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Crystal field theory treats interactions between the electrons on the metal and the ligands as a simple electrostatic effect. The presence of the ligands near the metal ion changes the energies of the metal d orbitals relative to their energies in the free ion. Both the color and the magnetic properties of a complex can be attributed to this crystal field splitting. The magnitude of the splitting (Δ oct ) depends on the nature of the ligands bonded to the metal. Strong-field ligands produce large splitting and favor low-spin complexes, in which the t 2 g orbitals are completely filled before any electrons occupy the e g orbitals. Weak-field ligands favor formation of high-spin complexes. The t 2 g and the e g orbitals are singly occupied before any are doubly occupied.
Determine the number of unpaired electrons expected for [Fe(NO 2 ) 6 ] 3− and for [FeF 6 ] 3− in terms of crystal field theory.
Draw the crystal field diagrams for [Fe(NO 2 ) 6 ] 4− and [FeF 6 ] 3− . State whether each complex is high spin or low spin, paramagnetic or diamagnetic, and compare Δ oct to P for each complex.
![A diagram is shown with two columns and two rows of squares outlined in yellow. The first column is labeled “[ F e ( N O subscript 2 ) subscript 6 ] superscript 4 negative sign.” The second is labeled, “[ F e F subscript 6 ] superscript 3 negative sign.” In the left column, three linked squares outlined in yellow are shown. Each of the squares contains two half arrows, one pointing up and one pointing down. In a row just above, two empty linked squares are shown. The label, “Low spin, diamagnetic, P less than capital delta subscript oct,” is provided below the column. In the right column, three linked squares outlined in yellow are shown. The square on the left contains two half arrows, one pointing up and one pointing down. The other two squares each contain a single upward pointing half arrow. In a row just above, two linked squares are shown which each contain a single upward pointing half arrow. The label, “High spin, paramagnetic, P greater than capital delta subscript oct,” is provided below the column.](/ocw/mirror/col11760/m51188/CNX_Chem_19_03_FECN6FEH2O_img.jpg)
Give the oxidation state of the metal, number of d electrons, and the number of unpaired electrons predicted for [Co(NH 3 ) 6 ]Cl 3 .
The solid anhydrous solid CoCl 2 is blue in color. Because it readily absorbs water from the air, it is used as a humidity indicator to monitor if equipment (such as a cell phone) has been exposed to excessive levels of moisture. Predict what product is formed by this reaction, and how many unpaired electrons this complex will have.
[Co(H 2 O) 6 ]Cl 2 with three unpaired electrons.
Is it possible for a complex of a metal in the transition series to have six unpaired electrons? Explain.
How many unpaired electrons are present in each of the following?
(a) [CoF 6 ] 3− (high spin)
(b) [Mn(CN) 6 ] 3− (low spin)
(c) [Mn(CN) 6 ] 4− (low spin)
(d) [MnCl 6 ] 4− (high spin)
(e) [RhCl 6 ] 3− (low spin)
(a) 4; (b) 2; (c) 1; (d) 5; (e) 0
Explain how the diphosphate ion, [O 3 P−O−PO 3 ] 4− , can function as a water softener that prevents the precipitation of Fe 2+ as an insoluble iron salt.
For complexes of the same metal ion with no change in oxidation number, the stability increases as the number of electrons in the t 2 g orbitals increases. Which complex in each of the following pairs of complexes is more stable?
(a) [Fe(H 2 O) 6 ] 2+ or [Fe(CN) 6 ] 4−
(b) [Co(NH 3 ) 6 ] 3+ or [CoF 6 ] 3−
(c) [Mn(CN) 6 ] 4− or [MnCl 6 ] 4−
(a) [Fe(CN) 6 ] 4− ; (b) [Co(NH 3 ) 6 ] 3+ ; (c) [Mn(CN) 6 ] 4−
Trimethylphosphine, P(CH 3 ) 3 , can act as a ligand by donating the lone pair of electrons on the phosphorus atom. If trimethylphosphine is added to a solution of nickel(II) chloride in acetone, a blue compound that has a molecular mass of approximately 270 g and contains 21.5% Ni, 26.0% Cl, and 52.5% P(CH 3 ) 3 can be isolated. This blue compound does not have any isomeric forms. What are the geometry and molecular formula of the blue compound?
Would you expect the complex [Co(en) 3 ]Cl 3 to have any unpaired electrons? Any isomers?
The complex does not have any unpaired electrons. The complex does not have any geometric isomers, but the mirror image is nonsuperimposable, so it has an optical isomer.
Would you expect the Mg 3 [Cr(CN) 6 ] 2 to be diamagnetic or paramagnetic? Explain your reasoning.
Would you expect salts of the gold(I) ion, Au + , to be colored? Explain.
No. Au + has a complete 5 d sublevel.
[CuCl 4 ] 2− is green. [Cu(H 2 O) 6 ] 2+ is blue. Which absorbs higher-energy photons? Which is predicted to have a larger crystal field splitting?
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