Crystal fields strength

Figure 4.6. Lowest triplet state orderings for different metal complexes showing the relative positions of the d-d, n-n, and MLCT states as a function of metal, ligand, and effective crystal field strength. (Reprinted with permission from Ref. 7. Copyright 1991 American Chemical Society.)...

Similarly, Ru(bpy)2(CN)2 emits well at room temperature while [Ru(bpy)2(CN)Cl]+ does not. The main factor is the much lower effective crystal field strength of Cl versus CN. 

Influence of Crystal Field Strength on Cr3 -Doped Materials... 

The regular cube used in Figure 5.5 to represent different symmetry centers suggests that these symmetries can be easily interrelated. In particular, following the same steps as in Appendix A2, it can be shown that the crystal field strengths, lODq, of the tetrahedral and cubic symmetries are related to that of the octahedral symmetry. Assuming the same distance A-B for all three symmetries, the relationships between the crystalline field strengths are as follows (Henderson and Imbusch, 1989) ... 

Sugano and Tanabe have calculated the energy of the states deriving from the 3d" ions (from n = 2to = 8)asa function of the octahedral crystal field strength. 

The energy separation between the " Tag and Eg excited states, AE rn -2500 cm is an indirect measure of the crystal field strength. The negative sign indicates that V + MgF2 is a low crystal field material. This value is given, in units of 5, by... 

The crystal field strength Dq is determined by the effective change of the ligands Q, by the average radius r of the d-orbital and by the ligand-metal distance R ... 

Divalent vanadium belongs to 3d ions and is isoelectronic with Cr. Hence all energy levels and spectral characteristics are similar. The difference between them lies in the lower crystal field strength for V in comparison with Cr. ... 

For octahedral dl, d > d3, d , and d cases, the ground state is derived from the lowest term of the free ion for all values of the crystal field strength (defined by AJ. Hence the multiplicity, the number of unpaired spins and, if the spin-only formula applies, the effective magnetic moment must all be the same as that of the free ion, no matter how strong the interaction between the ion and the ligands. For octahedral d4, d , d , and d7 cases the ground state is derived from... 

Fig. 22 Temperature dependence of magnetic functions (level-6) for different axial crystal-field strength F4(z) of Ti(III) complexes. From left to right Fnixy) = 4000, 8000, 13000, and 18000 cnr1. Black lines refer to the regular octahedron. Note temperature axis runs oppositely between the top and bottom panels...

Fig. 64 Effective magnetic moment of octahedral Mn(III) complexes for various crystal-field strengths showing the spin-transition...

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