Structures X-Ray crystallography
In order to qualitatively determine the structural orientation of some of these complexes, X-ray structural experiments were conducted. X-ray crystallography can be carried out at different temperatures. At 150 K, Fe [HB (3, 4, 5-Me3pz)Â 3]2Â complex structure proved to be a high spin. The iron- nitrogen single bond interaction has a span of 2.19 Ã…. (Reger et al. 8865). The angles are equally disorientated in a trigonal manner mostly due to pressure exerted by the rings. Moreover, the geometry of the nitrogen-iron single bonds is measured at 86.2o.
The structure of Fe [B (3-cyPrpz) 4]2 exhibits two molecules which are not related to each other. This is especially so when an x-ray is run at two temperature intervals of two hundred and ninety-four and ninety Kelvin. The mean linear distance of the nitrogen-iron bond at a temperature of two hundred and ninety-four Kelvin is 2.17 Å. The average distances for the other two complexes stood at 2.19 Å and 2.17 Å. This is another vivid demonstration that they both exist at high spin state (Nishio, Hirota & Umezawa 184). In the reverse process of cooling to a temperature of ninety Kelvin, there is an associated change from high spin to low spin while the Fe-N linear bond length reduces by about 0.17 Å. This is usually common with the iron (II) complex. The other iron site is, however, not affected by a temperature drop. Fe [HB (3, 4, 5-Me3pz) 3]2 has a molecular structure that is considered to be super with a 2D flat surface. The red lines in the structure below represent the methyl…pi bond. Each of the molecules has two donors and also two acceptors which are in a 2D structure. In Fe [B (3-cyPrpz) 4]2â (CH3OH), there are three groups consisting of bonds where there is no equal sharing of electrons.
In this case, CH…N, NH…O and CH…O associate in a way that the two crystallographic individual molecules containing both centers of iron into a 2D flat surface (Reger et al. 8867). This occurs when the temperature level is at ninety and two hundred and ninety-four Kelvin structures. The molecule which aptly corresponds to this feature is Fe [B (3-cyPrpz) 4]2 (CH3OH) as in figure 2 below. It should be noted that the green lines in the second figure represent the low spin state while the violet lines represent the high spin states. These supermolecular structures are obtained when the temperature is maintained at 90 Kelvin. It also puts more stress on how X-ray crystallography. Another area of importance in regard to low and high spin states is the effect of temperature. Besides, a complex like Fe [(p-HC2C6H4) B (3-Mepz) 3]2, disruption of ligands may have a significant effect on the nature of the spin state whether high or low. The iron (II) poly-(pyrazolyl) borate structures, for instance, have five unique types of geometric angle changes. Figure 3 shows how temperature influences the nature of the spin state of iron (II) or iron (III). On the same note, the size of the metal ion will tend to increase as the degree of ligand distortions is enhanced. For the sake of the complexes discussed here, the iron (II) complex is more favorable for coordination at low spin.
