Wydział Chemii

Janusz Gregoliński

Tadeusz Lis

M. Cyganik

Jerzy Lisowski

2008

Inorganic Chemistry

47

11527-11534

10.1021/ic8005986

Naukowa

Angielski

Artykuł

The La(III), Ce(III), Pr(III), Nd(III), Sm(III), and Eu(III) complexes of the racemic heterochiral nonaaza macrocyclic amine L have been synthesized and characterized by spectroscopic methods. The X-ray crystal structures of the [PrL][Pr(NO₃)₆]·CH₃OH and the isomorphic [NdL][Nd(NO₃)₆]·CH₃OH complexes show that all nine nitrogen atoms of the macrocycle coordinate to the Ln³⁺ ion, completing its coordination sphere. The macrocycle wraps tightly around the metal ion in double-helical fashion. The structures reveal the RRRRSS/SSSSRR configuration at the stereogenic carbon atoms of the three cyclohexane rings, confirming the heterochiral nature of the parent 3 + 3 macrocycle obtained in the condensation of racemic trans-1,2-diaminocyclohexane and 2,6-diformylpyridine. The NMR spectra of the isolated complexes indicate the presence of low C₁ symmetry [LnL]³⁺ complexes. The same symmetry is indicated by the X-ray crystal structures of Pr(III) and Nd(III) complexes, which show that for the RRRRSS enantiomer of the macrocycle L, the helix axis passes through the cyclohexane ring of RR chirality and the opposite pyridine ring. The NMR studies of complex formation in solution by the paramagnetic Pr³⁺ and Eu³⁺ ions indicate that the initially formed [LnL]³⁺ complexes are of C₂ symmetry. For the RRRRSS enantiomer of the macrocycle L in the C₂-symmetric species, the helix axis passes through the cyclohexane ring of SS chirality and the opposite pyridine ring. The C₁-symmetric and C₂-symmetric forms of the [LnL]³⁺ complexes constitute a new kind of isomers and the conversion of the kinetic complexation product of C₂ symmetry into the thermodynamic product of C₁ symmetry corresponds to an unprecedented switching of the orientation of the helix axis within the macrocycle framework.

Thermodynamics, Molecular structure, Kinetics, Macrocycles, Ions

https://doi.org/10.1021/ic8005986

https://www.acs.org/content/acs/en.html