Nickel energy level diagrams

In a nickel-containing enzyme various groups of atoms in the enzyme form a complex with the metal, which was found to be in the +2 oxidation state and to have no unpaired electrons. What is the most probable geometry of the Ni2+ complex (a) octahedral (b) tetrahedral (c) square planar (see Exercise 16.96) Justify your answer by drawing the orbital energy-level diagram of the ion. 

Fig. 22. Energy level diagrams for the nickel(II) ion in a five-coordinate chromo-phore. Left, Dsii symmetry. Right, the effect of the variation of angle on the energy levels (Dq — 1 kK)...

Fig. 36. Energy level diagram for trigonal bipyramidal complexes of nickel(II), d, ...

Delayed fluorescence from a very-short-lived upper excited singlet state populated by hetero-TTA has been observed for the first time using the system A = anthracene and X = xanthone (Nickel and Roden, 1982). An energy-level diagram for this system is shown in Figure 5.32, and the corrected spectrum of the delayed fluorescence of anthracene and xanthone in trichlorotrifluoroe-thane is depicted in Figure 5.33. The band at 36,000-40,000 cm has been assigned to the delayed fluorescence of anthracene produced by Tf +... 

Figure 5.32. Energy-level diagram of anthracene (A) and xanthone (X). Double lines denote the three different triplet pairs for which TTA processes are indicated asterisks mark the delayed fluorescence (DF) resulting from hetero-TTA (by permission from Nickel and Roden, 1982).

The electronic structures of iron, cobalt, nickel, and the platinum metals are given in Table 19-1, as represented in the energy-level diagram of Figure 5-6. It is seen that each of the atoms has two outermost electrons, in the 4s orbital for iron, cobalt, and nickel, the 55 orbital for ruthenium. 

The Orgel diagram for tetrahedral nickel(II), shown in Fig. 8, is similar to that for the octahedral case, but the levels are inverted. The lowest level, 3Ti(P), has the same symmetry properties as the higher level 3Ti(P), and the two influence each other therefore, since all transitions are from 3Ti(F), no transition corresponds to the splitting A. To a first approximation the transition energies should be given by 0.8 A, 1.8 A, and (3P — 3F) + 0.6 A 120). A is much smaller than in the octahedral case and the first transition, to 3Ti, lies in the far infrared and has not been observed. 

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