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Self‐Assembly of Multinuclear Coordination Species with Chiral Bipyridine Ligands: Silver Complexes of 5,6‐CHIRAGEN( o , m , p ‐xylidene) Ligands and Equilibrium Behaviour in Solution
Author(s) -
Mamula Olimpia,
Monlien Florence J.,
Porquet Alain,
Hopfgartner Gérard,
Merbach André E.,
von Zelewsky Alex
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010119)7:2<533::aid-chem533>3.0.co;2-q
Subject(s) - enantiopure drug , chirality (physics) , chemistry , ligand (biochemistry) , crystallography , bipyridine , metal , absolute configuration , racemic mixture , stereochemistry , enantiomer , crystal structure , enantioselective synthesis , chiral symmetry , receptor , organic chemistry , catalysis , biochemistry , physics , quantum mechanics , quark , nambu–jona lasinio model
The complexation reactions between Ag + and a series of enantiopure ligands belonging to the CHIRAGEN (from CHIRAlity GENerator) family ( L 1, L 2, L 3 , based on (−)‐5,6‐pinene bipyridine) have been studied in solution. It has been shown that the length of the bridge plays a fundamental role in the self‐assembly processes leading to different compounds: mononuclear complexes (with L 3 ), mixtures of polynuclear complexes (with L 2 ) and circular helicates (with L 1 ). Although the absolute configuration of the chiral centres in all three ligands is the same, the metal‐centred chirality of L 3 ( Δ ) is inverted with respect to that in the other two complexes with L 1 and L 2 ( Λ ). The metal configuration is thus opposite in the mononuclear complex with respect to the polynuclear species. Detailed thermodynamic studies were carried out for the Ag + and L 1 ligand system by 1 H and 109 Ag NMR spectroscopy (as a function of concentration, temperature and pressure). At low temperature and high pressure, the [Ag 6 L 1 6 ] 6+ hexanuclear circular helicate forms a tetranuclear circular helicate [Ag 4 L 1 4 ] 4+ : 2 [Ag 6 L 1 6 ] 6+ ⇌3 [Ag 4 L 1 4 ] 4+ . The thermodynamics parameters, obtained by temperature and pressure variation, have the following values: K 298 =(8.7±0.7)×10 −5 mol kg −1 , Δ H °=−15.65±0.8 kJ mol −1 , Δ S °=−130.2±3 J mol −1 K −1 and Δ V 0 (256 K)=−160±12 cm 3 mol −1 . The reaction volume calculated according to Connolly's method indicates that the calculated structure of [Ag 4 L 1 4 ] 4+ is plausible. Both the signs and large magnitudes of Δ S ° and Δ V ° are counterintuitive, yet can be understood by modelling methods.