Single crystal growth and structural characterization of synthetic U(VI) peroxide phases, studtite (UO₂(O₂)(H₂O)₂·2H₂O) and metastudtite (UO₂(O₂)(H₂O)₂)
Benthin, Grant C.; Flester, Cameron J.; Forbes, Tori; CrystEngComm  (2026) –; doi:10.1039/D6CE00118A

data_7251868
_publ_section_title
;
 Single crystal growth and structural characterization of synthetic U(vi)
 peroxide phases, studtite (UO2(O2)(H2O)2&#x00B7;2H2O) and metastudtite
 (UO2(O2)(H2O)2)
;
_journal_issue                   16
_journal_name_full               CrystEngComm
_journal_page_first              2542
_journal_page_last               2547
_journal_paper_doi               10.1039/D6CE00118A
_journal_volume                  28
_journal_year                    2026
_chemical_formula_moiety         'H4 O6 U'
_chemical_formula_sum            'H4 O6 U'
_chemical_formula_weight         338.06
_chemical_name_common            Metastudtite
_chemical_name_systematic        Diaquaperoxo(dioxouranium(VI))
_space_group_crystal_system      orthorhombic
_space_group_IT_number           71
_space_group_name_Hall           '-I 2 2'
_space_group_name_H-M_alt        'I m m m'
_atom_sites_solution_hydrogens   difmap
_atom_sites_solution_primary     dual
_audit_creation_date             2025-12-31
_audit_creation_method
;
Olex2 1.5
(compiled 2025.07.13 svn.rb7424aed for OlexSys, GUI svn.r7314)
;
_audit_update_record
;
2026-02-04 deposited with the CCDC.	2026-04-08 downloaded from the CCDC.
;
_cell_angle_alpha                90
_cell_angle_beta                 90
_cell_angle_gamma                90
_cell_formula_units_Z            2
_cell_length_a                   4.1946(5)
_cell_length_b                   6.5143(9)
_cell_length_c                   8.7339(13)
_cell_measurement_reflns_used    3658
_cell_measurement_temperature    100
_cell_measurement_theta_max      25.328
_cell_measurement_theta_min      3.902
_cell_volume                     238.65(6)
_computing_cell_refinement       'SAINT V8.40B (?, 2016)'
_computing_data_reduction        'SAINT V8.40B (?, 2016)'
_computing_molecular_graphics    'Olex2 1.5 (Dolomanov et al., 2009)'
_computing_publication_material  'Olex2 1.5 (Dolomanov et al., 2009)'
_computing_structure_refinement  'XL  (Sheldrick, 2008)'
_computing_structure_solution    'SHELXT 2018/2 (Sheldrick, 2018)'
_diffrn_ambient_temperature      100
_diffrn_measured_fraction_theta_full 1.000
_diffrn_measured_fraction_theta_max 1.000
_diffrn_measurement_device_type  'Bruker D8 Quest'
_diffrn_measurement_method       '\f and \w scans'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0617
_diffrn_reflns_av_unetI/netI     0.0171
_diffrn_reflns_Laue_measured_fraction_full 1.000
_diffrn_reflns_Laue_measured_fraction_max 1.000
_diffrn_reflns_limit_h_max       5
_diffrn_reflns_limit_h_min       -5
_diffrn_reflns_limit_k_max       7
_diffrn_reflns_limit_k_min       -7
_diffrn_reflns_limit_l_max       10
_diffrn_reflns_limit_l_min       -10
_diffrn_reflns_number            3334
_diffrn_reflns_point_group_measured_fraction_full 1.000
_diffrn_reflns_point_group_measured_fraction_max 1.000
_diffrn_reflns_theta_full        25.242
_diffrn_reflns_theta_max         25.328
_diffrn_reflns_theta_min         3.902
_diffrn_source_current           1.0
_diffrn_source_power             0.05
_diffrn_source_voltage           50.0
_diffrn_standards_number         0
_exptl_absorpt_coefficient_mu    33.938
_exptl_absorpt_correction_T_max  0.0613
_exptl_absorpt_correction_T_min  0.0263
_exptl_absorpt_correction_type   multi-scan
_exptl_absorpt_process_details
;
SADABS-2016/2 (Bruker,2016/2) was used for absorption correction.
wR2(int) was 0.1335 before and 0.0979 after correction.
The Ratio of minimum to maximum transmission is 0.4290.
The \l/2 correction factor is Not present.
;
_exptl_crystal_colour            'clear light yellow'
_exptl_crystal_colour_lustre     clear
_exptl_crystal_colour_modifier   light
_exptl_crystal_colour_primary    yellow
_exptl_crystal_density_diffrn    4.704
_exptl_crystal_description       needle
_exptl_crystal_F_000             288
_exptl_crystal_preparation
'Dehydration of a single crystal of studtite at ambient temperature and pressure'
_exptl_crystal_size_max          0.12
_exptl_crystal_size_mid          0.015
_exptl_crystal_size_min          0.005
_refine_diff_density_max         3.482
_refine_diff_density_min         -0.657
_refine_diff_density_rms         0.413
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.198
_refine_ls_hydrogen_treatment    refall
_refine_ls_matrix_type           full
_refine_ls_number_parameters     23
_refine_ls_number_reflns         143
_refine_ls_number_restraints     2
_refine_ls_restrained_S_all      1.188
_refine_ls_R_factor_all          0.0350
_refine_ls_R_factor_gt           0.0350
_refine_ls_shift/su_max          0.004
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'w=1/[\s^2^(Fo^2^)+(0.0602P)^2^+6.5168P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.0843
_refine_ls_wR_factor_ref         0.0843
_reflns_Friedel_coverage         0.000
_reflns_number_gt                143
_reflns_number_total             143
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            d6ce00118a2.cif
_cod_data_source_block           gcb_135_4_cr3_dry1_ds2_vfinal
_cod_depositor_comments
'Adding full bibliography for 7251867--7251868.cif.'
_cod_original_sg_symbol_H-M      Immm
_cod_database_code               7251868
_shelx_shelxl_version_number     2019/1
_publ_section_validation_response
;
PLAT088_ALERT_3_B
PROBLEM: Poor Data/Parameter Ratio
RESPONSE: The low data-to-parameter ratio of 6.22 arises from the reality 
that the crystal is highly symmetric and only contains a few atoms. 
After merging symmetry-equivalent reflections, only 143 unique 
reflections remain, while 23 parameters were refined. This ratio is 
typical for small, highly symmetric structures with heavy atoms. Despite 
the limited ratio, the refinement is of reasonable quality (R1 = 0.035, 
wR2 = 0.084, GOF = 1.20) and is chemically sensible. Given the nature 
of the compound and symmetry constraints, the ratio is unavoidable and 
does not compromise the validity of the structural model.

PLAT094_ALERT_2_B
PROBLEM: Ratio of Maximum / Minimum Residual Density
RESPONSE: The relatively high ratio of maximum to minimum residual 
density (5.3) is likely due to the presence of uranium in a small unit 
cell with only a few light atoms. The significant positive peaks and 
negative holes are located near the uranium atom and are likely the result 
of Fourier truncation effects around U center. These features are common 
in actinide structures, especially those with limited data resolution, and 
do not indicate missing atoms or disorder.

PLAT971_ALERT_2_B
PROBLEM: Check Calcd Resid. Dens.  1.10Ang From U1
RESPONSE: The relatively large residual peak of 3.31 eA-3 at about 1.1 A 
from U1 is typical for structures with heavy atoms like uranium. The peak 
does not correspond to any chemically reasonable additional atom or 
ligand. Attempts to model extra sites, split positions, twinning, or 
alternative unit cells/space groups did not lead to improvement in 
R-values. Given these factors, the residual peak is considered acceptable 
and does not affect the validity of the model.

PLAT215_ALERT_3_C
PROBLEM: Disordered O1 has ADP max/min Ratio
RESPONSE: O1 lies on a special position in space group Immm and was 
refined anisotropically with partial occupancy (0.5). The elevated ADP 
ratio of 3.9 may reflect residual anisotropy due to symmetry constraints 
and limited data rather than true physical disorder. Attempts to model 
alternative disorder or split positions did not improve refinement or 
R-values. The current model is chemically reasonable and consistent with 
expected U-O bonding.

PLAT975_ALERT_2_C (multiple)
PROBLEM: Check Calcd Resid. Dens.
RESPONSE: The positive residuals near the oxygen atoms are likely due to 
nearby hydrogen atoms restrained using DFIX and DANG restraints and the 
presence of a heavy uranium atom. These residuals are considered typical 
and are not indicative of modeling issues.

PLAT976_ALERT_2_C
PROBLEM: Check Calcd Resid. Dens.
RESPONSE: The small negative residual feature near O1 is generally 
considered acceptable given the presence of a heavy atom (uranium).
Attempts to model alternative disorder/occupancy for O1 did not improve 
R-values or reduce the feature. The refinement is otherwise robust (R1 = 
0.035, wR2 = 0.084, GOF = 1.20), and the model provides chemically 
sensible geometry for U-O(peroxo) and U-O(water) bonding. Overall, the 
feature is considered acceptable and not indicative of a model deficiency.
;
_shelx_estimated_absorpt_t_max   0.849
_shelx_estimated_absorpt_t_min   0.106
_olex2_refinement_description
;
1. Restrained distances
 O3-H3
 0.97 with sigma of 0.02
 H3-U1
 3.114 with sigma of 0.04
2. Others
 Fixed Sof: O2(0.25) O1(0.25)
;
_shelx_res_checksum              68314
_olex2_date_sample_completion    2025-01-06
_olex2_date_sample_data_collection 2025-01-03
_olex2_date_sample_submission    2025-01-03
_olex2_submission_original_sample_id GCB_135_4_cr3_dry1
_olex2_submission_special_instructions 'No special instructions were received'