Isolable zwitterionic pyridinio-semiquinone pi-radicals. Mild and efficient single-step access to stable radicals.
Yi, Chenyi; Blum, Carmen; Liu, Shi-Xia; Keene, Tony D.; Frei, Gabriela; Neels, Antonia; Decurtins, Silvio; Organic letters 11 (2009) 2261–2264; doi:10.1021/ol900559p

data_1503894
_publ_section_title
;
 Isolable zwitterionic pyridinio-semiquinone pi-radicals. Mild and
 efficient single-step access to stable radicals.
;
_journal_issue                   11
_journal_name_full               'Organic letters'
_journal_page_first              2261
_journal_page_last               2264
_journal_paper_doi               10.1021/ol900559p
_journal_volume                  11
_journal_year                    2009
_chemical_formula_sum            'C16 H12 N3 O4'
_chemical_formula_weight         310.29
_chemical_name_systematic
; 
 ? 
;
_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                 98.293(10)
_cell_angle_gamma                90.00
_cell_formula_units_Z            4
_cell_length_a                   6.3879(8)
_cell_length_b                   12.146(2)
_cell_length_c                   19.036(2)
_cell_measurement_reflns_used    5538
_cell_measurement_temperature    173(2)
_cell_measurement_theta_max      24.93
_cell_measurement_theta_min      2.00
_cell_volume                     1461.5(3)
_computing_cell_refinement       'STOE X-AREA'
_computing_data_collection       'STOE X-AREA'
_computing_data_reduction        'STOE X-RED'
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 1997)'
_computing_structure_solution    'SHELXS-97 (Sheldrick, 1990)'
_diffrn_ambient_temperature      173(2)
_diffrn_detector_area_resol_mean 6.67
_diffrn_measured_fraction_theta_full 0.991
_diffrn_measured_fraction_theta_max 0.991
_diffrn_measurement_device_type  'STOE IPDS 2'
_diffrn_measurement_method       'rotation method'
_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  0.1148
_diffrn_reflns_av_sigmaI/netI    0.0803
_diffrn_reflns_limit_h_max       7
_diffrn_reflns_limit_h_min       -7
_diffrn_reflns_limit_k_max       14
_diffrn_reflns_limit_k_min       -14
_diffrn_reflns_limit_l_max       22
_diffrn_reflns_limit_l_min       -21
_diffrn_reflns_number            16994
_diffrn_reflns_theta_full        25.17
_diffrn_reflns_theta_max         25.17
_diffrn_reflns_theta_min         2.00
_exptl_absorpt_coefficient_mu    0.104
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            orange
_exptl_crystal_density_diffrn    1.410
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       rod
_exptl_crystal_F_000             644
_exptl_crystal_size_max          0.40
_exptl_crystal_size_mid          0.30
_exptl_crystal_size_min          0.20
_refine_diff_density_max         0.555
_refine_diff_density_min         -0.282
_refine_diff_density_rms         0.096
_refine_ls_extinction_coef       0.036(7)
_refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^
_refine_ls_extinction_method     SHELXL
_refine_ls_goodness_of_fit_ref   0.988
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     210
_refine_ls_number_reflns         2605
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      0.988
_refine_ls_R_factor_all          0.1433
_refine_ls_R_factor_gt           0.0983
_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^)+(0.1598P)^2^] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.2605
_refine_ls_wR_factor_ref         0.2763
_reflns_number_gt                1246
_reflns_number_total             2605
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            ol900559p_si_004.cif
_cod_data_source_block           y321
_cod_original_cell_volume        1461.5(4)
_cod_original_sg_symbol_H-M      'P 21/c'
_cod_database_code               1503894