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  1. Free, publicly-accessible full text available April 6, 2023
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  3. [PdCl4]2− dianions are oriented within a crystal in such a way that a Cl of one unit approaches the Pd of another from directly above. Quantum calculations find this interaction to be highly repulsive with a large positive interaction energy. The placement of neutral ligands in their vicinity reduces the repulsion, but the interaction remains highly endothermic. When the ligands acquire a unit positive charge, the electrostatic component and the full interaction energy become quite negative, signalling an exothermic association. Raising the charge on these counterions to +2 has little further stabilizing effect, and in fact reduces the electrostatic attraction.more »The ability of the counterions to promote the interaction is attributed in part to the H-bonds which they form with both dianions, acting as a sort of glue.« less
    Free, publicly-accessible full text available April 1, 2023
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  5. The literature contains numerous instances where pairs of anions engage in a stable complex with one another, held together by hydrogen, halogen, and related noncovalent bonds, within the confines of a polarizable medium such as a crystal or solvent. But within the context of the gas phase, such pairs are only metastable, higher in energy than separated monomers, whose favorable dissociation is hindered by an energy barrier. Quantum calculations search for pairs of anions that might engage in a fully stable halogen-bonded dimer in the gas phase, lower in energy than the separate monomers. Each Lewis acid candidate contains anmore »I atom attached to an alkyne, alkene, or alkane chain of variable length, terminated by a O − or COO − group, and decorated with electron-withdrawing CN substituents. Also considered are aromatic systems containing I and COO − , along with four CN substituents on the phenyl ring. Lewis bases considered were of two varieties. In addition to the simple Cl − anion, an NH 2 group was separated from a terminal carboxylate by an alkyne chain of variable length. Exothermic association reactions are achieved with Cl − paired with CN-substituted alkenes and alkanes where the I and COO − of the Lewis acid are separated by at least four C atoms. The energetics are especially favorable for the longer alkanes where Δ E is roughly −30 kcal mol −1 .« less
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  8. The possibility of the transfer of the TH 3 group across a tetrel bond is considered by ab initio calculations. The TB is constructed by pairing PhTH 3 (Ph = phenyl; T = Si and Ge) with bases NH 3 , NHCH 2 , and the C 3 N 2 H 4 carbene. The TH 3 moves toward the base but only by a small amount in these dimers. However, when a Be 2+ or Mg 2+ dication is placed above the phenyl ring, the tetrel bond strength is greatly magnified reaching up to nearly 100 kcal mol −1 .more »This dication also induces a much higher degree of transfer which can be best categorized as half-transfer for the two N-bases and a near complete transfer for the carbene.« less
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  10. Inspection of the arrangement of tetrachloridopalladate( ii ) centers in a crystalline solid places the Cl of one [PdCl 4 ] 2− directly above the Pd center of its neighbor. A survey of the CSD provides 22 more examples of such MX 4 2− ⋯MX 4 2− complexes, with M being a Group 10 metal and X = Cl, Br, or I. Quantum calculations attribute this arrangement to a π-hole bond wherein Cl lone pairs of one unit transfer charge to vacant orbitals above the Pd center of its neighbor. The stabilizing effect of this bond must overcome the strongmore »Coulombic repulsion between the two dianions, which is facilitated by a polarizable environment as would be present in a crystal, but much more so when the effects of the neighboring counterions are factored in. These conclusions are extended to other [MX 4 ] 2− homodimers, where M represents other members of Group 10, namely Ni and Pt.« less
    Free, publicly-accessible full text available December 9, 2022