An Investigation of 1:1 Adducts of Gallium Trihalides with Triarylphosphines by Solid-State69/71Ga and31P NMR Spectroscopy

Crystal Structures of Gallium(III) Halides with Bulky Ligands

Three oxygen donor gallium(III) halide complexes, [GaX3(O=P(TMP)3] (TMP = trimethoxylphenyl and X = Cl− (1), Br− (2) and I− (3)), are prepared by oxidation in mixed solvents from their phosphine adducts of [GaX3(P(TMP)3]. Three crystalline compounds are obtained from the solutions and their crystal structures are determined in the solid state. It is rare to generate a crystalline phase for metal–adduct compounds of this bulky ligand; in this paper, three new crystal structures are presented.

Tailoring Cu+ for Ga3+ Cation Exchange in Cu2-xS and CuInS2 Nanocrystals by Controlling the Ga Precursor Chemistry

Nanoscale cation exchange (CE) has resulted in colloidal nanomaterials that are unattainable by direct synthesis methods. Aliovalent CE is complex and synthetically challenging because the exchange of an unequal number of host and guest cations is required to maintain charge balance. An approach to control aliovalent CE reactions is the use of a single reactant to both supply the guest cation and extract the host cation. Here, we study the application of GaCl₃-L complexes [L = trioctylphosphine (TOP), triphenylphosphite (TPP), diphenylphosphine (DPP)] as reactants in the exchange of Cu⁺ for Ga³⁺ in Cu_2-xS nanocrystals. We find that noncomplexed GaCl₃ etches the nanocrystals by S^2- extraction, whereas GaCl₃-TOP is unreactive. Successful exchange of Cu⁺ for Ga³⁺ is only possible when GaCl₃ is complexed with either TPP or DPP. This is attributed to the pivotal role of the Cu_2-xS-GaCl₃-L activated complex that forms at the surface of the nanocrystal at the onset of the CE reaction, which must be such that simultaneous Ga³⁺ insertion and Cu⁺ extraction can occur. This requisite is only met if GaCl₃ is bound to a phosphine ligand, with a moderate bond strength, to allow facile dissociation of the complex at the nanocrystal surface. The general validity of this mechanism is demonstrated by using GaCl₃-DPP to convert CuInS₂ into (Cu,Ga,In)S₂ nanocrystals, which increases the photoluminescence quantum yield 10-fold, while blue-shifting the photoluminescence into the NIR biological window. This highlights the general applicability of the mechanistic insights provided by our work.

[GaX2(dmpe)2][GaX4] (X = Cl, Br, I): a synthetic, solid state, and computational study

Derivatives of [GaX2(dmpe)2][GaX4] (X = Cl,Br, I) were prepared and characterized. The salts contain a cation involving two diphosphine ligands bound to GaX2+, imposing a pseudo-octahedral geometry at gallium. A variety of possible structural alternatives for the equimolar combination of GaX3 and dmpe have been computationally modelled and shown to be energetically similar to the observed cations, indicating potential fluxionality in the system, and are in agreement with spectroscopic characterization.

Spin-Spin Coupling between Quadrupolar Nuclei in Solids: (11)B-(75)As Spin Pairs in Lewis Acid-Base Adducts

Solid-state (11)B NMR measurements of Lewis acid-base adducts of the form R3AsBR'3 (R = Me, Et, Ph; R' = H, Ph, C6F5) were carried out at several magnetic field strengths (e.g., B0 = 21.14, 11.75, and 7.05 T). The (11)B NMR spectra of these adducts exhibit residual dipolar coupling under MAS conditions, allowing for the determination of effective dipolar coupling constants, Reff((75)As,(11)B), as well as the sign of the (75)As nuclear quadrupolar coupling constants. Values of Reff((75)As,(11)B) range from 500 to 700 Hz. Small isotropic J-couplings are resolved in some cases, and the sign of (1)J((75)As,(11)B) is determined. Values of CQ((75)As) measured at B0 = 21.14 T for these triarylborane Lewis acid-base adducts range from -82 ± 2 MHz for Et3AsB(C6F5)3 to -146 ± 1 MHz for Ph3AsBPh3. For Ph3AsBH3, two crystallographically nonequivalent sites are identified with CQ((75)As) values of -153 and -151 ± 1 MHz. For the uncoordinated Lewis base, Ph3As, four (75)As sites with CQ((75)As) values ranging from 193.5 to 194.4 ± 2 MHz are identified. At these applied magnetic field strengths, the (75)As quadrupolar interaction does not satisfy high-field approximation criteria, and thus, an exact treatment was used to describe this interaction in (11)B and (75)As NMR spectral simulations. NMR parameters calculated using the ADF and CASTEP program packages support the experimentally derived parameters in both magnitude and sign. These experiments add to the limited body of literature on solid-state (75)As NMR spectroscopy and serve as examples of spin-spin-coupled quadrupolar spin pairs, which are also rarely treated in the literature.

Recent NMR developments applied to organic-inorganic materials

In this contribution, the latest developments in solid state NMR are presented in the field of organic-inorganic (O/I) materials (or hybrid materials). Such materials involve mineral and organic (including polymeric and biological) components, and can exhibit complex O/I interfaces. Hybrids are currently a major topic of research in nanoscience, and solid state NMR is obviously a pertinent spectroscopic tool of investigation. Its versatility allows the detailed description of the structure and texture of such complex materials. The article is divided in two main parts: in the first one, recent NMR methodological/instrumental developments are presented in connection with hybrid materials. In the second part, an exhaustive overview of the major classes of O/I materials and their NMR characterization is presented.