Transition metals are elements in the d and ds blocks of the periodic table. Due to the presence of empty d orbitals, transition metals readily form complexes. Our understanding of transition metal complexes originates from Alfred Werner’s realization that their three-dimensional shape influences their properties and reactivity, and the intrinsic link between shape and electronic structure is now firmly underpinned by molecular-orbital theory. In transition metal complexes, the character of the d orbitals often plays an important role in the development and enhancement of novel physical and chemical properties. Transition metal complexes are widely used in the physical and biological sciences due to their unique electronic and stereochemical properties. The unique characteristics of transition metal complexes, including their molecular geometry (which is not readily accessible to organic molecules) and their ligand exchange, redox, catalytic, and photophysical reactions, make these compounds important in catalysis, synthesis, materials science, photophysics, and bioinorganic chemistry.
Structure
The complex is a compound composed of central atoms (or ions) and several molecules (or ions) around it. The central atom (or ion) is the coordination center of the complex, and several molecules (or ions) around it are called ligands. The coordination center of transition metal complexes is often transition metal ions or atoms. They have bond-forming ability and can form complexes with various ligands. When the ligand is different, it will show different effects. Generally, the coordination centers of transition metal complexes also have different oxidation states and coordination numbers.
Applications
It is well known that the excited states of the system have the characteristics of high energy and short life span. Due to the interaction between transition metals and ligands, the excited state characteristics of transition metal complexes are more complex and have more types, such as the charge transfer state between transition metals and ligands (metal-to-ligand charge transfer, MLCT; ligand-to-metal charge transfer, LMCT), metal centered (MC), ligand-centered (LC) and ligand-to-ligand charge transfer state (LLCT) between different ligands. Due to its special excited state properties, it has broad application prospects in the fields of energy, materials, biology, and catalysis.
- In the field of energy, transition metal complexes can be used for the conversion and storage of solar energy. On the one hand, they can be used for dye-sensitized solar cell (DSSC) to convert solar energy directly into electricity. On the other hand, artificial photosynthesis can also be used to convert solar energy into chemical energy, to realize the storage and utilization of energy.
- In the field of materials, transition metal complexes can be used to design organic light-emitting diodes (OLEDs) with excellent light-emitting properties by using their light-emitting properties. It can also use its nonlinear optical properties to realize the regulation of incident light.
- In the field of biological, transition metal complexes can be used for photodynamic therapy due to their intersystem crossing. In addition, it can be used for biological imaging and biosensors by using its luminescent properties.
- In the field of catalysis, transition metal complexes can be used as catalysts due to their high selectivity and catalytic activity.
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