Macrocyclic ligand complexes are involved in a variety of fundamental biological systems. Examples include photosynthesis, which proceeds due to the magnesium macrocycle chlorophyll, and various electron transfer reactions which occur in cytochromes. Nature chooses macrocyclic derivatives which give enhanced kinetic and thermodynamic stabilities, such that the metal ion is very firmly held in the central cavity of the ligand, so the … Read more
Metallic coordination compounds can be classified in various ways. The Electron number (EN): Treat the metal and ligands as neutral entities. Classify the ligands by the number of electrons they provide, l. The number of electrons the metal provides, m, is equivalent to its periodic group. Allow for any charge of the complex (q). Then EN=m+l-q. Oxidation State: Remove all ligands … Read more
A ligand is an ion or molecule which exists independently of any complex that it might form. In the complex [Co(NH3)6]3+, the ammonia molecules, which can exist outside of the complex, are acting as ligands. The complex is a combination of a Lewis acid (the central metal atom/ion) and some Lewis bases (the ligands). The main way of classifying ligands is by the number of … Read more
The term complex mechanism refers to the reactions which take place with metal ions. Complexes are formed with these metal ions in solution, and these undergo a range of reactions. The complexes are formed between a metal ion and a set of ligands. Ligands are ions or molecules which exist independently of the metal complex, and these are electron donors, and form … Read more
In photoelectron spectroscopy, PES, the kinetic energies of electrons emitted from a sample when it is irradiated with high energy ultraviolet radiation are measured. The use of ultraviolet radiation is sometimes reflected in the name UV-PES. The kinetic energy, EK, of an emitted electron, the so called photoelectron, can be related to the energy of the incident radiation, hν, and the … Read more
Symmetry Theory The importance of the symmetry of a molecule in determining the form of the molecular orbitals can be investigated by considering the molecular orbitals of the H3 molecule. There are two possible geometries for H3, linear and triangular. Linear H3 The basis set of atomic orbitals are the 1s orbitals in each H atom, named A, … Read more
In diatomic species, there is only one important coordinate, defined as the internuclear axis. We discuss the molecular orbitals in terms of the overlap of the atomic orbitals along this axis. In polyatomic species, this description must be extended to allow for the fact that there are many internuclear axes. Let us consider the water … Read more
The permanent magnetic moment of a molecule is due to the presence of unpaired electron spins in that molecule. The magnitude of the magnetic moment, m, of a single electron is given by the relationship below, where s is the spin angular momentum. ge is the electron’s g-factor and μB is the Bohr magneton, In a molecule there … Read more
The electrons in an atom occupy the atomic orbitals from the lowest energy upwards, according to the aufbau principle, and Hund’s rule. In molecules, the electrons occupy the molecular orbitals according to the same criteria. The electronic configuration of a molecule can therefore be written in the same way as an atomic electronic configuration, but using the molecular orbitals. … Read more
In the molecular orbital theory of H2, we consider the molecular orbitals as made up of the symmetric and antisymmetric combination of the individual 1s atomic orbitals on the two atoms. In general, however, there is more than one occupied orbital in the original atoms. The choice of the atomic orbitals needed to describe the molecular orbitals is … Read more