The effects of temperature on μeff

   So far, we have ignored the effects of temperature on μ_eff. If a complex obeys the Curie Law (equation 1.2), then μ_eff is independent of temperature; this follows from a combination of equations 1.1 and 1.2.

                    (1.1)

                                       (1.2)

 where C = Curie constant; T = temperature in K.   However, the Curie Law is rarely obeyed and so it is essential to state the temperature at which a value of μ_eff has been measured. For second and third row d-block metal ions in particular, quoting only a room temperature value of μ_eff is usually meaningless; when spin–orbit coupling is large, μ_effis highly dependent on T.

Fig. 1.1 Kotani plot for a t_2g⁴ configuration; λ is the spin– orbit coupling constant. Typical values of μ_eff(298 K) for Cr(II), Mn(III), Ru(IV) and Os(IV) are indicated on the curve.

For a given electronic configuration, the influence of temperature on μ_effcan be seen from a Kotani plot of μ_eff  against kT/λ where k is the Boltzmann constant, T is the temperature in K, and λ is the spin–orbit coupling constant. Remember that λ is small for first row metal ions, is large for a second row metal ion, and is even larger for a third row ion. Figure 1.1 shows a Kotani plot for a t₂g⁴ configuration; four points are indicated on the curve and correspond to typical values of μ_eff(298 K) for complexes of Cr(II) and Mn(III) from the first row, and Ru(IV) and Os(IV) from the second and third rows respectively. Points to note from these data are:

• since the points corresponding to μ_eff(298 K) for the first row metal ions lie on the near-horizontal part of the curve, changing the temperature has little effect on μ_eff;
• since the points relating to μ_eff(298 K) for the heavier metal ions lie on parts of the curve with steep gradients, μ_eff is sensitive to changes in temperature; this is especially true for Os(IV).

مواضيع ذات صلة

ايجاد الصيغة التركيبية للمعقدات

معقدات الخارصين

معقدات النحاس

كيمياء ومعقدات بعض عناصر السلسلة الانتقالية الاولى

تعريف المركبات المعقدة

Crystal Field Stabilization Energies

Colors of Transition-Metal Complexes

The Nature of the Ligands

Principal Quantum Number of the Metal

Charge on the Metal Ion

Factors That Affect the Magnitude of Δo

Electronic Structures of Metal Complexes