The electronic structure of platinum and palladium nitrosyls

By: Matthew J. G. Sinclair, Nil Roig, Nikolaos Tsoureas, Mercedes Alonso, Adrian B. Chaplin

Transition metal nitrosyl complexes are coordination compounds with applications ranging from catalysis to environmental remediation. These complexes play a crucial role in catalytic processes, particularly in reducing nitrogen oxides (NOx), yet their bonding characteristics are not fully understood.

Using advanced computational techniques and high-performance computing resources provided by the Vlaams Supercomputer Centrum (VSC), we investigated the electronic structure and bonding characteristics of a series of {MNO}10 nitrosyl complexes of the form [M(PR3)2(NO)]+ (M = Pd, Pt; R = tBu, Ad) and [Pd(Pincer)(NO)]+ (Pincer = PNP-tBu, PONOP-tBu). Our findings revealed unique bonding patterns and steric effects that challenge traditional coordination chemistry models.

Figure 1. X-ray crystal structures of some of the complexes

Computational Approach

To gain deeper insights into the electronic structure of these complexes, we employed Density Functional Theory (DFT) calculations alongside energy decomposition analysis (EDA), natural orbitals for chemical valence (NOCV), and effective oxidation state analysis (EOS). These methods allowed us to predict molecular structures with high accuracy, analyze the metal-nitrosyl bonding interactions, and deconvolute their stabilizing contributions.

This computational workflow was carried out using VSC’s high-performance computing infrastructure, enabling accurate simulations that would otherwise be computationally prohibitive.

Key Findings

Our computational analysis confirmed that the {MNO}10 complexes adopt a bent coordination mode, which by convention is usually characterized as NO -, suggesting a positive Pd/Pt +2 oxidation state. However, our calculations revealed that this bent geometry results from a delicate balance between electronic preferences and steric effects imposed by bulky phosphine ligands. The electronic study resulted in an M(0)/NO+ distribution with strong covalent interactions between the metals and the nitrosyls. This type of metal–nitrosyl interactions typically favour linear coordination modes, but the steric bulk of the supporting ligands bent the nitrosyl away from linearity.

These findings provide valuable insights into the electronic properties of late-transition metal nitrosyl complexes and their reactivity, shedding light on their potential applications in catalytic NOx reduction.

Figure 2. NOCV deformation densities of [Pd(PONOP-tBu)(NO)]+ (top) and activation strain model (ASM) deconvolutions of changing the M–N–O angle in [M(PtBu3)2(NO)]+ (M = Pd, Pt) (bottom).

Conclusion & Impact

Our study demonstrates the usefulness of computational chemistry in resolving complex bonding phenomena in inorganic chemistry and challenges conventional assumptions in the characterization of complex compounds. By leveraging VSC’s high-performance computing resources, we were able to characterize and rationalize these unique electronic structures.

The implications of this work extend to catalyst design and environmental chemistry, as a deeper understanding of metal-nitrosyl interactions can inform the development of more efficient catalytic systems for NOx abatement. Moving forward, further computational and experimental investigations could explore the reactivity and potential functionalization of these complexes, paving the way for new applications in sustainable chemistry.

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Read the full published article in Chemistry Europe here