d electron count

[1][2] The d electron count is an effective way to understand the geometry and reactivity of transition metal complexes.

There are a few exceptions with only one electron (or zero for palladium) in the ns orbital in favor of completing a half or a whole d shell.

The usual explanation in chemistry textbooks is that half-filled or completely filled subshells are particularly stable arrangements of electrons.

That leaves the (n − 1)d orbitals to be involved in some portion of the bonding and in the process also describes the metal complex's valence electrons.

Crystal field theory is an alternative description of electronic configurations that is simplified relative to LFT.

Each of the ten possible d electron counts has an associated Tanabe–Sugano diagram describing gradations of possible ligand field environments a metal center could experience in an octahedral geometry.

The Tanabe–Sugano diagram with a small amount of information accurately predicts absorptions in the UV and visible electromagnetic spectrum resulting from d to d orbital electron transitions.

What follows is a short description of common geometries and characteristics of each possible d electron count and representative examples.