# Introduction and Extension of the Unified Theory of Multicenter Bonding: The Role of the Charge-Shift Bonding

## TL;DR

This paper introduces a new unified theory of chemical bonding that includes charge-shift and multicenter bonds to better understand and design advanced materials.

## Contribution

The paper extends the unified theory of multicenter bonding to incorporate charge-shift bonds, offering a new framework for chemical bonding.

## Key findings

- The unified theory of multicenter bonding (UTMB) explains the formation of electron-rich and electron-deficient multicenter bonds.
- Charge-shift bonds are closely related to electron-rich multicenter bonds and are integrated into the UTMB framework.
- The UTMB provides a broader perspective on chemical bonding that can aid in the development of advanced materials.

## Abstract

Classical chemical bonding is typically categorized into primary, strong interactions, such as covalent, ionic, and metallic bonds, and secondary, weak interactions, such as van der Waals forces, the hydrogen bond, and their likes (halogen bond, chalcogen bond, etc.). However, other not-so-known bonding mechanisms also play a crucial role in chemical systems. Particularly important are the charge-shift bond (CSB) and the multicenter bonds, i.e., the electron-rich multicenter bond (ERMB), also known as hypervalent or three-center-four-electron (3c-4e) bond, and the electron-deficient multicenter bond (EDMB), also known as the three-center-two-electron (3c-2e) bond in molecules and, more recently, as the two-center-one-electron (2c-1e) bond in extended solids. We consider that these latter interactions have not yet received the proper attention of the scientific community, even though multicenter interactions were proposed in the early days of Quantum Mechanics. In this work, we aim at providing: (i) a concise historical overview of the two types of multicenter bonds; (ii) a short introduction to the recently proposed unified theory of multicenter bonding (UTMB), which elucidates the origin and mechanisms of formation of both ERMBs and EDMBs; and (iii) an extension of the UTMB to include CSBs, due to the strong relationship between ERMBs and CSBs. We hope that the integrated perspective of chemical bonding, the heartland of chemistry, offered by the UTMB (beyond traditional and historical assumptions) will help researchers to understand materials properties and will provide a framework allowing the development of advanced materials for enhanced technological applications.