Lanthanide complexes of 2 + 2 meso-type macrocycle derived from trans-1,2-diaminocyclohexane and 2,6-diformylpyridine: X-ray crystal structures of La(III) and Sm(III) complexes

The [LnL](NO3)3 · nH2O complexes of the series of all lanthanide(III) ions, except radioactive Pm, with the meso-type hexaazamacrocycle L, derived from racemic trans-1,2-diaminocyclohexane and 2,6-diformylpyridine, have been synthesised and characterized. The X-ray crystal structures of the isomorphic La(III) and Sm(III) complexes show that the lanthanide(III) ions are coordinated by six nitrogen atoms of the relatively flat macrocycle L as well as by two axial bidentate nitrate anions and methanol molecule. The complexes have been characterised by NMR spectroscopy and mass spectrometry. 1H NMR signals of the Ce+3, Pr+3, Nd+3, Eu+3 and Yb+3 complexes have been assigned on the basis of the COSY and HMQC spectra, and for the remaining lanthanide complexes the signals were assigned on the basis of linewidths analysis. The paramagnetic shifts of the series of lanthanide complexes [LnL](NO3)3 · nH2O have been analysed using both crystal-field dependent and independent methods. The results of this analysis indicate a change of coordination number along the series of Ln(III) complexes. The properties and stability of the lanthanide(III) complexes of the macrocycle L have been compared with those of the isomeric chiral macrocycle L1.

Graphical abstractThe title complexes have been synthesised and characterized by spectroscopic methods. The X-ray crystal structures of the isomorphic La(III) and Sm(III) complexes have been determined. The properties and stability of the lanthanide(III) complexes of the ligand L have been compared with those of the isomeric chiral ligand L1 derived from enantiopure (1R,2R)-trans-1,2-diaminocyclohexane.Figure optionsDownload full-size imageDownload as PowerPoint slide