The use of squaric acid as a scaffold for cofacial phenyl rings.
Muthyala, Rajeev S.; Subramaniam, Gopal; Todaro, Louis; Organic letters 6 (2004) 4663–4665; doi:10.1021/ol048139s

data_1506937
_publ_section_title
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 The use of squaric acid as a scaffold for cofacial phenyl rings.
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_journal_issue                   25
_journal_name_full               'Organic letters'
_journal_page_first              4663
_journal_page_last               4665
_journal_paper_doi               10.1021/ol048139s
_journal_volume                  6
_journal_year                    2004
_chemical_formula_sum            'C18 H16 N2 O2'
_chemical_formula_weight         292.33
_space_group_IT_number           14
_symmetry_cell_setting           monoclinic
_symmetry_space_group_name_Hall  '-P 2ybc'
_symmetry_space_group_name_H-M   'P 1 21/c 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                 92.82(3)
_cell_angle_gamma                90.00
_cell_formula_units_Z            4
_cell_length_a                   7.4230(15)
_cell_length_b                   14.598(3)
_cell_length_c                   13.890(3)
_cell_measurement_temperature    295(2)
_cell_volume                     1503.3(5)
_computing_cell_refinement       'Bruker XSCANS'
_computing_data_collection       'Bruker XSCANS'
_computing_data_reduction        'Bruker SHELXTL'
_computing_molecular_graphics    'Bruker SHELXTL'
_computing_publication_material  'Bruker SHELXTL'
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 1997)'
_computing_structure_solution    'SHELXS-97 (Sheldrick, 1990)'
_diffrn_ambient_temperature      295(2)
_diffrn_measured_fraction_theta_full 0.994
_diffrn_measured_fraction_theta_max 0.994
_diffrn_measurement_device_type  'Bruker-Nonius KappaCCD'
_diffrn_measurement_method       '\w scans'
_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  0.0351
_diffrn_reflns_av_sigmaI/netI    0.0599
_diffrn_reflns_limit_h_max       9
_diffrn_reflns_limit_h_min       -9
_diffrn_reflns_limit_k_max       13
_diffrn_reflns_limit_k_min       -18
_diffrn_reflns_limit_l_max       18
_diffrn_reflns_limit_l_min       -17
_diffrn_reflns_number            5690
_diffrn_reflns_theta_full        27.46
_diffrn_reflns_theta_max         27.46
_diffrn_reflns_theta_min         3.36
_exptl_absorpt_coefficient_mu    0.085
_exptl_absorpt_correction_T_max  0.9957
_exptl_absorpt_correction_T_min  0.9505
_exptl_absorpt_correction_type   none
_exptl_crystal_density_diffrn    1.292
_exptl_crystal_density_method    'not measured'
_exptl_crystal_F_000             616
_exptl_crystal_size_max          0.60
_exptl_crystal_size_mid          0.08
_exptl_crystal_size_min          0.05
_refine_diff_density_max         0.151
_refine_diff_density_min         -0.177
_refine_diff_density_rms         0.038
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.046
_refine_ls_hydrogen_treatment    mixed
_refine_ls_matrix_type           full
_refine_ls_number_parameters     201
_refine_ls_number_reflns         3414
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.046
_refine_ls_R_factor_all          0.1277
_refine_ls_R_factor_gt           0.0698
_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^)+(0.0635P)^2^+0.4758P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.1431
_refine_ls_wR_factor_ref         0.1666
_reflns_number_gt                2043
_reflns_number_total             3414
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            ol048139ssi20040914_034901.cif
_cod_data_source_block           x1498r
_cod_depositor_comments
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The following automatic conversions were performed:

'_symmetry_cell_setting' value 'Monoclinic' changed to 'monoclinic'
according to /home/saulius/struct/CIF-dictionaries/cif_core.dic
dictionary named 'cif_core.dic' version 2.4.1 from 2010-06-29.

Automatic conversion script
Id: cif_fix_values 1715 2011-07-08 13:25:40Z adriana 
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_cod_original_sg_symbol_H-M      P2(1)/c
_cod_database_code               1506937