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. 2023 Jan 30;62(4):1405-1413.
doi: 10.1021/acs.inorgchem.2c03381. Epub 2023 Jan 12.

Two-Electron Mixed Valency in a Heterotrimetallic Nickel-Vanadium-Nickel Complex

Michael K Wojnar  1 , Joseph W Ziller  1 , Alan F Heyduk  1
Affiliations

Two-Electron Mixed Valency in a Heterotrimetallic Nickel-Vanadium-Nickel Complex

Michael K Wojnar et al. Inorg Chem. .

Abstract

Mixed-valence complexes represent an enticing class of coordination compounds to interrogate electron transfer confined within a molecular framework. The diamagnetic heterotrimetallic anion, [V(SNS)2{Ni(dppe)}2]-, was prepared by reducing (dppe)NiCl2 in the presence of the chelating metalloligand [V(SNS)2]- [dppe = bis(diphenylphosphino)ethane; (SNS)3- = bis(2-thiolato-4-methylphenyl)amide]. Vanadium-nickel bonds span the heterotrimetallic core in the structure of [V(SNS)2{Ni(dppe)}2]-, with V-Ni bond lengths of 2.78 and 2.79 Å. One-electron oxidation of monoanionic [V(SNS)2{Ni(dppe)}2]- yielded neutral, paramagnetic V(SNS)2{Ni(dppe)}2. The solid-state structure of V(SNS)2{Ni(dppe)}2 revealed that the two nickel ions occupy unique coordination environments: one nickel is in a square-planar S2P2 coordination environment (τ4 = 0.19), with a long Ni···V distance of 3.45 Å; the other nickel is in a tetrahedral S2P2 coordination environment (τ4 = 0.84) with a short Ni-V distance of 2.60 Å, consistent with a formal metal-metal bond. Continuous-wave X-band electron paramagnetic resonance spectroscopy, electrochemical investigations, and density functional theory computations indicated that the unpaired electron in the neutral V(SNS)2{Ni(dppe)}2 cluster is localized on the bridging [V(SNS)2] metalloligand, and as a result, V(SNS)2{Ni(dppe)}2 is best described as a two-electron mixed-valence complex. These results demonstrate the important role that metal-metal interactions and flexible coordination geometries play in enabling multiple, reversible electron transfer processes in small cluster complexes.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1
Figure 1
Figure 1
ORTEPs of (left) [K(18-crown-6) (THF)2][V(SNS)2{Ni(dppe)}2] and (right) V(SNS)2{Ni(dppe)}2 with thermal ellipsoids shown at 50% probability. Hydrogen atoms, solvent molecules, and counterions have been omitted for clarity.
Figure 2
Figure 2
ORTEP of trimetallic cores of (top) anionic [V(SNS)2{Ni(dppe)}2]1– and (bottom) neutral V(SNS)2{Ni(dppe)}2 with thermal ellipsoids shown at 50% probability. A full list of bond distances and angles is included in the Supporting Information.
Figure 3
Figure 3
Solution cw X-band EPR spectra in THF of (top) in situ-prepared [V(SNS)2]2– and (bottom) V(SNS)2{Ni(dppe)}2 at 298 K.
Figure 4
Figure 4
Cyclic voltammograms of (top, blue) [V(SNS)2]1– and (bottom, green) V(SNS)2{Ni(dppe)}2 in THF containing 0.1 M [Bu4N][PF6], referenced to [Cp2Fe]+/0. Data were collected using a glassy carbon working electrode and a 200 mV s–1 scan rate. The arrow denotes the open-circuit potential and the direction of the scan.
Figure 5
Figure 5
Kohn–Sham SOMO of V(SNS)2{Ni(dppe)}2 with isovalues 0.1, as determined by DFT computations at the tpss/def2-TZVP level of theory.
Figure 6
Figure 6
(Top) Scheme denoting formal oxidation state assignments for [V(SNS)2Ni(dppe)}2]0/+ and (bottom) overlay of differential pulse voltammograms of V(SNS)2{Ni(dppe)}2 (green) and [V(SNS)2]2– (blue) in THF, denoting the locality of the redox couples [nickel (orange); vanadium (blue)].
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