichiometry. Under these conditions, [Ag₂(NN)₂(μ-dppm)]­(BF₄)₂ (NN = phen or Bphen) and [Ag₂(NN)₂(μ-dppp)]­(BF₄)₂ (NN = phen or Bphen) have been obtained upon crystallization. When compared to their copper­(I) analogues, the complexation scenario becomes more complex with silver­(I) as the system tolerates also coordinatively frustrated metal ligand assemblies, i.e., with a trigonal coordination geometry. Depending on the stoichiometry or on the nature of the PP partner, silver­(I) shows an adaptive capability leading to various complexes with different coordination geometries and composition. However, as in the case of copper­(I), their solution behavior is highly dependent on the relative thermodynamic stability of the various possible complexes. In most of the cases, a single Ag­(I) complex is observed in solution and the NMR data are in a perfect agreement with their solid state structures. The dppp-containing complexes are the only notable exception; both [Ag₂(NN)₂(μ-dppp)₂]­(BF₄)₂ and [Ag₂(NN)₂(μ-dppp)]­(BF₄)₂ are stable in the solid state but a dynamic mixture is observed as soon as these compounds are dissolved. Finally, whereas both dppe and dppp are chelating ligands for copper­(I), it is not the case anymore with silver­(I) for which a destabilization of species with chelating dppe and dppp ligands is clearly suggested by our results

Heteroleptic Silver(I) Complexes Prepared from Phenanthroline and Bis-phosphine Ligands

The heteroleptic coordination scenario of silver­(I) with various phenanthroline ligands (NN) and different bis-phosphine (PP) derivatives has been investigated. In addition to the X-ray crystal structural characterization of the resulting mixed ligand Ag­(I) complexes, detailed NMR studies have been performed to disclose the behavior of the prepared silver­(I) complexes in solution. The results obtained with silver­(I) have been also systematically related to the one obtained for copper­(I) with the same combination of PP and NN ligands. Starting from an equimolar mixture of AgBF₄, bis­[(2-diphenylphosphino)­phenyl] ether (POP), and 1,10-phenanthroline (phen), the mononuclear complex [Ag­(POP)­(phen)]⁺ has been obtained as the tetrafluoroborate salt. By following the same experimental procedure starting from bis­(diphenylphosphino)­methane (dppm) or 1,3-bis­(diphenylphosphino)­propane (dppp) as the PP ligand, dinuclear complexes with two bridging PP ligands, i.e., [Ag₂(NN)₂(μ-dppm)₂]²⁺ and [Ag₂(NN)₂(μ-dppp)₂]²⁺ with NN = phen or Bphen (bathophenanthroline), have been isolated as the tetrafluoroborate salts. Surprisingly, by using an equimolar ratio of AgBF₄, phen or Bphen, and 1,2-bis­(diphenyl-phosphino)­ethane (dppe), the corresponding monobridged diphosphine dinuclear complexes [Ag₂(NN)₂(μ-dppe)]²⁺ have been obtained as the tetrafluoroborate salts. These compounds have been also prepared in excellent yield by using a more appropriate 2:1:2 (phen:dppe:Ag) stoichiometry. These results prompted us to also perform the reactions with dppm and dppp using a 1:2:2 (PP:NN:Ag) stoichiometry. Under these conditions, [Ag₂(NN)₂(μ-dppm)]­(BF₄)₂ (NN = phen or Bphen) and [Ag₂(NN)₂(μ-dppp)]­(BF₄)₂ (NN = phen or Bphen) have been obtained upon crystallization. When compared to their copper­(I) analogues, the complexation scenario becomes more complex with silver­(I) as the system tolerates also coordinatively frustrated metal ligand assemblies, i.e., with a trigonal coordination geometry. Depending on the stoichiometry or on the nature of the PP partner, silver­(I) shows an adaptive capability leading to various complexes with different coordination geometries and composition. However, as in the case of copper­(I), their solution behavior is highly dependent on the relative thermodynamic stability of the various possible complexes. In most of the cases, a single Ag­(I) complex is observed in solution and the NMR data are in a perfect agreement with their solid state structures. The dppp-containing complexes are the only notable exception; both [Ag₂(NN)₂(μ-dppp)₂]­(BF₄)₂ and [Ag₂(NN)₂(μ-dppp)]­(BF₄)₂ are stable in the solid state but a dynamic mixture is observed as soon as these compounds are dissolved. Finally, whereas both dppe and dppp are chelating ligands for copper­(I), it is not the case anymore with silver­(I) for which a destabilization of species with chelating dppe and dppp ligands is clearly suggested by our results

Probing Highly Selective H/D Exchange Processes with a Ruthenium Complex through Neutron Diffraction and Multinuclear NMR Studies.

Deuterium labeling is a powerful way to gain mechanistic information in biology and chemistry. However, selectivity is hard to control experimentally, and labeled sites can be difficult to assign both in solution and in the solid state. Here we show that very selective high-deuterium contents can be achieved for the polyhydride ruthenium phosphine complex [RuH₂(H₂)₂(PCyp₃)₂] (<b>1</b>) (PCyp₃ = P­(C₅H₉)₃). The selectivity of the H/D exchange process is demonstrated by multinuclear NMR and neutron diffraction analyses. It has also been investigated through density functional theory (DFT) calculations. The reactions are performed under mild conditions at room temperature, and the extent of deuterium incorporation, involving selective C–H bond activation within the cyclopentyl rings of the phosphine ligands, can easily be tuned (solvent effects, D₂ pressure). It is shown that D₂ gas can inhibit the C–H/C–D exchange process