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Spectrochemical Series: Cr3+
• Safety:
– Aqueous Cr3+ complexes – dispose in liquid waste bottle.
– Ligands: en, acacˉ, NO3 ˉ, Clˉ, NH3, H2O
• Lab management
– Time is of the essence!!!
• Ligands
(Urea is source of NH3)
O
+
H2N
2 NH3
H2O
+ CO2
NH2
(acacˉ is a bidentate ligand)
O
H3C
H
O
C
H2
CH3
O
H3C
O
C
H
O
CH3
H3C
O
C
H
CH3
Spectrochemical Series: Cr3+
• What three factors affect the crystal field splitting of d-orbitals?
Geometry
(DT ~ 4/9 DO)
(octahedral, tetrahedral, tetragonal, square planar, square pyramidal, trigonal prismatic)
Ligands:
halides < OH- < C2O42- < H2O < NCS- < py < NH3 < en < phen < NO2- < CN- < CO
Nature of the transition metal
(1) 3d vs 4d vs 5d (2) higher oxidation state vs lower oxidation state (3) other
Mn2+ < Ni2+ < Co2+ < Fe2+ < V2+ < Fe3+ < Co3+ < Mn4+ < Mo3+< Rh3+ < Ru3+ < Pd4+ < Ir3+ < Pt4+
Crystal field splitting
Tanabe-Sugano d3
• Origin of diagram
• Possible transitions
• Selection rules
– Spin (superscript)
DS = 0
– Symmetry (g vs u)
no change (g→g)
Two allowed, one forbidden transition
Assigning transitions
(blue arrow reproduces observed transitions)
Spectrochem series: Cr3+
• E = hc/l = hn = hcn~
– Energy in units of wavelength, frequency, and wavenumbers
Rule of average environment
• CrCl2(H2O)4+
vs
CrCl63Cr(H2O)63+
• Crystal field gap is a weighted average of those of the
homoleptic (single type of ligand) complexes.
Beer’s law
• Saturation effects – avoid them by working at A < 0.25
• Guts of a spectrophotometer
(source, grating, sample, detector)