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Selectivity of Asymmetric Macrocyclic Compartmental Lanthanide( III ) Complexes towards Alkali and Alkaline‐Earth Metal Ions
Author(s) -
Barge Alessandro,
Botta Mauro,
Casellato Umberto,
Tamburini Sergio,
Alessandro Vigato P.
Publication year - 2005
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.200400812
Subject(s) - chemistry , lanthanide , alkali metal , pentagonal bipyramidal molecular geometry , monoclinic crystal system , crystallography , alkaline earth metal , crystal structure , coordination number , chloride , ionic radius , ligand (biochemistry) , ion , inorganic chemistry , organic chemistry , biochemistry , receptor
The asymmetric macrocyclic compartmental ligand H 2 L, derived from the [1+1] condensation of 3,3'‐(3‐oxapentane‐1,5‐diyldioxy)bis(2‐hydroxybenzaldehyde) with 1,5‐diamine‐3‐azamethylpentane, forms the complexes [LnNa(L)(Cl) 2 (CH 3 OH)] (Ln = La–Nd, Sm–Lu) where the lanthanide( III ) ion resides in the N 3 O 2 Schiff base coordination site and thesodium ion is located in the O 3 O 2 crown‐like cavity. The new heterodinuclear complexes [LnCa(L)(Cl) 2 (CH 3 OH)(H 2 O)]Cl (Ln = Tb, Dy, Tm, Yb) were prepared and characterised by single‐crystal X‐ray diffraction, IR, 1 H and 13 C NMR spectroscopy and their homogeneity and stoichiometry (Ln:Ca:Cl = 1:1:3 molar ratio) were ascertained by SEM‐EDS analysis. The single‐crystal X‐ray structure of [YbCa(L)(Cl 2 )(EtOH)(H 2 O)]·Cl·2H 2 O has been determined. The complex is monoclinic, space group P 2 1 / c , with a = 10.033(2), b = 11.702(2), c = 27.796(6) Å and β = 105.51(3)°. The ytterbium ion is seven‐coordinate within the N 3 O 2 site and is in a pentagonal bipyramidal environment and bonded, in the axial positions, to two chloride ions. The calcium ion is seven‐coordinate within the O 3 O 2 site and is bonded to the ethyl alcohol oxygen and to one water molecule. The significant contact between the calcium ion and the chloride ions increases the coordination number of the metal ion to eight in a square antiprismatic environment. The selectivity of the etheric site towards alkali and alkaline‐earth metal ions has been quantitatively assessed by evaluating, with 23 Na NMR spectroscopy, the transmetallation reaction involving the coordinated Na + ion in the complexes [LnNa(L)(Cl) 2 (CH 3 OH)] (Ln = Tb, Dy, Tm and Yb) and Li + , K + and Ca 2+ . The affinity constants follow the general order K Ca >> K Li ≥ K K . Quantitative kinetic analyses were performed on the complex [TmNa(L)(Cl) 2 (CH 3 OH)] using variable temperature 23 Na NMR spectroscopy in CD 3 OD. It was ascertained that the exchange rate Na bound /Na free is independent of the presence of increasing amounts of water in the methanolic solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)