Field tetrahedral

The five d orbitals of a metal atom or ion in a tetrahedral field. The top three orbitals 

The crystal field splitting of the d orbitals by a tetrahedral field. 

---

In tetrahedral fields the splitting of the free ion ground term is the reverse of that in octahedral fields so that, for d ions in tetrahedral fields A2g(F) lies lowest but three spin-allowed bands are still anticipated.In fact, the observed spectra usually consist of a broad, intense band in the visible region (responsible for the colour and often about 10 times as intense as in octahedral compounds) with a weaker one in the infrared. The only satisfactory interpretation is to assign these, respectively, as, wj = 7 i (P)-i A2(F) and ut = i(F)- A2(F) in which case U = ) should be... 

For d ions in tetrahedral fields the splitting of the free-ion ground term is the inverse of its splitting in an octahedral field, so that ig(F) lies lowest. In this ca.se three relatively intense bands are to be expected, arising from the transitions ... 

The only spin-triplets arising from the configuration are (ground) and P. The effects of an octahedral or tetrahedral field upon these two terms are summarized in Fig. 3-16. 

Although the effect on the d orbitals produced by a field of octahedral symmetry has been described, we must remember that not all complexes are octahedral or even have six ligands bonded to the metal ion. For example, many complexes have tetrahedral symmetry, so we need to determine the effect of a tetrahedral field on the d orbitals. Figure 17.5 shows a tetrahedral complex that is circumscribed in a cube. Also shown are lobes of the dz- orbital and two lobes (those lying along the x-axis) of the dx> y> orbital. 

IFIGU RE 17.6 The orbital splitting pattern in a tetrahedral field that is produced by four ligands. 

The spin-allowed transitions for ions having T and A ground states in tetrahedral fields are as follows ... 

For metal ions having d2, d3, d7, and d8 configurations, the ground state is an F state, but there is an excited P state that has the same multiplicity. For d1 and d7 ions in an octahedral field, the spectroscopic states are the same (except for the multiplicity) as they are for d3 and d8 ions in tetrahedral fields. Therefore, the expected spectral transitions will also be the same for the two types of complexes. The three spectral bands are assigned as follows (Tlg(F) means the Tis state arising from the F spectroscopic state) ... 

Figure 1.18 shows energy levels for d orbitals in crystal fields of differing symmetry. The splitting operated by the octahedral field is much higher than that of the tetrahedral field (A = lower than the effect imposed by the square... 

Figure 1.18 Crystal field splitting for d orbitals A = square-planar field B = octahedral field C = tetrahedral field.

Ion Electronic Configuration Spin Octahedral Field Tetrahedral Field OSPE... 

Selected entries from Methods in Enzymology [vol, page(s)] Degenerate perturbation treatment, 246, 84 ligand position functions, 246, 81-82 matrix elements, 246, 81-83 octahedral field potential, 246, 80 potential energy term, 246, 78-79 resource materials, 246, 16 tetrahedral field, 246, 81... 

In a tetrahedral field, the d-orbitals are split into a lower doublet (e) and an upper triplet (f2), giving the lowest configuration as (e)4(t2). The... 

Furlani and Morpurgo (98) have, however, obtained very good spectra of the complex anions in nitromethane addition of a small excess of halide was necessary in most cases. Their results are summarized in Table VI, together with the assignment in a regular tetrahedral field. The symbols used may be understood by reference to the Orgel diagram of Fig. 8. 

For both octahedral and tetrahedral symmetries, there are excited states close to the ground state, causing short spin-lattice-relaxation times and broad absorption lines at most temperatures. Thus the dl ion in an octahedral or tetrahedral field has only been detected at low temperatures (generally liquid He or H2). When the crystal field is highly distorted from these symmetries, as in the case of the V02+ ion, the spin-lattice time becomes longer, making detection of ESR possible at higher temperatures. 

The situation is different for d2 in a tetrahedral field. In this case the 3F state gives an orbital singlet as the ground state, with the crystal field states at much higher energies. In this case we would expect longer relaxation times and smaller values of Z), because the excited states that contribute are further removed from the ground state. Thus detection of the ESR in tetrahedral fields should be easier. 

Values of the spin Hamiltonian reported for d4 ions are given in Table XI. The difficulty in detecting the ESR is due most likely to short spin-lattice-relaxation times and large zero-field splittings. In both octahedral and tetrahedral fields the 5 D state of d4 gives degenerate orbital states which,... 

It has been assumed16 27 that the neon atom and other atoms with an s2p outer shell also may be described as tetrahedral. However, the four spa electrons with positive spin are independent of the four with negaiive spin, and the two corresponding tetrahedra are free to assume arbitrary relative orientation.28 Correlation requires that the most stable relative orientation be the inverse one hence the neon atom and the other s2p6 atoms can be described as cubic. Their polarizability in a cubic multipole electric field is large and that in a tetrahedral field small.29... 

---