The Electronic Spectra of Tetragonal Chromium(III) Complexes

Abstract

Methods for processing the electronic spectra of tetragonal chromium(II1) complexes are briefly reviewed. New criteria for assigning the spectra of these complexes are introduced and the data processed to yield a series of crystal field and molecular orbital parameters. The validity of these are discussed with particular reference to the apparent x bond contribution in the chromium ligand bonds.It is concluded that the bonding is better described in ionic rather than covalent terms.

Single crystal electronic spectra of a series of trans nickel(II) complexes with N,N′-diethyl- and N,N′-dimethylethylenediamine

“…Values for the parameter e,,' are for the most part close to zero. So it appears that n interactions between nickel(I1) and the axial ligands are of relatively little importance, in contrast to tetragonal chromium(111) complexes, where this parameter can be quite large (17). This is explicable if the n interactions are largely ligand to metal n donation, since Cr(II1) has a half-filled t,, (O,) shell, whereas that of Ni(I1) is full.…”

Mutual Influences of Ligands as Revealed by 2H NMR Shifts and the Angular Overlap Model Parameters: trans‐ and cis‐[CrX2(N)4]‐Type Complexes with Aliphatic Amine Ligands

“…This suggests that the transferability assumption from one complex to another [13] is invalid for both e σ (X) and e σ (N). In general, the AOM parameters have been evaluated by a conventional procedure that involves fitting the absorption bands in the spin-allowed ligand-field d-d transitions to the calculated energy levels by varying the AOM parameter values, [13,[18][19][20][21][22] which requires the correct assignment of the well-resolved ligand-field band components. However, the spin-allowed ligand-field bands of most trans-and cis-[CrX 2 N 4 ]-type complexes exhibit poorly defined or no splitting into degenerate or nondegenerate components, except for a limited number of complexes such as trans-difluorido tetraamine complexes.…”

“…In fact, the e σ (X) values decrease and the e σ (N) ones increase with increasing ∆δ, as shown in Figure 2, which leads to Equations (1) and (2) (in units of 10 3 cm -1 ). [21] NH 3 101.9 6.97 [19] NCS -103.7 6.41 [20] H 2 O 97.5 7.52 6.76 [13] Cl -109.0 7.40 5.56 [19] Br -113.7 7.68 5.34 [19] [a] Calculated from Equations (1-3), see text. (6) and the solid lines from e σ (F) = -0.048∆δ + 11.0 (7) for the difluorido complex [see Equations (f) and (g) in ref.…”

“…This correlation gives Equation (4). [18] Cl 2 85.6 5.56 [19] (NCS) 2 80.6 6.41 [20] (OH) 2 57.3 8.63 [19] (H 2 O) 2 70.3 6.76 [13] ox 78.3 6.75 [28] [a] Calculated from Equation (4). …”

The photochemistry of some bisethylenediamine and cyclam complexes of rhodium(III)

“…A crude estimate can be made of the mixing coeflicient if it is assumed that the magnitude of D, for the Rh(II1) complexes will be at least as great as that calculated for their Co(II1) analogues (15) and that the ratio D,/Ds found for tra~ls-[Cr(en)~X~J~ (16) may also be applied to the Rh(II1) complexes. The value thus calculated suggests at least a 90% contribution by the (lZz orbital which is conparable to the computed value for similar Cr(II1) con~plexes (17).…”