Supramolecular architectures of N,N,N′,N′-tetrakis-(2-hydroxyethyl)ethylenediamine and tris(2-hydroxyethyl)amine with La(iii) picrate†

The present work consists of synthesis, crystal structure and computational analyses of supramolecular architectures: complexes [La(THEEN)(PIC)(H₂O)₂](PIC)₂·2H₂O (1), [La(TEAH₃)₂(H₂O)₂](PIC)₃ (2) and compounds [THEENH₂⁺ (PIC^?)₂] (I) and [TEAH₄⁺( PIC^?)] (II) where THEEN is N,N,N′,N′-tetrakis-(2-hydroxyethyl)ethylenediamine (a tetrapodal ligand) and TEAH₃ is triethanolamine (a tripodal ligand). Compounds I and II are formed as a result of the proton-transfer from picric acid to the tetrapodand and tripodand respectively. The chains of tetrapodal ligand (THEEN) coordinate through all their six potential donor sites to the La(III) ion. The torsion angle of the N–C–C–N moiety is anti in compound (I) while it is gauche in compound 1. The chains of the tripodal ligand (TEAH₃) coordinate to La(III) through all their four potential donor sites. The complexes (1) and (2) have acquired distorted bicapped square-antiprismatic geometry with a coordination number 10. Computational studies of complexes 1 and 2 and compounds I and II in the gaseous state revealed a good coherence of structural parameters with that of crystal structure analyses. B3LYP/6-31G level of Gaussian 03 has been used for optimization, calculation of structural parameters and energy gaps of frontier orbitals (HOMO–LUMO) for complexes 1, 2 and compounds I and II. The additional LANL2DZ set was used to locate La(III) for performing calculations in complexes 1 and 2. Theoretically computed HOMO–LUMO studies predicted that both complexes and compounds are stable. The reported work is discussed from four aspects: supramolecular architectures, lanthanum coordination chemistry, torsion angles of the ligands in the proton-transfer species I and II with the complexes 1 and 2 and comparison of their crystal structures with the computationally optimized structures of all the four species i.e., complexes 1, 2 and supramolecular architectures I and II.