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Computational Insights into the Isomerism of Hexacoordinate Metal–Sarcophagine Complexes: The Relationship between Structure and Stability
Author(s) -
Algarra Andrés G.
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201402984
Subject(s) - hexacoordinate , chemistry , octahedron , ligand (biochemistry) , crystallography , metal , stereochemistry , crystal structure , receptor , biochemistry , organic chemistry , silicon
The hexacoordinate complexes that the macrobicyclic ligands {(NH 3 ) 2 sar} 2+ and {(NMe 3 ) 2 sar} 2+ (sar = 3,6,10,13,16,19‐hexaazabicyclo[6.6.6]icosane) form with transition metals such as Co III , Co II and Cu II can adopt several isomeric structures. In this article, we have firstly employed DFT methods to compute the relative stability of their Δ‐ ob 3 , Δ‐ ob 2 lel , Δ‐ lel 2 ob and Δ‐ lel 3 isomers, as well as the activation barriers for their interconversion. In agreement with the experimental data, the results show that, in general, the different isomers of the Co III and Co II complexes present similar free energies, whereas the Cu II complexes show a strong tendency towards the lel 3 form. In addition, the interplay between the structure and stability of these species has been studied by combining shape maps with a distortion/interaction energy analysis. In contrast to the geometries close to the ideal octahedron that all the studied Co complexes present, the lel 3 structures of [Cu{(NH 3 ) 2 sar}] 4+ and [Cu{(NMe 3 ) 2 sar}] 4+ are better described as trigonal prisms. In such structures the ligand adopts a conformation significantly more stable than in the other isomers, and this drives the formation of lel 3 ‐[Cu{(NH 3 ) 2 sar}] 4+ and lel 3 ‐[Cu{(NMe 3 ) 2 sar}] 4+ . Overall, the results show a clear relationship between the stability of a given isomer and its degree of distortion with respect to the ideal octahedron (or trigonal prism), with the latter being ultimately dependent on the transition metal and its radius.