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_7251867
_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, 2(H2 O)'
_chemical_formula_sum            'H8 O8 U'
_chemical_formula_weight         374.09
_chemical_name_common            Studtite
_chemical_name_systematic        'Diaquaperoxo(dioxouranium(VI)) Dihydrate'
_space_group_crystal_system      monoclinic
_space_group_IT_number           15
_space_group_name_Hall           '-C 2yc'
_space_group_name_H-M_alt        'C 1 2/c 1'
_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                 123.143(3)
_cell_angle_gamma                90
_cell_formula_units_Z            4
_cell_length_a                   13.9991(13)
_cell_length_b                   6.7481(7)
_cell_length_c                   8.4848(9)
_cell_measurement_reflns_used    1724
_cell_measurement_temperature    100
_cell_measurement_theta_max      25.39
_cell_measurement_theta_min      3.48
_cell_volume                     671.13(12)
_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 0.998
_diffrn_measured_fraction_theta_max 0.998
_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  0.0403
_diffrn_reflns_av_unetI/netI     0.0296
_diffrn_reflns_Laue_measured_fraction_full 0.998
_diffrn_reflns_Laue_measured_fraction_max 0.998
_diffrn_reflns_limit_h_max       16
_diffrn_reflns_limit_h_min       -16
_diffrn_reflns_limit_k_max       8
_diffrn_reflns_limit_k_min       -8
_diffrn_reflns_limit_l_max       9
_diffrn_reflns_limit_l_min       -10
_diffrn_reflns_number            2986
_diffrn_reflns_point_group_measured_fraction_full 0.998
_diffrn_reflns_point_group_measured_fraction_max 0.998
_diffrn_reflns_theta_full        25.242
_diffrn_reflns_theta_max         25.386
_diffrn_reflns_theta_min         3.476
_diffrn_source_current           1.0
_diffrn_source_power             0.05
_diffrn_source_voltage           50.0
_diffrn_standards_number         0
_exptl_absorpt_coefficient_mu    24.177
_exptl_absorpt_correction_T_max  0.4288
_exptl_absorpt_correction_T_min  0.2803
_exptl_absorpt_correction_type   multi-scan
_exptl_absorpt_process_details
;
SADABS-2016/2 (Bruker,2016/2) was used for absorption correction.
wR2(int) was 0.0892 before and 0.0513 after correction.
The Ratio of minimum to maximum transmission is 0.6537.
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    3.702
_exptl_crystal_description       needle
_exptl_crystal_F_000             656
_exptl_crystal_size_max          0.06
_exptl_crystal_size_mid          0.005
_exptl_crystal_size_min          0.005
_refine_diff_density_max         0.797
_refine_diff_density_min         -0.901
_refine_diff_density_rms         0.197
_refine_ls_extinction_coef       0.00045(13)
_refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^
_refine_ls_extinction_method     'SHELXL-2019/1 (Sheldrick 2019)'
_refine_ls_goodness_of_fit_ref   1.226
_refine_ls_hydrogen_treatment    refall
_refine_ls_matrix_type           full
_refine_ls_number_parameters     60
_refine_ls_number_reflns         619
_refine_ls_number_restraints     6
_refine_ls_restrained_S_all      1.220
_refine_ls_R_factor_all          0.0493
_refine_ls_R_factor_gt           0.0281
_refine_ls_shift/su_max          0.000
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'w=1/[\s^2^(Fo^2^)+14.5849P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.0427
_refine_ls_wR_factor_ref         0.0478
_reflns_Friedel_coverage         0.000
_reflns_number_gt                443
_reflns_number_total             619
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            d6ce00118a2.cif
_cod_data_source_block           gcb_124_5_crys6_0m
_cod_depositor_comments
'Adding full bibliography for 7251867--7251868.cif.'
_cod_original_sg_symbol_H-M      C2/c
_cod_database_code               7251867
_shelx_shelxl_version_number     2019/1
_shelx_estimated_absorpt_t_max   0.889
_shelx_estimated_absorpt_t_min   0.325
_diffrn_oxdiff_ac3_digest_hkl    41454ae477728725998f2bddbc712ec285e04a
_olex2_refinement_description
;
1. Restrained distances
 O4-H4A
 0.97 with sigma of 0.02
 O4-H4B
 0.97 with sigma of 0.02
 O3-H3A
 0.97 with sigma of 0.02
 O3-H3B
 0.97 with sigma of 0.02
 H3B-H3A
 1.534 with sigma of 0.04
 H4A-H4B
 1.534 with sigma of 0.04
;
_shelx_res_checksum              82218
_olex2_date_sample_completion    2024-09-13
_olex2_date_sample_data_collection 2024-07-08
_olex2_date_sample_submission    2024-07-08
_olex2_submission_original_sample_id GCB-124-5-crys6
_olex2_submission_special_instructions 'No special instructions were received'
_special_details
;
Validation Responses to checkCIF Alerts:

PLAT041_ALERT_1_C
PROBLEM: Calc. and Reported SumFormula   Strings Differ
Response: The difference arises because the uranium atom lies on a 
special position in space group C2/c, reducing the number of independent 
atoms in the asymmetric unit. checkCIF interprets this as Z = 2, but 
the correct value is Z = 4, as stated in the CIF and confirmed by the 
UNIT line (H32 O32 U4). The reported formula (H8 O8 U) represents one 
asymmetric unit, while the full unit cell contains four formula units. 
No structural issues are present; the difference is due to the handling 
of special positions and asymmetric unit representation.

PLAT042_ALERT_1_C
PROBLEM: Calc. and Reported MoietyFormula Strings  Differ 
RESPONSE: See response to PLAT041. The reported and calculated moiety 
formulas differ because checkCIF interprets this structure as Z = 2, 
while the correct value is Z = 4. All relevant values differ by the same 
factor, so this alert can be safely ignored.

PLAT906_ALERT_3_C (multiple)
PROBLEM: Large K Value in the Analysis of Variance
RESPONSE: These alerts indicate large K values in the analysis of 
variance (K = 31.109 and K = 3.380). These high K values likely result 
from the presence of heavy atoms (U) and the standard weighting scheme 
used. The refinement is stable (shift/su max = 0.000), with good R-values 
(R1 = 0.0281, wR2 = 0.0478)and no signs of modeling issues. The alerts 
are not considered significant for this structure type.

PLAT975_ALERT_2_C (multiple)
PROBLEM: Check Calcd Resid. Dens.
RESPONSE: The positive residuals near O2 and O3 are likely due to nearby 
hydrogen atoms restrained using DFIX and DANG restraints and the presence 
of heavy uranium atoms. These residuals are typical and not indicative 
of modeling issues.

PLAT976_ALERT_2_C (multiple)
PROBLEM: Check Calcd Resid. Dens.
RESPONSE: The negative residuals near O2 and O3 are common in structures 
with heavy atoms like uranium. They likely result from scattering 
contrast and idealized hydrogen placement. No signs of disorder or 
instability were found.

PLAT977_ALERT_2_C
PROBLEM: Check Negative Difference Density on H4B
RESPONSE: The small negative difference density near H4B (-0.31 eA-3) 
is typical for hydrogen atoms refined with idealized positions and 
isotropic displacement parameters, especially in the presence of heavy 
atoms like uranium. This does not indicate a modeling issue or disorder.
;