An “Intermediate Spin” Nickel Hydride Complex Stemming from Delocalized Ni₂(μ-H)₂ Bonding

The nickel hydride complex [Cp′Ni­(μ-H)]₂ (<b>1</b>, Cp′ = 1,2,3,4-tetra­isopropyl­cyclo­penta­dienyl) is found to have a strikingly short Ni–Ni distance of 2.28638(3) Å. Variable temperature and field magnetic measurements indicate an unexpected triplet ground state for <b>1</b> with a large zero-field splitting of +90 K (63 cm^–1). Electronic structure calculations (DFT and CASSCF/CASPT2) explain this ground state as arising from half occupation of two nearly degenerate Ni–Ni π* orbitals

Covalent Attachment of Catalyst Molecules to Conductive Diamond: CO₂ Reduction Using “Smart” Electrodes

We report here covalent attachment of a catalytically active cobalt complex onto boron-doped, p-type conductive diamond. Peripheral acetylene groups were appended on a cobalt porphyrin complex, and azide–alkyne cycloaddition was used for covalent linking to a diamond surface decorated with alkyl azides. The functionalized surface was characterized by X-ray photoelectron spectroscopy and Fourier transform IR spectroscopy, and the catalytic activity was characterized using cyclic voltammetry and FTIR. The catalyst-modified diamond surfaces were used as “smart” electrodes exhibiting good stability and electrocatalytic activity for electrochemical reduction of CO₂ to CO in acetonitrile solution

Electronic Structure of Ni₂E₂ Complexes (E = S, Se, Te) and a Global Analysis of M₂E₂ Compounds: A Case for Quantized E₂^<i>n</i>– Oxidation Levels with <i>n</i> = 2, 3, or 4

The diamagnetic compounds Cp′₂Ni₂E₂ (<b>1</b>: E = S, <b>2</b>: E = Se, <b>3</b>: E = Te; Cp′ = 1,2,3,4,-tetraisopropylcyclopentadienyl), first reported by Sitzmann and co-workers in 2001 [Sitzmann, H.; Saurenz, D.; Wolmershauser, G.; Klein, A.; Boese, R. <i>Organometallics</i> <b>2001</b>, 20, 700], have unusual E···E distances, leading to ambiguities in how to best describe their electronic structure. Three limiting possibilities are considered: case <b>A</b>, in which the compounds contain singly bonded E₂^2– units; case <b>B</b>, in which a three-electron E∴E half-bond exists in a formal E₂^3– unit; case <b>C</b>, in which two E^2– ions exist with no formal E–E bond. One-electron reduction of <b>1</b> and <b>2</b> yields the new compounds [Cp*₂Co]­[Cp′₂Ni₂E₂] (<b>1red</b>: E = S, <b>2red</b>: E = Se; Cp* = 1,2,3,4,5-pentamethylcyclopentadieyl). Evidence from X-ray crystallography, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy suggest that reduction of <b>1</b> and <b>2</b> is Ni-centered. Density functional theory (DFT) and ab initio multireference methods (CASSCF) have been used to investigate the electronic structures of <b>1</b>–<b>3</b> and indicate covalent bonding of an E₂^3– ligand with a mixed-valent Ni₂(II,III) species. Thus, reduction of <b>1</b> and <b>2</b> yields Ni₂(II,II) species <b>1red</b> and <b>2red</b> that bear unchanged E₂^3– ligands. We provide strong computational and experimental evidence, including results from a large survey of data from the Cambridge Structural Database, indicating that M₂E₂ compounds occur in quantized E₂ oxidation states of (2 × E^2–), E₂^3–, and E₂^2–, rather than displaying a continuum of variable E–E bonding interactions

Electronic Structure of Ni₂E₂ Complexes (E = S, Se, Te) and a Global Analysis of M₂E₂ Compounds: A Case for Quantized E₂^<i>n</i>– Oxidation Levels with <i>n</i> = 2, 3, or 4

The diamagnetic compounds Cp′₂Ni₂E₂ (<b>1</b>: E = S, <b>2</b>: E = Se, <b>3</b>: E = Te; Cp′ = 1,2,3,4,-tetraisopropylcyclopentadienyl), first reported by Sitzmann and co-workers in 2001 [Sitzmann, H.; Saurenz, D.; Wolmershauser, G.; Klein, A.; Boese, R. <i>Organometallics</i> <b>2001</b>, 20, 700], have unusual E···E distances, leading to ambiguities in how to best describe their electronic structure. Three limiting possibilities are considered: case <b>A</b>, in which the compounds contain singly bonded E₂^2– units; case <b>B</b>, in which a three-electron E∴E half-bond exists in a formal E₂^3– unit; case <b>C</b>, in which two E^2– ions exist with no formal E–E bond. One-electron reduction of <b>1</b> and <b>2</b> yields the new compounds [Cp*₂Co]­[Cp′₂Ni₂E₂] (<b>1red</b>: E = S, <b>2red</b>: E = Se; Cp* = 1,2,3,4,5-pentamethylcyclopentadieyl). Evidence from X-ray crystallography, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy suggest that reduction of <b>1</b> and <b>2</b> is Ni-centered. Density functional theory (DFT) and ab initio multireference methods (CASSCF) have been used to investigate the electronic structures of <b>1</b>–<b>3</b> and indicate covalent bonding of an E₂^3– ligand with a mixed-valent Ni₂(II,III) species. Thus, reduction of <b>1</b> and <b>2</b> yields Ni₂(II,II) species <b>1red</b> and <b>2red</b> that bear unchanged E₂^3– ligands. We provide strong computational and experimental evidence, including results from a large survey of data from the Cambridge Structural Database, indicating that M₂E₂ compounds occur in quantized E₂ oxidation states of (2 × E^2–), E₂^3–, and E₂^2–, rather than displaying a continuum of variable E–E bonding interactions