Sarcophaginates calculations

Since sarcophaginates and sepulchrates are relatively easy to crystallize, a great number of these compounds are studied by X-ray crystallography, which together with molecular geometry calculations makes it possible to establish their three-dimensional structures both in crystal and in solution. The optical activity of such clathrochelates enables one routinely to utilize circular dichroism measurements to investigate their structure. The spatial and electronic structures of sarcophaginates and sepulchrates are much more seldomly determined by alternative spectral techniques compared with clathrochelates of other types. 

Thus, for theoretical calculations of the sarcophaginate and sepulchrate structures, one should take into account inter- and intramolecular nonbonded interactions and electronic effects. The calculations based on geometric and/or repulsion models are obviously justified only for complexes with insufficient or no preference for TAP or TP structure (ALFSE = 0). In this case, the ligand determines the complex geometry. In all other cases, the contribution of the metal ion electronic configuration cannot be neglected [178],... 

For cobalt(III) compounds, P. Comba calculated five of the six conformations possible for sarcophaginate complexes (Fig. 3), using strain energy minimization [230]. The sixth Dsleh conformation does not exist in cobalt(III) cages. Some structural parameters of the strain energy-minimized structures of the cobalt (III) complex conformers are presented in Table 4. 

Thus, the application of the ligand field model [178] in combination with the strain energy minimization model [230] makes it possible to calculate with high accuracy the geometrical parameters of sepulchrate and sarcophaginate frameworks. 

The static and dynamic Janh-Teller effects in copper(II) [Cu(diAMHsar)](N03)4 H20 sarcophaginate and the dynamic one in analogous iron(II) complex were detected by variable temperature EPR, optical, and magnetic studies, and by Fe Mdssbauer spectroscopy, respectively [245, 246], and calculated using a density functional approach [247]. 

For amine cobalt complexes, the E values correlate with the calculated differences in strain energy for cobalt(III)/cobalt(II) complex pair. The structures of all the cobalt(III) complexes are more strained than those of the corresponding cobalt(II) complexes. The correlation does not hold when the number of protons in the coordinated amino groups is changed (for example, [Co(NH3)6], [Co(en)3] ", [Co(sep)]3+, and [Co(sar)]3+ cations). For a series of Ns-sarcophaginates with different apical substituents, no calculation of differences in strain energy changes has been done [344]. 

The transportability of these parameters determined from a limited number of compounds is illustrated by the excellent linear relationship between the calculated Zcte for any clathrochelate and the experimental Em values for this compound (Fig. 52). Data for oxosar, azasar, and ahsar ligand complexes, where Scte parameters for Ne-sarcophaginates were used, are included in this correlation (Table 46). 

The measured rate constants for cross-reactions and those calculated from Eq. (104) are listed in Tables 53-55. A comparison of the calculated and observed constants indicates that Eq. (104) is solved with an accuracy of an order of magnitude. An attempt to solve this equation by introducing several adjusted 2 values was made in Ref. 364. Eqs. (105-108) are justified at appreciable differences in the charges of the reacting species. But in this case, the correction makes no marked contribution to the improvement in data coincidence [106]. Even for the structurally very similar complexes with close properties, i.e., various isomers of sarcophaginate [Co(diAMHl,2pnsar)] + cation, the experimental rate constants differ from those calculated from Eq. (104) by a factor of 5-7. Sargeson attributed this difference to the... 

Calculated for the crystal structures of [Cr(sarcophagine)][R(L2-2H)3] after averaging to >3-symmetry. 

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