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...