Identifying Coordination Geometries of Metal Aquaions in Water: Application to the Case of Lanthanoid and Actinoid Hydrates

Abstract

The angular distribution function (ADF) associated with the oxygen-metal ion-oxygen angle (OMO) of several trivalent lanthanoid and actinoid aquaions has been used to identify the most probable coordination geometry of these aquaions in aqueous solutions. The ADFs extracted from the molecular dynamics trajectories have been compared with continuous distribution functions corresponding to the geometry of a reference polyhedron pattern. The procedure incorporates specific quantum-mechanical information on the aquaion under study. The new method is applied to the analysis of four M(HO) aquaions in water, M = Lu and Cf for n = 8, and M = La and Ac for n = 9. For those that are 8-coordinated, the square antiprism (SA) coordination geometry is preferred. For the 9-fold coordination, the simulation ADFs are more similar to the continuous ADF derived from a Gyro-elongated-SA rather than to the usually proposed trigonal tricapped prism. Advantages of these continuous distributions with respect to the usually employed discrete distributions are emphasized as well as further applications are suggested.

Ion Association in Lanthanide Chloride Solutions

“…Figure S4 in the Supporting Information shows O‐Ln‐O angles and Ln‐O‐ M angle probability distributions in which M is the bisector between the two water O−H bonds; hence, the Ln‐O‐ M angle quantifies the relative tilt of water molecules surrounding the cation. Bimodal distributions are observed in both DFT‐MD and C‐MD for Nd, consistent with earlier work . As discussed by Qiao et al., the peaks centred around 70° and 135° represent either the TTP or the gyroelongated square‐antiprism (GySQAP) geometries with slight deformations.…”

“…Bimodal distributionsa re observed in both DFT-MD and C-MD for Nd, consistent with earlier work. [41,50,88,89] As discussed by Qiao et al, [50] the peaks centred around7 0 8 and 1358 represente ither the TTP or the gyroelongated square-antiprism (GySQAP) geometries with slight deformations. The TTP geometries dominated our simulations of nona-aquo Nd complexes but we did find as maller population of GySQAP complexes.…”

Advancing understanding of actinide(iii) (Ac, Am, Cm) aqueous complexation chemistry

“…Hence, the compounds were homoleptic and no bound H 2 O was observed. This 9-coordinate geometry approached a mono-capped square antiprism, 24 which is wellestablished for lanthanides 25 and actinides. 26 Average metal-O O2CMe distances have been provided in Table 1.…”

On the development of polarizable and Lennard-Jones force fields to study hydration structure and dynamics of actinide(III) ions based on effective ionic radii

“…MD simulations reported for An 3+ ions are scarce (most of them refer to Cm 3+ and Cf 3+ ), and different authors have developed in the last few years different force fields (generally polarizable) for these ions. 9,[12][13][14][15][16] In Table II, we report these results, as well as some density functional theory (DFT)-based and Monte Carlo (MC) simulations. 10,14 For Cm 3+ , previous simulations report longer distances and a CN generally of 9, with the exception of the AMOEBA force field 15 which provides distances similar to our results for both Cm 3+ and Am 3+ .…”

“…Investigations of An 3+ ions in liquid water were thus performed in recent years by a number of experimental and theoretical studies. 2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Note that experimental data are mainly a) Electronic mail: riccardo.spezia@univ-evry.fr present from U 3+ to Cf 3+ , while for Es 3+ , only a diffusion coefficient value is reported. 19 A particularly useful theoretical method aimed at understanding water structure and dynamics around these ions (and thus characterizing their hydration behavior) is molecular dynamics (MD).…”