Formation of a Heterometallic Al^III/Sm^III Complex Involving a Novel [EtAl(2-py)₂O]^2– Ligand (2-py = 2‑Pyridyl)

Controlled O₂ oxidation of the Sm­(II) sandwich compound [{EtAl­(2-py)₃}₂­Sm] (<b>1a</b>) gives the Sm­(III)/Al­(III) compound [{EtAl­(2-py)₃}­{EtAl­(2-py)₂O}­Sm]₂ (<b>2</b>), containing the novel multifunctional dianionic ligand [EtAl­(2-py)₂­O]^2–. The formation of an O-bridged Al-O-Sm arrangement in the structure of <b>2</b> is potentially relevant to the catalytic epoxidation of styrene with dry air using heterobimetallic sandwich compounds like <b>1a</b>

Structures, Electronics, and Reactivity of Strained Phosphazane Cages: A Combined Experimental and Computational Study

A series of formamidine-bridged P₂N₂ cages have been prepared. Upon deprotonation, these compounds serve as valuable precursors to hybrid <i>N</i>-heterocyclic carbene ligands, whereas direct metalation gives rearranged dimetallic complexes as a result of cleavage of the formamidine bridge. The latter metal complexes contain an intact cyclophosphazane moiety that coordinates two distinct metal centers in a monodentate and a chelating fashion. A computational study has been carried out to elucidate the bonding within the P₂N₂ framework as well as the reactivity patterns. Natural bond orbital analysis indicates that the cage motif is poorly described by localized Lewis structures and that negative hyperconjugation effects govern the stability of the bicyclic framework. The donor capacity of the cyclophosphazane unit was assessed by inspection of the frontier molecular orbitals, highlighting the fact that π-back-donation from the metal fragments is crucial for effective metal–ligand binding

Structure and Bonding of the Manganese(II) Phosphide Complex (<i>t</i>-BuPH₂)(η⁵-Cp)Mn{μ-(<i>t</i>-BuPH)}₂Mn(Cp)(<i>t</i>-BuPH₂)

Rather than achieving bis-deprotonation of the phosphine, reaction of Cp₂Mn (Cp = cyclopentadienyl) with <i>t</i>-BuPH₂ at room temperature yields monodeprotonation of half of the available phosphine in the product (<i>t</i>-BuPH₂)­(η⁵-Cp)­Mn­{μ-(<i>t</i>-BuPH)}₂Mn­(Cp)­(<i>t</i>-BuPH₂) (<b>1</b>). This complex comprises a Mn­(II) phosphide and is a dimer in the solid state, containing a Mn₂P₂ diamond core. Consistent with the observation of a relatively short intermetal distance of 2.8717(4) Å in <b>1</b>, DFT analysis of the full structure points to a singlet ground state stabilized by a direct Mn–Mn single bond. This is in line with the diamagnetic character of <b>1</b> and an 18-electron count at Mn

Structure and Bonding of the Manganese(II) Phosphide Complex (<i>t</i>-BuPH₂)(η⁵-Cp)Mn{μ-(<i>t</i>-BuPH)}₂Mn(Cp)(<i>t</i>-BuPH₂)

Rather than achieving bis-deprotonation of the phosphine, reaction of Cp₂Mn (Cp = cyclopentadienyl) with <i>t</i>-BuPH₂ at room temperature yields monodeprotonation of half of the available phosphine in the product (<i>t</i>-BuPH₂)­(η⁵-Cp)­Mn­{μ-(<i>t</i>-BuPH)}₂Mn­(Cp)­(<i>t</i>-BuPH₂) (<b>1</b>). This complex comprises a Mn­(II) phosphide and is a dimer in the solid state, containing a Mn₂P₂ diamond core. Consistent with the observation of a relatively short intermetal distance of 2.8717(4) Å in <b>1</b>, DFT analysis of the full structure points to a singlet ground state stabilized by a direct Mn–Mn single bond. This is in line with the diamagnetic character of <b>1</b> and an 18-electron count at Mn

Ab Initio Structure Search and in Situ ⁷Li NMR Studies of Discharge Products in the Li–S Battery System

The high theoretical gravimetric capacity of the Li–S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li–S phase diagram using computational techniques and complement this with an in situ ⁷Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li₂S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li⁺-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li₂S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li₂S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition