Question

Inorganic;

You are attempting to synthesize some magnetic material using either Vanandium, Manganese or Cobalt and have available the ligands pyridine, I^-, CO, and OH-. What complexes (oxidation states, geometeries, etc.) might you expect to make good magnetic materials?

Answer 1

vanadium has the electronic configuration [Ar] 3d³4s².

V is [Ar] 4s² 3d³
V²⁺ is [Ar] 4s⁰ 3d³
V³⁺ is [Ar] 4s⁰ 3d²
V⁴⁺ is [Ar] 4s⁰ 3d¹
V⁵⁺ is [Ar] 4s⁰ 3d⁰

And thus, V³⁺ is paramagnetic, because it has two unpaired 3d electrons. In fact, all the ions above are paramagnetic, except V⁵⁺.

In case of Manganese the electronic configuration is [Ar] 4s² 3d⁵. The most stable electronic configuration is Mn²⁺. The stable Mn²⁺ ion has a d⁵ electronic configuration and thus will be magnetic in low spin as well as high spin complexes. The highly oxidizing Mn⁺⁷ has no valence electron and thus can never be magnetic. The single electron species Mn⁶⁺ has a small magnetism which is independent of the ligand present. The magnetism of Mn⁺⁴ also depends upon the ligands present in the complex.

For cobalt the electronic configuration for the elemental stage is [Ar] 4s² 3d⁷ . The +2 and +3 oxidation stages both are magnetic in nature and their magnetic property depends on ligand.

The spectrochemical series is a list that orders ligands on the basis of their field strength. Ligands that have a low field strength, and thus high spin, are listed first and are followed by ligands of higher field strength, and thus low spin. This trend also corresponds to the ligands abilities to split d orbital energy levels. The ones at the beginning, such as I⁻, produce weak splitting (small Δ) and are thus weak field ligands. The ligands toward the end of the series, such as ​CN⁻, will produce strong splitting (large Δ) and thus are strong field ligands. A picture of the spectrochemical series is provided below.

(weak) I⁻ < Br⁻ < S²⁻ < SCN⁻ < Cl⁻ < NO₃⁻ < N₃⁻ < F⁻ < OH⁻ < C₂O₄²⁻ ≈ H₂O <

NCS⁻ < CH₃CN < py < NH₃ < en < bipy < phen < NO₂⁻ < PPh₃ < CN⁻ ≈ CO (strong)

From the series it is clear that CO and Pyridine are strong field ligands and generates high spin complexes. Hydroxide and Iodide ions are weak field in nature and thus generates low spin complexes. The magnetic property of a complex depends on the number of unpaired electrons. Hence CO and Pyridine are suitable for magnetic materials.