Ni(salen): a System That Forms Many Solvates with Interacting Ni Atoms

Recrystallization of [N,N’-Ethylene-bis(salicylideneiminato)]-nickel(II) [Ni(salen)] has been carried out from a large selection of solvents. Crystals can be either solvent free or solvates. This study is based on X-ray crystal structure determinations, which include the redetermination of Ni(salen) at low-temperature, the finding of three new solvates of Ni(salen), that is, Ni(salen)·CH2Cl2, Ni(salen)·AcOH, and Ni(salen)·1.5MeOH, and the reexamination of the known solvate Ni(salen)·chloroform at low- and room-temperature. The crystal structures of Ni(salen) and its solvates are stabilized by salen···salen and/or solvent···salen and/or solvent···solvent intermolecular interactions. A special case is the crystal structure of Ni(salen)·1.5MeOH where the salen/solvent ratio is 2:3 rather than 1:1. For all solvated structures, the solvent and Ni(salen) molecules always interact via Dsolvent−H···Osalen (Dsolvent = C, O) hydrogen bond interactions, the strengths of which depend on the solvent of recrystallization. All structures are characterized by weak Ni−Ni interactions, which are found either in centrosymmetric dimeric units or along one-dimensional chains. Such interactions are favored because of the d8 electronic configuration of Ni(II) and the pseudoplanar geometry of Ni(salen)

Ni(salen): a System That Forms Many Solvates with Interacting Ni Atoms

Recrystallization of [N,N’-Ethylene-bis(salicylideneiminato)]-nickel(II) [Ni(salen)] has been carried out from a large selection of solvents. Crystals can be either solvent free or solvates. This study is based on X-ray crystal structure determinations, which include the redetermination of Ni(salen) at low-temperature, the finding of three new solvates of Ni(salen), that is, Ni(salen)·CH2Cl2, Ni(salen)·AcOH, and Ni(salen)·1.5MeOH, and the reexamination of the known solvate Ni(salen)·chloroform at low- and room-temperature. The crystal structures of Ni(salen) and its solvates are stabilized by salen···salen and/or solvent···salen and/or solvent···solvent intermolecular interactions. A special case is the crystal structure of Ni(salen)·1.5MeOH where the salen/solvent ratio is 2:3 rather than 1:1. For all solvated structures, the solvent and Ni(salen) molecules always interact via Dsolvent−H···Osalen (Dsolvent = C, O) hydrogen bond interactions, the strengths of which depend on the solvent of recrystallization. All structures are characterized by weak Ni−Ni interactions, which are found either in centrosymmetric dimeric units or along one-dimensional chains. Such interactions are favored because of the d8 electronic configuration of Ni(II) and the pseudoplanar geometry of Ni(salen)

A Protonated Quinone Methide Stabilized by a Combination of Partial Aromatization and π‑Interaction: Spectroscopic and Crystallographic Analysis

We have expanded the repertoire of cation−π interactions to include a carbocation−π system resulting from the protonation of a π-stacked para-quinone methide (p-QM). This unusual carbocation is stabilized by a combination of partial aromatization of the QM moiety and through-space interaction with the π-system of the adjacent aromatic ring. Single crystal X-ray analysis of the protonated form reveals a structure consisting of a hydrogen-bound complex involving two molecules of the precursor and one proton

Close Amide NH···F Hydrogen Bonding Interactions in 1,8-Disubstituted Naphthalenes

In this note, we present a series of N-(8-fluoronaphthalen-1-yl)­benzamide derivatives designed to maximize amide-NH···F hydrogen bond interactions therein. A combination of IR and NMR spectroscopy indicates a linear correlation between the high energy shift in NH stretching frequency and the electron withdrawing nature of the substituent, consistent with the trend predicted by DFT calculations. Additionally, a limiting case of hydrogen bonding is observed when the benzamide derivatives are replaced with trifluoroacetamide, causing an additional red shift of 44 cm–1 in the NH stretching frequency. Most importantly, 1H–19F coupling constants in this series are among the largest measured for amide-NH···F interactions. X-ray crystallography reveals face-to-face alignment of naphthalene rings in these derivatives resulting in part from the NH···F hydrogen bonds. This motif also dictates the formation of sheets composed of stacked naphthalene rings in the crystal structure as opposed to unfluorinated analogues wherein NH···OC hydrogen-bonding interactions force benzamide and naphthalene rings to engage in T-shaped π–π interactions instead. Additionally, the NH proton in the trifluoroacetamide derivative engages in extended H-bond interactions in its crystal structure

A Protonated Quinone Methide Stabilized by a Combination of Partial Aromatization and π‑Interaction: Spectroscopic and Crystallographic Analysis

We have expanded the repertoire of cation−π interactions to include a carbocation−π system resulting from the protonation of a π-stacked para-quinone methide (p-QM). This unusual carbocation is stabilized by a combination of partial aromatization of the QM moiety and through-space interaction with the π-system of the adjacent aromatic ring. Single crystal X-ray analysis of the protonated form reveals a structure consisting of a hydrogen-bound complex involving two molecules of the precursor and one proton

A Case of Serendipity: Synthesis, Characterization, and Unique Chemistry of a Stable, Ring-Unsubstituted Aliphatic <i>p</i>‑Quinone Methide

We report the serendipitous synthesis of an indefinitely solution-stable ring-unsubstituted aliphatic p-quinone methide (p-QM) and detail its remarkable reaction chemistry through three archetypical chemical transformations: hydrogenation, hydride reduction, and nucleophilic addition. For example, the p-QM hydrogenates in a counterintuitive way; it resists all attempts at aromatization by catalytic reduction. Paradoxically, it does undergo aromatization/rearrangement upon reduction with LiAlH4. Nucleophilic addition of thiol results in an unanticipated rearrangement instead of the expected 1,6-conjugate addition. We hope that this highly stable p-QM and its unique reactivity provide some new insights into the chemistry of this important class of organic molecules

Close Amide NH···F Hydrogen Bonding Interactions in 1,8-Disubstituted Naphthalenes

In this note, we present a series of N-(8-fluoronaphthalen-1-yl)­benzamide derivatives designed to maximize amide-NH···F hydrogen bond interactions therein. A combination of IR and NMR spectroscopy indicates a linear correlation between the high energy shift in NH stretching frequency and the electron withdrawing nature of the substituent, consistent with the trend predicted by DFT calculations. Additionally, a limiting case of hydrogen bonding is observed when the benzamide derivatives are replaced with trifluoroacetamide, causing an additional red shift of 44 cm–1 in the NH stretching frequency. Most importantly, 1H–19F coupling constants in this series are among the largest measured for amide-NH···F interactions. X-ray crystallography reveals face-to-face alignment of naphthalene rings in these derivatives resulting in part from the NH···F hydrogen bonds. This motif also dictates the formation of sheets composed of stacked naphthalene rings in the crystal structure as opposed to unfluorinated analogues wherein NH···OC hydrogen-bonding interactions force benzamide and naphthalene rings to engage in T-shaped π–π interactions instead. Additionally, the NH proton in the trifluoroacetamide derivative engages in extended H-bond interactions in its crystal structure

Heme/Copper Assembly Mediated Nitrite and Nitric Oxide Interconversion

The heme_<i>a</i>3/Cu_B active site of cytochrome <i>c</i> oxidase is responsible for cellular nitrite reduction to nitric oxide; the same center can return NO to the nitrite pool via oxidative chemistry. Here, we show that a partially reduced heme/Cu assembly reduces NO₂^– ion, producing nitric oxide. The heme serves as the reductant, but the Cu^II ion is also required. In turn, a μ-oxo heme-Fe^III–O–Cu^II complex facilitates NO oxidation to nitrite; the final products are the reduced heme and Cu^II–nitrito complexes