# Asymmetric Ligand Field Effects in Electron‐Rich Heterometallic Extended Metal Atom Chain Compounds

## TL;DR

This paper studies how electron-donating ligands affect different metals in a chain, finding unexpected asymmetry in their impact.

## Contribution

The study reveals asymmetric ligand field effects in heterometallic complexes, contrary to electronegativity expectations.

## Key findings

- The Mo2 site experiences a stronger ligand field effect than the heterometal.
- Electron-donating substituents make the complexes more electron-rich and easier to oxidize.
- New electronic transitions, including a possible triplet δ-δ* state, become visible with the modified ligand.

## Abstract

In heterometallic systems, electron donation from the ligands may influence the metal atoms in either a symmetric or asymmetric way, with the expected case being that the more electronegative metal is favored. Here, we describe a systematic study of heterometallic compounds where this expectation is not observed. In this study, we use a modification of the symmetric 2,2′‐dipyridylamine (dpa) ligand with electron donating ethyl groups, the 4,4′‐diethyl‐2,2′‐dipyridylamine ligand (dedpa), to prepare heterometallic extended metal atom chain (HEMAC) complexes with formula Mo2M′(dedpa)4Cl2 (M′ = Cr, Mn, Fe, Co, Ni). The effects of the electron donating substituents were studied through techniques including crystallography, magnetometry, cyclic voltammetry, EPR, Mössbauer, electronic absorption spectroscopy, and DFT calculations. We find that the new HEMACs are indeed more electron rich, easier to oxidize, and, most interestingly, the impact of the ethyl substituents is not applied equally to all the metals in the chain. The ligand field is stronger at the Mo2 site, but is surprisingly weaker at the M′ center when compared to Mo2M′(dpa)4Cl2 complexes. We also find that changing the ligand field allows for previously unassigned electronic transitions to become visible, including excitations tentatively assigned to a triplet δ‐δ* state within the Mo2 unit.

Synthesis of multimetallic compounds with modifiable scaffolding ligands raises questions about the distribution of electronic effects in heterometallic systems. Here we investigate the asymmetry of the substituent effects in a modified 2,2′‐dipyradylamine ligand applied to a heterotrimetallic extended metal atom chain (HEMAC) framework. We find that the Mo2 core experiences a stronger effect than the heterometal, counter to expectations based on metal atom electronegativity.