The photochemical properties of metal complexes, such as absorption spectra, wavelength of maximum absorption, and photostability, can be significantly influenced by the coordination number and geometry around the metal center. These factors affect the electronic structure of the complex, which in turn determines its photochemical behavior.1. Coordination number: The coordination number refers to the number of ligands atoms, ions, or molecules that are directly bonded to the central metal ion in a complex. Changing the coordination number can alter the energy levels and distribution of electrons in the complex, which affects its absorption spectra and the wavelength of maximum absorption.For example, increasing the coordination number can lead to a higher number of possible electronic transitions, resulting in more complex absorption spectra. Additionally, higher coordination numbers can cause a redshift i.e., a shift to longer wavelengths in the maximum absorption wavelength due to the stabilization of the metal's d-orbitals.2. Geometry around the metal center: The geometry around the metal center refers to the arrangement of ligands around the central metal ion. Common geometries include octahedral, tetrahedral, square planar, and linear. The geometry can significantly influence the energy levels and distribution of electrons in the complex, which in turn affects its photochemical properties.For example, different geometries can lead to different types of electronic transitions, such as d-d transitions, charge-transfer transitions, or ligand-to-metal charge-transfer LMCT transitions. These transitions can have different absorption spectra and maximum absorption wavelengths. Furthermore, the geometry can also affect the photostability of the complex, as certain geometries may be more prone to photodegradation or photoisomerization.In summary, changing the coordination number and geometry around the metal center can significantly influence the photochemical properties of metal complexes. These changes can affect the absorption spectra, wavelength of maximum absorption, and photostability of the complex, which are important factors to consider when designing metal complexes for applications such as photocatalysis, solar energy conversion, and photodynamic therapy.