Precursor approaches to MN (M = Ga, In) and BST for optical and memory devices

Abstract

Reactions of $Et_3SiNH_2$ with $R_3Ga$ in a 1:1 ratio have produced dimeric silylamidogallanes, $[R_2Ga(\mn -NHSiEt_3)]_2$ (II-1, R = Me, trans:cis = 1.5:1; (II-2), R = Et, trans:cis = 1.3:1), as a mixture of trans (a) and cis (b) isomers. Purification of II-1 by either recrystallization or sublimation gives only trans isomer II-1a as colorless crystals. Colorless liquid II-2 has been obtained only as a mixture of the two isomers. The trans$\rightarrow$ cis isomerization of II-1 has been studied by $^1H NMR spectroscopy. The equilibrium has been observed to follow reversible first order kinetics with $\delta H^o = _0.64 \pm 0.03 kJ mol^{-1}$ and $\delta S^o = _4.4 \pm 0.2 J K^{-1} mol^{-1}$. The activation parameters for the trans (II-1a) $\rightarrow$ cis (II-1b) conversion are $\deltaH^\ddagger _1 = 72.4 \pm 1.3 kJ mol^{-1}$ and $\delta S^\ddagger _1 = _38.8 \pm 4.5 J K mol^{-1}$, and those for the reverse process are $\delta H$_{-1}$ = 73.0 ∂ 0.4 kJ mol$^{-1}$ and $\delta S^\ddagger _{-1} = _34.4 \pm 1.7 J K mol^{-1}$. The isomerization is markedly accelerated in the presence of Lewis bases. A crossover experiment indicates that the isomer interconversion is a unimolecular process. The thermodynamic and kinetic data have been explained based on the solvent effect and the silyl substituent effect on the nitrogen atom. The molecular structure of II-1a has been determined by a single-crystal X-ray diffraction study. The molecular geometry of II-1a consists of a centrosymmetric and dimeric unit with two bridging (triethylsilyl)amido groups and two terminal methyl groups bound to each gallium atom. The two silyl groups are trans to each other with respect to the planar (Ga-N)$_2$ ring framework. The coordination geometry of both gallium and nitrogen atoms is distorted tetrahedral. Dimeric dimethylindium azide, $[Me_2In(\mu -N_3)]_2$ (III-1), has been prepared from the reaction of Me$_3$In with HN$_3$. A single-crystal X-ray diffraction study reveals that (III-...