‘Facial’ and ‘meridional’ coordination geometries and luminescence properties of tris(N-[(imidazol-4-yl)methylidene]-dl-alaninato)europium(III) and tris(N-[(imidazol-4-yl)methylidene]-dl-phenylalaninato)europium(III)

Two racemic tridentate ligands, N-[(imidazol-4-yl)methylidene]-dl-alanine (H2Ldl-ala) and N-[(imidazol-4-yl)methylidene]-dl-phenylalanine (H2Ldl-phe), were synthesized by the 1:1 condensation reaction of 4-formylimidazole and either of dl-alanine and dl-phenylalanine, respectively. The EuIII complexes ‘fac’-[EuIII(HLdl-ala)3]·8H2O (1) and ‘mer’-[EuIII(HLdl-phe)3]·7.75H2O (2) were synthesized by mixing the ligand and EuIII(acetate)3 n-hydrate with 3:1M ratio in methanol and the crystal structures were determined. Compounds 1 and 2 with three tridentate ligands have ‘facial’ and ‘meridional’ geometries, respectively, while they have a tricapped trigonal prismatic (TTP) and a capped square antiprismatic (CSAP) coordination geometry, respectively. In the crystal lattice, 1 consists of enantiomers ‘fac’-[EuIII(HLd-ala)3] and ‘fac’-[EuIII(HLl-ala)3], while 2 consists of ‘mer’-[EuIII(HLd-phe)2(HLl-phe)] and ‘mer’-[EuIII(HLd-phe)(HLl-phe)2]. Compounds 1 and 2 displayed sharp emission bands based on the f−f transitions by excitation and showed a different emission pattern due to their ‘fac’- and ‘mer’-coordination geometries. The luminescence quantum yields and life times of 1 and 2 were estimated to be (Φ=0.25 and 1.40ms) and (Φ=0.30 and 1.23ms), respectively.