Electronic Structure of
Nickel(II) and Zinc(II) Borohydrides
from Spectroscopic Measurements and Computational Modeling
Patrick J. Desrochers
Christopher
A. Sutton
Micah L. Abrams
Shengfa Ye
Frank Neese
Joshua Telser
Andrew Ozarowski
J. Krzystek
10.1021/ic201775c.s001
https://acs.figshare.com/articles/journal_contribution/Electronic_Structure_of_Nickel_II_and_Zinc_II_Borohydrides_from_Spectroscopic_Measurements_and_Computational_Modeling/2544277
The previously reported Ni(II) complex, Tp*Ni(κ<sup>3</sup>-BH<sub>4</sub>) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate
anion),
which has an <i>S</i> = 1 spin ground state, was studied
by high-frequency and -field electron paramagnetic resonance (HFEPR)
spectroscopy as a solid powder at low temperature, by UV–vis–NIR
spectroscopy in the solid state and in solution at room temperature,
and by paramagnetic <sup>11</sup>B NMR. HFEPR provided its spin Hamiltonian
parameters: <i>D</i> = 1.91(1) cm<sup>–1</sup>, <i>E</i> = 0.285(8) cm<sup>–1</sup>, <b>g</b> = [2.170(4),
2.161(3), 2.133(3)]. Similar, but not identical parameters were obtained
for its borodeuteride analogue. The previously unreported complex,
Tp*Zn(κ<sup>2</sup>-BH<sub>4</sub>), was prepared, and IR and
NMR spectroscopy allowed its comparison with analogous closed shell
borohydride complexes. Ligand-field theory was used to model the electronic
transitions in the Ni(II) complex successfully, although it was less
successful at reproducing the zero-field splitting (zfs) parameters.
Advanced computational methods, both density functional theory (DFT)
and ab initio wave function based approaches, were applied to these
Tp*MBH<sub>4</sub> complexes to better understand the interaction
between these metals and borohydride ion. DFT successfully reproduced
bonding geometries and vibrational behavior of the complexes, although
it was less successful for the spin Hamiltonian parameters of the
open shell Ni(II) complex. These were instead best described using
ab initio methods. The origin of the zfs in Tp*Ni(κ<sup>3</sup>-BH<sub>4</sub>) is described and shows that the relatively small
magnitude of <i>D</i> results from several spin–orbit
coupling (SOC) interactions of large magnitude, but with opposite
sign. Spin–spin coupling (SSC) is also shown to be significant,
a point that is not always appreciated in transition metal complexes.
Overall, a picture of bonding and electronic structure in open and
closed shell late transition metal borohydrides is provided, which
has implications for the use of these complexes in catalysis and hydrogen
storage.
2012-03-05 00:00:00
Ni
ab initio methods
Hamiltonian parameters
magnitude
11 B NMR
zf
transition metal complexes
transition metal borohydrides
ab initio wave function
SSC
cm
DFT
interaction
HFEPR
spectroscopy
UV
Tp
SOC
IR
shell borohydride complexes