# Scorpionate Complexes [(κ n ‑TpPh,Me)NiS2CNR2] (n = 2, 3) as a Structural and Spectroscopic Model for Reduced Nickel-Dependent Superoxide Dismutase

## TL;DR

This paper describes nickel complexes that model the structure and function of a nickel-dependent enzyme involved in neutralizing harmful molecules.

## Contribution

The study introduces new nickel complexes that mimic the reduced state of nickel-dependent superoxide dismutase with variable coordination modes.

## Key findings

- The complexes exhibit different spin states and geometries, including red diamagnetic and green paramagnetic forms.
- X-ray crystallography confirmed the structural diversity of the complexes in the solid state.
- Density Functional Theory calculations aligned the electronic structures of the complexes with those of the enzyme.

## Abstract

Scorpionato-dithiocarbamate Ni­(II) complexes [(TpPh,Me)­NiS2CNR2], where TpPh,Me = hydrotris­(3-phenyl-5-methylpyrazol-1-yl)­borate
and NR2 = NMe2, NEt2, NPh2, carbazolyl, are advanced as structural and spectroscopic models
for the active site of nickel-dependent superoxide dismutase in its
reduced state. The TpPh,Me ligand can adopt variable κ2- and κ3-coordination modes in the synthetic
complexes that give rise to several ligand field conformations: square-planar,
elongated square-pyramidal, square-pyramidal, and trigonal-bipyramidal.
The first two are red and diamagnetic (S = 0), and
the latter two are green and paramagnetic (S = 1).
The different spin states are facilitated by a range of resonance
structures within the dithiocarbamate coligand. These different geometric
and spin isomers have been captured in the solid state and structurally
characterized by X-ray crystallography. Electronic structures of a
simplified [(Tp)­NiS2CNMe2] model in relevant
conformations, spin and oxidation states were calculated using Density
Functional Theory and compared to the enzyme. Reversible one-electron
redox couples were observed at biologically relevant potentials. We
propose that the diamagnetic, square-planar and elongated square-pyramidal
conformations at Ni­(II) are relevant to the base-off and base-on conformations,
respectively, reported for NiSOD.