4 research outputs found
Formation of the Imide [Ta(NMe<sub>2</sub>)<sub>3</sub>(Ī¼-NSiMe<sub>3</sub>)]<sub>2</sub> through an Unprecedented Ī±-SiMe<sub>3</sub> Abstraction by an Amide Ligand
TaĀ(NMe<sub>2</sub>)<sub>4</sub>[NĀ(SiMe<sub>3</sub>)<sub>2</sub>] (<b>1</b>) undergoes the elimination of Me<sub>3</sub>Si-NMe<sub>2</sub> (<b>2</b>), converting the āNĀ(SiMe<sub>3</sub>)<sub>2</sub> ligand to the ī»NSiMe<sub>3</sub> ligand,
to give the imide āTaĀ(NMe<sub>2</sub>)<sub>3</sub>(ī»NSiMe<sub>3</sub>)ā (<b>3</b>) observed as
its dimer <b>4</b>. CyNī»Cī»NCy captures <b>3</b> to yield guanidinates TaĀ(NMe<sub>2</sub>)<sub>3ā<i>n</i></sub>(ī»NSiMe<sub>3</sub>)Ā[CyNCĀ(NMe<sub>2</sub>)ĀNCy]<sub><i>n</i></sub> [<i>n</i> = 1 (<b>5</b>), 2 (<b>6</b>)]. The kinetic study of Ī±-SiMe<sub>3</sub> abstraction
in <b>1</b> gives Ī<i>H</i><sup>ā§§</sup> = 21.3(1.0) kcal/mol and Ī<i>S</i><sup>ā§§</sup> = ā17(2) eu
Reactions of Group 4 Amide Guanidinates with Dioxygen or Water. Studies of the Formation of Oxo Products
Reactions
of the zirconium amide guanidinates (R<sub>2</sub>N)<sub>2</sub>MĀ[<sup><i>i</i></sup>PrNCĀ(NR<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub> (R = Me, M = Zr, <b>1</b>; M = Hf, <b>2</b>; R = Et, M = Zr, <b>3</b>) with O<sub>2</sub> or H<sub>2</sub>O give products that are consistent with the oxo dimers {MĀ(Ī¼-O)Ā[<sup><i>i</i></sup>PrNCĀ(NR<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub>}<sub>2</sub> (R = Me, M = Zr, <b>4</b>; M = Hf, <b>5</b>; R = Et, M = Zr, <b>6</b>) and polymers
{MĀ(Ī¼-O)Ā[<sup><i>i</i></sup>PrNCĀ(NR<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub>}<sub><i>n</i></sub> (R = Me, M = Zr, <b>7</b>; M = Hf, <b>8</b>; R = Et,
M = Zr, <b>9</b>). Mass spectrometric (MS) analyses of the reactions
of water in air with <b>1</b> and <b>2</b> show formation
of the Zr monomer ZrĀ(ī»O)Ā[<sup><i>i</i></sup>PrNCĀ(NMe<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub> (<b>10</b>), oxo dimers <b>4</b> and <b>5</b>, and dihydroxyl complexes
MĀ(OH)<sub>2</sub>[<sup><i>i</i></sup>PrNCĀ(NMe<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub> (M = Zr, <b>11</b>; Hf, <b>12</b>). Similar MS analyses of the reaction of diethylamide
guanidinate <b>3</b> with water in air show the formation of
ZrĀ(ī»O)Ā[<sup><i>i</i></sup>PrNCĀ(NEt<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub> (<b>13</b>), ZrĀ(OH)<sub>2</sub>[<sup><i>i</i></sup>PrNCĀ(NEt<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub> (<b>14</b>), <b>6</b>, and {(Et<sub>2</sub>N)ĀZrĀ[<sup><i>i</i></sup>PrNCĀ(NEt<sub>2</sub>)ĀN<sup><i>i</i></sup>Pr]<sub>2</sub>}<sup>+</sup> (<b>15</b>). Kinetic studies of the reaction between <b>1</b> and a continuous flow of 1.0 atm of O<sub>2</sub> at 80ā105
Ā°C indicate that it follows pseudo-first-order kinetics with
Ī<i>H</i><sup>ā§§</sup> = 8.7(1.1) kcal/mol,
Ī<i>S</i><sup>ā§§</sup> = ā54(3) eu, Ī<i>G</i><sup>ā§§</sup><sub>358Ā K</sub> = 28(2) kcal/mol,
and a half-life of 213(1) min at 85 Ā°C
Hot Carrier Cooling Mediated Efficiency Enhancement in Diamine Passivated Perovskite Solar Cells
Slowing hot carrier (HC) cooling
in halide perovskites emerges
as an efficient strategy to enhance the power conversion efficiency
(PCE) of perovskite solar cells (PSCs). This approach facilitates
the rapid extraction of HCs before they dissipate within the intricate
lattice of the perovskite structure. In this investigation, we delve
into the impact of amine-based additives on the relaxation of HCs
in perovskite solar cells using a diamine 4,4ā²-diaminodiphenylmethaneiodide
salt (MDA). The diamine has been used as an in situ additive in the
perovskite precursor. The ultrafast femtosecond transient absorption
(fs-TA) spectroscopy study confirms that the diamine-modified film
slows the HC cooling time to 672 fs from the control (538 fs). Moreover,
MDA additive helps to improve crystallization and passivate the traps
for inhibiting nonradiative recombination, leading to higher PCE compared
to the control device. The passivated devices show impressive ambient
stability and retain 80% of initial PCE after 500 h. Our study provides
an in-depth understanding of how precise control of HC cooling through
additive engineering can improve the PSCās efficiency and stability
A Spatial Modeling Framework to Evaluate Domestic Biofuel-Induced Potential Land Use Changes and Emissions
We present a novel bottom-up approach
to estimate biofuel-induced
land-use change (LUC) and resulting CO<sub>2</sub> emissions in the
U.S. from 2010 to 2022, based on a consistent methodology across four
essential components: land availability, land suitability, LUC decision-making,
and induced CO<sub>2</sub> emissions. Using high-resolution geospatial
data and modeling, we construct probabilistic assessments of county-,
state-, and national-level LUC and emissions for macroeconomic scenarios.
We use the Cropland Data Layer and the Protected Areas Database to
characterize availability of land for biofuel crop cultivation, and
the CERES-Maize and BioCro biophysical crop growth models to estimate
the suitability (yield potential) of available lands for biofuel crops.
For LUC decisionmaking, we use a county-level stochastic partial-equilibrium
modeling framework and consider five scenarios involving annual ethanol
production scaling to 15, 22, and 29 BG, respectively, in 2022, with
corn providing feedstock for the first 15 BG and the remainder coming
from one of two dedicated energy crops. Finally, we derive high-resolution
above-ground carbon factors from the National Biomass and Carbon Data
set to estimate emissions from each LUC pathway. Based on these inputs,
we obtain estimates for average total LUC emissions of 6.1, 2.2, 1.0,
2.2, and 2.4 gCO2e/MJ for Corn-15 Billion gallons (BG), <i>Miscanthus
Ć giganteus</i> (MxG)-7 BG, Switchgrass (SG)-7 BG, MxG-14
BG, and SG-14 BG scenarios, respectively