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High-resolution X-ray diffraction experiments, theoretical calculations and atom-specific X-ray absorption experiments were used to investigate two nickel complexes, (MePh 3 P) 2 [Ni II (bdtCl 2 ) 2 ]·2(CH 3 ) 2 SO [complex (1)] and (MePh 3 P)[Ni III (bdtCl 2 ) 2 ] [complex (2)]. Combining the techniques of nickel K - and sulfur K -edge X-ray absorption spectroscopy with high-resolution X-ray charge density modeling, together with theoretical calculations, the actual oxidation states of the central Ni atoms in these two complexes are investigated. Ni ions in two complexes are clearly in different oxidation states: the Ni ion of complex (1) is formally Ni II ; that of complex (2) should be formally Ni III , yet it is best described as a combination of Ni 2+ and Ni 3+ , due to the involvement of the non-innocent ligand in the Ni— L bond. A detailed description of Ni—S bond character (σ,π) is presented.
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Scrutinizing formally Ni IV centers through the lenses of core spectroscopy, molecular orbital theory, and valence bond theory
Nickel K- and L 2,3 -edge X-ray absorption spectra (XAS) are discussed for 16 complexes and complex ions with nickel centers spanning a range of formal oxidation states from II to IV. K-edge XAS alone is shown to be an ambiguous metric of physical oxidation state for these Ni complexes. Meanwhile, L 2,3 -edge XAS reveals that the physical d-counts of the formally Ni IV compounds measured lie well above the d 6 count implied by the oxidation state formalism. The generality of this phenomenon is explored computationally by scrutinizing 8 additional complexes. The extreme case of NiF 6 2− is considered using high-level molecular orbital approaches as well as advanced valence bond methods. The emergent electronic structure picture reveals that even highly electronegative F-donors are incapable of supporting a physical d 6 Ni IV center. The reactivity of Ni IV complexes is then discussed, highlighting the dominant role of the ligands in this chemistry over that of the metal centers.
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- PAR ID:
- 10436500
- Publisher / Repository:
- RSC
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 14
- Issue:
- 25
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 6915 to 6929
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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