Ligand-field splittings, absorption bands and colours

Octahedral (or tetrahedral) splittings Δ, spin-allowed d–d absorption bands, free-ion pairing energies P and observed colours of transition-metal complexes. The crystal-field, spin-state and colour widgets and the spectrophotometer experiment all compute from this table.


$\ce{[Ti(H2O)6]^3+}$	1	octahedral	20300	242.8	lowest band	20,300	493	—	—	1	violet
$\ce{[CrF6]^3-}$	3	octahedral	14900	178.2	lowest band	14,900 / 22,700	671	—	—	3	green
$\ce{[Cr(H2O)6]^3+}$	3	octahedral	17400	208.2	lowest band	17,400 / 24,600	575	—	—	3	grey blue-violet
$\ce{[Cr(C2O4)3]^3-}$	3	octahedral	17544	209.9	lowest band	17,544 / 23,866	570	—	—	3	deep purple
$\ce{[Cr(NH3)6]^3+}$	3	octahedral	21550	257.8	lowest band	21,550 / 28,500	464	—	—	3	yellow-orange
$\ce{[Cr(en)3]^3+}$	3	octahedral	21850	261.4	lowest band	21,850 / 28,500	458	—	—	3	yellow-orange
$\ce{[Cr(CN)6]^3-}$	3	octahedral	26700	319.4	lowest band	26,700 / 32,200	375	—	—	3	pale yellow
$\ce{[Cr(H2O)6]^2+}$	4	octahedral	13900	166.3	Δ table	—	—	23500	high spin	4	—
$\ce{[Mn(H2O)6]^3+}$	4	octahedral	21000	251.2	Δ table	—	—	28000	high spin	4	—
$\ce{[Mn(H2O)6]^2+}$	5	octahedral	8500	101.7	Δ table	—	—	25500	high spin	5	very pale pink (almost colourless)
$\ce{[Fe(H2O)6]^3+}$	5	octahedral	14300	171.1	Δ table	—	—	30000	high spin	5	—
$\ce{[Fe(CN)6]^3-}$	5	octahedral	35000	418.7	Δ table	—	—	30000	low spin	1	—
$\ce{[Fe(H2O)6]^2+}$	6	octahedral	10400	124.4	Δ table	10,400	962	17600	high spin	4	very pale blue-green
$\ce{[Fe(CN)6]^4-}$	6	octahedral	32800	392.4	Δ table	31,000 / 37,000	323	17600	low spin	0	pale yellow
$\ce{[CoF6]^3-}$	6	octahedral	13000	155.5	Δ table	—	—	21000	high spin	4	—
$\ce{[Co(H2O)6]^3+}$	6	octahedral	18300	218.9	Δ table	—	—	21000	high spin	4	—
$\ce{[Co(NH3)6]^3+}$	6	octahedral	22900	273.9	Δ table	21,000 / 29,500	476	21000	low spin	0	orange-yellow
$\ce{[Co(CN)6]^3-}$	6	octahedral	34800	416.3	Δ table	32,400	309	21000	low spin	0	almost colourless (pale yellow)
$\ce{[CoCl4]^2-}$	7	tetrahedral	3300	39.5	Δ table	14,700	680	22500	—	3	deep blue
$\ce{[Co(H2O)6]^2+}$	7	octahedral	9300	111.3	Δ table	8,100 / 19,400	1235	22500	high spin	3	pink
$\ce{[Ni(H2O)6]^2+}$	8	octahedral	8500	101.7	lowest band	8,500 / 13,800 / 25,300	1176	—	—	2	green
$\ce{[Ni(NH3)6]^2+}$	8	octahedral	10750	128.6	lowest band	10,750 / 17,500 / 28,200	930	—	—	2	blue-violet
$\ce{[Ni(en)3]^2+}$	8	octahedral	11200	134.0	lowest band	11,200 / 18,350 / 29,000	893	—	—	2	violet
$\ce{[Cu(H2O)6]^2+}$	9	octahedral	—	—	—	12,500	800	—	—	1	light blue
$\ce{[Cu(NH3)4(H2O)2]^2+}$	9	octahedral	—	—	—	16,500	606	—	—	1	deep blue

For d¹, d³ and d⁸ ions Δo is the lowest-energy band itself (where it differs from the splitting table by 50–100 cm⁻¹, as for [Cr(NH₃)₆]³⁺, 21 550 against 21 500 cm⁻¹, the band is listed); other ions use the Shriver–Atkins–Langford table. Cu(II) is Jahn–Teller distorted and has no single Δo. The two “model” columns are computed by the site’s kernel by comparing Δ with the free-ion pairing energy P: for [Co(H₂O)₆]³⁺, Δo (18 300 cm⁻¹) is below the free-ion P (21 000 cm⁻¹), so the model says high spin, but the complex is actually low spin and diamagnetic — inside a complex P is about 20 % smaller. Ions without a P value have only one arrangement, so their unpaired counts are unaffected.

Sources

D. F. Shriver, P. W. Atkins, C. H. Langford, Inorganic Chemistry, 2nd ed., Oxford University Press (1994), table of ligand-field splitting energies.
A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Elsevier (1984), band maxima as quoted in C. E. Housecroft & A. G. Sharpe, Inorganic Chemistry, 5th ed. (2018).
J. E. Huheey, E. A. Keiter, R. L. Keiter, Inorganic Chemistry, 4th ed., HarperCollins (1993): mean spin-pairing energies of the free ions (after L. E. Orgel).
A. F. Holleman, E. Wiberg, N. Wiberg, Inorganic Chemistry, 34th ed., Academic Press (2001): Δo of [Co(H₂O)₆]³⁺.

Sources

Used in these lessons