External electric fields drive the formation of P → C dative bonds

Abstract

Chemical interactions driven by external electric fields (EFs) can serve as a catalytic force for molecular machines and linkers for smart materials. In this context, the EF-driven dative bond is demonstrated through the study of interactions between PH₃ and curved carbon-based nanostructures. The P → C dative bonds emerge only in the presence of EFs, whereas the interactions in the absence of EFs lead to van der Waals (vdW) complexes. The formation of EF-driven dative bonds can be verified with distinctive signals in vibrational, carbon-13 NMR, and UV/vis spectra. The nature of EF-driven dative bonds was theoretically analyzed with the block-localized wavefunction (BLW) method and the associated energy decomposition (BLW-ED) approach. It was found that the charge transfer interaction plays a dominating role and that even in the presence of EFs, complexes dissociate to monomers once the charge transfer interaction is "turned off". Notably, the inter-fragment orbital mixing stabilizes the complexes and alters their multipoles, leading to additional stability through field-multipole interactions. This conclusion was supported by further decomposition of the charge transfer energy component, clarifying the precise role of orbital mixing. The inter-fragment orbital mixing, which occurs exclusively in the presence of EFs, was elucidated using "in situ" orbital correlation diagrams. Specifically, both external EFs and intermolecular perturbations remarkably reduce the energy gap between the frontier orbitals of the monomers, thereby facilitating inter-fragment orbital interactions. Significant covalency was confirmed through ab initio valence bond (VB) theory calculations of the EF-driven dative bonds, aligning with the crucial role of the charge transfer interaction. This pronounced covalency emerges as a key feature of EF-driven interactions, setting them apart from traditional dative bonds studied in parallel throughout this work.

Scheme 1. (a) Illustration of the complete VB wavefunction with two Lewis (resonance) structures; (b) definition of the electric field direction in this work.

Fig. 1. Optimal structures of the vdW complexes (a–c) in the absence of EFs and the dative bonding (DB) complexes (d–f) in the presence of EFs, with the shortest P⋯C distances (R in Å) and binding energy (ΔE_b in kcal mol⁻¹) denoted, and the fluctuations of the P → C distances over time in the AIMD simulations of dative bonding complexes in the presence of EFs (g–i).

Fig. 2. Calculated IR spectra (a–c), carbon-13 NMR spectra (d–f) and UV absorption spectra (g–i) of the vdW (blue line) and dative bonding (red line) complexes.

Fig. 3. “In situ” orbital correlation diagrams upon the formation of EF-driven dative bonds. The superscript “F” denotes fragments perturbed by the external EF, while block-localized monomers in the presence of EFs are prefixed with “BL-”.

Fig. 4. Decomposition results of the charge transfer interaction energy (a), correlation between the dipole moments of the electron localized and delocalized states (b) and the relationship between the induced potential energies and the corresponding estimated values (c).

Fig. 5. VB mixing diagram for the EF-driven dative bonds (a–c) and the reference H₃P-C₂₀ (d) and H₃P-BH₃ complexes (e), with the resonance energies (in blue) and the energy differences between VB structures (in grey) denoted.