Synthesis and Characterization of the {Si(NHCH2CH2NH)3[Mo(CO)3]2}2- Complex Comprising the Si(NHCH2CH2NH)32- Octahedron.

Reactions of K12Si17 with the low-valent transition-metal complex Mo(CO)3(C7H8) in ethylenediamine/toluene solutions in the presence of 2,2,2-cryptand yield the {Si(NHCH2CH2NH)3[Mo(CO)3]2}2- dianion, which contains an octahedral Si(NHCH2CH2NH)32- subunit. The SiN6 core comprises a rare example of a doubly deprotonated ethylenediame ligand in a coordination complex and is also the first structurally characterized example of a homoleptic Si(N∩N)3 trischelate. Its structure and spectroscopic properties are described.

Synthesis, Structure, and Properties of Al((R)bpy)3 Complexes (R = t-Bu, Me): Homoleptic Main-Group Tris-bipyridyl Compounds.

The neutral homoleptic tris-bpy aluminum complexes Al((R)bpy)3, where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral (R)bpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies. The collective data show that 1 and 2 contain Al(3+) metal centers coordinated by three bipyridine (bpy(•))(1-) monoanion radicals. Electrochemical studies show that six redox states are accessible from the neutral complexes, three oxidative and three reductive, that involve oxidation or reduction of the coordinated bpy ligands to give neutral (R)bpy or (R)bpy(2-) dianions, respectively. Magnetic susceptibility measurements (4-300 K) coupled with DFT studies show strong antiferromagnetic coupling of the three unpaired electrons located on the (R)bpy ligands to give S = (1)/2 ground states with low lying S = (3)/2 excited states that are populated above 110 K (1) and 80 K (2) in the solid-state. Complex 2 shows weak 3D magnetic interactions at 19 K, which is not observed in 1 or the related [Al(bpy)3] complex.

Growth of metalloid aluminum clusters on graphene vacancies.

Ab initio simulations are used to show that graphene vacancy sites may offer a means of templated growth of metalloid aluminum clusters from their monohalide precursors. We present density functional theory and ab initio molecular dynamics simulations of the aluminum halide AlCl interacting with a graphene surface. Unlike a bare Al adatom, AlCl physisorbs weakly on vacancy-free graphene with little charge transfer and no hybridization with carbon orbitals. The barrier for diffusion of AlCl along the surface is negligible. Covalent bonding is seen only with vacancies and results in strong chemisorption and considerable distortion of the nearby lattice. Car-Parrinello molecular dynamics simulations of AlCl liquid around a graphene single vacancy show spontaneous metalloid cluster growth via a process of repeated insertion reactions. This suggests a means of templated cluster nucleation and growth on a carbon substrate and provides some confirmation for the role of a trivalent aluminum species in nucleating a ligated metalloid cluster from AlCl and AlBr solutions.

Molecular Aluminum Additive for Burn Enhancement of Hydrocarbon Fuels.

Additives to hydrocarbon fuels are commonly explored to change the combustion dynamics, chemical distribution, and/or product integrity. Here we employ a novel aluminum-based molecular additive, Al(I) tetrameric cluster [AlBrNEt3]4 (Et = C2H5), to a hydrocarbon fuel and evaluate the resultant single-droplet combustion properties. This Al4 cluster offers a soluble alternative to nanoscale particulate additives that have recently been explored and may mitigate the observed problems of particle aggregation. Results show the [AlBrNEt3]4 additive to increase the burn rate constant of a toluene-diethyl ether fuel mixture by ∼20% in a room temperature oxygen environment with only 39 mM of active aluminum additive (0.16 wt % limited by additive solubility). In comparison, a roughly similar addition of nano-aluminum particulate shows no discernible difference in burn properties of the hydrocarbon fuel. High speed video shows the [AlBrNEt3]4 to induce microexplosive gas release events during the last ∼30% of the droplet combustion time. We attribute this to HBr gas release based on results of temperature-programmed reaction (TPR) experiments of the [AlBrNEt3]4 dosed with O2 and D2O. A possible mechanism of burn rate enhancement is presented that is consistent with microexplosion observations and TPR results.