3D-RISM-MP2 Approach to Hydration Structure of Pt(II)
and Pd(II) Complexes: Unusual H‑Ahead Mode vs Usual O‑Ahead
One
Shinji Aono
Toshifumi Mori
Shigeyoshi Sakaki
10.1021/acs.jctc.5b01137.s001
https://acs.figshare.com/articles/journal_contribution/3D_RISM_MP2_Approach_to_Hydration_Structure_of_Pt_II_and_Pd_II_Complexes_Unusual_H_Ahead_Mode_vs_Usual_O_Ahead_One/2823544
Solvation of transition metal complexes
with water has been one
of the fundamental topics in physical and coordination chemistry.
In particular, Pt(II) complexes have recently attracted considerable
interest for their relation to anticancer activity in cisplatin and
its analogues, yet the interaction of the water molecule and the metal
center has been obscured. The challenge from a theoretical perspective
remains that both the microscopic solvation effect and the dynamical
electron correlation (DEC) effect have to be treated simultaneously
in a reasonable manner. In this work we derive the analytical gradient
for the three-dimensional reference interaction site model Møller–Plesset
second order (3D-RISM-MP2) free energy. On the basis of the three-regions
3D-RISM self-consistent field (SCF) method recently proposed by us,
we apply a new layer of the Z-vector method to the CP-RISM equation
as well as point-charge approximation to the derivatives with respect
to the density matrix elements in the RISM-CPHF equation to remarkably
reduce the computational cost. This method is applied to study the
interaction of H<sub>2</sub>O with the d<sup>8</sup> square planar
transition metal complexes in aqueous solution, trans-[Pt<sup>II</sup>Cl<sub>2</sub>(NH<sub>3</sub>)(glycine)] (<b>1a</b>), [Pt<sup>II</sup>(NH<sub>3</sub>)<sub>4</sub>]<sup>2+</sup> (<b>1b</b>), [Pt<sup>II</sup>(CN)<sub>4</sub>]<sup>2–</sup> (<b>1c</b>), and their Pd(II) analogues <b>2a</b>, <b>2b</b>, and <b>2c</b>, respectively, to elucidate whether the usual H<sub>2</sub>O interaction through O atom (O-ahead mode) or unusual one through
H atom (H-ahead mode) is stable in these complexes. We find that the
interaction energy of the coordinating water and the transition metal
complex changes little when switching from gas to aqueous phase, but
the solvation free energy differs remarkably between the two interaction
modes, thereby affecting the relative stability of the H-ahead and
O-ahead modes. Particularly, in contrast to the expectation that the
O-ahead mode is preferred due to the presence of positive charges
in <b>1b</b>, the H-ahead mode is also found to be more stable.
The O-ahead mode is found to be more stable than the H-ahead one only
in <b>2b</b>. The energy decomposition analysis (EDA) at the
3D-RISM-MP2 level revealed that the O-ahead mode is stabilized by
the electrostatic (ES) interaction, whereas the H-ahead one is mainly
stabilized by the DEC effect. The ES interaction is also responsible
for the difference between the Pd(II) and Pt(II) complexes; because
the electrostatic potential is more negative along the <i>z</i>-axis in the Pt(II) complex than in the Pd(II) one, the O-ahead mode
prefers the Pd(II) complexes, whereas the H-ahead becomes predominant
in the Pt(II) complexes.
2016-02-10 00:00:00
2 b
Pt
density matrix elements
Pd
DEC
SCF
H 2O interaction
reference interaction site model M øller
ES
EDA
energy decomposition analysis
transition metal complexes