Glycine complexation with uranyl ion: absorptiometric, luminescence, and X-ray structural studies of tetrakis(glycine)dioxouranium(VI) nitrate

Abstract

Addition of glycine to uranyl nitrate in aqueous acidic solution induces shifts in both the highly structured absorption and emission bands in the visible region. An analysis by Job's method indicates the formation of a complex of stoicheiometry uranyl ion : glycine of 1 : 4. The structure determination of a single crystal of the complex [UO,(O,CCH,NH,),][NO,], by X-ray diffraction methods confirms this formulation. The structure has been refined to an R factor of 0.026 using 2 281 'observed' measured intensities. The complex is triclinic, space group P i , with hexagonal bipyramidal co-ordination about the uranium atom. All the glycine ligands are in the zwitterionic form, NH: CH, CO; and act as 0-donors; two are bidentate [U-0 = 2.562(5)-2.489(6) A], and two unidentate [mean U-0 = 2.437(4) A]. The uranyl U=O distance is 1.771 ( 5) A (mean).Complexation of the dioxouranium(v1) (or uranyl) ion, [UO,]", by carboxylic acids has been widely studied and has been thoroughly reviewed recently. ' Of particular interest has been the site and extent of co-ordination by ambidentate ligands, especially with N-donor atoms. ' y 2 The simplest aminoacid, glycine, has attracted over 20 investigations of which the most recent3 provides a reasonably unified picture of the situation prevailing in fairly dilute solution, namely that ligation proceeds through the carboxylate group with no involvement of the amino-group. This potentiometric study indicates that 1 : 1 and 1 :2 complexes are formed with log p2 = 2.20 which agrees well with a value of 2.14 obtained p~larographically.~ No complexes higher than 1 : 2 were detected which contrasts with the situation both for RhIV and, according to one r e p ~r t , ~ for complexation of glycine with dioxo(suIphato)uranium(vr), for which tris-glycine formulations are given. While the bulk of the evidence clearly favours co-ordination via the carboxylate group, Sergeev and Korshunov suggest participation of the amino-group both in the glycinato(1 -)uranyl complex6 and in glycinato(1 -)thorium(rv) complexes,' on the basis both of the observed stability constants and of the NH frequency in the i.r. spectra. Such N-co-ordination is established for the bis(g1ycinato)complex of Cu", which is bis-chelated in a single plane with glycine as the monoanion, while reaction of glycine with ~i s -[ P t ( N H ~) ~( H ~0 ) , 1 ~+ in water gives initially cis-[Pt11(NH3)2(gly)(H20)]Z + [gly = 0-co-ordinated zwitterion of glycine] which converts slowly into the (N,O)-chelate complex.8bAccordingly, we have undertaken a study of the interaction of glycine with uranyl ion utilising absorptiometric and luminescence methods in solution and, in the solid state, a structure determination by X-ray crystallography. ExperimentalAbsorption spectra were recorded on Perkin-Elmer model 552 and Shimadzu model UV-365 instruments. Luminescence spectra were recorded on a Perkin-Elmer model MPF-3 spectrofluorimeter. Luminescence lifetimes were determined with our laser flash kinetic spectrophotometer (Applied Photophysics, Lond...

Uranyl-Glycine-Water Complexes in Solution: Comprehensive Computational Modeling of Coordination Geometries, Stabilization Energies, and Luminescence Properties

“…This scenario is also found in the crystal structures of solid uranyl glycine complexes. 15,16 Upon increase of CN eq by 1 unit, we observe the common increase of the coordination distances, for U-O aq around 0.08 Å and for U-O Gly a little less. The U-O aq distances of the internally hydrogen-bonded H 2 O in the monodentate cases are about 0.08 Å shorter.…”

“…These trends are again consistent with experimental results of related crystal structures. 15,16,25 The structures with low relative energies are displayed in Table 2. The energy changes due to embedding the species in the model solvent are relatively small, that is, comparable to room temperature kT (∼0.6 kcal/mol).…”

Investigation on uranyl interaction with bioactive ligands. Synthesis and structural studies of the uranyl complexes with glycine and N-(2-mercaptopropionyl)glycine

“…The neutral charge of the complex suggests that the two amino groups are protonated. The U VI =O bond lengths at 1.771(5) and 1.777(5) Å are in the range 1.71 to 1.82 Å reported in the literature for the uranyl complexes, ( Table 2) (see Although the coordination of the uranyl moiety with carboxylate groups has been studied thoroughly in the past with single crystal X-ray analysis [10,[15][16][17][18], there is only one other example in the literature of uranium complex, [UO 2 (Hgly) 4 ](NO 3 ) 2 , with amino acids characterized by crystallography [19]. The uranium atom in this complex is coordinated with four oxygen donor zwitterionic glycines, two of them are bidentate with U−O bond distance range between 2.562-2.489 Å and the other two are monodentate with mean U−O 2.437 Å.…”

Synthesis and characterization of uranyl(VI) chiral Schiff-base complexes derived from salicylaldehyde and L-aminoacids

“…The most reported studies focus on U(VI) complexes with aminoacids based on L-glycine [14,15], L-cysteine [16], histidine [17], tyrosine [18], and tryptophan [19]. Heteroditopic chiral uranyl-salen can be used as receptor for molecular recognition of amino acid ammonium salts [20].…”