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

Abstract

Organometallics 2001, 20, 700], have unusual E•••E distances, leading to ambiguities in how to best describe their electronic structure. Three limiting possibilities are considered: case A, in which the compounds contain singly bonded E 2 2− units; case B, in which a threeelectron E∴E half-bond exists in a formal E 2 3− unit; case C, in which two E 2− ions exist with no formal E−E bond. One-electron reduction of 1 and 2 yields the new compounds [Cp* 2 Co][Cp′ 2 Ni 2 E 2 ] (1red: E = S, 2red: 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 1 and 2 is Ni-centered. Density functional theory (DFT) and ab initio multireference methods (CASSCF) have been used to investigate the electronic structures of 1−3 and indicate covalent bonding of an E 2 3− ligand with a mixed-valent Ni 2 (II,III) species. Thus, reduction of 1 and 2 yields Ni 2 (II,II) species 1red and 2red that bear unchanged E 2 3− ligands. We provide strong computational and experimental evidence, including results from a large survey of data from the Cambridge Structural Database, indicating that M 2 E 2 compounds occur in quantized E 2 oxidation states of (2 × E 2− ), E 2 3− , and E 2 2− , rather than displaying a continuum of variable E−E bonding interactions.

In Situ Electrochemical Production of Ultrathin Nickel Nanosheets for Hydrogen Evolution Electrocatalysis

“…As shown in the X-ray absorption near-edge structure (XANES) spectra (Figure 1E), the appearance of a shoulder peak at 8336 eV indicated that Ni 2+ in Ni-BDT was in a low-spin square-planar configuration, in contrast to the high-spin octahedral configuration in Ni(OH) 2 . 42,43 Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra showed that the Ni-O and Ni-Ni bonds in Ni(OH) 2 were replaced by Ni-S bonds in Ni-BDT with a coordination number of $4 (Figure 1F and Table S2), confirming the presence of the NiS 4 coordination motifs as suggested by the observation from the Raman spectra. As revealed by Raman, the BDT ligands in Ni-BDT were fully deprotonated with the absence of S-H vibration.…”

Reactions of Schiff Base‐Substituted Diselenides and ‐tellurides with Ni(II), Pd(II) and Pt(II) Phosphine Complexes

“…Of all ca. 40 structurally characterized compounds with a Ni–Te bond, [Ni(NH‐C 6 H 4 ‐Te) 2 ] as well as [(NiCp i Pr 4 ) 2 ‐µ 2 ‐(Te 2 )] (2.440(2) Å), [ 57 ] [(NiCp i Pr 4 ) 2 ‐µ‐(Te) 2 ] (2.44–2.45 Å), [ 58 ] [CpFe(C 5 H 4 )‐Te(I) 2 Ni(NHC)Cp] (2.4407(8) Å) [ 59 ] and (µ 4 ‐telluro)‐hexakis(µ 3 ‐telluro)‐bis(µ 2 ‐bis(diphenylphosphino)methane)‐bis(η 5 ‐ tert ‐butylcyclopentadienyl)‐pentanickeldiniobium (2.436(5) Å) [ 60 ] show the overall shortest Ni–Te bond lengths. The Ni–Te bond in [Ni(L Te )(PPh 3 )] is therefore not only the shortest so far crystallographically determined Ni–Te bond length for an aryltellurolato ligand, but also the shortest Ni–Te distance observed in any compound with a Ni–Te bond.…”

“…Selected bond lengths [Å] and angles (°) in the dichalcogenides {HL Y } 2 [30] and their nickel, palladium and platinum complexes [M(L Y )(PPh 3 )] (Y = Se, Te). [21,[25][26][27][28][29]34,[36][37][38] and platinum [39][40][41][42][43][44][45][46][47][48][49][50][51][52] [53] Ni(TeMes)Cp(PEt 3 ), [54] [W(CO) 5 -μ-(TePh)NiCp(PPh 3 )] [55] and [57] [(NiCpiPr 4 ) 2 -μ-( Te) 2 ] (2.44-2.45 Å), [58] [CpFe(C 5 H 4 )-Te(I) 2 -Ni(NHC)Cp] (2.4407(8) Å) [59] and (μ 4 -telluro)-hexakis(μ 3 -telluro)bis(μ 2 -bis(diphenylphosphino)methane)-bis(η 5 -tert-butylcyclopentadienyl)-pentanickeldiniobium (2.436(5) Å) [60] show the overall shortest Ni-Te bond lengths. (m/z = 538.0818) can be observed.…”

Two-Center/Three-Electron Sigma Half-Bonds in Main Group and Transition Metal Chemistry

“…In practice, the S K-edge XAS data for Cp′ 2 Ni 2 S 2 are not as easy to interpret. Due to the strong covalency of the Ni–S bonds, there are several unoccupied orbitals in the compound that have Ni–S antibonding character (vide infra), all of which contribute to a strong pre-edge feature in the S XAS spectrum . Because of the prominence of this pre-edge transition, accurate edge energies are difficult to determine.…”