Structural effect of ligand chirality and its spectroscopic consequences

Two series of pure and diluted lanthanide crystals with L and DL-isoleucine of formula [Ln(Ile)(2)(H2O)(4)](2)(ClO4)(6) (Ln=Eu, Nd) isomorphic for Eu and Nd ions were synthesised. The europium complex with L-isoleucine (1) an d the neodymium one with the DL form (2) have been studied by single-crysta l X-ray diffraction. The space groups are monoclinic C2 and triclinic P (1) over bar for L and DL isoleucine, respectively, and Z=2 and 1. The crystal structures consist of non-centrosymmetric and centrosymmetric dimer units for the L and DL ligand forms, respectively. Thus, the structural effect of ligand chirality was found and its spectroscopic consequences are reported . An attempt has been made to show the relation between the symmetry of the dimeric units and splitting of the electronic transitions. Well resolved a bsorption spectra down to 5 K are measured. Concentration effects on the in tensities of electronic transition are examined. The vibronic coupling and cooperative interaction are analysed and confronted for complexes with L-ha nded and racemic ligand form. Following the vibrational analysis of the Ram an spectra the assignment of [Nd(Ile)(2)(H2O)(4)](2)(ClO4)(6) vibronics are given. The nature of observed phenomena is briefly discussed. (C) 1999 Els evier Science Ltd. All rights reserved.