Leucopterin, the white pigment in butterfly wings: structural analysis by PDF fit, FIDEL fit, Rietveld refinement, solid-state NMR and DFT-D.
Bravetti, Federica; Tapmeyer, Lukas; Skorodumov, Kathrin; Alig, Edith; Habermehl, Stefan; Hühn, Robert; Bordignon, Simone; Gallo, Angelo; Nervi, Carlo; Chierotti, Michele R.; Schmidt, Martin U.; IUCrJ 10 (2023) 448–463; doi:10.1107/S2052252523004281

data_1569411
_publ_section_title
;
 Leucopterin, the white pigment in butterfly wings: structural analysis by
 PDF fit, FIDEL fit, Rietveld refinement, solid-state NMR and DFT-D.
;
_journal_coeditor_code           LT5058
_journal_issue                   4
_journal_name_full               IUCrJ
_journal_page_first              448
_journal_page_last               463
_journal_paper_doi               10.1107/S2052252523004281
_journal_volume                  10
_journal_year                    2023
_chemical_formula_moiety         'C6 H5 N5 O3, 0.17(H2O)'
_chemical_formula_sum            'C6 H5.34 N5 O3.17'
_chemical_formula_weight         198.52
_chemical_melting_point          'decomposition at about 410 C'
_chemical_name_common
;
Leucopterin (variable hydrate)

Remark: According to Rietveld refinement, the structure contains a partially 
occupied H2O molecule, which is represented by a single oxygen atom O1W. 
Its occupancy value Occ(O1W) = 0.421(8) corresponds to 0.17 H2O per 
leucopterin molecule. But this value is very uncertain (Powder data 
of limited quality).
Hence, the water content of this structure should be regarded as being 
between 0 and 0.2 molecules of water per leucopterin molecule.
The crystal structure and the tautomeric state were confirmed by DFT-D
and SSNMR.
;
_space_group_crystal_system      monoclinic
_space_group_IT_number           13
_space_group_name_Hall           '-P 2yc'
_space_group_name_H-M_alt        'P 1 2/c 1'
_cell_angle_alpha                90
_cell_angle_beta                 88.5310(42)
_cell_angle_gamma                90
_cell_formula_units_Z            4
_cell_length_a                   8.10257(40)
_cell_length_b                   4.83656(29)
_cell_length_c                   17.8289(14)
_cell_measurement_reflns_used    310
_cell_measurement_temperature    296(2)
_cell_measurement_theta_max      70
_cell_measurement_theta_min      4
_cell_volume                     698.46(8)
_computing_structure_refinement  'TOPAS Academic 4.2 (Coelho, 2018)'
_computing_structure_solution
'FIDEL (Habermehl et al., Acta Cryst. 2014, B70, 347.)'
_diffrn_ambient_temperature      296(2)
_diffrn_measurement_device_type
'STOE Stadi-P with Ge(111) monochromator and linear PSD'
_diffrn_radiation_type           'Cu K\a~1~'
_diffrn_radiation_wavelength     1.54056
_diffrn_reflns_limit_h_max       9
_diffrn_reflns_limit_h_min       -9
_diffrn_reflns_limit_k_max       5
_diffrn_reflns_limit_k_min       -5
_diffrn_reflns_limit_l_max       21
_diffrn_reflns_limit_l_min       -21
_diffrn_reflns_theta_full        70
_diffrn_reflns_theta_max         70
_diffrn_reflns_theta_min         4
_diffrn_source                   'Cu tube'
_exptl_absorpt_coefficient_mu    1.365
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            white
_exptl_crystal_density_diffrn    1.888
_exptl_crystal_density_meas      'about 1.83'
_exptl_crystal_density_method    'suspension in iodobenzene does not separate'
_exptl_crystal_description       powder
_exptl_crystal_F_000             406.7
_pd_calc_method                  'Rietveld Refinement'
_pd_proc_2theta_range_inc        0.01
_pd_proc_2theta_range_max        70.
_pd_proc_2theta_range_min        4.
_pd_proc_ls_background_function  'Chebyshev polynomial with 20 terms'
_pd_proc_ls_pref_orient_corr     none
_pd_proc_ls_profile_function     'fundamental parameters'
_pd_proc_ls_prof_R_factor        0.10091
_pd_proc_ls_prof_wR_expected     0.06609
_pd_proc_ls_prof_wR_factor       0.10517
_pd_proc_wavelength              1.54056
_pd_spec_mounting                '0.7 mm capillary'
_pd_spec_mount_mode              transmission
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_all   1.591
_refine_ls_hydrogen_treatment    refall
_refine_ls_number_parameters     101
_refine_ls_number_reflns         310
_refine_ls_number_restraints     52
_refine_ls_R_factor_all          0.01192
_refine_ls_shift/su_max          0.01
_refine_ls_structure_factor_coef Fsqd
_reflns_number_total             1325
_cod_data_source_file            lt5058.cif
_cod_data_source_block           Leuco_hydrate
_cod_original_cell_volume        698.461(77)
_cod_original_sg_symbol_H-M      'P 2/c'
_cod_database_code               1569411