title: 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: The diamagnetic compounds Cp'2Ni2E2 (1: E = S, 2: E = Se, 3: 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. 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 E2(2-) units; case B, in which a three-electron E∴E half-bond exists in a formal E2(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*2Co][Cp'2Ni2E2] (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 E2(3-) ligand with a mixed-valent Ni2(II,III) species. Thus, reduction of 1 and 2 yields Ni2(II,II) species 1red and 2red 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.
authors: †Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors: Shu A
authors: SA
authors: Yao
authors: ‡Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470, Mülheim/Ruhr, Germany.
authors: Vlad
authors: V
authors: Martin-Diaconescu
authors: §Kimika Fakultatea, Euskal Herriko Unibertsitatea, and Donostia International Physics Center (DIPC), P. K. 1072, 20080 Donostia, Euskadi, Spain.
authors: Ivan
authors: I
authors: Infante
authors: ∥Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
authors: Kyle M
authors: KM
authors: Lancaster
authors: ⊥San Diego Supercomputer Center, University of California-San Diego, La Jolla, California 92093, United States.
authors: Andreas W
authors: AW
authors: Götz
authors: ‡Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470, Mülheim/Ruhr, Germany.|∥Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
authors: Serena
authors: S
authors: DeBeer
authors: †Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors: John F
authors: JF
authors: Berry
mesh_terms: D004583:Electrons; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D012643:Selenium / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*; D013691:Tellurium / Q000737:chemistry*
chemical_list: D013455:Sulfur; D009532:Nickel; D012643:Selenium; D013691:Tellurium