Inner sphere complex

Not to be confused with Inner sphere electron transfer.

Inner sphere complex at the solid-water interface is a type of surface complex that refers to the solid-water interface between water, the solute, and sorbent. Formation of inner sphere complexes occurs when ions bind directly to the surface with no intervening water molecules. These types of surface complexes are restricted to ions that have a high affinity for surface sites and include specifically adsorbed ions that can bind to the surface through covalent bonding.

Inner Sphere Complexes

Inner sphere complexes describe active surface sites that are involved in nucleation, crystal growth, redox processes, soil chemistry, alongside other reactions taking place between a cation and surface.

However, inner sphere complexes have surface hydroxyl groups that function as $\sigma$-donor ligands, increasing the coordinated metal ion's electron density. This is an example of competitive complex formation, in which ligands will compete for space on an activation site of a metal ion.

Surface structure are able to reduce and oxidize ligands, whereas transport phenomena do not. Therefore, surface structure serves an important role in surface reactivity, with the coordination environment at the solid-water interface changing intensity or rate of a reaction.

Solid-Liquid Interfaces

Wetting is a phenomenon where one fluid replaces a another medium, like a gas, on a surface. In the case of a solid-gas to solid-water interface, the water spreads to increase the solid-liquid and liquid-gas interfacial area, and decreases the solid-gas interfacial area as a result.

The spreading coefficient of the liquid water is described by the Gibb's Free Energy over the area

$S=-\Delta G_{s}/A$

The Gibb's Free Energy is spontaneous only when S is positive or zero.

External links

• http://www.jhu.edu/~dsverje1/sdarticle.pdf