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Chiral Pt(Me-BPCH): Synthesis and theoretical investigation of parity violation sensitivity

Eduardus, J. Wietze J. van Boven, Charles Silva, Philip Karageorghis, D. Scott Bohle, Benoît Darquié, Anastasia Borschevsky, Lukáš F. Pašteka

TL;DR

This work addresses the challenge of detecting parity-violating energy differences in chiral molecules by leveraging heavy-metal complexes to amplify PV effects in vibrational spectra. It combines a synthesis of Pt(Me-BPCH) with a computational workflow to predict PV-induced shifts for Pt-Me-BPCH and two derivatives, Au-Me-BPCH and Pt(CF$_3$-BPCH), across 500–2000 cm$^{-1}$. The study finds PV sensitivities in the 10$^{-14}$–10$^{-13}$ range for many transitions, identifies mode families (e.g., skeletal deformations and C=O stretches) with strong PV signals, and notes sign and redistribution differences between Pt and Au derivatives due to electronic structure changes. It highlights experimentally accessible targets, particularly around 1750 cm$^{-1}$ with high IR intensity, and outlines a path toward an actual PV measurement using Ramsey spectroscopy and metrology-grade mid-IR lasers, reinforcing the potential of heavy-metal chiral complexes as platforms for low-energy tests of the Standard Model.

Abstract

A complex of platinum and the tetra-coordinate chelating ligand, R,R'-6,6'-dimethyl-N,N'-bis(2'-pyridine-carboxamide)-1-cyclohexane (Me-BPCH) is investigated as a potential candidate for measurement of parity violation (PV) in chiral molecules. The synthesis of Pt(Me-BPCH) is presented alongside computational investigation of PV sensitivity in its vibrational spectrum. Pt(Me-BPCH) is compared to other two derivatives of this complex, Au(Me-BPCH) and Pt(CF$_3$-BPCH) in terms of their PV response and suitability for measurement. We identify the most promising vibrational transitions based on their enhanced PV effects and practical experimental considerations and analyze the relationship between the vibrational structure and the corresponding PV sensitivity for all three molecules.

Chiral Pt(Me-BPCH): Synthesis and theoretical investigation of parity violation sensitivity

TL;DR

This work addresses the challenge of detecting parity-violating energy differences in chiral molecules by leveraging heavy-metal complexes to amplify PV effects in vibrational spectra. It combines a synthesis of Pt(Me-BPCH) with a computational workflow to predict PV-induced shifts for Pt-Me-BPCH and two derivatives, Au-Me-BPCH and Pt(CF-BPCH), across 500–2000 cm. The study finds PV sensitivities in the 10–10 range for many transitions, identifies mode families (e.g., skeletal deformations and C=O stretches) with strong PV signals, and notes sign and redistribution differences between Pt and Au derivatives due to electronic structure changes. It highlights experimentally accessible targets, particularly around 1750 cm with high IR intensity, and outlines a path toward an actual PV measurement using Ramsey spectroscopy and metrology-grade mid-IR lasers, reinforcing the potential of heavy-metal chiral complexes as platforms for low-energy tests of the Standard Model.

Abstract

A complex of platinum and the tetra-coordinate chelating ligand, R,R'-6,6'-dimethyl-N,N'-bis(2'-pyridine-carboxamide)-1-cyclohexane (Me-BPCH) is investigated as a potential candidate for measurement of parity violation (PV) in chiral molecules. The synthesis of Pt(Me-BPCH) is presented alongside computational investigation of PV sensitivity in its vibrational spectrum. Pt(Me-BPCH) is compared to other two derivatives of this complex, Au(Me-BPCH) and Pt(CF-BPCH) in terms of their PV response and suitability for measurement. We identify the most promising vibrational transitions based on their enhanced PV effects and practical experimental considerations and analyze the relationship between the vibrational structure and the corresponding PV sensitivity for all three molecules.

Paper Structure

This paper contains 10 sections, 2 equations, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Material and Methods
  3. Synthesis of Pt(Me-BPCH)
  4. Computational Details
  5. Outline of the planned PV measurement
  6. Results and discussion
  7. Characterization and comparison to theory
  8. Sensitivity to Parity Violation
  9. Measurement prospects
  10. Conclusions and outlook

Figures (4)

  • Figure 1: Thermal ellipsoid plot of Pt(Me-BPCH). Note, the asymmetric unit contains two complexes. Key metric parameters (°,Å) include: Pt(1)-N(1) 1.971(8), Pt(1)-N(2) 1.954(7), Pt(1)-N(3) 2.064(3), Pt(1)-N(4) 2.069(7), N(1)-C(2) 1.327(12), C(2)-O(1) 1.251(11), N(2)-C(3) 1.343(11), C(3)-O(2) 1.224(11), N(1)-Pt(1)-N(2) 85.2(3), N(3)-Pt(1)-N(4) 114.0(3). Top: view perpendicular to the C$_2$ axis; bottom: view along C$_2$ axis.
  • Figure 2: Schematic representation of the left- (S) and right-handed (R) enantiomers of Pt(Me-BPCH) and response of their respective vibrational transitions to parity violation effects.
  • Figure 3: Comparison of the experimental (KBr matrix) and calculated IR spectra of Pt(Me-BPCH). Both spectra are normalized to the highest peak. The calculated stick spectrum is based on harmonic vibrational analysis with empirically scaled frequencies using a factor 0.94. The experimental spectrum is vertically shifted for increased legibility.
  • Figure 4: Comparison of the potential energy curves $V(q)$ (blue lines) and the PV potential curves $V^\text{PV}(q)$ (red lines) of the asymmetric (top) and symmetric (bottom) C=O strecthing modes of Pt(Me-BPCH), Au(Me-BPCH) and Pt(CF$_3$-BPCH). The displacement vectors (i.e. the $q$ axes) are aligned and oriented in the same direction for easier visual comparison.