Structural and selectivity of 18-crown-6 ligand in lanthanide–picrate complexes

Coordination of trivalent lanthanum with polyethylene glycol in the presence of picrate anion: Spectroscopic and X-ray structural studies

“…The conformation in the inner coordination sphere of [La(Pic) 2 (EO5)] + (Fig. 2(c)) is similar to that of the 18-crown-6 complexes [1,[5][6][7][8]17]. The acyclic PEG ligand was coordinated to La 3+ in I-IV, which exhibited pseudo-cyclic behavior (Fig.…”

“…The absorption band due to the (C-H) symmetric stretching at 2879-2874 cm −1 was significantly shifted to the higher wavelength, namely 2954-2949 cm −1 , indicating that the PEG ligands rearranged to the cyclic conformation [5][6][7][8]24]. The stretching bands from s (NO 2 ) were split into two bands, which indicates that the Pic anion was coordinated to La 3+ through the phenolic oxygen and the oxygen of one ortho-nitro group, forming a bidentate ligand [5][6][7][8][25][26][27]. The absorption band assigned to (C-N) at 920-940 cm −1 was shifted to 936-945 cm −1 , indicating that the coordinated Pic anion affected the C-N bonds.…”

“…The preparations of the complexes were carried out as described previously [5][6][7][8]. A mixture of EO3 (0.454 g, 3.0 mmol), HPic (0.917 g, 4 mmol), and [La(NO3)3·7H2O] (0.434 g, 1 mmol) was dissolved in 30 mL acetonitrile:methanol:water (3:3:1, v/v).…”

“…The use of PEG as a ligand coordinated to Ln 3+ in the presence of picrate anion (Pic) has been structurally characterized in our laboratory [5][6][7][8]. The light and heavy rare-earth elements effectively control the geometry of the coordination sphere [8].…”

“…In addition, the Pic anion dictates the structure of the complexes through strong steric effects [7,8]. Lanthanide complexes with PEG have previously been reported [1,[9][10][11][12][13][14][15][16][17][18][19], while complexes of PEG-Pic coordinated to the lanthanides in the coordination sphere have yet to be described in the literature.…”