Two phases of C~9~H~12~O~4~: why is the structure at 295K so complicated?
Duncan, Laura L.; Patrick, Brian O.; Brock, Carolyn Pratt; Acta Crystallographica, Section B: Structural Science 58 (2002) 502–511; doi:10.1107/S0108768102000630

data_2103117
_publ_section_title
;
 Two phases of C~9~H~12~O~4~: why is the structure at 295K so
 complicated?
;
_journal_coden_ASTM              ASBSDK
_journal_issue                   3
_journal_name_full
;
 Acta Crystallographica, Section B: Structural Science
;
_journal_page_first              502
_journal_page_last               511
_journal_paper_doi               10.1107/S0108768102000630
_journal_volume                  58
_journal_year                    2002
_chemical_formula_moiety         'C9 H12 O4'
_chemical_formula_sum            'C9 H12 O4'
_chemical_formula_weight         184.19
_chemical_melting_point          396.15
_chemical_name_systematic
;
4,4'-dimethyl-2-hydroxy-6-oxo-cyclohexene-1-carboxylic acid
;
_space_group_IT_number           36
_symmetry_cell_setting           orthorhombic
_symmetry_space_group_name_Hall  'C 2c -2'
_symmetry_space_group_name_H-M   'C m c 21'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_atom_sites_solution_secondary   difmap
_audit_creation_method
;
SHELXL-97, macros written locally, and C. P. Brock
;
_cell_angle_alpha                90.
_cell_angle_beta                 90.
_cell_angle_gamma                90.
_cell_formula_units_Z            20
_cell_length_a                   10.474(5)
_cell_length_b                   66.24(3)
_cell_length_c                   6.662(3)
_cell_measurement_reflns_used    23801
_cell_measurement_temperature    295.0(10)
_cell_measurement_theta_max      27.5
_cell_measurement_theta_min      1.0
_cell_volume                     4622(4)
_computing_cell_refinement       'DENZO-SMN (Otwinowski & Minor, 1997)'
_computing_data_collection       'COLLECT software (Nonius, 1998)'
_computing_data_reduction        'SCALEPACK (Otwinowski & Minor, 1997)'
_computing_molecular_graphics    'SHELXTL PC (Sheldrick, 1990)'
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 1997)'
_computing_structure_solution
;
SIR92 (Altomare, Cascarano, Giacovazzo, Guagliardi, Burla,
Polidori & Camalli, 1994) in maXus (Mackay, Gilmore,
Edwards, Tremayne, Stewart & Shankland, 1998);
SHELXS-97 (Sheldrick, 1990) in maXus (Mackay, Gilmore,
Edwards, Tremayne, Stewart & Shankland, 1998)
;
_diffrn_ambient_temperature      295.0(10)
_diffrn_detector_area_resol_mean 18
_diffrn_measured_fraction_theta_full 0.979
_diffrn_measured_fraction_theta_max 0.979
_diffrn_measurement_device_type  'Nonius Kappa-CCD diffractometer'
_diffrn_measurement_method       '\f and \w scans with 2.0\% steps'
_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  0.048
_diffrn_reflns_av_sigmaI/netI    0.046
_diffrn_reflns_limit_h_max       13
_diffrn_reflns_limit_h_min       0
_diffrn_reflns_limit_k_max       85
_diffrn_reflns_limit_k_min       0
_diffrn_reflns_limit_l_max       8
_diffrn_reflns_limit_l_min       -8
_diffrn_reflns_number            11377
_diffrn_reflns_theta_full        27.50
_diffrn_reflns_theta_max         27.5
_diffrn_reflns_theta_min         2.07
_diffrn_standards_decay_%        <5.
_exptl_absorpt_coefficient_mu    0.104
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            colourless
_exptl_crystal_density_diffrn    1.323
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       Laths
_exptl_crystal_F_000             1960
_exptl_crystal_size_max          0.50
_exptl_crystal_size_mid          0.30
_exptl_crystal_size_min          0.15
_refine_diff_density_max         0.17
_refine_diff_density_min         -0.15
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.50
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     388
_refine_ls_number_reflns         2987
_refine_ls_number_restraints     430
_refine_ls_restrained_S_all      1.50
_refine_ls_R_factor_all          0.145
_refine_ls_R_factor_gt           0.070
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.06P)^2^] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.156
_refine_ls_wR_factor_ref         0.191
_reflns_number_gt                1388
_reflns_number_total             2987
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            br0109.cif
_cod_depositor_comments
;
The following automatic conversions were performed:

'_chemical_melting_point' value '123_C' was changed to '396.15' - it
was converted from degrees Celsius(C) to Kelvins(K).

Automatic conversion script
Id: cif_fix_values 1646 2011-03-28 12:23:43Z adriana 
;
_cod_original_sg_symbol_H-M      'Cm c 21'
_cod_database_code               2103117