Spin States (d Electrons) - High-spin and Low-spin Systems

High-spin and Low-spin Systems

The first d electron count (special version of electron configuration) with the possibility of holding a high spin or low spin state is octahedral d4 since it has more than the 3 electrons to fill the non bonding d orbitals according to ligand field theory or the stabilized d orbitals according to crystal field splitting. The spin state of the complex also affects an atom's ionic radius.

d4
Octahedral high-spin: 4 unpaired electrons, paramagnetic, substitutionally labile. Includes Cr2+ ionic radius 80 pm, Mn3+ ionic radius 64.5 pm.
Octahedral low-spin: 2 unpaired electrons, paramagnetic, substitutionally inert. Includes Cr2+ ionic radius 73 pm, Mn3+ ionic radius 58 pm.
d5
Octahedral high-spin: 5 unpaired electrons, paramagnetic, substitutionally labile. Includes Fe3+ ionic radius 64.5 pm.
Octahedral low-spin: 1 unpaired electron, paramagnetic, substitutionally inert. Includes Fe3+ ionic radius 55 pm.
d6
Octahedral high-spin: 4 unpaired electrons, paramagnetic, substitutionally labile. Includes Fe2+ ionic radius 78 pm, Co3+ ionic radius 61 pm.
Octahedral low-spin: no unpaired electrons, diamagnetic, substitutionally inert. Includes Fe2+ ionic radius 62 pm, Co3+ ionic radius 54.5 pm, Ni4+ ionic radius 48 pm.
d7
Octahedral high-spin: 3 unpaired electrons, paramagnetic, substitutionally labile. Includes Co2+ ionic radius 74.5 pm, Ni3+ ionic radius 60 pm.
Octahedral low-spin:1 unpaired electron, paramagnetic, substitutionally labile. Includes Co2+ ionic radius 65 pm, Ni3+ ionic radius 56 pm.
d8
Octahedral high-spin: 2 unpaired electrons, paramagnetic, substitutionally labile. Includes Ni2+ ionic radius 69 pm.
Square planar low-spin: no unpaired electrons, diamagnetic, substitutionally inert. Includes Ni2+ ionic radius 49 pm.

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