[Introspect]

Could somebody explain the concept of the Inner sphere electron transfer and Outer sphere electron transfer or provide a link to some article or a book which explains it clearly i.e. something more clear than the Wikipedia articles for these terms, since I checked these and couldn't understand most of it, what is behind, what kind of processes these are, what is happening, the Taube complex, the application or influence on properties etc.

[Corribus]

Briefly put, the rate of electron transfer, like the rates of most reactions, can be formulated as an Arrhenius expression dependent on a pre-exponential factor and an activation energy. The activation energy is often expressed on a Gibbs energy reaction coordinate.  In turn, the Gibbs energy between the precursor and activated complex can be expressed basically in terms of the amount of work required to bring reactants to the optimum separation in the activated complex, as well as a reorganization energy, often abbreviated by λ, and a benchmark Gibbs energy of the overall reaction (determined experimentally via oxidation and reduction potentials of the reactants and products).

The reorganization energy contains two components, called inner and outer sphere energies. The former is a way to quantify the free energy change associated with changing all the bond lengths and angles between the reactants and the transition state (activated complex). The outer sphere energy incorporates polarization of nearby solvent molecules associated with the electron transfer event. The outer sphere energy usually involves a number of approximations (reactants are spherical, etc.) depending on the sophistication of the computation.

Actually some of the best places to find a clear, basic explanation of Marcus theory are advanced biochemistry textbooks. The classic Bioinorganic Chemistry textbook Bertini, Gray, Lippard and Valentine has a very nice section that is easy to follow.

If you have more specific questions, feel free to ask them, though it's been a (very) long time since I thought about this topic.