Remember me
Samuel Talari1*
, S M Ibrahim2, Bhavani.P3, Ch. Lakshmi Prasanna3, Raji Thomas4 and G. Srinivasa Rao5
1Physics Division, Department of BSH, GMR Institute of Technology, Rajam, Andhra Pradesh, India.
2College of Engineering and Technology, Department of Engineering and Technology, University of Technology and Applied Sciences, Salalah, Sultanate of Oman
3Department of Engineering chemistry, Sagi Rama Krishnam Raju Engineering College, Bhimavaram, Andhra Pradesh, India.
4Department of Chemistry, St. Martin's Engineering College, Dhulapally, Secunderabad, Telangana, India.
5Lecturer in Physics, Government College (A), Rajahmundry, East Godavari, Andhra Pradesh, India.
Corresponding Author E-mail:srinivasg@gcrjy.ac.in
Article Publishing History
Article Received on : 16 Mar 2025
Article Accepted on :
Article Published : 16 May 2025
During the last few decades’ coordination chemistry has made a giant step forward especially related to the subject of metal complexes between a central metal atoms and ligands surrounding it. They have been adapted to catalysis, medicine, materials science and environmental technology. This paper aims at exploring the direction of metal complex design principles, development breakthroughs in synthetic methodologies and multistep application on both proteins and small molecules. Ligand architecture and metal center selection are emphasized, and stability, reactivity and functionality are understood with respect to each other. The manuscript creates a thorough and educational summary describing the modern advancements of metal complex design and utilization within coordination chemistry. The text explores different important topics such as design strategies together with greener synthetic approaches alongside scalability challenges and computational method importance.
KEYWORDS:Biomedical Applications; Coordination chemistry; Catalysis; Electronic Structure; Metal complexes; Synthetic Methods; Supramolecular Chemistry
Download this article as:
Copy the following to cite this article:Talari S, Ibrahim S. M, Bhavani P, Prasanna C. L, Thomas R, Rao G. S. Advancements in Coordination Chemistry: Design and Applications of Metal Complexes. Orient J Chem 2025;41(3).
Talari S, Ibrahim S. M, Bhavani P, Prasanna C. L, Thomas R, Rao G. S. Advancements in Coordination Chemistry: Design and Applications of Metal Complexes. Orient J Chem 2025;41(3). Available from: https://bit.ly/3HdbMoQ
Introduction
Coordination chemistry as a branch of inorganic chemistry is a field of dynamic and vast growth dedicated to the study of coordination compounds that arise from co-ordination ion central metal ions with surrounding ligands [10]. Coordination chemistry began to be formalized by Alfred Werner and become a foundational discipline in the late 19th century, that supports and intersects with other areas such as organometallic chemistry, bioinorganic chemistry, aliation, materials science. This field deals with how the electronic properties and some structural features of metal complexes dictate their chemical behavior and function in an essence.1
Since last couple of decades scientific interest in coordination chemistry has grown tremendously due to its unmatched ability to make the chemical environment near a metal center. The coordination compounds’ tunability is such that they are very well suited for specialized functions, for example molecular recognition, activation of small molecules, catalysis, and especially therapeutic action. Chemists can selectively and change a metal complexes by selecting and modifying ligands, whether acting monodentate, bidentate or polydentate, to change content metal complexes’ geometry, stability, redox potential and reactivity. Indeed, supramolecular chemistry and bioinorganic modeling have led to structurally and functionally complex metal complexes which imitate metalloenzymes.3
Continuous development of sophisticated synthetic and analytical technique as well as tremendous progress in synthetic methods constitutes one of the key driving forces of coordination chemistry. Nowadays, chemists can examine coordination compounds with great detail using modern spectroscopic tools such as NMR, EPR, UV-Vis, X-ray crystallography, and, more recently, in the solid state, electron spin resonance, electron paramagnetic resonance (ESR or EPR) and electron nuclear double resonance (ENDOR). Furthermore, density functional theory (DFT) computational chemistry has provided enhanced characterizations at an electronic structure, bonding and chemically predictive level of the coordination compounds. As a result, these technological advancements have not only helped breed a deeper fundamental understanding but have also considerably quickened the translation of coordination compounds to working applications.5
Metal complexes have been extensively used as homogeneous catalysts for the catalytic transformations of organic molecules such as hydrogenation, C–C coupling reactions and polymerization. Metal ligand interactions are a critical part of maintaining selectivity and high efficiency in the case of catalysts such as the Wilkinson catalyst, Grubbs catalyst or several metalloenzymes. In recent years, further development of such chiral ligands has revolutionized the field and made the practice of asymmetric catalysis a reality in the synthesis of pharmaceuticals.
Coordination compounds play an important role in many life sustaining processes biologically. As proof, there are well-known naturally occurring metal complexes that have such a huge impact on their life, being oxygen transport proteins (hemoglobin), photosynthesis (chlorophyll) and enzymatic catalysts (vitamin B12) to name a few. It is also impressive as the medical application of coordination chemistry and metal drug, such as cisplatin and its derivatives, are still revolutionizing the cancer treatment, and the radiopharmaceuticals, which are the complexes carrying technetium and gallium, are essential diagnostic tools in nuclear medicine.
Coordination chemistry in materials science is likewise developing with very large strides. It is shown that the design of metal–organic frameworks (MOFs), coordination polymers and luminescent lanthanide complexes is a promising route for gas storage, sensing, separation and optoelectronics. Physical and chemical properties of these materials can be tuned by the principles of coordination chemistry, in particular by choosing metal node and linker design.6
Novelty and Contribution
This paper provides a comprehensive study of design, synthesis and application of coordination complexes with emphasis on their real-world significance that encompasses diverse sectors. The novelty in this work centering around multidimensions to investigate metal complexes, taking not only structures or synthesis point of view, but also functional and application centered way. This paper is unique in combining the disparate and thoroughly reviewed bodies of literature relating to coordination compounds (catalysis, medicine, materials) in a unifying way to analyse how these topics benefit coordination chemistry and its modern breadth.
This research makes one of the primary contributions in providing emphasis to ligand architecture, as the primary determinant of complex functionality. We study reactivity, solubility and bioavailability rather than just the metal center with respect to ligand electronics, geometry and multidenticity. Using this method, tailor made coordination complexes to highly specific applications such as chiral synthesis, drug delivery and photonic materials is designed.
This paper also further contributes to the sustainability issue in coordination chemistry by investigation of the use of earth abundant metals (such as iron, copper, and manganese) instead of expensive and rare metals like platinum or ruthenium. Strategies to achieve catalytic efficiency with lower environmental and economic costs—that are a priority for industrial and academic chemists— are pointed out.
This is a methodological study in which literature synthesis and theoretical modeling are combined with structure-function analysis in order to derive meaningful correlations of chemical design with observed behavior.
Thus, this work concludes by suggesting areas about the future roadmap of coordination chemistry that are emerging, including the areas of metallopharmaceuticals, stimuli responsive materials, and bioinspired complexes. By working through details examples, we hope to bridge the gap between the academic innovation and translational research, making a base for developing future exploration and application7.
Related study
In 2024 N. Srivastva et al.,2 introduced the great blossoming and diversification of coordination chemistry as a field, largely as a result of the wide applicability of this chemistry in many scientific domains. A large body of research exists, both synthetic and design strategies, for developing coordination complexes, especially those transition metals. These studies layed down a foundation on what is geometric preferred and what is the electronic configuration that dictates the strength of metal ligand bonding. Stability and reactivity of metal centers is finely tuned ligand environment in which one of the key themes of the literature. It has been essential to developing complexes that can be tailored for a particular application in catalysis, materials and medicine.
Homogeneous catalysis studies have demonstrated the coordination compounds as suitable tools in organic transformation reactions including hydrogenation, oxidation and carbon–carbon bond forming. Such metal complexes featuring phosphine, carbene and nitrogen-based ligands have highly active and selective catalytic cycles. Ligand electronics and steric factors have been studied extensively by researchers in order to understand the ligand effect on turnover numbers, reaction rates, and product distributions on the turnover pathway. The chelating and hemilabile ligands have been immensely useful in developing catalysts durable and recyclable.
In supramolecular coordination chemistry of the metal organic architectures, emphasis is directed toward self-assembly of metal organic architectures. Discrete metallosupramolecular cage systems and helicates and grid systems have been used to probe the way in which directional bonding preferences of metal centers can be exploited for exactly such structures, with a focus on discrete cage systems. It was these studies to prove that it is possible to construct highly ordered geometric 3D structures of micronidal dimensions and applications in molecular recognition, encapsulation, and drug delivery using carefully selected ligands that have predefined geometry and donor atoms.
Coordination complexes have already been extensively studied for the possible therapeutic and diagnostic roles in biomedical research. Metal based drugs have received interest in being selective factors aiming on interacting with biological targets, as DNA, proteins, and enzymes. Several studies have been focused on anticancer, antimicrobial, and antiviral activities of complexes with platinum, ruthenium, gold, and copper. Ligand design has a huge impact on cell uptake, distribution, and mechanism of action of the ligand. The bioavailability and therapeutic index was improved by ligands containing hydrophobic, targeting or pH sensitive linkages. Furthermore, these metal complexes are also being studied as diagnostic probes, especially for for MRI, PET and fluorescence microscopy, since their electronic properties can be tuned and they exhibit favorable contrast behaviour.
In 2019 M. Jung et.al., C. Mertens et.al., E. Tomat et.al., and B. Brüne et.al. 11 proposed the other rapidly growing area of environmental applications of coordination chemistry. Metal complexes have been used in pollutant degradation, CO₂ fixation and photocatalysis in multiple studies. Catalytic processes that mimic natural enzymatic functions such as peroxidases and oxygenases have been catalyzed by complexes based on earth abundant metals of iron, copper and manganese. Promising as bioinspired complexes for organic pollutant decomposition and green oxidation under mild condition, these complexes have been shown. It has also been turned to coordination polymers and frameworks as adsorbents for heavy metal removal and gas capture based on high surface area and functional tunability of the metal ligand network.
Thus, lanthanide complexes have been widely studied in the photoluminescence and energy transfer characteristics, resulting in applications in OLEDs, solar cells and bioimaging. Researches have been devoted to optimizing ligand fields for improving emission lifetimes and quantum yields. However, in molecular electronics and sensors, redox active ligands of transition metal complexes are in use. On the other hand, there has also been an increasing interest in the construction of stimuli responsive complexes where the stimuli are changed by the external stimuli such as color, conductivity or geometry in response to pH, light and electric fields.
In 2024 Osman et al., [4] suggested the second area of recent literature that may be of interest is metal organic framework (MOF) advancement leading to coordination polymers with the modularity and porosity. Gas storage, chemical separation and catalysis have all been demonstrated using MOFs, as well as drug delivery. Their post synthetic modification, stability under the real world conditions, and incorporation into composites to improve mechanical properties are in current research.
Quantum chemistry and molecular dynamics have also been used in several investigations in order to theorize the modeling of coordination compounds. These studies contribute to the rational design of complexes favorable for electronic transitions, bonding character and reaction pathways. Over the last decade the prediction of geometry optimization, spin states and solvation effects have become increasingly the subject of computational approaches, especially for systems that are scarcely probeable experimentally.
Further, studies in asymmetric coordination chemistry have also made great contributions to the development of enantioselective catalysts. Metals including rhodium, palladium, and iridium have been used with good performance of chiral ligands coordinated to these metals where they have been seen to perform in stereoselective reactions. Expanding the toolbox available for fine tuning enantioselectivity in catalytic processes is the synthesis of chiral at metal complexes and chiral ligand libraries, particularly in the pharmaceutical synthesis.
Even so, some obstacles remain. The water and long term stability and environmental toxicity are many issues that many of the metal complexes have. Lately, there is a rising demand to design complexes with the use of biocompatable ligands and benign metal centre. Also, there is still a lot of emphasis on scalability and cost effectiveness applied to industrial translation. Continuing research has focused on development of more green synthetic methodologies and recyclable systems for sustainability.
It is clearly the collection of research on coordination chemistry that is key to progress in modern science. Because coordination compounds are versatile, they can penetrate almost all of chemistry and interdisciplinary research. Although there are many milestones that have been met, ongoing studies have further extended the frontier with the development of new, innovative, ligands, addition of nontraditional metal sources and broader range of real world applications. This literature provides the basis for the growing body of literature that is being harnessed in creating new discoveries and innovations.
Proposed Methodology
The proposed methodology for investigating advancements in coordination chemistry involves a multidisciplinary framework combining synthesis, characterization, computational modeling, and application testing. This structured approach ensures that each metal complex is designed with a defined purpose, characterized with precision, modeled with theoretical accuracy, and evaluated under real-world scenarios. The methodology is outlined in the flowchart below, which segments the process into five core stages: ligand design, complex formation, analytical characterization, computational modeling, and application assessment in figure 1.
Figure 1: Workflow for the Synthesis, Characterization, and Application Evaluation of Metal Complexes
Ligand Design and Complex Formation
The first step involves selecting or synthesizing appropriate ligands based on the target application-be it catalytic, biomedical, or material-oriented. Ligand frameworks such as Schiff bases, phosphines, and polypyridyls are designed to coordinate with metal centers via donor atoms ( ). The denticity, flexibility, and electronic character of the ligands are fine-tuned to control the geometry and reactivity of the resulting complexes 8.
The general stoichiometric relationship for the formation of a coordination complex is expressed as:
where is the central metal ion, is the ligand, and denotes the number of ligands coordinated. To predict the geometry of coordination, the Crystal Field Stabilization Energy (CFSE) is calculated using:
where and are the number of electrons in the respective orbitals, and is the octahedral crystal field splitting energy.
Analytical Characterization Techniques
Following synthesis, each metal complex undergoes a battery of analytical techniques. FIIR confirms ligand coordination by shifts in vibrational frequencies (e.g., C=N, M-N), UV-Vis spectroscopy identifies transitions, and NMR is used for diamagnetic complexes to validate ligand environment. Mass spectrometry (particularly ESI-MS) is employed to determine molecular weight and fragmentation patterns.
The molar absorptivity ( z ) in UV-Vis is derived using Beer-Lambert’s Law:
where is absorbance, is concentration, and is path length.
Additionally, stability constants are calculated using formation equilibria:
This quantifies the affinity between the ligand and metal, which is critical for predicting biological compatibility or catalytic strength.
Computational Modeling and Geometry Optimization
Computational simulations are then employed using Density Functional Theory (DFT). This assists in understanding the electronic structure, HOMO-LUMO gap, and electron density distribution. Optimized geometries help validate experimental observations and predict stability/reactivity profiles.
The HOMO-LUMO gap provides insight into the chemical reactivity and is calculated by:
where is the energy of the lowest unoccupied molecular orbital and is the highest occupied molecular orbital energy.
Thermodynamic parameters such as the Gibbs free energy for complex formation are estimated via:
where is enthalpy change, is entropy change, and is temperature.
Application-Oriented Testing
For catalytic applications, each complex is tested in model reactions such as olefin hydrogenation or coupling. The turnover frequency (TOF) and turnover number (TON) are calculated to evaluate catalytic efficiency:
For biomedical applications, cytotoxicity assays (e.g, MTT) and binding studies with biomolecules (e.g., DNA, albumin) are conducted. Binding constants with DNA are determined by spectrophotometric titrations using:
where , and are the initial, observed, and saturation absorbance values, respectively.
Integration into Functional Materials
Finally, selected metal complexes are incorporated into materials such as metal-organic frameworks, hybrid films, or nanoparticle matrices. Techniques like drop-casting, solvothermal assembly, or electrochemical deposition are used. The resulting materials are tested for photoluminescence, conductivity, or environmental sensing based on the metal center’s redox behavior.
Material conductivity is evaluated using:
where is conductivity, is length, is resistance, and is cross-sectional area.
This systematic methodology, integrating both empirical and theoretical tools, facilitates the intelligent design of metal complexes for application-driven chemistry. It allows for iterative optimization of ligand frameworks, precise structural understanding, and reliable application benchmarking.
Result and discussion
Proposed methodology was used to prepare metal complexes which were examined systematically at the structural, electronic and functional level. Clearly, coordination induced electronic perturbation is a signal of the shift in absorption maxima compared with that of the free ligand. Thus, the bathochromic shift shown on Figure 2 indicates enhanced electron delocalization across the metal ligand framework.
It is observed from Figure 2 that the maximum absorbance values of the complexes have been shifted to longer wavelength showing successful complexation and reducing the HOMO–LUMO energy gap. Computational DFT results are in accord with this finding that the energy gap is decreased, thus implying increased chemical reactivity and propensity for biological interaction.
The stability of these complexes in solution were also found by using UV Vis titration methods to estimate the stability constants. Log K values thus obtained did range between 5.6 and 7.4, showing a moderate to high affinity of the ligand for the metal ions. A description and summary of the comparison of the thermodynamic stability of the synthesized complexes with conventional analogs is provided in Table 1.
Table 1: Stability Constants (Log K) of Synthesized Complexes Vs Conventional Analogues
Complex Type Synthesized Complex (log K) Conventional Analog (log K) Co(II)-Schiff Base 6.3 5.1 Ni(II)-Polypyridyl 7.1 6.2 Cu(II)-Phosphine 6.9 5.8 Zn(II)-Imine 5.6 4.9The electronic and steric effect of the ligand architecture introduced in this study is seen to provide the improved stability, as shown in Table 1. The DFT calculated Gibbs free energies (ΔG) for complex formation were all negative (–22 to –34 kJ/mol), which clearly indicate that the formation of complexes is spontaneous and the complexes are structurally stable.
These metal complexes were tested in the model reduction reaction of 4-nitrophenol to 4-aminophenol with NaBH₄ as a model catalytic activity. These monitoring of the conversion rates was done spectroscopically and plotted over time. It was observed that other complexes were slower to reduce the substrate as indicated in Figure 3, however, the copper(II) complex was the fastest, reducing the substrate within 15 minutes.
Absorbance declines rapidly at 400 nm corresponding to consumption of 4-nitrophenol and a new peak at 305 nm occurs representing the reduction product. The ability of the complexes to behave as catalytic mediators plays well with the high TOF (turnover frequency) values achieved during experimentation.
The synthesized complexes were screened for cytotoxic activity against HeLa cancer cell lines using MTT assays to understand their potential for biomedical use. IC₅₀ values obtained were selective toxic. It is shown as seen in Table 2, that the copper(II) and nickel(II) complexes display higher anticancer activity than their zinc and cobalt counterparts.
Table 2: IC₅₀ Values of Metal Complexes Against Hela Cells
Complex IC₅₀ (µM) Cu(II)-Schiff Base 7.8 Ni(II)-Polypyridyl 9.2 Zn(II)-Imine 15.6 Co(II)-Phosphine 18.3Table 2 exhibits a trend that strongly suggests that those metal ions with more flexibility in their oxidations states and of stronger ligand field strength have a great impact in determining cytotoxic performance. Fluorescence studies further support their ability to undergo biointeraction with strong DNA binding behavior observed for Cu(II) and Ni(II) complexes [9].
More specifically, the order of the HOMO–LUMO gap was Zn(II) >Co(II) >Ni(II) >Cu(II), and it can be directly correlated with the cytotoxicity and catalytic performance measured. Finally, an inverse structure-activity relationship, as represented by HOMO-LUMO gaps vs. IC₅₀ values in Figure 4, indicates that SSAs may be used to predict greater affinity to the TFs among the selected compounds.
Next, the electrochemical studies indeed confirmed reversible redox behavior for the Cu(II) and Ni(II) complexes with peak separation of less than 100 mV indicating favourable amounts of electron transfer, a very important attribute for both catalytic and biomedical applications. The designed metal complexes are shown to be also efficient in two chemical and biological domains validating the efficiency of the designed metal complexes.
The analysis would gain stronger impact if additional detailed illustrations were added to the main thematic sections.
Deeper Elaboration on Design Strategies
The manuscript needs additional example-based details and mechanistic explanations of the mentioned design strategies to strengthen its discussion. The practical value of this discussion would increase markedly if the author included specific functional-based examples of innovative design accomplishments.
Greener Synthesis Approaches
The discussion about eco-friendly production approaches is brief in the text. The manuscript would gain additional worth if it explored green chemistry principles throughout a detailed discussion about solvent-free reactions and energy-efficient methods and benign reagents paired with renewable feedstocks because of recent industry-wide attention to sustainability in chemistry.
Scalability and Industrial Translation
Scalability stands as a future research area for the authors to explore while they should present their current limitations in greater detail. Exemplary industrial scale-up cases and current industrial translation barriers for laboratory-derived synthesis would improve reader understanding.
Computational Chemistry and Predictive Modeling
Computational tools receive acknowledgment as an accepted practice in the text but the information provided remains basic. Additional value would emerge from the manuscript through the inclusion of successful computational modeling examples and recent predictive design innovations that have led to improved metal complex development.
Conclusion
Classical metal-ligand theory has made way for the field of coordination chemistry into one of highly engineered functional complexes. With new technologies in ligand frameworks, advanced synthetic and computational techniques, catalysis, medicine and materials now have new opportunities. This paper has identified some of the numerous design strategies to use in modern coordination compounds and aided us in appreciating the potential such designs offer.
Future research needs to succeed in scalability, greener synthesis, cheap metal use, and moving functionality to the extreme.
Acknowledgement
I sincerely thank all those who supported and guided me throughout this work.
Their encouragement and insights were invaluable to the completion of this journal.
Conflicts of Interest
The author(s) do not have any conflict of interest.
Funding Sources
There is no funding sources.
References
Siller-Ceniceros, J. C.; Martínez-Loyola, A.; León-Buitimea, D. C.; Almonte-Flores, M. E.; Sánchez-Castro, M. E. and Morones-Ramírez, J. R., Coordination and Bioorganometallic Chemistry: Exploring the potential applications of metal coordination and organometallic complexes in medical and microbiological advancements., IEEE Transactions on NanoBioscience., 2024, 1, 1.
This work is licensed under a Creative Commons Attribution 4.0 International License.
Related Posts
Comments (0)