# Tailored GAFF Parameters for Pentamethylcyclopentadienyl Rh(I/III) Complexes with α‑Diimine Ligands: Validation and Solvation Studies

## TL;DR

This paper develops and validates molecular dynamics parameters for rhodium complexes with specific ligands, enabling accurate simulations of their solvation and structural behavior.

## Contribution

The paper introduces tailored GAFF parameters for Rh(I/III) complexes with α-diimine ligands, validated against DFT data and applied to solvation studies.

## Key findings

- Tailored GAFF parameters accurately model Rh–Cp* bonding using a σ-bonded approach.
- Validation against DFT data confirms accuracy in bond lengths, angles, and energy profiles.
- Solvation studies reveal structural and environmental interactions in aqueous solutions.

## Abstract

Rhodium­(III) complexes of the general structure [(bpy)­Rh­(Cp*)­X]
n+ (bpy = 2,2′-bipyridine, Cp* = pentamethylcyclopentadienyl,
X = H2O, OH–, Cl–)
are potent catalysts in a wide range of reactions, including NAD+ reduction and NADH oxidation, CO2 reduction, and
hydrogenation of small organic molecules. Computational studies of
these complexes require tailored force field parameters for accurate
classical molecular dynamics. Here, we develop parameters compatible
with the general Amber force field for [(bpy)­RhIII(Cp*)­Cl]+ and the reduced [(bpy)­RhI(Cp*)], an important
intermediate in many applications. As the general Amber force field
is unable to describe the η5 hapticity of the Rh–Cp*
bond, we implement a σ-bonded model. The force field is validated
against density functional theory reference data including bond lengths,
angles, dihedrals, and potential energy profiles. Finally, we demonstrate
its applicability by analyzing the aqueous solvation environment around
the RhIII and RhI complexes, highlighting its
utility for studying structure–environment interactions.