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Published November 18, 2019 | Supplemental Material
Journal Article Open

Electronic Structure of Tetracyanonickelate(II)

Abstract

Tetracyanonickelate(II) has been a poster child of ligand field theory for several decades. We have revisited the literature assignments of the absorption spectrum of [Ni(CN) ₄]²⁻ and the calculated ordering of orbitals with metal d character. Using low-temperature single-crystal absorption spectroscopy and accurate ab initio and density functional quantum mechanical methods (NEVPT2-CASSCF, EOM-CCSD, TD-DFT), we find an ordering of the frontier d- and p-orbitals of xy < xz, yz < z² < z < x²–y² < x, y and assign the d-d bands in the absorption spectrum to ¹A_(1g) → ³B_(1g) < ³E_g < ³A_(2g) < ¹B_(1g) < ¹E_g < ¹A_(2g). While differing from all previous interpretations, our assignments accord with an MO model in which strong π-backbonding in the plane of the molecule stabilizes d_(xy) more than out-of-plane bonding stabilizes d_(xz) and d_(yz).

Additional Information

© 2019 American Chemical Society. Received: July 17, 2019; Published: November 7, 2019. Time on a computing cluster was provided by the Beckman Institute Materials and Process Simulation Center; absorption spectroscopy was performed in the BI Laser Center (with assistance from Jay Winkler). We thank Garnet Chan, Daniel Weitekamp, Thomas Gallup, Christopher Lamartina, Jonathan Chan, and Kaitlyn Takata for helpful discussions. Our work was supported by NSF CHE-1763429. The authors also appreciate and acknowledge a quote given in a lecture at the ICCC meeting in Vienna in 1964 by one of the authors of this paper (H.B.G.), where he announced: "As there are so many square planar d-orbital energy orderings in the literature, one must be correct, so all we need to do is to find who found it!" The authors declare no competing financial interest.

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August 19, 2023
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October 18, 2023