Trimethylaluminum and Borane Complexes of Primary Amines

Trimethylaluminum (TMA) complexes of methyl-, <i>n</i>-propyl-, cyclopropyl-, allyl-, and propargylamine were synthesized and their experimental properties and theoretical characteristics were compared with the respective amine–borane analogues. The amine ligand of an amine–TMA Lewis acid–base complex can be easily changed by another amine through a 2:1 amine–TMA intermediate in pentane at room temperature. The exchange of the same ligands in the case of amine–boranes requires remarkably more time in line with the calculated relative energy of the respective transition state. The ¹H and ¹³C NMR experiments examining the addition of one or more equivalent of amine to the respective Lewis acid–base complex conclude in the fast exchange of the amine ligand in the NMR time scale only in the cases of amine–TMA complexes, which could also be caused by similar 2:1 complexes. However, in gas phase, only 1:1 amine–TMA complexes are present as evidenced by ultraviolet photoelectron spectroscopy (UPS). The observed UP spectra, which are the first recorded photoelectron spectra of primary amine–TMA compounds, indicate that the stabilization effect of the lone electron pair of nitrogen atom in amines during the borane complexation is stronger than that of the TMA complexation. In line with this observation, the destabilization of the σ_Al–C orbitals is lower than that of σ_B–H orbitals during the formation of amine–TMA and amine–borane complexes, respectively. As showed by theoretical calculations, the CH₄ elimination of the studied amine–TMA complexes is exothermic, indicating the possibility of using these compounds in metal organic chemical vapor deposition techniques (MOCVD). On the other hand, our experimental conditions avoid this methane elimination and constitutes the first procedure employing distillation to isolate primary amine–TMA complexes

Characterization and Luminescence Properties of Lanthanide-Based Polynuclear Complexes Nanoaggregates

For the first time, hexanuclear complexes with general chemical formula [Ln₆O­(OH)₈­(NO₃)₆(H₂O)_<i>n</i>]²⁺ with <i>n</i> = 12 for Ln = Sm–Lu and Y and <i>n</i> = 14 for Ln = Pr and Nd were stabilized as nanoaggregates in ethylene glycol (EG). These unprecedented nanoaggregates were structurally characterized by ⁸⁹Y and ¹H NMR spectroscopy, UV–vis absorption and luminescence spectroscopies, electrospray ionization mass spectrometry, diffusion ordered spectroscopy, transmission electron microscopy, and dynamic light scattering. These nanoaggregates present a 200 nm mean solvodynamic diameter. In these nanoaggregates, hexanuclear complexes are isolated and solvated by EG molecules. The replacement of ethylene glycol by 2-hydroxybenzyl alcohol provides new nanoaggregates that present an antenna effect toward lanthanide ions. This results in a significant enhancement of the luminescence properties of the aggregates and demonstrates the suitability of the strategy for obtaining highly tunable luminescent solutions