What configuration of Fe is characterized by electrons being "spread out"?

The characteristic of having electrons "spread out" refers to the arrangement of electrons in the d orbitals of a transition metal complex. In a high-spin configuration, the energy gap between the t2g and eg orbitals is relatively small, allowing electrons to occupy higher energy orbitals rather than pairing up in lower energy orbitals. This leads to unpaired electrons and results in increased magnetic properties.

When iron (Fe) is in a high-spin state, its d electrons are less paired, meaning more are placed in higher-energy orbitals. This is often observed in complexes where the surrounding ligands exert weak field strengths, allowing the electrons to maintain higher energy states rather than pairing up, which would require greater energy input.

In contrast, a low-spin configuration would have electrons more paired due to a larger energy gap, which is characteristic of strong field ligands. The other terms—neutral Fe and ferrous Fe—do not refer to the electron arrangements within complex ions but to the oxidation state and overall charge of iron.