data_a _publ_requested_journal J.Org.Chem. _publ_contact_author_name 'Jiaxi Xu' _publ_contact_author_address ;College of Chemistry and Molecular Engineering, Peking University Beijing, 100871 P. R. China ; _publ_contact_author_email jxxu@pku.edu.cn _publ_contact_author_phone 86-10-62751497 _publ_contact_author_fax 86-10-62751708 loop_ _publ_author_name _publ_author_address 'Xu, J. X.' ;College of Chemistry and Molecular Engineering, Peking University Beijing, 100871 P. R. China ; 'Jiao, Lei' ;College of Chemistry and Molecular Engineering, Peking University Beijing, 100871 P. R. China ; 'Liang, Yong' ;College of Chemistry and Molecular Engineering, Peking University Beijing, 100871 P. R. China ; 'Zhang, Shiwei' ;College of Chemistry and Molecular Engineering, Peking University Beijing, 100871 P. R. China ; _audit_creation_method SHELXL-97 _chemical_name_systematic 8-Benzyloxycarbonylaminomethyl-1-phenyl-2-thia-6-aza-bicyclo[4.2.0]octan-7-one _chemical_name_common ? _chemical_melting_point 423-424 _chemical_formula_moiety 'C21 H22 N2 O3 S' _chemical_formula_sum 'C21 H22 N2 O3 S' _chemical_formula_weight 382.47 loop_ _atom_type_symbol _atom_type_description _atom_type_scat_dispersion_real _atom_type_scat_dispersion_imag _atom_type_scat_source C C 0.0033 0.0016 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4' H H 0.0000 0.0000 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4' N N 0.0061 0.0033 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4' O O 0.0106 0.0060 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4' S S 0.1246 0.1234 'International Tables Vol C Tables 4.2.6.8 and 6.1.1.4' _symmetry_cell_setting triclinic _symmetry_space_group_name_H-M 'P -1' _symmetry_int_tables_number 2 loop_ _symmetry_equiv_pos_as_xyz 'x, y, z' '-x, -y, -z' _cell_length_a 9.5000(19) _cell_length_b 10.950(2) _cell_length_c 11.140(2) _cell_angle_alpha 62.38(3) _cell_angle_beta 79.77(3) _cell_angle_gamma 80.06(3) _cell_volume 1005.0(3) _cell_formula_units_Z 2 _cell_measurement_temperature 293(2) _cell_measurement_reflns_used 6045 _cell_measurement_theta_min 2.77 _cell_measurement_theta_max 25.00 _exptl_crystal_description Block _exptl_crystal_colour Colourless _exptl_crystal_size_max 0.60 _exptl_crystal_size_mid 0.30 _exptl_crystal_size_min 0.20 _exptl_crystal_density_meas ? _exptl_crystal_density_diffrn 1.264 _exptl_crystal_density_method 'not measured' _exptl_crystal_F_000 404 _exptl_absorpt_coefficient_mu 0.184 _exptl_absorpt_correction_type Empirical _exptl_absorpt_correction_T_min 0.895 _exptl_absorpt_correction_T_max 0.964 _exptl_special_details ; ABSCOR by T.Higashi 8 March, 1995 ; _diffrn_ambient_temperature 293(2) _diffrn_radiation_probe x-ray _diffrn_radiation_type MoK\a _diffrn_radiation_wavelength 0.71073 _diffrn_source 'fine-focus sealed tube' _diffrn_source_type 'Rigaku RAXIS RAPID IP' _diffrn_radiation_monochromator graphite _diffrn_measurement_device_type 'Rigaku RAXIS RAPID IP' _diffrn_measurement_method Oscillation _diffrn_detector_area_resol_mean '100x100 microns' _diffrn_standards_number ? _diffrn_standards_interval_count ? _diffrn_standards_interval_time ? _diffrn_standards_decay_% ? _diffrn_reflns_number 6045 _diffrn_reflns_av_R_equivalents 0.0707 _diffrn_reflns_av_sigmaI/netI 0.0616 _diffrn_reflns_limit_h_min -11 _diffrn_reflns_limit_h_max 11 _diffrn_reflns_limit_k_min -12 _diffrn_reflns_limit_k_max 12 _diffrn_reflns_limit_l_min -13 _diffrn_reflns_limit_l_max 11 _diffrn_reflns_theta_min 2.77 _diffrn_reflns_theta_max 25.00 _reflns_number_total 3258 _reflns_number_gt 1942 _reflns_threshold_expression >2sigma(I) _computing_data_collection ; Molecular Structure Corporation (1994) MSC/AFC Diffractometer Control Software SC, 3200 Research Forest Drive, The Woodlands, TX 77381, USA. ; _computing_cell_refinement ; Molecular Structure Corporation (1994) MSC/AFC Diffractometer Control Software MSC, 3200 Research Forest Drive, The Woodlands, TX 77381 USA. ; _computing_data_reduction ; Sheldrick, G. M. (1998) SHELXS98, Program for the Solution of Crystal Structure, University of Gottingen, Germany. ; _computing_structure_solution ; Sheldrick, G. M. (1998) SHELXS98, Program for the Solution of Crystal Structure, University of Gottingen, Germany. ; _computing_structure_refinement ; Sheldrick, G. M. (1998) SHELXL98, Program for the Refinement of Crystal Structure, University of Gottingen, Germany. ; _computing_molecular_graphics ; Interactive Molecular Graphics XP, Virsion 4.2 for MSDOS (1990), Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. ; _computing_publication_material ; Sheldrick, G. M. (1998) SHELXL98, Program for the refinement of Crystal Structure, University of Gottingen, Germany. ; _refine_special_details ; Refinement of F^2^ against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F^2^, conventional R-factors R are based on F, with F set to zero for negative F^2^. The threshold expression of F^2^ > 2sigma(F^2^) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F^2^ are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. ; _refine_ls_structure_factor_coef Fsqd _refine_ls_matrix_type full _refine_ls_weighting_scheme calc _refine_ls_weighting_details 'calc w=1/[\s^2^(Fo^2^)+(0.0795P)^2^+0.0000P] where P=(Fo^2^+2Fc^2^)/3' _atom_sites_solution_primary direct _atom_sites_solution_secondary difmap _atom_sites_solution_hydrogens ; hydrogen atoms are generated by HFIX instructions or difmap ; _refine_ls_hydrogen_treatment ; hydrogen coordinates ride on the coordinates of the previous atom, the isotropic U values are 1.2 OR 1.5 time over the U values of the previous atom. ; _refine_ls_extinction_method SHELXL _refine_ls_extinction_coef 0.017(4) _refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^ _refine_ls_number_reflns 3258 _refine_ls_number_parameters 249 _refine_ls_number_restraints 0 _refine_ls_R_factor_all 0.0927 _refine_ls_R_factor_gt 0.0563 _refine_ls_wR_factor_ref 0.1545 _refine_ls_wR_factor_gt 0.1439 _refine_ls_goodness_of_fit_ref 1.018 _refine_ls_restrained_S_all 1.018 _refine_ls_shift/su_max 0.000 _refine_ls_shift/su_mean 0.000 loop_ _atom_site_label _atom_site_type_symbol _atom_site_fract_x _atom_site_fract_y _atom_site_fract_z _atom_site_U_iso_or_equiv _atom_site_adp_type _atom_site_occupancy _atom_site_symmetry_multiplicity _atom_site_calc_flag _atom_site_refinement_flags _atom_site_disorder_assembly _atom_site_disorder_group S1 S -0.11687(9) -0.14795(9) 0.12532(8) 0.0537(3) Uani 1 1 d . . . O1 O 0.0488(3) -0.1236(3) 0.4442(2) 0.0684(7) Uani 1 1 d . . . O2 O 0.0445(3) 0.3288(2) 0.0474(2) 0.0628(7) Uani 1 1 d . . . O3 O 0.1287(2) 0.3619(2) 0.2078(2) 0.0596(7) Uani 1 1 d . . . N1 N -0.1522(3) -0.1684(3) 0.3800(2) 0.0487(7) Uani 1 1 d . . . N2 N -0.0603(3) 0.2417(3) 0.2659(3) 0.0558(8) Uani 1 1 d . . . HN2 H -0.047(4) 0.225(3) 0.345(3) 0.055(10) Uiso 1 1 d . . . C1 C -0.1777(4) -0.3215(4) 0.2304(3) 0.0644(10) Uani 1 1 d . . . H1A H -0.2819 -0.3128 0.2446 0.077 Uiso 1 1 calc R . . H1B H -0.1470 -0.3771 0.1816 0.077 Uiso 1 1 calc R . . C2 C -0.1190(4) -0.3961(4) 0.3692(4) 0.0679(10) Uani 1 1 d . . . H2A H -0.1495 -0.4886 0.4178 0.081 Uiso 1 1 calc R . . H2B H -0.0148 -0.4049 0.3554 0.081 Uiso 1 1 calc R . . C3 C -0.1712(4) -0.3186(4) 0.4556(3) 0.0605(9) Uani 1 1 d . . . H3A H -0.2723 -0.3292 0.4875 0.073 Uiso 1 1 calc R . . H3B H -0.1188 -0.3601 0.5349 0.073 Uiso 1 1 calc R . . C4 C -0.1925(3) -0.0726(3) 0.2433(3) 0.0450(8) Uani 1 1 d . . . C5 C -0.0892(3) 0.0301(3) 0.2388(3) 0.0456(8) Uani 1 1 d . . . H5 H -0.0110 0.0476 0.1642 0.055 Uiso 1 1 calc R . . C6 C -0.0458(4) -0.0936(4) 0.3714(3) 0.0510(8) Uani 1 1 d . . . C7 C -0.3523(3) -0.0238(3) 0.2362(3) 0.0473(8) Uani 1 1 d . . . C8 C -0.4051(4) 0.0561(4) 0.1125(4) 0.0705(11) Uani 1 1 d . . . H8 H -0.3420 0.0839 0.0327 0.085 Uiso 1 1 calc R . . C9 C -0.5518(6) 0.0959(5) 0.1052(6) 0.0938(15) Uani 1 1 d . . . H9 H -0.5859 0.1505 0.0210 0.113 Uiso 1 1 calc R . . C10 C -0.6454(5) 0.0551(5) 0.2208(7) 0.0943(16) Uani 1 1 d . . . H10 H -0.7437 0.0795 0.2155 0.113 Uiso 1 1 calc R . . C11 C -0.5956(5) -0.0205(5) 0.3428(6) 0.0928(14) Uani 1 1 d . . . H11 H -0.6599 -0.0464 0.4218 0.111 Uiso 1 1 calc R . . C12 C -0.4484(4) -0.0606(4) 0.3529(4) 0.0703(11) Uani 1 1 d . . . H12 H -0.4154 -0.1120 0.4380 0.084 Uiso 1 1 calc R . . C13 C -0.1595(3) 0.1664(3) 0.2451(3) 0.0545(9) Uani 1 1 d . . . H13A H -0.2010 0.2267 0.1607 0.065 Uiso 1 1 calc R . . H13B H -0.2374 0.1443 0.3187 0.065 Uiso 1 1 calc R . . C14 C 0.0375(4) 0.3115(3) 0.1636(3) 0.0511(8) Uani 1 1 d . . . C15 C 0.2406(4) 0.4398(4) 0.1041(4) 0.0638(10) Uani 1 1 d . . . H15A H 0.1979 0.5154 0.0266 0.077 Uiso 1 1 calc R . . H15B H 0.3064 0.3798 0.0725 0.077 Uiso 1 1 calc R . . C16 C 0.3188(4) 0.4951(4) 0.1730(4) 0.0602(10) Uani 1 1 d . . . C17 C 0.2635(5) 0.6134(4) 0.1894(4) 0.0791(12) Uani 1 1 d . . . H17 H 0.1804 0.6634 0.1503 0.095 Uiso 1 1 calc R . . C18 C 0.3260(7) 0.6594(6) 0.2606(6) 0.1127(19) Uani 1 1 d . . . H18 H 0.2860 0.7380 0.2712 0.135 Uiso 1 1 calc R . . C19 C 0.4507(9) 0.5846(10) 0.3161(6) 0.126(3) Uani 1 1 d . . . H19 H 0.4950 0.6126 0.3660 0.151 Uiso 1 1 calc R . . C20 C 0.5097(6) 0.4701(8) 0.2986(6) 0.118(2) Uani 1 1 d . . . H20 H 0.5951 0.4229 0.3348 0.142 Uiso 1 1 calc R . . C21 C 0.4441(5) 0.4226(5) 0.2273(5) 0.0830(12) Uani 1 1 d . . . H21 H 0.4842 0.3439 0.2169 0.100 Uiso 1 1 calc R . . loop_ _atom_site_aniso_label _atom_site_aniso_U_11 _atom_site_aniso_U_22 _atom_site_aniso_U_33 _atom_site_aniso_U_23 _atom_site_aniso_U_13 _atom_site_aniso_U_12 S1 0.0563(6) 0.0607(6) 0.0418(5) -0.0218(4) 0.0027(4) -0.0123(4) O1 0.0559(15) 0.0955(19) 0.0491(14) -0.0228(14) -0.0167(12) -0.0132(13) O2 0.0767(17) 0.0708(16) 0.0447(14) -0.0250(12) -0.0048(12) -0.0217(13) O3 0.0600(14) 0.0704(16) 0.0512(14) -0.0238(12) -0.0018(11) -0.0278(12) N1 0.0472(16) 0.0574(17) 0.0351(14) -0.0123(13) -0.0055(12) -0.0131(13) N2 0.0628(19) 0.066(2) 0.0423(17) -0.0203(15) -0.0061(15) -0.0263(15) C1 0.074(2) 0.064(2) 0.058(2) -0.030(2) 0.0063(19) -0.0214(19) C2 0.077(3) 0.052(2) 0.060(2) -0.0153(19) 0.003(2) -0.0103(19) C3 0.063(2) 0.058(2) 0.0450(19) -0.0092(18) -0.0013(17) -0.0122(18) C4 0.0460(19) 0.0514(19) 0.0329(16) -0.0120(14) -0.0063(14) -0.0115(15) C5 0.0427(18) 0.053(2) 0.0401(17) -0.0171(15) -0.0048(14) -0.0140(15) C6 0.0419(19) 0.067(2) 0.0409(18) -0.0209(17) -0.0016(15) -0.0099(16) C7 0.0447(19) 0.049(2) 0.0512(19) -0.0231(16) -0.0096(16) -0.0061(15) C8 0.073(3) 0.073(3) 0.067(3) -0.032(2) -0.025(2) 0.006(2) C9 0.088(3) 0.098(4) 0.124(4) -0.069(3) -0.061(3) 0.029(3) C10 0.052(3) 0.090(4) 0.160(5) -0.071(4) -0.023(3) 0.000(2) C11 0.054(3) 0.099(4) 0.117(4) -0.047(3) 0.014(3) -0.013(2) C12 0.048(2) 0.085(3) 0.071(3) -0.032(2) 0.0024(19) -0.0072(19) C13 0.052(2) 0.063(2) 0.0469(19) -0.0194(17) -0.0058(16) -0.0168(17) C14 0.057(2) 0.050(2) 0.048(2) -0.0209(17) -0.0100(17) -0.0107(17) C15 0.053(2) 0.075(3) 0.056(2) -0.022(2) 0.0015(18) -0.0217(19) C16 0.053(2) 0.062(2) 0.064(2) -0.0247(19) 0.0059(18) -0.0214(18) C17 0.074(3) 0.071(3) 0.088(3) -0.033(2) 0.012(2) -0.026(2) C18 0.130(5) 0.113(4) 0.123(4) -0.076(4) 0.044(4) -0.070(4) C19 0.120(5) 0.199(7) 0.102(4) -0.088(5) 0.036(4) -0.112(5) C20 0.074(4) 0.184(6) 0.114(4) -0.071(5) -0.011(3) -0.046(4) C21 0.061(3) 0.100(3) 0.095(3) -0.049(3) -0.003(2) -0.015(2) _geom_special_details ; All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. ; loop_ _geom_bond_atom_site_label_1 _geom_bond_atom_site_label_2 _geom_bond_distance _geom_bond_site_symmetry_2 _geom_bond_publ_flag S1 C1 1.841(4) . ? S1 C4 1.841(3) . ? O1 C6 1.218(4) . ? O2 C14 1.210(4) . ? O3 C14 1.366(4) . ? O3 C15 1.468(4) . ? N1 C6 1.372(4) . ? N1 C4 1.468(4) . ? N1 C3 1.487(4) . ? N2 C14 1.345(4) . ? N2 C13 1.465(4) . ? C1 C2 1.532(5) . ? C2 C3 1.527(5) . ? C4 C7 1.523(4) . ? C4 C5 1.594(4) . ? C5 C6 1.535(5) . ? C5 C13 1.554(4) . ? C7 C8 1.376(5) . ? C7 C12 1.380(5) . ? C8 C9 1.392(6) . ? C9 C10 1.358(7) . ? C10 C11 1.345(6) . ? C11 C12 1.399(5) . ? C15 C16 1.516(5) . ? C16 C21 1.377(6) . ? C16 C17 1.392(5) . ? C17 C18 1.370(6) . ? C18 C19 1.383(9) . ? C19 C20 1.367(9) . ? C20 C21 1.401(6) . ? loop_ _geom_angle_atom_site_label_1 _geom_angle_atom_site_label_2 _geom_angle_atom_site_label_3 _geom_angle _geom_angle_site_symmetry_1 _geom_angle_site_symmetry_3 _geom_angle_publ_flag C1 S1 C4 97.72(15) . . ? C14 O3 C15 115.6(2) . . ? C6 N1 C4 94.1(2) . . ? C6 N1 C3 132.4(3) . . ? C4 N1 C3 126.6(3) . . ? C14 N2 C13 120.3(3) . . ? C2 C1 S1 112.8(3) . . ? C3 C2 C1 111.9(3) . . ? N1 C3 C2 113.0(3) . . ? N1 C4 C7 115.2(3) . . ? N1 C4 C5 87.6(2) . . ? C7 C4 C5 118.1(3) . . ? N1 C4 S1 109.1(2) . . ? C7 C4 S1 113.0(2) . . ? C5 C4 S1 111.1(2) . . ? C6 C5 C13 118.1(3) . . ? C6 C5 C4 83.3(2) . . ? C13 C5 C4 118.0(2) . . ? O1 C6 N1 130.5(3) . . ? O1 C6 C5 135.8(3) . . ? N1 C6 C5 93.6(2) . . ? C8 C7 C12 118.2(3) . . ? C8 C7 C4 120.6(3) . . ? C12 C7 C4 121.2(3) . . ? C7 C8 C9 120.8(4) . . ? C10 C9 C8 120.3(5) . . ? C11 C10 C9 119.8(4) . . ? C10 C11 C12 121.0(5) . . ? C7 C12 C11 119.9(4) . . ? N2 C13 C5 114.3(3) . . ? O2 C14 N2 125.1(3) . . ? O2 C14 O3 123.9(3) . . ? N2 C14 O3 111.0(3) . . ? O3 C15 C16 105.9(3) . . ? C21 C16 C17 118.9(4) . . ? C21 C16 C15 119.3(4) . . ? C17 C16 C15 121.7(4) . . ? C18 C17 C16 122.9(5) . . ? C17 C18 C19 117.6(5) . . ? C20 C19 C18 120.9(5) . . ? C19 C20 C21 121.2(6) . . ? C16 C21 C20 118.4(5) . . ? loop_ _geom_torsion_atom_site_label_1 _geom_torsion_atom_site_label_2 _geom_torsion_atom_site_label_3 _geom_torsion_atom_site_label_4 _geom_torsion _geom_torsion_site_symmetry_1 _geom_torsion_site_symmetry_2 _geom_torsion_site_symmetry_3 _geom_torsion_site_symmetry_4 _geom_torsion_publ_flag C4 S1 C1 C2 -59.4(3) . . . . ? S1 C1 C2 C3 62.4(4) . . . . ? C6 N1 C3 C2 -95.5(4) . . . . ? C4 N1 C3 C2 47.6(4) . . . . ? C1 C2 C3 N1 -48.8(4) . . . . ? C6 N1 C4 C7 -129.1(3) . . . . ? C3 N1 C4 C7 77.3(4) . . . . ? C6 N1 C4 C5 -9.0(2) . . . . ? C3 N1 C4 C5 -162.6(3) . . . . ? C6 N1 C4 S1 102.6(2) . . . . ? C3 N1 C4 S1 -51.1(4) . . . . ? C1 S1 C4 N1 48.8(2) . . . . ? C1 S1 C4 C7 -80.7(2) . . . . ? C1 S1 C4 C5 143.8(2) . . . . ? N1 C4 C5 C6 8.1(2) . . . . ? C7 C4 C5 C6 125.5(3) . . . . ? S1 C4 C5 C6 -101.5(2) . . . . ? N1 C4 C5 C13 -110.2(3) . . . . ? C7 C4 C5 C13 7.2(4) . . . . ? S1 C4 C5 C13 140.2(2) . . . . ? C4 N1 C6 O1 -168.3(4) . . . . ? C3 N1 C6 O1 -17.2(6) . . . . ? C4 N1 C6 C5 9.4(2) . . . . ? C3 N1 C6 C5 160.5(3) . . . . ? C13 C5 C6 O1 -73.0(5) . . . . ? C4 C5 C6 O1 168.8(4) . . . . ? C13 C5 C6 N1 109.6(3) . . . . ? C4 C5 C6 N1 -8.6(2) . . . . ? N1 C4 C7 C8 -174.1(3) . . . . ? C5 C4 C7 C8 84.4(4) . . . . ? S1 C4 C7 C8 -47.7(4) . . . . ? N1 C4 C7 C12 4.5(5) . . . . ? C5 C4 C7 C12 -97.0(4) . . . . ? S1 C4 C7 C12 130.9(3) . . . . ? C12 C7 C8 C9 -1.5(5) . . . . ? C4 C7 C8 C9 177.2(3) . . . . ? C7 C8 C9 C10 -0.6(6) . . . . ? C8 C9 C10 C11 2.0(7) . . . . ? C9 C10 C11 C12 -1.4(7) . . . . ? C8 C7 C12 C11 2.1(6) . . . . ? C4 C7 C12 C11 -176.6(3) . . . . ? C10 C11 C12 C7 -0.7(7) . . . . ? C14 N2 C13 C5 73.8(4) . . . . ? C6 C5 C13 N2 71.6(4) . . . . ? C4 C5 C13 N2 169.2(3) . . . . ? C13 N2 C14 O2 6.8(5) . . . . ? C13 N2 C14 O3 -173.6(3) . . . . ? C15 O3 C14 O2 -0.6(5) . . . . ? C15 O3 C14 N2 179.8(3) . . . . ? C14 O3 C15 C16 175.2(3) . . . . ? O3 C15 C16 C21 96.2(4) . . . . ? O3 C15 C16 C17 -80.4(4) . . . . ? C21 C16 C17 C18 -1.8(6) . . . . ? C15 C16 C17 C18 174.7(4) . . . . ? C16 C17 C18 C19 1.0(7) . . . . ? C17 C18 C19 C20 0.8(8) . . . . ? C18 C19 C20 C21 -1.7(9) . . . . ? C17 C16 C21 C20 0.9(6) . . . . ? C15 C16 C21 C20 -175.8(4) . . . . ? C19 C20 C21 C16 0.9(8) . . . . ? loop_ _geom_hbond_atom_site_label_D _geom_hbond_atom_site_label_H _geom_hbond_atom_site_label_A _geom_hbond_distance_DH _geom_hbond_distance_HA _geom_hbond_distance_DA _geom_hbond_angle_DHA _geom_hbond_site_symmetry_A N2 HN2 O1 0.84(3) 2.08(3) 2.884(4) 160(3) 2_556 _diffrn_measured_fraction_theta_max 0.921 _diffrn_reflns_theta_full 25.00 _diffrn_measured_fraction_theta_full 0.921 _refine_diff_density_max 0.208 _refine_diff_density_min -0.257 _refine_diff_density_rms 0.048 _chemical_compound_source synthetic _exptl_crystal_recrystallization_method 'from ethanol, 25 degree centigrade'