Formation of a new type of uranium(iv) poly-oxo cluster {U38} based on a controlled release of water via esterification reaction

A strategy for the formation of uranium(iv) clusters consists of water release from esterification reaction to generate {U38} species.


Esterification reaction scheme
: Classical scheme of the reaction of benzoic acid with isopropanol resulting in the formation of an ester and the release of one water molecule.

Checkcif comments
Comments on the Alert A in the checkcif file for the compounds 1 and 2. For 1, the alert A correspond to a problem for converging one H atom of the disordered isopropanol molecule attached to the ligand ("B" backbone), due to its proximity of other neighboring H atoms induced by the disordering situation.
For 2, The six alerts A in the checkcif file concern residual density located on the heavy uranium atoms (about 3.2-2.2 e.Å -3 ). This abnormally values would be due to the fact that the crystal has been enveloped with a too large amount of grease in order to prevent any decomposition under air atmosphere. It induces some problems with adsorption and diffusion processes, which interfere on the electron density map.

Figure S3a
: Detailed view of the disorder of the attached isopropanol ligands to the uranium center U1 in complex 1. One of the two isopropanol molecules is found disordered on two close positions with the ratio 75/25 for the "A'(grey bonds) and "B" (purple bonds) backbones, respectively. Figure S3b: Representation of the disordered isopropanol molecules intercalated between two dinuclear entities U 2 Cl 4 (bz) 4 (ipa) 4 ], in complex 1. This isopropanol species has been refined with an occupancy factor of 0.25, and is located on two close positions. Hydrogen bonds interactions (dotted orange line) are observed between the OH groups of the attached isopropanol, and OH groups of the isopropanol. The bond valence sum is expected to be 2.0 for an oxo group, 1.2 for a hydroxo group and 0.4 for an aquo group.

UV-Vis spectroscopy
The UV-Visible absorption spectra were measured for the supernatants obtained after the solvothermal treatment at 100 °C with different reaction times (8, 24 and 96 h) ( Figure S4). The spectra indicate strong absorption bands in the range between 580 and 720 nm, which are typically assigned to the electronic transitions of 3 H 4  3 P 0 , 3 H 4  1 G 4 and 3 H 4  1 D 2 of U(IV). Indeed, two intense bands are appeared at 644 and 674 nm together with a shoulder at 602 nm. Another significant absorption is also clearly visible at 560 nm, which is assigned to the electronic transitions of 3 H 4  3 P 1 . The intensities of these bands slightly decreased then the reaction time increased from 8 to 24 h, which is related to the reaction yields of 3.3 and 36.7%, respectively. The intensities further decreased when the reaction time was 96 h, corresponding to the yield of 80.9%. This reflects the consumption of soluble uranium species for the crystallization of the {U 38 } cluster.

Figure S6a
: Kinetic curve of the crystallization rate of the {U 38 } polyoxo cluster (heating at 100°C), between 8 and 120 hours. Black lozenges: experimental data; red curve: calculated fit using the Avrami Arofe'ev equation.  Figure S7: 1 H NMR spectra of the supernatants obtained after the solvothermal reactions to produce the {U 38 } cluster at 100°C for 8 (blue), 16 (green) and 24 hours (red). The data were recorded at 400 MHz and 285K. The range corresponds to the free -OH group of isopropanol (broad signal) and -CH groups of the ester molecule (weak multiplet signals).  Figure S9b: Powdered X-ray diffraction patterns (copper radiation) of the resulting precipitate from the reaction of UCl 4 with different amounts of water in isopropanol solvent, after heating at 100°C. The reference of the dense uranium dioxide UO 2 with the fluorite-structure type (PDF No 03-065-0285) is indicated in red, for comparison. S10 Figure S10a: Evolution of the room temperature SAXS curves of the supernatant as a function of time (t = 0h, 4h, 8h, 10h, 16h, 24h). The liquid phase analyzed by SAXS corresponds to the resulting solution from the mixture of UCl 4 and benzoic acid in isopropanol after heating at 100°C.

Figure S10b
: Time-dependent evolution of the concentration of condensed species in the supernatant derived from the SAXS curves collected after heating at 100 °C. The data were collected at room temperature.