Review Article

A Review of Azo–Metal Complexes: Coordination Modes, Structure–Property Relationships, and Emerging Applications

Abstract

Azo ligands are versatile π-conjugated donors whose coordination to metal ions can substantially alter molecular geometry, charge distribution, redox behavior, optical response, thermal stability, and biological properties. This review examines azo–metal complexes from a coordination-chemistry perspective, with emphasis on donor-atom identity, denticity, coordination geometry, metal-ion effects, and the resulting structure–property relationships. Monodentate, bidentate, tridentate, and tetradentate systems are discussed using representative N-, N,O-, N,N-, and higher-denticity coordination modes. Particular attention is given to the fact that azo groups can participate in metal coordination and, in selected systems, display redox non-innocent behavior, allowing metal–ligand cooperativity and ligand-centered electron transfer. The review then evaluates biological, optical, catalytic, sensing, and energy-related applications. In biological systems, increased activity of some metal complexes relative to their parent ligands has been associated with changes in lipophilicity, membrane transport, metal-dependent reactivity, reactive oxygen species generation, enzyme interactions, and DNA binding; however, these mechanisms are system-dependent and should not be generalized from in vitro observations alone. Recent developments in photoresponsive and electroactive azo–metal systems further demonstrate the importance of integrating experimental spectroscopy with computational approaches such as density functional theory and time-dependent DFT. Finally, current limitations including aqueous stability, metal-associated toxicity, mechanistic uncertainty, reproducibility, scalability, and the need for in vivo or device-level validation—are identified to guide future design of multifunctional azo–metal complexes.

Author Affiliation:

Hawraa S. Ibrahim (ORCID): Department of Medical Laboratory Techniques, College of Health and Medical Techniques / Kufa, University of Al-Furat Al-Awsat Technical University, Najaf 31003, Iraq.
Zahraa Jalil Salman (ORCID): Department of Dental Technology, College of Health and Medical Techniques / Kufa, University of Al-Furat Al-Awsat Technical University, Najaf 31003, Iraq 
Abeer A. Tuaimah (ORCID): Department of Pharmaceutical Chemistry, College of Pharmacy, University of Kufa, Najaf, Iraq.

How To Cite: H.S. Ibrahim, Z.J. Salman, and A.A. Tuaimah. A Review of Azo–Metal Complexes: Coordination Modes, Structure–Property Relationships, and Emerging Applications. Interdisciplinary Studies on Applied Science, 3(2):7–14, 2026. https://doi.org/10.58613/isas322