A "hidden" co-crystal of caffeine and adipic acid.
Bucar, Dejan-Kresimir; Henry, Rodger F; Lou, Xiaochun; Borchardt, Thomas B; Zhang, Geoff G Z; Chemical communications (Cambridge, England)  (2007) 525–527; doi:10.1039/b611749j

data_7101670
_publ_section_title
;
 A "hidden" co-crystal of caffeine and adipic acid.
;
_journal_issue                   5
_journal_name_full               'Chemical communications (Cambridge, England)'
_journal_page_first              525
_journal_page_last               527
_journal_paper_doi               10.1039/b611749j
_journal_year                    2007
_chemical_formula_moiety         'C8 H10 N4 O2, C6 H10 O4'
_chemical_formula_sum            'C14 H20 N4 O6'
_chemical_formula_weight         340.34
_chemical_name_common
;(1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione).(1,4-
butanedicarboxylic acid)
;
_chemical_name_systematic
;
(1,3,7-trimethyl-1H-purine-2,6(3H,7H)-dione).(1,4-butanedicarboxylic acid)
;
_space_group_IT_number           2
_symmetry_cell_setting           triclinic
_symmetry_space_group_name_Hall  '-P 1'
_symmetry_space_group_name_H-M   'P -1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_atom_sites_solution_secondary   difmap
_audit_creation_method           SHELXL-97
_cell_angle_alpha                82.705(3)
_cell_angle_beta                 87.649(3)
_cell_angle_gamma                67.236(2)
_cell_formula_units_Z            2
_cell_length_a                   9.5480(16)
_cell_length_b                   9.5862(16)
_cell_length_c                   9.6682(16)
_cell_measurement_reflns_used    919
_cell_measurement_temperature    193(2)
_cell_measurement_theta_max      28.2525
_cell_measurement_theta_min      2.9515
_cell_volume                     809.4(2)
_computing_cell_refinement       'Bruker saintplus (Bruker 1999)'
_computing_data_collection       'Bruker SMART (Bruker 2001)'
_computing_data_reduction        'Bruker saintplus (Bruker 1999)'
_computing_molecular_graphics    '(MS Modeling(Accelrys 2004)'
_computing_structure_refinement  'SHELXL (Sheldrick, 2000)'
_computing_structure_solution    'SHELXL (Sheldrick, 2000)'
_diffrn_ambient_temperature      193(2)
_diffrn_measured_fraction_theta_full 0.965
_diffrn_measured_fraction_theta_max 0.965
_diffrn_measurement_device_type  CCD
_diffrn_measurement_method       omega-phi
_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  0.0690
_diffrn_reflns_av_sigmaI/netI    0.0509
_diffrn_reflns_limit_h_max       12
_diffrn_reflns_limit_h_min       -12
_diffrn_reflns_limit_k_max       12
_diffrn_reflns_limit_k_min       -12
_diffrn_reflns_limit_l_max       12
_diffrn_reflns_limit_l_min       -12
_diffrn_reflns_number            9608
_diffrn_reflns_theta_full        28.29
_diffrn_reflns_theta_max         28.29
_diffrn_reflns_theta_min         2.12
_exptl_absorpt_coefficient_mu    0.110
_exptl_absorpt_correction_type   none
_exptl_crystal_colour            colourless
_exptl_crystal_density_diffrn    1.397
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       paralellepiped
_exptl_crystal_F_000             360
_exptl_crystal_size_max          0.6
_exptl_crystal_size_mid          0.4
_exptl_crystal_size_min          0.3
_refine_diff_density_max         0.365
_refine_diff_density_min         -0.215
_refine_diff_density_rms         0.048
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.066
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     222
_refine_ls_number_reflns         3877
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.066
_refine_ls_R_factor_all          0.0454
_refine_ls_R_factor_gt           0.0418
_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^)+(0.0648P)^2^+0.0892P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.1195
_refine_ls_wR_factor_ref         0.1223
_reflns_number_gt                3433
_reflns_number_total             3877
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            b611749j.txt
_cod_data_source_block           x238t
_cod_original_sg_symbol_H-M      P-1
_cod_database_code               7101670