Why are B2O2 rings rare?
Burke, Jacquelyn M.; Fox, Mark A.; Goeta, Andrés E.; Hughes, Andrew K.; Marder, Todd B.; Chemical Communications  (2000) 2217–; doi:10.1039/b006685k

data_7111103
_publ_section_title
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 Why are B2O2 rings rare?
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_journal_issue                   22
_journal_name_full               'Chemical Communications'
_journal_page_first              2217
_journal_paper_doi               10.1039/b006685k
_journal_year                    2000
_chemical_formula_sum            'C18 H16 B2 F5 O P'
_chemical_formula_weight         395.90
_space_group_IT_number           14
_symmetry_cell_setting           monoclinic
_symmetry_space_group_name_Hall  '-P 2yn'
_symmetry_space_group_name_H-M   'P 1 21/n 1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_atom_sites_solution_secondary   difmap
_audit_creation_method           SHELXL-97
_cell_angle_alpha                90.00
_cell_angle_beta                 93.688(3)
_cell_angle_gamma                90.00
_cell_formula_units_Z            4
_cell_length_a                   11.638(3)
_cell_length_b                   12.174(3)
_cell_length_c                   13.542(3)
_cell_measurement_reflns_used    617
_cell_measurement_temperature    150(2)
_cell_measurement_theta_max      21.10
_cell_measurement_theta_min      13.80
_cell_volume                     1914.7(8)
_computing_cell_refinement       'SMART-NT V5.0 (Bruker, 1998a)'
_computing_data_collection       'SMART-NT V5.0 (Bruker, 1998a)'
_computing_data_reduction        'SAINT-NT V5.0 (Bruker, 1998b)'
_computing_molecular_graphics    'SHELXTL-NT V5.1 (Bruker, 1998c)'
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 1997)'
_computing_structure_solution    'SHELXS-97 (Sheldrick, 1990)'
_diffrn_ambient_temperature      150(2)
_diffrn_measured_fraction_theta_full 0.931
_diffrn_measured_fraction_theta_max 0.931
_diffrn_measurement_device_type  'Bruker SMART-CCD'
_diffrn_measurement_method       \w
_diffrn_radiation_monochromator  graphite
_diffrn_radiation_source         'fine-focus sealed tube'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0390
_diffrn_reflns_av_sigmaI/netI    0.0340
_diffrn_reflns_limit_h_max       16
_diffrn_reflns_limit_h_min       -16
_diffrn_reflns_limit_k_max       17
_diffrn_reflns_limit_k_min       -17
_diffrn_reflns_limit_l_max       18
_diffrn_reflns_limit_l_min       -18
_diffrn_reflns_number            22662
_diffrn_reflns_theta_full        30.49
_diffrn_reflns_theta_max         30.49
_diffrn_reflns_theta_min         2.24
_diffrn_standards_decay_%        0
_diffrn_standards_number         0
_exptl_absorpt_coefficient_mu    0.194
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            colourless
_exptl_crystal_density_diffrn    1.373
_exptl_crystal_density_meas      ?
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       irregular
_exptl_crystal_F_000             808
_exptl_crystal_size_max          0.34
_exptl_crystal_size_mid          0.22
_exptl_crystal_size_min          0.18
_refine_diff_density_max         0.569
_refine_diff_density_min         -0.404
_refine_diff_density_rms         0.055
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.032
_refine_ls_hydrogen_treatment    mixed
_refine_ls_matrix_type           full
_refine_ls_number_parameters     248
_refine_ls_number_reflns         5437
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.032
_refine_ls_R_factor_all          0.0763
_refine_ls_R_factor_gt           0.0482
_refine_ls_shift/su_max          0.000
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.0553P)^2^+1.0293P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.1137
_refine_ls_wR_factor_ref         0.1287
_reflns_number_gt                3923
_reflns_number_total             5437
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            b006685ksup1.cif
_cod_data_source_block           2
_cod_depositor_comments
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The following automatic conversions were performed:

'_exptl_crystal_density_meas' value 'not measured' was changed to '?'
- the value is perceived as not measured.

Automatic conversion script
Id: cif_fix_values 3008 2015-01-20 13:52:24Z robertas 
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_cod_original_cell_volume        1914.6(8)
_cod_original_sg_symbol_H-M      P2(1)/n
_cod_database_code               7111103