Refinement of the crystal structure of fresnoite, Ba<sub>2</sub>TiSi<sub>2</sub>O<sub>8</sub>, from Löhley (Eifel district, Germany); Gladstone-Dale compatibility, electronic polarizability and vibrational spectroscopy of minerals and inorganic compounds with pentacoordinated Ti<sup>IV</sup> and a titanyl bond.
Chukanov, Nikita V.; Kazheva, Olga N.; Fischer, Reinhard X.; Aksenov, Sergey M.; Acta crystallographica Section B, Structural science, crystal engineering and materials 79 (2023) 184–194; doi:10.1107/S2052520622012045

data_2109101
_publ_section_title
;
 Refinement of the crystal structure of fresnoite,
 Ba<sub>2</sub>TiSi<sub>2</sub>O<sub>8</sub>, from L&#xf6;hley (Eifel
 district, Germany); Gladstone-Dale compatibility, electronic
 polarizability and vibrational spectroscopy of minerals and inorganic
 compounds with pentacoordinated Ti<sup>IV</sup> and a titanyl bond.
;
_journal_coeditor_code           RA5120
_journal_issue                   2
_journal_name_full
'Acta crystallographica Section B, Structural science, crystal engineering and materials'
_journal_page_first              184
_journal_page_last               194
_journal_paper_doi               10.1107/S2052520622012045
_journal_volume                  79
_journal_year                    2023
_chemical_formula_sum            'Ba2 O8 Si2 Ti'
_chemical_formula_weight         506.76
_space_group_crystal_system      tetragonal
_space_group_IT_number           100
_space_group_name_Hall           'P 4 -2ab'
_space_group_name_H-M_alt        'P 4 b m'
_audit_creation_method           SHELXL-2018/3
_cell_angle_alpha                90
_cell_angle_beta                 90
_cell_angle_gamma                90
_cell_formula_units_Z            2
_cell_length_a                   8.5104(12)
_cell_length_b                   8.5104(12)
_cell_length_c                   5.1975(10)
_cell_measurement_reflns_used    11109
_cell_measurement_temperature    293(2)
_cell_measurement_theta_max      33.378
_cell_measurement_theta_min      3.385
_cell_volume                     376.44(10)
_computing_structure_refinement  'SHELXL-2018/3 (Sheldrick, 2018)'
_diffrn_ambient_temperature      293(2)
_diffrn_measured_fraction_theta_full 1.000
_diffrn_measured_fraction_theta_max 1.000
_diffrn_measurement_device_type  'Xcalibur, Eos'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0325
_diffrn_reflns_av_unetI/netI     0.0087
_diffrn_reflns_Laue_measured_fraction_full 1.000
_diffrn_reflns_Laue_measured_fraction_max 1.000
_diffrn_reflns_limit_h_max       13
_diffrn_reflns_limit_h_min       -13
_diffrn_reflns_limit_k_max       13
_diffrn_reflns_limit_k_min       -13
_diffrn_reflns_limit_l_max       8
_diffrn_reflns_limit_l_min       -8
_diffrn_reflns_number            25512
_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         33.378
_diffrn_reflns_theta_min         3.385
_exptl_absorpt_coefficient_mu    11.710
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            yellow
_exptl_crystal_density_diffrn    4.471
_exptl_crystal_description       parallelepiped
_exptl_crystal_F_000             452
_exptl_crystal_size_max          0.25
_exptl_crystal_size_mid          0.14
_exptl_crystal_size_min          0.13
_refine_diff_density_max         0.868
_refine_diff_density_min         -0.648
_refine_diff_density_rms         0.120
_refine_ls_abs_structure_details
;
 Refined as an inversion twin.
;
_refine_ls_abs_structure_Flack   0.01(3)
_refine_ls_extinction_coef       0.0165(7)
_refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^
_refine_ls_extinction_method     'SHELXL-2018/3 (Sheldrick 2018)'
_refine_ls_goodness_of_fit_ref   1.196
_refine_ls_hydrogen_treatment    undef
_refine_ls_matrix_type           full
_refine_ls_number_parameters     40
_refine_ls_number_reflns         807
_refine_ls_number_restraints     1
_refine_ls_restrained_S_all      1.196
_refine_ls_R_factor_all          0.0115
_refine_ls_R_factor_gt           0.0115
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'w=1/[\s^2^(Fo^2^)+(0.0047P)^2^+0.9597P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.0267
_refine_ls_wR_factor_ref         0.0267
_reflns_Friedel_coverage         0.834
_reflns_Friedel_fraction_full    1.000
_reflns_Friedel_fraction_max     1.000
_reflns_number_gt                806
_reflns_number_total             807
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            ra5120sup1.cif
_cod_data_source_block           I
_cod_depositor_comments          'Adding full bibliography for 2109101.cif.'
_cod_original_cell_volume        376.44(13)
_cod_database_code               2109101
_cod_database_fobs_code          2109101
_shelx_shelxl_version_number     2018/3
_shelx_res_checksum              49922
_shelx_hkl_checksum              34325