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Synthesis, crystal and molecular structure of the 3:2 complex between europium nitrate and the A ‐isomer of dicyclohexyln‐18‐crown‐6: Conformational study of the ligand
Author(s) -
Nicolò Francesco,
Plancherel Dominique,
Bünzli JeanClaude G.,
Chapuis Gervais
Publication year - 1987
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19870700716
Subject(s) - chemistry , europium , crystallography , monoclinic crystal system , crystal structure , ligand (biochemistry) , ring (chemistry) , cyclohexane conformation , ion , crown ether , stereochemistry , molecule , hydrogen bond , biochemistry , receptor , organic chemistry
The crystal and molecular Structure of bis[dinitrato‐(2,5,8,15,18,21‐hexaoxatricyclo[20.4.0.0 9,14 ]hexa‐consane)europium(III)]pentakis(nitrato) europiate(III) ([Eu(NO 3 ) 2 ·L A ] 2 [Eu(NO 3 ) 5 ]) has been determined from single‐crystal X‐ray diffraction. The complex crystallizes in the monoclinic space group P 2 1 /c (ITC No. 14): a = 13.614(3)Å, b = 21.697(4)Å, c = 22.591(5)Å, β = 107.15(2)°, Z = 4. The structure was refined to a final R value of 0.055 ( R w = 0.055). The asymmetric unit contains three independent ions with approximate C 2 symmetry: [Eu(NO 3 ) 5 ] 2− and two distinct [Eu(NO 3 ) 2 .L a ] + cations with the macrocyclic ligand in the cis‐syn‐cis ‐conformation (A‐isomer). The Eu(III) ions are 10‐coordinated with the following mean bond lengths: EuO(nitrate) = 2.46(3)Å in the anion and the two cations, EuO(ether) = 2.55(9)Å in both cations. For the uncomplexed A‐and B‐isomers, as well as for their complexes with various metal ions, a conformational analysis has been made on the six O‐atoms of the ligand which can be considererd as a fluxional ring. In the presently reported europium complex cations, the oxygen‐ring conformation is almost a perfect boat with the metal ions lying in the least‐sqiares plane of the O‐atoms (deviation: 0.02–0.05Å). The same conformation prevails in all the complexes containing the A‐isomer(exception: dimethylthallium complex) and in most of the complexes with the B‐isomer. For this isomer, a chair conformation is found in the uncomplexed ligand, in the sodium complex, and in the complex with dimethylthallium. The occurrence of these conformations is discussed with respect to the crystallographic symmetry of the complexes and the relative mean MO and OO distances.